Opening Up a 722.3 Transmission

[gsxr]

You are correct, I SHOULD start in 2nd, but when I hit the "B" to the left of the "2" on the selector nothing happens. Shouldn't it shift down into 1st?

Yes. If it is not dropping to 1st gear in the "B" position, the kickdown circuit is not working correctly. Start by checking if the wire is connected to the solenoid at the passenger rear of the transmission.

That makes sense, the internal pistons are for shift firmness. Honestly the car shifts well it just skips the "2nd" gear, which you may be right, is actually 3rd. Maybe I start in 2nd and go to 4th immediately meaning I skip 3rd. But i will say i can go like 30mph at around 1k rpm in this gear so I think it has to be 3rd doesn't it? Otherwise highway speeds would be like 6k rpm or something and at around 50 im at around 3k RPM i believe. Not sure what to make of this.

Try shifting manually to verify each gear and shift. With the shift lever in 2, it will not upshift to 3rd until you move the lever to 3, and so on.

I bought the car with this issues, it had been sitting for 4 years so its my current restoration project until I can get to my other V12 lol. PO had issues with this, supposedly had trans rebuilt (same issue) and had donor trans put in which is in the car now (same issue).

I wonder if the original trans was sent out for a rebuild, or if it was an "exchange" unit - not the same transmission. You can verify by looking at the serial number on the side of the trans and compare to the EPC datacard.

Bowden is adjusted to have the pointers matching on throttle body and cable side. there is play like 2-3mm when applying throttle but that's normal right?

Pointers lined up is the ballpark setting. You can adjust to personal preference. Tightening the cable by adjusting the linkage rods should make a noticeable difference in shift RPM's, both upshift and downshift. Experiment and set it where you are happy with the shift points. If you get it wrong, you'll know pretty quickly.

Also, vacuum modulator and shift advance lines were not hooked up by PO lol so i did that but honestly it only helped the shift no happen at 4k RPM, now it will shift 2-3K but still skips that gear. Not sure how to proceed.

That's odd. The vac modulator only affects shift firmness (would be REALLY firm with no vacuum applied), and the other vac lines on the passenger side normally would need vacuum applied to increase the shift RPM (intended to heat the catalysts after a cold start).

For starters, try and confirm if you are starting in 2nd, skipping 3rd, and going to 4th.

What is that TSB you mentioned, can you find it? i wonder how deep I would have to go

It's not a public TSB that I know of, it's buried in a dealer tech training manual. But, need to confirm if you are skipping 2nd or skipping 3rd, as those are different issues.

 

[AngryZacMan]

Yes. If it is not dropping to 1st gear in the "B" position, the kickdown circuit is not working correctly. Start by checking if the wire is connected to the solenoid at the passenger rear of the transmission.

It feels like its 1st because car is so slow, but I am not 100%. wire should be connected from what ive seen down there. I think the real test will be signal test and just shorting solenoid to 12v. is it a ground wire that connects to it or power wire? I think its just 1 wire correct?

Try shifting manually to verify each gear and shift. With the shift lever in 2, it will not upshift to 3rd until you move the lever to 3, and so on.

I tried and it kind of stays in gear but the B to 2 move does nothing. going to 3 will upshift so I THINK its skipping second. do you know the ratios for 1st vs 2nd so i can compare speeds at like 3k rpm and see which im really in?

I wonder if the original trans was sent out for a rebuild, or if it was an "exchange" unit - not the same transmission. You can verify by looking at the serial number on the side of the trans and compare to the EPC datacard.

I have a spare trans so one is bound to be the original haha I will check which one.

Pointers lined up is the ballpark setting. You can adjust to personal preference. Tightening the cable by adjusting the linkage rods should make a noticeable difference in shift RPM's, both upshift and downshift. Experiment and set it where you are happy with the shift points. If you get it wrong, you'll know pretty quickly.

I messed with it to shift up past 4k but the skipping is still there so no help. i had it set right before so this is internal issue.

That's odd. The vac modulator only affects shift firmness (would be REALLY firm with no vacuum applied), and the other vac lines on the passenger side normally would need vacuum applied to increase the shift RPM (intended to heat the catalysts after a cold start).

For starters, try and confirm if you are starting in 2nd, skipping 3rd, and going to 4th.

It was really harsh ar first but after hook up it got better. what idiots must have worked on this car it now has the skipping issue but otherwise is smooth. no harsh downshifts or upshifts when it does shift. I do need to figure out what gear im in. as i asked before, i need gear ratios to figure out speed at 1st vs 2nd to see what rpm im at and deterine, unless theres another way to figure this out.

 

[gsxr]

It feels like its 1st because car is so slow, but I am not 100%. wire should be connected from what ive seen down there.

Try this. Put the shifter in "B" position and accelerate slowly to redline. The transmission should start in 1st gear and pull to the rev limiter (~6300rpm), and not upshift to 2nd. If you are in 1st gear, redline / 6000rpm will be around 45mph. Therefore at 3000rpm you should be around 2500rpm. If you are going a lot faster (say, 40mph at 3000rpm)... that means you are in 2nd gear, not 1st gear. This also means the kickdown solenoid is not working with the shifter in "B" position.

I think the real test will be signal test and just shorting solenoid to 12v. is it a ground wire that connects to it or power wire? I think its just 1 wire correct?

It is a single wire, that provides +12v to energize the kickdown solenoid. With the engine running and "B" position selected, you should measure +12v at that wire.

I tried and it kind of stays in gear but the B to 2 move does nothing. going to 3 will upshift so I THINK its skipping second. do you know the ratios for 1st vs 2nd so i can compare speeds at like 3k rpm and see which im really in?

1st = 3.87 (approx 45mph at 6000rpm)
2nd = 2.24 (approx 80mph at 6000rpm)
3rd = 1.44 (approx 125mph at 6000rpm)
4th = 1.00 (approx 180mph at 6000rpm)
Rear axle ratio = 2.65

It was really harsh ar first but after hook up it got better. what idiots must have worked on this car it now has the skipping issue but otherwise is smooth. no harsh downshifts or upshifts when it does shift. I do need to figure out what gear im in. as i asked before, i need gear ratios to figure out speed at 1st vs 2nd to see what rpm im at and deterine, unless theres another way to figure this out.

Most Mercedes speedometers have yellow/orange hash marks to indicate the max RPM in each gear. Oddly, the 140 chassis with electronic odometer does not have those markings. I did not know this! Strange. The early 140 with mechanical odometers does have the shift point markings, which match fairly well with my estimated speeds above.

 

[AngryZacMan]

Try this. Put the shifter in "B" position and accelerate slowly to redline. The transmission should start in 1st gear and pull to the rev limiter (~6300rpm), and not upshift to 2nd. If you are in 1st gear, redline / 6000rpm will be around 45mph. Therefore at 3000rpm you should be around 2500rpm. If you are going a lot faster (say, 40mph at 3000rpm)... that means you are in 2nd gear, not 1st gear. This also means the kickdown solenoid is not working with the shifter in "B" position.

Oof, good one. I will do that. are the V12 ratios that much similar to the E400-500 ones? I ask because is that a generic 722.3 value of 45mph in 1st ar redline or specific to a certain car version?

It is a single wire, that provides +12v to energize the kickdown solenoid. With the engine running and "B" position selected, you should measure +12v at that wire.

Awesome, I will test it.

Most Mercedes speedometers have yellow/orange hash marks to indicate the max RPM in each gear. Oddly, the 140 chassis with electronic odometer does not have those markings. I did not know this! Strange. The early 140 with mechanical odometers does have the shift point markings, which match fairly well with my estimated speeds above.

Interesting as hell, I did not notice that. I will have to look at mine and see but I don't think it has it. I guess I need to just do that B test to really be able to tell.

 

[gsxr]

Oof, good one. I will do that. are the V12 ratios that much similar to the E400-500 ones? I ask because is that a generic 722.3 value of 45mph in 1st ar redline or specific to a certain car version?

Max speed in each gear varies by chassis and engine combination, as the engine redlines, rear axle ratio, and tire sizes all vary.

The 45mph estimate above is specifically for 1st gear in the S600 with 2.65 axle ratio and 722.3 transmission.

IIRC most/all the 722.3 gearboxes have the same, or nearly the same, gear ratios.

 

[AngryZacMan]

Max speed in each gear varies by chassis and engine combination, as the engine redlines, rear axle ratio, and tire sizes all vary.

The 45mph estimate above is specifically for 1st gear in the S600 with 2.65 axle ratio and 722.3 transmission.

IIRC most/all the 722.3 gearboxes have the same, or nearly the same, gear ratios.

Got it. I figured it was the rear end that makes all the difference really. I will see about that test in the coming days and report. back. Thanks @gsxr for all the help seriously

 

[Seangbadee]

The valvebody piston/spring movements generally control shift firmness... stiffer springs = firmer shifts. It would be very unlikely any pistons are binding, and I'm not sure what the symptoms would be. The round covers on the outside of the transmission, on the passenger side, are B1 (front) and B2 (rear), which are brake bands. The "K" clutches are discs inside the transmission housing.

Anyway. What you describe is an odd problem, assuming your transmission is unmodified and normally starts in 2nd gear. You could try adjusting the Bowden (control pressure) cable and see what effect that has. This will adjust all part-throttle shift points. If the other shifts become unacceptable, adjust back to where it is now. But, this could help your early 2-3 upshift.

IIRC there's a TSB about "skipping" 2nd gear but the solution was not simple. Try the Bowden adjustment first.

I had a similar problem after rebuilding my 722.369 transmission, and as @gsxr mentioned, the Bowden cable is always the first place to start when diagnosing these shift issues. My second gear felt really short, almost like it went straight into third. I noticed that the longer the cable (more visible screws), the longer the time between the shifts become, while a shorter cable results in quicker shifts. There’s a “sweet spot” you need to find for optimal performance. I adjusted the Bowden cable, and found my sweet spot, and now the shifts are smooth as butter with the 'right' intervals.

 

[AngryZacMan]

I had a similar problem after rebuilding my 722.369 transmission, and as @gsxr mentioned, the Bowden cable is always the first place to start when diagnosing these shift issues. My second gear felt really short, almost like it went straight into third. I noticed that the longer the cable (more visible screws), the longer the time between the shifts become, while a shorter cable results in quicker shifts. There’s a “sweet spot” you need to find for optimal performance. I adjusted the Bowden cable, and found my sweet spot, and now the shifts are smooth as butter with the 'right' intervals.

I messed with it and it just made my shifts hang to 4k RPM but still shifts quick into next gear. it actually made it easier to see cause i could see the needle go from 4k to 3k to 2k so i saw it double shift in real time. sadly doesn't look like that my issue

 

[AngryZacMan]

Alright y'all, I had some time to test the trans. It ran about 25mph at 3k RPM and just above 40 mph at 6k RPM before it shifted twice down to like 3k RPM. I then had to slow down on the road so I didn't get to see past that, but it does seem like it is stuck in first and skipping to 3rd right?
Based on the speeds @gsxr mentioned, it is stuck in first. So now how do i fix this is the question. Any suggestions where to start?
For context, Bowden was adjusted, vacuum hooked up, I will test vac modulator for holding pressure to be sure but it shifts smooth when it does shift so not too convinced it's that. Trans has fresh fluid and filter at proper level 80C temp in P running engine.

 

[gsxr]

Alright y'all, I had some time to test the trans. It ran about 25mph at 3k RPM and just above 40 mph at 6k RPM before it shifted twice down to like 3k RPM. I then had to slow down on the road so I didn't get to see past that, but it does seem like it is stuck in first and skipping to 3rd right?
Based on the speeds @gsxr mentioned, it is stuck in first. So now how do i fix this is the question. Any suggestions where to start?
For context, Bowden was adjusted, vacuum hooked up, I will test vac modulator for holding pressure to be sure but it shifts smooth when it does shift so not too convinced it's that. Trans has fresh fluid and filter at proper level 80C temp in P running engine.

OK, that was starting in 1st, then it sounds like 2 rapid upshifts. As noted earlier, this model normally starts in 2nd gear unless you manually select "B" position from a stop, or floor the accelerator from a stop.

Assuming the part throttle shift RPM's vary based on throttle position, the Bowden cable is connected properly and working.

Seems like something weird with the valvebody causing the early upshift but I don't know what to suggest at this point.

 

[AngryZacMan]

OK, that was starting in 1st, then it sounds like 2 rapid upshifts. As noted earlier, this model normally starts in 2nd gear unless you manually select "B" position from a stop, or floor the accelerator from a stop.

Assuming the part throttle shift RPM's vary based on throttle position, the Bowden cable is connected properly and working.

Seems like something weird with the valvebody causing the early upshift but I don't know what to suggest at this point.

Yeah I am assuming some valves in the body stick or leak pressure. I think I need an overhauled valvebody at this point. I mean that's easier than pulling the whole trans out for rebuild so I'll take it.

Do you know if sun valley MB trans in CA sells just valve bodies?

 

[gsxr]

Yeah I am assuming some valves in the body stick or leak pressure. I think I need an overhauled valvebody at this point. I mean that's easier than pulling the whole trans out for rebuild so I'll take it.

I'd look for a used one to swap in for testing. Or maybe a complete used transmission and raid the VB from that. Open / inspect the spare if you go this route, before installing... check for broken springs, clean it out, etc.

Do you know if sun valley MB trans in CA sells just valve bodies?

I don't believe so. However, you could ask them about refurbishing yours... not sure if they do that either.

Another option is to disassemble and clean yours out, but there's no guarantee anything will change afterwards, unless you find a smoking gun inside.

 

[AngryZacMan]

I'd look for a used one to swap in for testing. Or maybe a complete used transmission and raid the VB from that. Open / inspect the spare if you go this route, before installing... check for broken springs, clean it out, etc.

I do have a spare so I just have to open it up and see. It was supposedly "rebuilt" but I don't know how true that is honestly.

I don't believe so. However, you could ask them about refurbishing yours... not sure if they do that either.

Another option is to disassemble and clean yours out, but there's no guarantee anything will change afterwards, unless you find a smoking gun inside.

Yeah they will rebuild it all but the trans inside here is supposedly rebuilt already so I'd hate to spend $3k to do this for nothing. I will open up VB and see.
Do you know of a shift kit or repair kit for these 722.3? I only know of the 722.6 shift kits

 

[gsxr]

If you have a spare VB... swap that in!! It's messy, but may also fix the problem - and there's almost no cost, if you save the fluid and re-use it.

There are no repair kits for 722.6 VB's. There is a Superior shift kit but that is intended to adjust firmness on specific shifts which may either be too soft (flaring) or too harsh, while other shifts are normal. I think the Superior kit may have some adjustment for shift timing but you'd need to read the instructions. I would call their tech support line before you buy that kit or attempt using it.

 

[Seangbadee]

Yeah I am assuming some valves in the body stick or leak pressure. I think I need an overhauled valvebody at this point. I mean that's easier than pulling the whole trans out for rebuild so I'll take it.

Do you know if sun valley MB trans in CA sells just valve bodies?

@AngryZacMan , what type of transmission fluid are you using? I don't recall seeing this in any of your posts.

 

[AngryZacMan]

If you have a spare VB... swap that in!! It's messy, but may also fix the problem - and there's almost no cost, if you save the fluid and re-use it.

There are no repair kits for 722.6 VB's. There is a Superior shift kit but that is intended to adjust firmness on specific shifts which may either be too soft (flaring) or too harsh, while other shifts are normal. I think the Superior kit may have some adjustment for shift timing but you'd need to read the instructions. I would call their tech support line before you buy that kit or attempt using it.

Yeah IF that one works. I think I'll take it apart and verify first but if its good, I will use it for sure. Good idea @gsxr

@AngryZacMan , what type of transmission fluid are you using? I don't recall seeing this in any of your posts.

I normally use the old Febi Dex 3 stuff with 236.12/10 approval. Now since last flushing I bought the regular Valvoline Dex 3 to use, once I figure out the issue i will flush one last time and leave the Febi in there. there are MANY febi part numbers for ATF, do you recommend a specific one so i can make sure its the one I use?

 

[gsxr]

236.10 fluid is preferred, this is the thicker fluid, equivalent to Dexron-III and the viscosity is around 7.5 cSt.

236.12 (and 236.14) are thinner viscosity, around 6.0 cSt, basically equivalent to Dexron-VI. These are ok, but may require slight adjustment to the vacuum modulator. The first and only time I tried a Dex-VI fluid, the result was a slight flare at upshifts, which was cured by twiddling the modulator. I'm not sure there are any particular benefits to the thinner fluid (it was primarily designed for fuel economy, same as thinner engine oils). I like the older/thicker stuff.

I like Red Line ATF but it's gotten crazy expensive.

 

[Seangbadee]

Yeah IF that one works. I think I'll take it apart and verify first but if its good, I will use it for sure. Good idea @gsxr



I normally use the old Febi Dex 3 stuff with 236.12/10 approval. Now since last flushing I bought the regular Valvoline Dex 3 to use, once I figure out the issue i will flush one last time and leave the Febi in there. there are MANY febi part numbers for ATF, do you recommend a specific one so i can make sure its the one I use?

I’ve used Castrol Dex/Merc for many years and never ran any of the thinner ATFs. Now, after my rebuild and 500 miles of driving, I’m going to drain the whole system including the torque converter, change the filter, and refill with Red Line. Since all my seals are brand new, I’ll be sticking with a full synthetic ATF from here on out

 

[gerryvz]

I’ve used Castrol Dex/Merc for many years and never ran any of the thinner ATFs. Now, after my rebuild and 500 miles of driving, I’m going to drain the whole system including the torque converter, change the filter, and refill with Red Line. Since all my seals are brand new, I’ll be sticking with a full synthetic ATF from here on out
View attachment 228284

This (Castrol TransMax Dex/Merc, which is Dex II/III compatible per our transmissions) is what I have always used in my transmissions, and it has worked very well. If you re-seal your transmission, as @Seangbadee did, then I would go with RedLine synthetic all the way. However, I would not put a synthetic ATF in a transmsision that is "used" to having dino-based Dex III in it for many years.

 

[AngryZacMan]

Hey y'all, sorry for the MIA. Work has me running around a lot so I haven't had the chance to touch the car and I probably won't be able to for another week or so, got both lifts taken with client cars. I will be diving into the spare valve body though to see if it can pass the test and if that's good, i plan to just swap it into the (supposedly) bad one in the car, mostly to save time so I'm not pulling the car one, opening, diagnosing, ordering parts, rebuilding, and finally installing. Does that sound like a good idea to y'all or just rebuild the one in car and wait it out for parts?

236.10 fluid is preferred, this is the thicker fluid, equivalent to Dexron-III and the viscosity is around 7.5 cSt.

Which fluids besides Redline have this spec? Is the Valvoline Dexron this or the 236.12? The regular blue bottle. i can post a pic if needed.
Yeah redline is damn good but its expensive, I stopped using it a few years ago and use Febi, it is cheaper .

I’ve used Castrol Dex/Merc for many years and never ran any of the thinner ATFs. Now, after my rebuild and 500 miles of driving, I’m going to drain the whole system including the torque converter, change the filter, and refill with Red Line. Since all my seals are brand new, I’ll be sticking with a full synthetic ATF from here on out

Haven't used that, i wonder how the Castrol stacks up. I do think after rebuild Redline is the shit to use, it's just pricey if you're flushing and pulling apart several times. Once i get it situated i will do final fill with Castrol maybe since Gerry also recommends it.

This (Castrol TransMax Dex/Merc, which is Dex II/III compatible per our transmissions) is what I have always used in my transmissions, and it has worked very well. If you re-seal your transmission, as @Seangbadee did, then I would go with RedLine synthetic all the way. However, I would not put a synthetic ATF in a transmsision that is "used" to having dino-based Dex III in it for many years.

Got ya, wise advise as always Gerry. Mine is 120k so no Redline here lol.

 

[gsxr]

I will be diving into the spare valve body though to see if it can pass the test and if that's good, i plan to just swap it into the (supposedly) bad one in the car, mostly to save time so I'm not pulling the car one, opening, diagnosing, ordering parts, rebuilding, and finally installing. Does that sound like a good idea to y'all or just rebuild the one in car and wait it out for parts?

Sounds like a good plan to me.

Which fluids besides Redline have this spec? Is the Valvoline Dexron this or the 236.12? The regular blue bottle. i can post a pic if needed.
Yeah redline is damn good but its expensive, I stopped using it a few years ago and use Febi, it is cheaper.

You'll need to check current spec sheets on various fluids. There are still some out there with 7.5 viscosity. Mfr's change their formula periodically and sometimes change the specs as well, so if you want a certain viscosity, make sure to look up a current spec sheet on that particular fluid.

236.12 and 236.14 are both thinner, 6.0 viscosity, equivalent to Dexron-VI.

Haven't used that, i wonder how the Castrol stacks up. I do think after rebuild Redline is the shit to use, it's just pricey if you're flushing and pulling apart several times. Once i get it situated i will do final fill with Castrol maybe since Gerry also recommends it.

Yeah, I generally wait until I know a transmission is working properly and leak-free before feeding it Red Line. However, while experimenting / testing, you can save the fluid and re-use it if you are careful. Drain into a clean container, etc. Pour it through a filter of some sort if you are concerned that debris may have gotten into it somehow while draining. The fluid will get pulled through the filter in the transmission before getting pumped throughout the trans. It's time consuming, but given the insane cost of ATF these days, I re-use when possible.

 

[dreaming.haze]

For those who are more of a visual learner, here is a great video that was just put out with a guy opening up a 722.362. Helped me out with some of the mystery in certain elements of a transmission and how things function.

 

[AngryZacMan]

For those who are more of a visual learner, here is a great video that was just put out with a guy opening up a 722.362. Helped me out with some of the mystery in certain elements of a transmission and how things function.

Oh JM is a good dude, he is learning along with us but his videos are so good, much like M539 restorations

 

[AngryZacMan]

You'll need to check current spec sheets on various fluids. There are still some out there with 7.5 viscosity. Mfr's change their formula periodically and sometimes change the specs as well, so if you want a certain viscosity, make sure to look up a current spec sheet on that particular fluid.

236.12 and 236.14 are both thinner, 6.0 viscosity, equivalent to Dexron-VI.

Got it, I will do some digging then and find out.

eah, I generally wait until I know a transmission is working properly and leak-free before feeding it Red Line. However, while experimenting / testing, you can save the fluid and re-use it if you are careful. Drain into a clean container, etc. Pour it through a filter of some sort if you are concerned that debris may have gotten into it somehow while draining. The fluid will get pulled through the filter in the transmission before getting pumped throughout the trans. It's time consuming, but given the insane cost of ATF these days, I re-use when possible.

I usually do too, but I also want to use these drains and service works as a proper flush procedure so so far I did it 2 times with new fluid to get the old out. now i think it's time to start saving it until the final flush and fill.

 

[Seangbadee]

For those who are more of a visual learner, here is a great video that was just put out with a guy opening up a 722.362. Helped me out with some of the mystery in certain elements of a transmission and how things function.

The level of detail, clarity and technical explanations are spot-on, especially for anyone who’s worked on the 722.3 family before. I’ll be rebuilding another 722.369 next year once the weather warms up a bit.