Weak acceleration

[Mbijee]

1993 500SL
Hello all, I’ve been trying to track down a problem with my car. From a complete stop, full throttle doesn’t go past 2k rpms for the first 2 gears. It doesn’t bog or hesitate, it just feels like it has a rev limiter or something. The car gets up to highway speeds, just not at the intended v8 power. Also while I’m cruising in the final gear, full throttle doesn’t drop a gear/ engage overdrive. It just slowly climbs up the RPM’s. The car runs and idles smooth with no warning lights. I do get a strong gas smell from the outside/exhaust, but I’d assume it’s normal for a 32 year old car. I did just install 8 new OEM plugs, but not much luck. Any ideas?

 

[gsxr]

1993 500SL
Hello all, I’ve been trying to track down a problem with my car. From a complete stop, full throttle doesn’t go past 2k rpms for the first 2 gears. It doesn’t bog or hesitate, it just feels like it has a rev limiter or something. The car gets up to highway speeds, just not at the intended v8 power.

Will it ever go above 2000rpm? For example, leaving the shift lever in "B" position and accelerating from a stop, will it pull to 6000rpm redline?

Also while I’m cruising in the final gear, full throttle doesn’t drop a gear/ engage overdrive. It just slowly climbs up the RPM’s.

Sound like the Bowden cable is disconnected from the accelerator linkage behind the airbox, and/or the electric kickdown solenoid is not functioning.

The car runs and idles smooth with no warning lights.

You won't get warning lights unless there's a major fault that causes ABS or ASR to be non-functional, or if an emission system error triggers the CEL. There can be many fault codes stored but no light on the dash to tell you this.

I do get a strong gas smell from the outside/exhaust, but I’d assume it’s normal for a 32 year old car.

This is NOT normal. If it's from the exhaust... often this is related to misfiring, dumping unburned fuel into the catalysts, which is dangerous. Are you absolutely certain there's no misfiring?

I did just install 8 new OEM plugs, but not much luck.

Make sure they are non-resistor plugs, either Bosch F8DC4 or the Beru plugs from the dealership. This won't cause a major issue, but these cars with distributor ignition are not happy with resistor plugs. Opening the gap to 1.0mm can help a bit also (wider than stock spec of 0.8mm).

Any ideas?

Start by checking fault codes on all powertrain modules, using a hand-held blink code reader. The R129 powertrain computers use the same diagnostics as the 500E, so the information in this thread is identical for your 500SL. Clear all codes on all modules, then drive the car for a bit, and see which codes return quickly. Note that misfiring (secondary ignition problems) will NOT store a fault code. More info in the De-Coding forum stickies here.

BTW - welcome to the forum!

 

[maw1124]

My bet is Bowden cable as well, not letting in enough air to burn the fuel. What did the old plugs look like and what do the air filters look like?

Take off the airbox, run the car and have someone give it gas. You should see the throttle body jump open and the engine come to life. If not, Bowden cable. If it does it with the airbox off but not on, air filters.

maw

 

[Mbijee]

Will it ever go above 2000rpm? For example, leaving the shift lever in "B" position and accelerating from a stop, will it pull to 6000rpm redline?

I just took it for a spin. Yes, the motor ROARS at “B”, can finally hear that v8. Rpm’s go up and beyond. On D it’ll go past 2000 but after holding the throttle down for like 3 secs, and it SLOWLY drags up the rpm and speed.

Sound like the Bowden cable is disconnected from the accelerator linkage behind the airbox, and/or the electric kickdown solenoid is not functioning.

Any pics of what these look like?

You won't get warning lights unless there's a major fault that causes ABS or ASR to be non-functional, or if an emission system error triggers the CEL. There can be many fault codes stored but no light on the dash to tell you this.

This is NOT normal. If it's from the exhaust... often this is related to misfiring, dumping unburned fuel into the catalysts, which is dangerous. Are you absolutely certain there's no misfiring?

My 300ce also has a gas smell so I assumed it’s normal lol. I’m pretty confident there’s no misfire. It idles nicely, no rpm fluctuations. Starts up good. Drives nicely

Make sure they are non-resistor plugs, either Bosch F8DC4 or the Beru plugs from the dealership. This won't cause a major issue, but these cars with distributor ignition are not happy with resistor plugs. Opening the gap to 1.0mm can help a bit also (wider than stock spec of 0.8mm).

Yes the new plugs from the dealer ( I believe beru) gapped to 1.0mm non resistor

Start by checking fault codes on all powertrain modules, using a hand-held blink code reader. The R129 powertrain computers use the same diagnostics as the 500E, so the information in this thread is identical for your 500SL. Clear all codes on all modules, then drive the car for a bit, and see which codes return quickly. Note that misfiring (secondary ignition problems) will NOT store a fault code. More info in the De-Coding forum stickies here.

I have an obd1-obd2 adapter. I was thinking about hooking it up to a screen and getting live data, would that work? Anything I should check for before digging into codes?

BTW - welcome to the forum!

Thank you. You,Gerry,and klinker are legends. I’ve read hundreds of your guys forums.

 

[Mbijee]

My bet is Bowden cable as well, not letting in enough air to burn the fuel. What did the old plugs look like and what do the air filters look like?

Take off the airbox, run the car and have someone give it gas. You should see the throttle body jump open and the engine come to life. If not, Bowden cable. If it does it with the airbox off but not on, air filters.

maw

New air filters. Old plugs looked fine, normal wear and tear and dry

 

[dreaming.haze]

@Mbijee You'll be looking on the back side of the air filter housing. In this image, you can see the hose clamp / then the clip in bag that would need to be replaced.

 

[Mbijee]

My bet is Bowden cable as well, not letting in enough air to burn the fuel. What did the old plugs look like and what do the air filters look like?

Take off the airbox, run the car and have someone give it gas. You should see the throttle body jump open and the engine come to life. If not, Bowden cable. If it does it with the airbox off but not on, air filters.

maw

Also this only happens on D. On P rpms do shoot up

 

[Mbijee]

@Mbijee You'll be looking on the back side of the air filter housing. In this image, you can see the hose clamp / then the clip in bag that would need to be replaced.

View attachment 214228

 

[Mbijee]

View attachment 214229

It doesn’t look broken.

 

[Mbijee]

Full throttle at stop

Full throttle from 4th gear

Full throttle from a stop on "B". I let go off the throttle at 4k, but it'll go up higher


Here’s some videos

 

[Mbijee]

@gsxr is this the kickdown solenoid you’re referring to? And is there anyway to test it?

 

[Mbijee]

Ok, this is what I’ve come to so far. The car will rev high RPM’s on “P” and “B”, but very weak acceleration on “D”. Full throttle only gets me to about 2k rpm’s and then it’ll slowly climb from there. Pushing the pedal against the kickdown switch doesn’t do anything. If the kickdown switch is defective, shouldn’t I still have some acceleration upon mid-full throttle? At least get to the 4k RPM range.

Could it be a clogged cat or a bad maf sensor?

 

[maw1124]

Combined with the gas smell, I absolutely suspect clogged converters. But that would inhibit airflow, power and RPM in all cases not just Drive.

If pushing lockdown doesn't do anything, it's definitely suspect. Someone else would need to weigh in on "testing" assuming you're talking about resistance, signal, etc. For me, pushing the pedal to the floor is the test.

Now for the bad news. Your car acts like mine was acting when I blew up some piston band in the transmission (by playing around with the B switch mechanism -- improperly must have been -- trying to engage 1st gear). But I don't want to jump to that conclusion. My solution was a new transmission with full time first gear start via a different valve body. How does your transmission feel otherwise. "Weak" is all I recall about how mine felt, like full time limp mode.

I don't understand the connection between the kickdown and "limp mode" on these transmissions. But I can imagine that MB would have been smart enough to disable the kickdown function when the car is in "limp mode". @gsxr would know.

This is admittedly applying new computerized logic to a vacuum pressure modulated transmission, so it may be descriptive but not mechanically proper.

Hope this helps.

maw

 

[Mbijee]

Combined with the gas smell, I absolutely suspect clogged converters. But that would inhibit airflow, power and RPM in all cases not just Drive.

If pushing lockdown doesn't do anything, it's definitely suspect. Someone else would need to weigh in on "testing" assuming you're talking about resistance, signal, etc. For me, pushing the pedal to the floor is the test.

Right, but if the switch is bad, shouldn’t I still be able to reach 4k rpms at mid-full throttle?

Now for the bad news. Your car acts like mine was acting when I blew up some piston band in the transmission (by playing around with the B switch mechanism -- improperly must have been -- trying to engage 1st gear). But I don't want to jump to that conclusion. My solution was a new transmission with full time first gear start via a different valve body. How does your transmission feel otherwise. "Weak" is all I recall about how mine felt, like full time limp mode.

Hmmm. My “B” doesn’t upshift, so I assume I’m good on that part. Honestly the transmission shifts pretty smoothly and no jerks.

I don't understand the connection between the kickdown and "limp mode" on these transmissions. But I can imagine that MB would have been smart enough to disable the kickdown function when the car is in "limp mode". @gsxr would know.

Anyway to check if the transmission is in limp mode?

This is admittedly applying new computerized logic to a vacuum pressure modulated transmission, so it may be descriptive but not mechanically proper.

Hope this helps.

maw

 

[Mbijee]

i also noticed a squirrel had gotten in and chewed up some wires behind the module box while it was being stored. I rewired it, but maybe there’s another chewed up wire somewhere else I haven’t seen yet?

 

[gsxr]

@gsxr is this the kickdown solenoid you’re referring to? And is there anyway to test it?

Sorry for the late replies - I've been away from my computer the last couple of days, and will be away through this weekend.

Anyway - the photo shows the kickdown SWITCH behind the gas pedal. This is probably fine but you can test if you want. This triggers the kickdown SOLENOID at the transmission, which could be disconnected, or faulty.

However, you should get kickdown to lower gears based on the accelerator pedal position, via the throttle linkage behind the airbox. Need to start there.

 

[gsxr]

Could it be a clogged cat or a bad maf sensor?

Absolutely! MAF is easy to test, disconnect it and see if the car runs better. If not, reconnect it. (This will store fault codes that you will need to clear.)

To test for clogged cats, remove the exhaust crossover pipe, and go for a noisy test drive. If full power is restored, your cats are toast. Alternately you can install a backpressure gauge in place of the O2 sensor but that's a lot more work, and you need a gauge. You then need to test drive and watch the gauge at full throttle. It should never exceed ~3psi even at high RPM's (4k-6k) at full throttle.

 

[gsxr]

I have an obd1-obd2 adapter. I was thinking about hooking it up to a screen and getting live data, would that work? Anything I should check for before digging into codes?

This adapter does nothing. You'll need to use a hand-held blink code reader to view analog fault codes from each module (see the De-Coding subforum).

Live data requires either SDS with HHT-Win, or an aftermarket system that will communicate with these old OBD-1 systems (like the Snap-On MT2500 with MB software cartridge). Very, very few aftermarket scanners will work with 1992-1995 Mercedes, period.

Note that clogged cats will not store codes, neither will misfires that are dumping fuel into the cats... no codes for low fuel pressure either. Which reminds me, if you have a major power loss, a bad fuel pump (or 2 bad pumps) can also cause a massive power loss.

 

[Mbijee]

This adapter does nothing. You'll need to use a hand-held blink code reader to view analog fault codes from each module (see the De-Coding subforum).

Live data requires either SDS with HHT-Win, or an aftermarket system that will communicate with these old OBD-1 systems (like the Snap-On MT2500 with MB software cartridge). Very, very few aftermarket scanners will work with 1992-1995 Mercedes, period.

Note that clogged cats will not store codes, neither will misfires that are dumping fuel into the cats... no codes for low fuel pressure either. Which reminds me, if you have a major power loss, a bad fuel pump (or 2 bad pumps) can also cause a massive power loss.

@gsxr Did you get a chance to watch the videos I linked?

My main question is, all of the possible causes you listed, wouldn’t they have the same symptoms when in “P” and “B”, not just “D”? Also, why would I need the kickdown when in first gear and taking off? Shouldn’t the RPM’s shoot up when I floor it to up shift?

Do you think it could possibly be a faulty transmission? Bad fuel pumps doesn’t sound like a bad idea, especially with the strong gas smell I get.

 

[Mbijee]

Sorry for the late replies - I've been away from my computer the last couple of days, and will be away through this weekend.

Anyway - the photo shows the kickdown SWITCH behind the gas pedal. This is probably fine but you can test if you want. This triggers the kickdown SOLENOID at the transmission, which could be disconnected, or faulty.

However, you should get kickdown to lower gears based on the accelerator pedal position, via the throttle linkage behind the airbox. Need to start there.

Sorry, I don’t understand this one, could you explain it in a simpler form

 

[maw1124]

I couldn't tell from your videos whether you were getting no kickdown and hence no RPMs ... or whether you were getting great kickdown and still no RPMs. That would speak to kickdown switch and solenoid.

If you're getting kickdown and still no RPMs, my money moves to clogged cats. And no I don't think that would be common to D and P. It seems like it would be intellectually but from experience I can tell you it's not so.

The reason might be as simple as the extra air when the car is moving at 40mph v stationary. But I don't know exactly. I can tell you I've had clogged cats that only showed up while driving and only at higher RPM (over 4500). That is, they only restricted flow in the extreme but no restriction at all sitting there revving the car in P.

maw

 

[Mbijee]

I did a simple test, not sure if it’s worth anything. I unplugged the wire from the kickdown solenoid, and took it for a spin. I didn’t notice any difference in shifting or accelerating, it drove exactly the same. Does that mean anything, or should I be checking the wire and the solenoid with a multimeter? What kind of numbers should I be looking for?

(Maf sensor test passed so that’s off the list)

 

[Mbijee]

I did a simple test, not sure if it’s worth anything. I unplugged the wire from the kickdown solenoid, and took it for a spin. I didn’t notice any difference in shifting or accelerating, it drove exactly the same. Does that mean anything, or should I be checking the wire and the solenoid with a multimeter? What kind of numbers should I be looking for?

(Maf sensor test passed so that’s off the list)

Also, with the key on (to get voltage to the solenoid), I pressed the switch to hear if the solenoid clicks, and no clicking. I had the top and windows down, so I’m sure I would hear it click.

 

[gsxr]

Sorry, I don’t understand this one, could you explain it in a simpler form

At low speeds in higher gears - for example, 25mph in 4th gear, applying 1/2 to 3/4 throttle should cause the transmission to downshift based on the throttle position, which is sent to the transmission via the control pressure (Bowden) cable.

The electrical kickdown switch+solenoid tells the transmission that FULL throttle is present, which will hold the transmission in gear until redline (6000rpm) before each upshift.

Full throttle shifts look like this:

 

[gsxr]

I did a simple test, not sure if it’s worth anything. I unplugged the wire from the kickdown solenoid, and took it for a spin. I didn’t notice any difference in shifting or accelerating, it drove exactly the same. Does that mean anything, or should I be checking the wire and the solenoid with a multimeter? What kind of numbers should I be looking for?

As described above, the electrical kickdown should force the transmission to not upshift until redline.

 

[gsxr]

@gsxr Did you get a chance to watch the videos I linked?

Just watched them. In the video "Full throttle from a stop on "B""... what happens if you keep it floored to redline? That looked like normal power until you let off the gas. See video above, you need to test to higher speeds. I still can't tell what's going on here. Also, get video that shows both tachometer AND speedometer. Not sure if those stupid YouTube "shorts" allow video in landscape mode.

My main question is, all of the possible causes you listed, wouldn’t they have the same symptoms when in “P” and “B”, not just “D”? Also, why would I need the kickdown when in first gear and taking off? Shouldn’t the RPM’s shoot up when I floor it to up shift?

We're trying to figure out what exactly is going on. You are asking about weak acceleration, which generally means loss of engine power. However if your transmission is starting out in the wrong gear somehow, that could appear to be low power. I think the 500SL starts in 2nd gear which doesn't help. Putting the shift lever in "B" forces it to start in 1st gear, AND also proves the electrical kickdown solenoid is working if you start in 1st in B. (If it won't start in 1st in "B", something is wrong with the kickdown solenoid/circuit.)

Do you think it could possibly be a faulty transmission?

Still not sure. Can't tell from your videos what gear the transmission is starting in, and also can't tell where teh shift points are. But you say the shifts are normal. Need more info.

Bad fuel pumps doesn’t sound like a bad idea, especially with the strong gas smell I get.

Bad fuel pumps can cause a lack of engine power. This has nothing to do with the strong gas odor, that's a separate problem. If it's strong odor from the exhaust, that indicates misfiring, which is a secondary ignition issue... and this can also damage the catalysts, which can cause lack of power.

You have a bunch more diagnostic work to do, I'm afraid.

 

[maw1124]

Between no kickdown, gas smell and that exhaust sound I'm pretty sure he has both problems. That's not exactly a full throated M119 in any of those videos. But like @gsxr says there's a lot more diagnostic work between here and a conclusion.

maw

 

[Mbijee]

Updated video

@gsxr @maw1124 heres an updated video from full throttle on “B” and “D”. Since “B” is accelerating nicely without upshifting, does that mean it’s operating as it should, therefore the kickdown solenoid and the cable are good and off the list?
The solenoid was also measuring 14.4 OHM.

I know it’s hard to tell from the second part of the video, but it really doesn’t help considering my car starts in 2nd gear

I’m kind of leaning towards a kickdown switch and/or Bowden cable needs adjustment.

As far as misfiring goes, my car drives and idles nicely. No hesitations. The only possible “sign” of misfiring I have is when I start the car for the first time of the day (only the first start of the day), it fluctuates between 700-1100 RPM. It does like 5 small revs in that range and goes back to normal. I doubt that’s a misfire, I think it’s more of fuel “issue”.

I appreciate your guys’ feedback

 

[TerryA]

@Mbijee,
When you start in drive “D” the car does start in second gear BUT when you FLOOR IT! in “D” it’s supposed to drop down into 1st “FIRST GEAR”.

Your B Video shows pretty lame acceleration. I would think either the kick down switch in inoperative or the Bowden Cable needs adjusting.

 

[maw1124]

@Mbijee,
When you start in drive “D” the car does start in second gear BUT when you FLOOR IT! in “D” it’s supposed to drop down into 1st “FIRST GEAR”.

Your B Video shows pretty lame acceleration. I would think either the kick down switch in inoperative or the Bowden Cable needs adjusting.

Thanks @TerryA you're reading my mind from across the country, and saved me some typing.

@Mbijee quick test... adjust the Bowden cable 1/4 inch further out and see what you get from full throttle in D. If it gives 1st gear and a 6000 RPM shift you'll know what's what.

maw

 

[Mbijee]

Thanks @TerryA you're reading my mind from across the country, and saved me some typing.

@Mbijee quick test... adjust the Bowden cable 1/4 inch further out and see what you get from full throttle in D. If it gives 1st gear and a 6000 RPM shift you'll know what's what.

maw

@maw1124 stupid question, but when you say further out, are you saying make it looser? Also I don’t see an adjustment nut on the Bowden cable, do I have to adjust the throttle cable for the Bowden to adjust?

 

[maw1124]

Tighter.

You probably just want your trusty mechanic to do it according to your (these) instructions.

That's what I did. I don't even pretend to wrench on cars.

Just gotta know enough to know what you don't know, you know?

maw

 

[Mbijee]

Just gotta know enough to know what you don't know, you know?

@maw1124 lol, unfortunately I’m in Michigan (near the Detroit area) and not many knowledgeable mechanics that are familiar with this car. I feel safer doing this myself. I’m sure I can find a forum on this somewhere. Thanks for the input.

 

[maw1124]

So am I. Go see Satish at Motorwerks (Commerce) or The Auto Lounge on M5 and Maple. Either of them can do it.

maw

PS ... but yes I'm sure there's a DIY here somewhere... GL

 

[gsxr]

Updated video

Much better video!

https://youtube.com/shorts/m8ADH4kq7i0?si=bCdGfErGgmgxTYt8

@gsxr @maw1124 heres an updated video from full throttle on “B” and “D”. Since “B” is accelerating nicely without upshifting, does that mean it’s operating as it should, therefore the kickdown solenoid and the cable are good and off the list?
The solenoid was also measuring 14.4 OHM.

Yes - this shows that your kickdown solenoid is good, the B-switch is good, and your engine power is normal - pulls to redline in 1st gear, no problem.

I know it’s hard to tell from the second part of the video, but it really doesn’t help considering my car starts in 2nd gear

It actually appears to be starting in 3rd gear - or, it's starting in 2nd and the upshift from 2-3 is not visible on the tachometer.

I’m kind of leaning towards a kickdown switch and/or Bowden cable needs adjustment.

Correct. If you have pressed the pedal to the floor, engaging the kickdown switch, that should drop the transmission to 1st gear.

Even without the kickdown switch engaged, from a dead stop, the Bowden cable should cause the transmission to drop to 1st gear. This is not happening.

As far as misfiring goes, my car drives and idles nicely. No hesitations. The only possible “sign” of misfiring I have is when I start the car for the first time of the day (only the first start of the day), it fluctuates between 700-1100 RPM. It does like 5 small revs in that range and goes back to normal. I doubt that’s a misfire, I think it’s more of fuel “issue”.

The pull to redline in 1st gear shows the engine is running normally - you have a transmission problem.


Almost looks to me like the Bowden cable is disconnected or broken. If not... you might have a more serious (internal) transmission issue. This could be difficult to troubleshoot, and is also very, very rare.

 

[Mbijee]

@gsxr thanks for the reply. The car does start in second, and shift to 3rd but the rpm needle doesn’t drop so it hard to tell from the video. Also when I’m cursing in 4th gear, I’ll manually change the shifter to “3”, and it downshifts and I can even redline it then. It’s only when I put it in drive it loses it power. I’m gonna adjust the Bowden cable and come back with an update. Fingers crossed .

 

[gsxr]

@gsxr thanks for the reply. The car does start in second, and shift to 3rd but the rpm needle doesn’t drop so it hard to tell from the video.

THis also sounds like the Bowden cable is broken or disconnected... which will result in upshifting from 2nd to 3rd, when the transmission should instead be downshifting from 2nd to 1st.

Also when I’m cursing in 4th gear, I’ll manually change the shifter to “3”, and it downshifts and I can even redline it then.

How about if you are cruising in 4th, manually select 3, and then manually select 2? It should drop to 2nd.

It’s only when I put it in drive it loses it power. I’m gonna adjust the Bowden cable and come back with an update. Fingers crossed .

Also try starting in "B" from a stop, then moving to 2 when you want 2nd gear, move to 3 when you want 3rd gear, etc...

 

[Mbijee]

THis also sounds like the Bowden cable is broken or disconnected... which will result in upshifting from 2nd to 3rd, when the transmission should instead be downshifting from 2nd to 1st.

@gsxr Let me ask you this… if the Bowden cable is disconnected or broken, wouldn’t it not shift at all since the cable won’t be pulling? Also what area should I be checking to see if it’s broken/disconnected.

How about if you are cruising in 4th, manually select 3, and then manually select 2? It should drop to 2nd.

Haven’t tried that I’m gonna give it a try. I have the 119.97 so the Bowden cable adjustment is a little different, it has to be done through the connecting rod. According to the manual, the two “points” should align and they do. Should I still try adjusting it? I tightened the throttle cable, and it tightened the Bowden aswel, but then I started getting high idle rpms so I loosened it (I thought it would be a little shortcut for the Bowden adjustment).

Also try starting in "B" from a stop, then moving to 2 when you want 2nd gear, move to 3 when you want 3rd gear, etc...

Will try that aswel. Thank you for your patience and responses.

 

[gsxr]

@gsxr Let me ask you this… if the Bowden cable is disconnected or broken, wouldn’t it not shift at all since the cable won’t be pulling? Also what area should I be checking to see if it’s broken/disconnected.

if the Bowden cable is disconnected or broken, the transmission would still shift, but it would upshift at very, very low RPM.

Haven’t tried that I’m gonna give it a try. I have the 119.97 so the Bowden cable adjustment is a little different, it has to be done through the connecting rod. According to the manual, the two “points” should align and they do. Should I still try adjusting it? I tightened the throttle cable, and it tightened the Bowden aswel, but then I started getting high idle rpms so I loosened it (I thought it would be a little shortcut for the Bowden adjustment).

I'd disconnect the Bowden cable ball/socket joint and pull on the end with your fingers. It should have substantial spring tension, and pull back when you let go. If not, something is wrong on the transmission side.

Will try that aswel. Thank you for your patience and responses.

I forgot to ask earlier - did this problem occur suddenly, i.e. you parked the car one evening and it was fine, and the next morning it was not behaving properly? Or was some repair work done, and it hasn't been right since the work? If the latter - what work was performed?

 

[Mbijee]

@gsxr Newly acquired vehicle. I bought it with a non-working convertible top. I fixed that, but I just recently realized this issue, as I had never really “floored” it. Does the Bowden cable ball just pry off? I also wanted to ask, does the “b” switch use the same electric cable as the kickdown switch to send signal to the solenoid? I want to make sure so I don’t crawl up under it again to test the voltage when pressing on the pedal switch lol.

P.S. I can’t find much info on adjusting the connecting rod to tighten up the Bowden cable

 

[gsxr]

@gsxr Newly acquired vehicle. I bought it with a non-working convertible top. I fixed that, but I just recently realized this issue, as I had never really “floored” it.

ohhhhh. I wonder how long this was happening. I'm sure the previous owner (dealer?) knew about it as well.

Does the Bowden cable ball just pry off?

Yes. It may be tight. Clean the ball & socket and apply a dab of grease when installing (same for all other ball/socket connections on the throttle linkage).

I also wanted to ask, does the “b” switch use the same electric cable as the kickdown switch to send signal to the solenoid? I want to make sure so I don’t crawl up under it again to test the voltage when pressing on the pedal switch lol.

The "B" switch is part of the kickdown circuit. However as noted previously, your solenoid is working because you can pull to redline in 1st gear (B). Basic diagram PDF at this link, just ignore the K29/1 relay which won't be present on your R129.

P.S. I can’t find much info on adjusting the connecting rod to tighten up the Bowden cable

This almost certainly is not an "adjustment" issue. It's acting like the Bowden cable is broken, or disconnected at either end. Test as I described above first (separate ball/socket, pull on cable with your fingers).

 

[Mbijee]

@gsxr i took it for a spin… while cruising in 4th, I can downshift to 3 and 2 no problem. Also can upshift from “B” upwards no problem.
Did the Bowden test, and there’s some resistance that springs it back when I let go…
Here’s a video, hopefully it shows something
Bowden test

Should I still check the tranny end of the cable for disconnection?

 

[gsxr]

@gsxr i took it for a spin… while cruising in 4th, I can downshift to 3 and 2 no problem.

Do you mean a manual downshift, using the shift lever? That's good!

Also can upshift from “B” upwards no problem.

I assume this is also manual with the shift lever.

Did the Bowden test, and there’s some resistance that springs it back when I let go…
Here’s a video, hopefully it shows something
Bowden test

OK - that looks normal. Which is good and bad...

https://youtube.com/shorts/OJLSYbwEHjg?si=2QKP8Ahl1KEwttYc

Should I still check the tranny end of the cable for disconnection?

I don't think so... from memory, if it was disconnected inside the transmission, there would be no spring tension to pull the cable back. Good news is the Bowden cable appears to be installed properly, bad news is your transmission seems to act like it's not receiving any signal from the Bowden cable.

If it were my car, possibly my next attempt would be swapping in a known-good valve body, but that's not something most people usually have available. There was one for sale by a forum member recently but it's sold now.

 

[Mbijee]

Do you mean a manual downshift, using the shift lever? That's good!

Correct

I assume this is also manual with the shift lever.

Yes

OK - that looks normal. Which is good and bad...

I don't think so... from memory, if it was disconnected inside the transmission, there would be no spring tension to pull the cable back. Good news is the Bowden cable appears to be installed properly, bad news is your transmission seems to act like it's not receiving any signal from the Bowden cable.

If it were my car, possibly my next attempt would be swapping in a known-good valve body, but that's not something most people usually have available. There was one for sale by a forum member recently but it's sold now.

I might just drive it as is for the summer and take care of the transmission issue when it’s ready for storage. If I really wanna rip her I’ll just use the shift lever for now…

Thanks for your help @gsxr

 

[gsxr]

Yup, for now, you can just shift it manually. This might get old quick in city traffic though. I wouldn't let it continue upshifting early, this is hard on the transmission and torque converter, when you are at high load and stuck at 2000rpm.

Next steps for diagnostics would be pulling the transmission pan for a visual inspection inside.

If you are near Satish's shop, I'm sure they could figure it out. However it might not be cheap to have them diagnose it. I dunno if they will want to dig inside the transmission or just recommend a replacement, which is sorta using a shotgun on a mosquito. Most shops would generally want to replace the transmission (possibly after a fluid & filter change, which is quite likely a waste of money) because they don't know how the internals work...

 

[maw1124]

Yup, for now, you can just shift it manually. This might get old quick in city traffic though. I wouldn't let it continue upshifting early, this is hard on the transmission and torque converter, when you are at high load and stuck at 2000rpm.

Next steps for diagnostics would be pulling the transmission pan for a visual inspection inside.

If you are near Satish's shop, I'm sure they could figure it out. However it might not be cheap to have them diagnose it. I dunno if they will want to dig inside the transmission or just recommend a replacement, which is sorta using a shotgun on a mosquito. Most shops would generally want to replace the transmission (possibly after a fluid & filter change, which is quite likely a waste of money) because they don't know how the internals work...

Satish did the transmission in the car you sold to Eric... He's good for it but like you said I doubt it's cheap.

If @Mbijee wants to just get a Sun Valley Rebuild and have a shop remove and replace I can talk to The Auto Lounge guys for a better rate.

But those seem like the options to me. It's what I would do if it was my car and it was in MI. But my car was in FL when the trans went (and still is).

maw

 

[maw1124]

Now for the bad news. Your car acts like mine was acting when I blew up some piston band in the transmission (by playing around with the B switch mechanism -- improperly must have been -- trying to engage 1st gear). But I don't want to jump to that conclusion. My solution was a new transmission with full time first gear start via a different valve body. How does your transmission feel otherwise. "Weak" is all I recall about how mine felt, like full time limp mode.

maw

Problem with this condition is you can limp around town with it like this, but as soon as you put your foot past 1/2 throttle you get this 1/2 response, half confusion. That was obviously not gonna work for me. So I got to know Marc at Sun Valley, and we've been good ever since. I haven't spoken to him about the availability of these boxes in some time, but as these cars age I can't imagine they're as plentiful as when I did mine a decade ago. So move quickly whatever you decide would be my advice.

maw

 

[Mbijee]

@gsxr @maw1124 would a 5spd manual swap be possible on these? Any options?

 

[R129 UK]

@gsxr @maw1124 would a 5spd manual swap be possible on these? Any options?

I've just read this thread with interest, unfortunately I can't help with your issue but yes, you can do a manual swap...

This is a multipart video and is part 6/7:

Personally, although it is possible, I would stick with what you have and get that working correctly for now.

 

[gsxr]

@gsxr @maw1124 would a 5spd manual swap be possible on these? Any options?

Possible, yes. Practical, no. Reasonable cost, ROTFLMAO.

Personally, although [a manual transmission conversion] is possible, I would stick with what you have and get that working correctly for now.

Plus eleventybillion: ^^^