I snagged the B switch out of a junk yard car and then pulled the switch out of my 129. They both test good. I'll swap in the junk yard switch, but I expect the issue to remain.
What's next? Solenoid or wiring?
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The $500 500SL Offroadster
- Thread starter Beater400E
- Start date
What's next? Solenoid or wiring?
Solenoid is fairly easy to test, apply +12v to the pin and listen for a solid "thunk" with voltage applied. If that's good, then you get to figure out what's wrong in betwixt the two...
Sounds pretty easy. I just discovered the rear subframe is falling out of the car, so as soon as I can get my Jeep off the lift, I'll get this thing up there and have a look. I'm hoping to go hit another Gambler event next weekend in southern Oregon, and it would be nice if the transmission would behave and the rear suspension would stay attached.Solenoid is fairly easy to test, apply +12v to the pin and listen for a solid "thunk" with voltage applied. If that's good, then you get to figure out what's wrong in betwixt the two...
I got the car up on the lift. The rear subframe ripped one of the factory M12 subframe mount captive nuts out of the unibody. So now I get to figure out how to fix that. It's almost like this car wasn't designed for off roading.
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Got the subframe reattached to the car. It ain't pretty but it's in there. Getting ready to test everything.
My check engine light has been on forever. It's diagnostic mode code 4, air injection system faulty. Do we know the exact circumstances that will trigger that code? I'm obviously not too worried about it, but I am curious.
Edit: looks like I had code 6 as well. Idle speed control faulty.
My check engine light has been on forever. It's diagnostic mode code 4, air injection system faulty. Do we know the exact circumstances that will trigger that code? I'm obviously not too worried about it, but I am curious.
Edit: looks like I had code 6 as well. Idle speed control faulty.
The DM looks for a lean condition w hen the air pump runs (typically after a cold start, although I've heard the pump run at operating temp). If the DM isn't happy about the O2 readings when the air pump runs, it will trigger a code.
That's usually related to E-GAS or ETA, both of which need to be happy to keep the idle speed in spec.
I fiddled with the shift solenoid. It seemed to be working. I ended up just putting it all back together with the junk yard B switch, and now it works properly. I don't know what the actual problem was, but it's working now so I'm not complaining.
The suspension feels much better now. On the last trip the rear end started feeling very floppy and the left rear tire would rub on the wheel well whenever I got on the gas or turned right. Now that the subframe is bolted back in it drives much better.
The suspension feels much better now. On the last trip the rear end started feeling very floppy and the left rear tire would rub on the wheel well whenever I got on the gas or turned right. Now that the subframe is bolted back in it drives much better.
I decided with 4 days until my next event to try to sort out a couple more modifications if I can. The car has always had a vibration at speed. I tried 3 different sets of tires, and a total of 6 balance jobs, and the vibration only moved around. It never went away. I concluded that the issue is probably the wheel spacers I'm using to fit the big off road tires.
They're generic spacers, and are not hubcentric. I pulled a wheel off today and put an indicator on the spacer and saw around 0.020" runout. Keep in mind, that's just the spacer. Depending on exactly how the wheel is bolted up, total runout could be a fair bit worse than that.
I probably could use and indicator to carefully get each of the spacers dialed in perfectly, and then do the same for each wheel. Of course then I'll bounce the car around off road and mess it all up I'm sure.
Good news though. I have a lathe. I started whittling up a set of hubcentric spacer rings this evening. They'll be a close fit to the inside diameter of the wheel spacers, and then they'll index on the hub, and provide a pilot for the wheel to slide onto. In theory, I should be able to get everything within 0.001".
I also tossed one of my Brembo calipers on and tested my wheel fitment. Turns out both my 16 inch W140 wheels and my CLK wheels fit with the 1.25" spacer. Fitment is not an issue with the inside diameter of the wheel. Fitment is only an issue between the caliper and the inside face of the wheel.
Even so, my 400E doesn't need the big brakes, but the convertible with the big heavy off road tires will benefit from some beefier binders. I'm going to go ahead and get them mounted up.
I probably won't swap the rears before the weekend, especially because I'm planning on swapping the entire hub, and I'll have to replace lower control arm bushings. Just too much to do in 3 evenings after work.
They're generic spacers, and are not hubcentric. I pulled a wheel off today and put an indicator on the spacer and saw around 0.020" runout. Keep in mind, that's just the spacer. Depending on exactly how the wheel is bolted up, total runout could be a fair bit worse than that.
I probably could use and indicator to carefully get each of the spacers dialed in perfectly, and then do the same for each wheel. Of course then I'll bounce the car around off road and mess it all up I'm sure.
Good news though. I have a lathe. I started whittling up a set of hubcentric spacer rings this evening. They'll be a close fit to the inside diameter of the wheel spacers, and then they'll index on the hub, and provide a pilot for the wheel to slide onto. In theory, I should be able to get everything within 0.001".
I also tossed one of my Brembo calipers on and tested my wheel fitment. Turns out both my 16 inch W140 wheels and my CLK wheels fit with the 1.25" spacer. Fitment is not an issue with the inside diameter of the wheel. Fitment is only an issue between the caliper and the inside face of the wheel.
Even so, my 400E doesn't need the big brakes, but the convertible with the big heavy off road tires will benefit from some beefier binders. I'm going to go ahead and get them mounted up.
I probably won't swap the rears before the weekend, especially because I'm planning on swapping the entire hub, and I'll have to replace lower control arm bushings. Just too much to do in 3 evenings after work.
Got the hubcentric rings finished up today. They came out really nice. I also swapped the 334mm brakes over. Still need to bleed the brakes and then hopefully tomorrow it'll get a test drive.
I have a new minor issue. I'm trying to bleed the brakes on this car using my Motive power bleeder. When I pressurize the reservoir, I'm getting fluid coming out of the little black cap next to the fill port. I'm assuming this is a vent of some sort, but if so it must have a check valve to allow air in but not fluid out. Does anyone know if there's a simple solution for this?
Things are getting interesting. I got the brakes bled and put some test miles on the car. The hubcentric rings are amazing. The car drives so much better now.
Or at least it did.
I left home earlier this afternoon to head for the Gambler event in southern Oregon. Several hours in, I began to notice a grinding noise in the front end during low speed tight cornering. I parked outside an O'Reilly Auto Parts in Redmond and yanked the left front wheel.
The inside of the 334mm rotor is scraping on the lower ball joint when I corner.
My best guess is wheel bearings?
The bearings feel fairly ok when I shake the wheel. I'm not really in a great position to disassemble just to inspect.
Any thoughts or suggestions?
The car does ok on the highway, so I may just continue on to my hotel and hope to deal with it there.
Or at least it did.
I left home earlier this afternoon to head for the Gambler event in southern Oregon. Several hours in, I began to notice a grinding noise in the front end during low speed tight cornering. I parked outside an O'Reilly Auto Parts in Redmond and yanked the left front wheel.
The inside of the 334mm rotor is scraping on the lower ball joint when I corner.
My best guess is wheel bearings?
The bearings feel fairly ok when I shake the wheel. I'm not really in a great position to disassemble just to inspect.
Any thoughts or suggestions?
The car does ok on the highway, so I may just continue on to my hotel and hope to deal with it there.
OH - I forgot... your SL500 has the early LCA's! The 334mm rotors sit about 6mm deeper vs the 300mm and there's only 6-7mm air gap. Cheap solution is to cut a hole in the dust shield and also grind 1-2mm off the face of the LCA to create necessary clearance. About 2mm air gap is needed.
That's what it looks like. I already cut the holes, but I think I'll need some grinder action on the ball joints.
The car did fine through the rest of the trip. The grinding only happened during low speed parking lot maneuvers. Now that I'm back home, I'll pull it apart and either clearance the ball joints, or see if I can swap in later control arms.
The junk yard donor SL500 that I sourced the brakes from might have a usable pair. It was hit in the left front and I know that the left side tie rod was bent, but not sure if the control arm was damaged.
I plan to go out there in the next couple days anyway to snag the steering box, blower motor, and a power window motor or two.
My steering box has been badly leaking forever, and I haven't been able to get a seal kit yet. I'll continue trying to track one down, but a used steering box for $50 is probably a good option too. I have no real way of knowing if the steering box took damage when the tie rod got bent, but I may risk it for $50.
My blower motor stopped working over the weekend. It's probably just the regulator, but I'll go pull the whole mess out of the junk yard car and have spares just in case.
The driver side window motor has been slow since day one, and seems to be getting slower, so I'm thinking it would be smart to grab the one from this junk yard car as well.
My soft top's rear windows also split in half over the weekend. It was bound to happen soon. Not sure what I'll do about that. Maybe a cheap ebay replacement top for $200. Maybe I try to replace the windows myself. I don't know.
I also sold the Evo wheels off this car over the weekend. $1800 for the used set. After shipping and eBay fees I'm netting just under $1500. Not bad considering I paid $500 for the whole car.
The junk yard donor SL500 that I sourced the brakes from might have a usable pair. It was hit in the left front and I know that the left side tie rod was bent, but not sure if the control arm was damaged.
I plan to go out there in the next couple days anyway to snag the steering box, blower motor, and a power window motor or two.
My steering box has been badly leaking forever, and I haven't been able to get a seal kit yet. I'll continue trying to track one down, but a used steering box for $50 is probably a good option too. I have no real way of knowing if the steering box took damage when the tie rod got bent, but I may risk it for $50.
My blower motor stopped working over the weekend. It's probably just the regulator, but I'll go pull the whole mess out of the junk yard car and have spares just in case.
The driver side window motor has been slow since day one, and seems to be getting slower, so I'm thinking it would be smart to grab the one from this junk yard car as well.
My soft top's rear windows also split in half over the weekend. It was bound to happen soon. Not sure what I'll do about that. Maybe a cheap ebay replacement top for $200. Maybe I try to replace the windows myself. I don't know.
I also sold the Evo wheels off this car over the weekend. $1800 for the used set. After shipping and eBay fees I'm netting just under $1500. Not bad considering I paid $500 for the whole car.
I ordered a few clearance parts from RockAuto for the SL. I fully expected to receive cheap Chinese junk, but sometimes you win the discount parts lottery.
I paid $29 for the O2 sensor and $10 for the thermostat.
I paid $29 for the O2 sensor and $10 for the thermostat.
Threw in an order for a couple o2 sensors, will see what arrives in a few days time. Thanks for the heads up.
Long story short, I ended up with another parts car this weekend. It's a 91 300SL. This thing is disgusting, but it was essentially free. I actually traded the guy some old power tools I didn't need for it.
Initially I was trying to just get the differential from the guy, but after discussing a bit I negotiated to just take the whole thing.
This car has the M104 motor with the 5 speed auto trans. The rear diff is a 3.69 ratio. My math says a 3.69 diff with the 31 inch tires should be similar to my 400E with 25 inch tires and a 3.06. It's aggressive, but still usable on the highway.
One challenge I'll have is the fact that this car does not have ASR. The 500SL does. I think I have two options to make it work.
Option 1 is to install the 3.69 diff, and then swap the rear knuckles to the set I snagged from a 2000 500SL. Those have wheel speed sensors in the knuckles. I'm not sure which axles to use. I have a couple sets. None have tone rings, but I have a set of tone rings I should be able to affix to whichever axles I use. I think that will allow me to keep ASR and more importantly ABS.
I think another option would be to swap the ring and pinion into the 500SL housing. I know the 500SL housing is the 1.4 liter reinforced unit, and I believe the 300SL housing is the 500E style 1.3 liter housing, but I THINK the ring and pinion gear set should interchange.
I'm guessing that the ring gear offset would be wrong, so I'd probably have to machine a spacer and get longer ring gear bolts, but I could do that.
Obviously this option would allow me to retain the ASR and ABS without messing with outboard wheel speed sensors, or CV axle changes. It does require custom parts (I think) and a full gear setup though, which is a lot of work.
I think I'll probably try option 1 first. If for some reason it doesn't work, I can pivot to option 2.
I wish I had some kind of limited slip I could install at the same time. I have a buddy who has a 98 300td parts car that supposedly has a limited slip. The Quaife limited slip lists the W210 as an application, which makes me think the factory W210 LSD carrier may interchange with my 1.3 liter carrier from the 300SL. I could be wrong on that though.
If anyone has any knowledge on this, please chime in. Most of the research I've done doesn't detail much with the W210 diffs, or the 3.69 ratio stuff since that stuff is usually outside the scope of 500E work.
Initially I was trying to just get the differential from the guy, but after discussing a bit I negotiated to just take the whole thing.
This car has the M104 motor with the 5 speed auto trans. The rear diff is a 3.69 ratio. My math says a 3.69 diff with the 31 inch tires should be similar to my 400E with 25 inch tires and a 3.06. It's aggressive, but still usable on the highway.
One challenge I'll have is the fact that this car does not have ASR. The 500SL does. I think I have two options to make it work.
Option 1 is to install the 3.69 diff, and then swap the rear knuckles to the set I snagged from a 2000 500SL. Those have wheel speed sensors in the knuckles. I'm not sure which axles to use. I have a couple sets. None have tone rings, but I have a set of tone rings I should be able to affix to whichever axles I use. I think that will allow me to keep ASR and more importantly ABS.
I think another option would be to swap the ring and pinion into the 500SL housing. I know the 500SL housing is the 1.4 liter reinforced unit, and I believe the 300SL housing is the 500E style 1.3 liter housing, but I THINK the ring and pinion gear set should interchange.
I'm guessing that the ring gear offset would be wrong, so I'd probably have to machine a spacer and get longer ring gear bolts, but I could do that.
Obviously this option would allow me to retain the ASR and ABS without messing with outboard wheel speed sensors, or CV axle changes. It does require custom parts (I think) and a full gear setup though, which is a lot of work.
I think I'll probably try option 1 first. If for some reason it doesn't work, I can pivot to option 2.
I wish I had some kind of limited slip I could install at the same time. I have a buddy who has a 98 300td parts car that supposedly has a limited slip. The Quaife limited slip lists the W210 as an application, which makes me think the factory W210 LSD carrier may interchange with my 1.3 liter carrier from the 300SL. I could be wrong on that though.
If anyone has any knowledge on this, please chime in. Most of the research I've done doesn't detail much with the W210 diffs, or the 3.69 ratio stuff since that stuff is usually outside the scope of 500E work.
@Beater400E Just a point to note, a 91 car will have a 4 speed transmission.
Actually in the States they got the 5 speed. It's a 722.500.
Thanks for the info, good to know.
EPC shows the 1.4L "reinforced" differential has different ring & pinion part number (despite identical 2.65 ratio), but I don't know if they are interchangeable. I have a feeling they are NOT interchangeable, all the pinion bearings / nut / flange / etc are different part numbers as well.
Good to know. Thanks Dave. Swapping to the outboard wheel speed sensors should work though, right?EPC shows the 1.4L "reinforced" differential has different ring & pinion part number (despite identical 2.65 ratio), but I don't know if they are interchangeable. I have a feeling they are NOT interchangeable, all the pinion bearings / nut / flange / etc are different part numbers as well.
My research indicates the 400E ASR cv axles I have should be perfect. I'll just need to install tone rings. I'd been planning to put those in my 400E as an upgrade, but my only other options are the stock 93 500SL axles, which I believe will be too short, or the stock 300SL axles, which are pretty dainty.
I suppose I could also install the 400E ASR axles in my 400E and then install the stock non-ASR 400E axles in the 500SL, but I don't know if those are any beefier than the 300SL axles.
I'd love to find another set of 034 ASR/036/129.060 axles so I can just have a set for both cars. If I have to choose one or the other though, the heavier car with the offroad tires and 3.69 gears probably needs them the most.
Any luck on that order?
AFAICT, yes, this SHOULD work fine. I've been wanting to try the same thing as it would allow some additional options for different ratios on early ASR models with the sensors in the diff.
From memory, the chassis connector is different between inboard vs outboard sensors, but I'm not certain. If the connector is the same, next concern is wire length for the late/outboard sensor. If the connector is different, I'm pretty sure you can splice the outboard sensor to the connector needed for the early 124/129.
Yep! Received 2 MB OE o2 sensors in the mail. Pretty sure a few other members put in some orders as well.
That's awesome.
Well, I have all the parts, so I think we'll find out.AFAICT, yes, this SHOULD work fine. I've been wanting to try the same thing as it would allow some additional options for different ratios on early ASR models with the sensors in the diff.
From memory, the chassis connector is different between inboard vs outboard sensors, but I'm not certain. If the connector is the same, next concern is wire length for the late/outboard sensor. If the connector is different, I'm pretty sure you can splice the outboard sensor to the connector needed for the early 124/129.
Incidentally, it's worth noting that the 500E and the 129.060 use the same axles, both with the 1.3 liter differential case. It stands to reason that if anyone wanted to try to put a 1.4 liter case in a 034/036 car, the 129.067 axles should work to make that possible.
I got the 3.69 diff pulled out of the parts car yesterday after a brief battle with some accidentally imported Washingtonian spiders.
It just occurred to me that the axle stub shafts and the input flange from my stock 500SL 2.65 differential probably aren't going to work with this 3.69 diff. The 500SL diff is the larger reinforced case, and the 3.69 is the smaller 1.3 liter case.
So I'll need to track down those bits. Funny, because just a few months ago I pulled those exact parts from a junk yard and sent them to Dave. That's ok. There are more out there.
One of my local junk yards has a 1990 Mercedes "500" in their inventory. Since the only US market 500 model in 1990 was the 500SL, I'm hoping that's what it is. If so, it'll probably have the parts I need. It'll also have another set of 500E/400E ASR cv axles, which I need.
I'm going to go have a look at that car this afternoon and see what it really is. If it's an ASR car I might just pull the whole diff. My thinking is that since my 500SL has ASR, and the 3.69 diff does not, I can either swap the whole diff and then swap the later rear hubs with outboard wheel speed sensors, OR I could potentially swap the ring and pinion from the 3.69 into the 1.3L ASR case and run it that way.
It just occurred to me that the axle stub shafts and the input flange from my stock 500SL 2.65 differential probably aren't going to work with this 3.69 diff. The 500SL diff is the larger reinforced case, and the 3.69 is the smaller 1.3 liter case.
So I'll need to track down those bits. Funny, because just a few months ago I pulled those exact parts from a junk yard and sent them to Dave. That's ok. There are more out there.
One of my local junk yards has a 1990 Mercedes "500" in their inventory. Since the only US market 500 model in 1990 was the 500SL, I'm hoping that's what it is. If so, it'll probably have the parts I need. It'll also have another set of 500E/400E ASR cv axles, which I need.
I'm going to go have a look at that car this afternoon and see what it really is. If it's an ASR car I might just pull the whole diff. My thinking is that since my 500SL has ASR, and the 3.69 diff does not, I can either swap the whole diff and then swap the later rear hubs with outboard wheel speed sensors, OR I could potentially swap the ring and pinion from the 3.69 into the 1.3L ASR case and run it that way.
Do we know if the axle stub shafts from an ASR case will work fine in a non-ASR case?
AFAIK they are not interchangeable, the design is quite different. The ASR stub shaft is longer to accommodate the "tone ring", which the non-ASR stub does not have. This is for the 210mm, 1.3L case.
Interesting. Then the parts I sent you wouldn't have worked for me anyway. Ok then. If this parts car is a 500SL, and if it has ASR, I could just take the whole diff and see about swapping the ring and pinion. Granted, the 3.69 ring gear probably won't work with the 2.65 carrier. Hmmm. And I'm not sure that the non-ASR carrier would work in the ASR case. I guess I could make a spacer for the 3.69 gear and use longer bolts.AFAIK they are not interchangeable, the design is quite different. The ASR stub shaft is longer to accommodate the "tone ring", which the non-ASR stub does not have. This is for the 210mm, 1.3L case.
Maybe I should just try to find the non-ASR axle flanges. I know they were used in a bunch of W126 cars, so they shouldn't be too tough to find.
The carriers are ratio-specific, but will work for both ASR and non-ASR cases. For the 210mm diffs, every single ratio uses a different carrier! Spacers could work if the carrier is for a higher numerical ratio, but spacers have their own issues.
I'm not sure if the 126 uses the same flange as the R129 non-ASR, since the housing is also different IIRC? My spreadsheet didn't include any 126 info.
I'm not sure if the 126 uses the same flange as the R129 non-ASR, since the housing is also different IIRC? My spreadsheet didn't include any 126 info.
The small case 210mm non-ASR axle flange is 126-350-18-45 on the spreadsheet. Just looking up applications for that part online I'm seeing 85-up V8 W126 cars used it. I'd have to do some more research to pinpoint which exact options would have it, but they should be out there somewhere.
Ok, then install theory I could pull the complete carrier and ring gear out of the 3.69 and drop it in an ASR case, swap the pinion, and it should work. Obviously there's gear setup to deal with, but if I measure everything carefully there's a pretty good chance I can nail that on the first try. Too bad this 300SL donor didn't have ASR. That would have made this much easier.
It is a 500SL. No ASR. It has skinny cv axles though, so no point grabbing those. Dave, do you have some good side by side pics of the reinforced and standard cases? Just want to make sure I know what I'm looking at here. The spreadsheet indicates it should be a standard case, but I'd hate to go to all the trouble of pulling the flanges just to discover they won't work for me.
This car also had the silly little back seat, in nice shape. I don't want it, but for $40 I grabbed it anyway. I figure someone out there will want it.
This car also had the silly little back seat, in nice shape. I don't want it, but for $40 I grabbed it anyway. I figure someone out there will want it.
Click here for the only pics I know of with a reinforced diff next to a standard one. Blurry photos of both internals attached, you can see enough to get the idea nothing interchanges.
Reinforced diffs appeared on the 140 chassis with 5.0L or larger engines, and showed up on the 129.067 chassis (1993 500SL) and all R129 with V12.
The early 500SL, 129.066 with M119.960, only came with the standard 210mm diff which bolts in to the 124 and interchanges with the 034/036 (other than the non-ASR part).
Reinforced diffs appeared on the 140 chassis with 5.0L or larger engines, and showed up on the 129.067 chassis (1993 500SL) and all R129 with V12.
The early 500SL, 129.066 with M119.960, only came with the standard 210mm diff which bolts in to the 124 and interchanges with the 034/036 (other than the non-ASR part).
That's what I thought. I'll go yank those this weekend some time.Click here for the only pics I know of with a reinforced diff next to a standard one. Blurry photos of both internals attached, you can see enough to get the idea nothing interchanges.
Reinforced diffs appeared on the 140 chassis with 5.0L or larger engines, and showed up on the 129.067 chassis (1993 500SL) and all R129 with V12.
The early 500SL, 129.066 with M119.960, only came with the standard 210mm diff which bolts in to the 124 and interchanges with the 034/036 (other than the non-ASR part).
View attachment 202316
The silly little seats make very good money over this side of the pond - did you get the seatbelts too?
Attachments
I didn't have the tools I'd need for the seat belts, but I'll probably grab them when I go back out for the diff flanges. They're nothing special. They're just standard off the shelf seat belts.
They seem to be pretty sought after over here too. I'm going to give them a good cleaning and repair a couple very minor issues, and then they'll go on eBay. I'll probably ask $800.
I also grabbed the soft top control module. I need to test it, but if it's good it's probably worth $300-400. Not bad for a $50 junk yard trip.
I had another dumb idea. I'd really love to have some kind of traction device for this car, but I'm not willing to spend a fortune making it happen. I thought about just welding up the spider gears, but that's a little too hacky, even for me. I started thinking about other types of traction devices.
What about a lunchbox locker?
Obviously no one makes a lunchbox locker for a Mercedes differential, but I wonder if it would be possible to adapt one from something else.
For anyone not familiar, a lunchbox locker is a mechanical locking device that gets installed inside a stock open diff carrier. They're inexpensive, and easy to install. They provide 100% locking under load, but allow one wheel to spin faster than the ring gear when not under load.
In practice that means you need to be off the throttle around tight corners, or the rear end will lock and scrub. When you let off the gas and coast around corners the locker makes a characteristic "clack clack clack" sound, which makes everyone in the parking lot wonder if your junk is about to fall apart. I have one in the rear axle if my Jeep and it works great. I can lift a tire completely in the air and it'll remain locked.
So how would I make that work in the Mercedes?
I'd need to find a locker for a differential that is dimensionally close to the 210mm Mercedes diff. It would also need to have the same axle spline count and diameter. That's a tall order, but I figured there was a chance.
I tore apart my 3.69 diff to get some basic measurements. The most important thing right off is the axle splines. The Mercedes diff uses 27 spline axles that measure 1.155 inches in diameter. That diameter is a rough measurement of course since we're measuring across the splines.
The ring gear is 210mm, which is 8.27 inches.
So, is there a differential out there with 27 spline shafts and a roughly 8.27 inch ring gear?
There sure is. A Chrysler 8.25 differential. Specifically, a 91-95 Jeep Cherokee rear axle. They use 27 spline axles, which measure 1.170 inches in diameter, and the ring gear is 8.25 inches in diameter.
To be clear, the ring gear diameter doesn't really matter, but it's a good indication of the approximate size of the parts. The axle diameters are only 0.015 inches, or 0.38mm apart. That's a rough measurement, and splined shafts do not need a high precision fit.
I know it won't be a direct fit, but I think there's a reasonable chance I could make it work. I think what I'll do is pull a set of spider gears from an appropriately equipped Jeep when I'm back out at the junk yard this weekend pulling axle flanges. I can then mock those up in the Mercedes carrier and determine whether or not it would be possible. Basically, if I can make the stock Jeep spider gears work in the Mercedes carrier, then a locker should also work.
I anticipate I'd need to do some machining on both the Mercedes carrier and the Jeep gears, and maybe even make some custom spacers to get it all to fit. 3.69 gears with a locker would throw some serious dirt in the air off road though.
In truth, I doubt it's viable, but I should be able to find out just how not viable for almost nothing.
What about a lunchbox locker?
Obviously no one makes a lunchbox locker for a Mercedes differential, but I wonder if it would be possible to adapt one from something else.
For anyone not familiar, a lunchbox locker is a mechanical locking device that gets installed inside a stock open diff carrier. They're inexpensive, and easy to install. They provide 100% locking under load, but allow one wheel to spin faster than the ring gear when not under load.
In practice that means you need to be off the throttle around tight corners, or the rear end will lock and scrub. When you let off the gas and coast around corners the locker makes a characteristic "clack clack clack" sound, which makes everyone in the parking lot wonder if your junk is about to fall apart. I have one in the rear axle if my Jeep and it works great. I can lift a tire completely in the air and it'll remain locked.
So how would I make that work in the Mercedes?
I'd need to find a locker for a differential that is dimensionally close to the 210mm Mercedes diff. It would also need to have the same axle spline count and diameter. That's a tall order, but I figured there was a chance.
I tore apart my 3.69 diff to get some basic measurements. The most important thing right off is the axle splines. The Mercedes diff uses 27 spline axles that measure 1.155 inches in diameter. That diameter is a rough measurement of course since we're measuring across the splines.
The ring gear is 210mm, which is 8.27 inches.
So, is there a differential out there with 27 spline shafts and a roughly 8.27 inch ring gear?
There sure is. A Chrysler 8.25 differential. Specifically, a 91-95 Jeep Cherokee rear axle. They use 27 spline axles, which measure 1.170 inches in diameter, and the ring gear is 8.25 inches in diameter.
To be clear, the ring gear diameter doesn't really matter, but it's a good indication of the approximate size of the parts. The axle diameters are only 0.015 inches, or 0.38mm apart. That's a rough measurement, and splined shafts do not need a high precision fit.
I know it won't be a direct fit, but I think there's a reasonable chance I could make it work. I think what I'll do is pull a set of spider gears from an appropriately equipped Jeep when I'm back out at the junk yard this weekend pulling axle flanges. I can then mock those up in the Mercedes carrier and determine whether or not it would be possible. Basically, if I can make the stock Jeep spider gears work in the Mercedes carrier, then a locker should also work.
I anticipate I'd need to do some machining on both the Mercedes carrier and the Jeep gears, and maybe even make some custom spacers to get it all to fit. 3.69 gears with a locker would throw some serious dirt in the air off road though.
In truth, I doubt it's viable, but I should be able to find out just how not viable for almost nothing.
I emailed one of the major manufacturers of differential lockers and shared my stupid idea and asked if they could share some blueprints or dimensions with me so I could determine how feasible this idea was. They told me they could not share those details, but if I gave them the critical measurements from the Mercedes differential they could tell me whether my idea was possible or not.
I shared the measurements and they told me it would not work. They cited a couple specifics that just didn't sound right to me. Since I had been asking a favor anyway, I didn't think it was appropriate to debate it, so I decided instead to just get my hands on the parts in question and take my own measurements.
I went back out to the junk yard yesterday and stipped a bunch of parts off the 1990 500SL I'd found out there. I pulled the grille, front corner lights, rear jump seat seatbelts, aluminum cam oil tubes, radiator, and of course the differential stub axles and driveshaft flange. It was a nasty, rainy, muddy day, but I came away with a nice haul of parts. I ran out of time before I was able to seek out the Chrysler differential parts though.
So this morning I went back out and tore apart a 93 Dodge Dakota differential. I harvested the side gears and cross shaft, and then took some key measurements. Sure enough, the measurements did not match what I'd been told. Perhaps more importantly, when I got home I test fitted the Chrysler side gear on a Merceses stub axle shaft. They fit perfectly.
I will still need to do some machining to get everything to work, but I'm confident enough that I think I'm going to order the locker.
Assuming this works, I guess it could be an option for a traction device for any car with a 210mm differential, but a locker is far more aggressive than a limited slip, so I wouldn't recommend it unless you're willing to deal with some unpleasantness. I mean, that, and you'd need to have a machine shop do some custom work to make it happen.
I shared the measurements and they told me it would not work. They cited a couple specifics that just didn't sound right to me. Since I had been asking a favor anyway, I didn't think it was appropriate to debate it, so I decided instead to just get my hands on the parts in question and take my own measurements.
I went back out to the junk yard yesterday and stipped a bunch of parts off the 1990 500SL I'd found out there. I pulled the grille, front corner lights, rear jump seat seatbelts, aluminum cam oil tubes, radiator, and of course the differential stub axles and driveshaft flange. It was a nasty, rainy, muddy day, but I came away with a nice haul of parts. I ran out of time before I was able to seek out the Chrysler differential parts though.
So this morning I went back out and tore apart a 93 Dodge Dakota differential. I harvested the side gears and cross shaft, and then took some key measurements. Sure enough, the measurements did not match what I'd been told. Perhaps more importantly, when I got home I test fitted the Chrysler side gear on a Merceses stub axle shaft. They fit perfectly.
I will still need to do some machining to get everything to work, but I'm confident enough that I think I'm going to order the locker.
Assuming this works, I guess it could be an option for a traction device for any car with a 210mm differential, but a locker is far more aggressive than a limited slip, so I wouldn't recommend it unless you're willing to deal with some unpleasantness. I mean, that, and you'd need to have a machine shop do some custom work to make it happen.
My good fortune continues. The locker I'll need for this is $310 new, which is not bad, but after some searching I found a guy selling a lightly used one for $125 in Arizona. It's now on its way to me.
I received the locker from Arizona. Sure enough, the side gears engage perfectly with the axle shafts.
I won't go into all the gory details, but suffice it to say there is a ton of machining involved to make it actually work. I had to turn the ends down on the side gears, then do a reverse countersink on the inside of the case, which is a crazy operation. I also had to bore the cross pin holes, ream and tap the cross pin retainer hole and make a new retaining pin, and then make 4 new spacers to get everything aligned.
It's not quite finished, but the machining is almost done. I have a heavy duty cross pin on the way, along with new seals. I'm hoping to have those parts in hand in the next few days.
I'm also still dealing with a power steering leak. I ended up replacing the steering box, but I think the steering box wasn't the source of the leak. After cleaning everything up and replacing the steering box, I can now see the leak is actually coming from the pump.
I've already replaced the reservoir hose, so at this point I decided to just yank the pump and disassemble and reseal the whole thing. I have the pump out and disassembled right now, but discovered I'd ordered the wrong seal kit by mistake, so I'm waiting on the correct seals.
Little by little, I'm getting details sorted.
I won't go into all the gory details, but suffice it to say there is a ton of machining involved to make it actually work. I had to turn the ends down on the side gears, then do a reverse countersink on the inside of the case, which is a crazy operation. I also had to bore the cross pin holes, ream and tap the cross pin retainer hole and make a new retaining pin, and then make 4 new spacers to get everything aligned.
It's not quite finished, but the machining is almost done. I have a heavy duty cross pin on the way, along with new seals. I'm hoping to have those parts in hand in the next few days.
I'm also still dealing with a power steering leak. I ended up replacing the steering box, but I think the steering box wasn't the source of the leak. After cleaning everything up and replacing the steering box, I can now see the leak is actually coming from the pump.
I've already replaced the reservoir hose, so at this point I decided to just yank the pump and disassemble and reseal the whole thing. I have the pump out and disassembled right now, but discovered I'd ordered the wrong seal kit by mistake, so I'm waiting on the correct seals.
Little by little, I'm getting details sorted.
Machining complete. Fits beautifully. Just waiting on seals now so I can complete assembly.
Stupid car. We got a fair bit of snow this morning and I decided to drive the SL to get coffee. It ran a little rough at start up, but soon cleared up and seemed to be running fine. After warming up I noticed a little of the hot idle misfire. I figured I'd probably need to give the ignition system a good once-over.
On the way home it got worse and worse and then it eventually stalled and didn't want to restart. It would crank over and then backfire. Did that maybe a half dozen times before it eventually fired up and ran. It was a little rough, and seemed to lack power. Definitely down a couple cylinders. It stalled out again pulling into the driveway and absolutely refused to restart.
It will backfire when I try to start it. I'm guessing this is probably the classic moisture in the distributors. I'll tear into it after work and see if that's it. I'll probably check the fuel pressure too. When I bought the car I threw a cheap set of Amazon fuel pumps in it to see if it would run, and I've never replaced them since. We'll see. I'm sure it's nothing major either way.
On the way home it got worse and worse and then it eventually stalled and didn't want to restart. It would crank over and then backfire. Did that maybe a half dozen times before it eventually fired up and ran. It was a little rough, and seemed to lack power. Definitely down a couple cylinders. It stalled out again pulling into the driveway and absolutely refused to restart.
It will backfire when I try to start it. I'm guessing this is probably the classic moisture in the distributors. I'll tear into it after work and see if that's it. I'll probably check the fuel pressure too. When I bought the car I threw a cheap set of Amazon fuel pumps in it to see if it would run, and I've never replaced them since. We'll see. I'm sure it's nothing major either way.
Yup - textbook symptoms for moisture in the caps (passenger side usually is worse). Clean & dry them, and then cut the additional slots with a Dremel. No need to replace the caps unless they are severely corroded / carbon tracked. Here's a photo of mine:
I've already cut the extra slots, but I wouldn't be surprised if there's still moisture in there. I'm guessing the isolator plates are bad. I wish there was a way to definitively test them. I hate throwing parts at something just to test. If they were $10 that would be one thing, but at $60 each, I hesitate to replace them just to find out.
OH! Well that's different.
Remove the insulators and inspect the back side. They should be bone dry. I don't believe these really "go bad", but rather somehow become conductive - although I don't understand how or why.
Also, if you have engine oil leaking from the cam solenoids so the lower edge of the cap has oil on it... that is another potential cause of the issues. Read my post here, note there was liquid inside the caps during a hot, dry, Boise summer and the liquid was not water.
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