I have googled and forum-searched and read the WSM ad nauseum, and I can't figure this out. Car is an '84 S.

Symptoms: worked great for several months for all kinds of driving, then after a 20-minute freeway run, it won't upshift past 2nd gear.

Engages in reverse quickly and solidly, engages in forward gear quickly and solidly, <1 second switching from R to D. Shift from 1-2 under light and heavy throttle is swift and smooth, and happens at appropriate RPM. No weird noises or shudders. No slip in 1st or 2nd under load. Zooms up to redline with authority. No clunky downshift when coming to a stop. No signs of TQ or OWC trouble - stall speed good and coasts normally.

If it was a 2-speed gearbox, it would seem perfectly healthy. It blew a filter in the past, but has been normal ever since after a thorough cleaning and new fluid. The only odd thing it has done since the "stuck in 2nd" behavior began, was twice, as I was doing the zoom/coast/repeat routine to limp home, it reluctantly up-shifted at about 55mph, and allowed me to cruise normally at highway speeds. Very convenient, made getting home much easier, but hasn't repeated that since. The magic went away as soon as I slowed down again.

I have checked:

Fluid & filter - old fluid looked great. Minimal sediment in pan. Level correct. No signs of foaming or water fouling. No metal in pan.

Radiator OK - no signs of leaks or blockage in cooler lines or cooler. No signs of fluid and coolant mixing in either direction.

Kickdown switch, relay and solenoid. Removed and tested solenoid. O-rings OK. Switch isn't stuck. Relay OK. Test drove with solenoid wire unplugged - no change.

Governor - gear clean and unworn, valve operates smoothly, no signs of trouble, housing clean.

Removed valve body and lower cover. Everything super clean. All valves and plastic doodads clean and operational. Separator plate gasket looked questionable, so replaced it with correct MB gasket. Cleaned a little debris from the screens in the lower cover.

Gear selector cable OK. Selector lever and detents in transmission are in sync.

Bowden cable OK, no binding, socket mounts to ball with no slack or tension. Test drove with Bowden disconnected, no change.

Vacuum modulator OK. No leak at modulator. Vacuum line at modulator pulling good vacuum.

B1 piston and band (what I can see of it) look good. Everything visible in the trans with the separator plate off looked super clean.

So... What's next? Anything left to check without tearing the rear end out of the car? I'm stumped.

 

I think your issue is in the valve body, either a broken/hard o-ring, a broken spring, or debris causing one of the spool valves to stick. That the unit has twice upshifted into the higher gear range, albeit reluctantly, says to me the gear sets and clutches/bands are intact and functioning correctly. They just aren't being engaged at the appropriate times. This is all controlled by the valve body. You can refresh the body yourself or perhaps you can send it to Greg Brown at Precision Motorwerks for a rebuild. He stocks all the latest revision parts necessary to rebuild these boxes.

Mike

 

I had this happen recently with my nephew's 928. I pulled the valve body completely apart and cleaned everything. I did not see anything out of the ordinary and none of the springs were broken. I put it back together with fresh fluid and filter and his gears came back. You could always just try new fluid and filter first unless you are comfortable with disassembling the valve body.

 

I did disassemble the valve body (and even pulled the separator plate and lower cover housing), new fluid and filter. It was very clean and everything moved smoothly... That's a big part of why I'm so stumped. I guess I could do it again.

 

I am on the end of a Trans rebuild that I have documented on this forum. The condition you describe is the same my 1984 suffered. In the end I had worn out plates in the k1 clutch and a leaking seal in the k2 clutch. After ahat I have seen in my rebuild. Bite the bullet and rebuild it. Chances are your problem is not the valve body.
Check out my post called "Transmission Rebuild"

 

I read your thread - lots of info in there!

Today I removed, disassembled, cleaned, and reassembled my valve body. It wasn't very dirty, and I could only find one obvious problem (broken end coil on a small spring in the 1-2 command valve). The center plate shows some obvious wear at various ball/check valve interfaces.

Put it back together and back in the car, and now it TRIES to shift from 2-3, but just ends up out of gear altogether. Have to move the selector back to 2 to get it back in gear. Seems like K1 is not getting the signal to engage. But, seems like a definite valve body issue since fiddling with the valve body caused this change, and 3rd gear never slipped at all before.

Before I dive into a rebuild (which I'm sure I will be looking at soon), I need to know I have a functional valve body. I'm guessing it's time to either get the VB rebuilt or replace it.

:/

 

Did you try the K1 piston kit see:
http://www.benzworld.org/forums/w201...3-722-4-a.html

 

My '89 has less than 40k miles on it. First problems seem liked the vacuum modular pressure symptoms. Then it would not go in reserve (b2 brake band). Then it would not shift out of second. I rebuild the valve body, installed shift kit, replaced pistons in the valve body and it still did not work. I finally towed it to a transmission re-builder. I have this theory that the internals of these transmission are just going bad. Like the insides are deteriorating due to old age. Unless you have the vehicle since the day it was sold of the lot you really don't know the history. It could have sat for a while, developed some kind of contamination in the fluid, then ran fine until it all caught up.

 

The o rings deteriorate inside the trans. I got 6 month's extra out of mine with trans_x .In the end if the inside needs a rebuild you just have to bite the bullet. I'll tell you my outcome in about a week or as soon as I have time to finish.

 

Didn't do the k1 kit, but I didn't have flare or harsh shift problems before. It is the old-style spring assembly, but appeared to be in good shape. I guess I'll order up the kit, since I'm clearly going to be opening up this valve body at least one more time whether I like it or not.

Up until the recent "no upshift past 2nd" thing, which came on very suddenly, everything was working great. Now after cleaning the VB, it went from "no upshift to 3rd to "completely disengages instead of going into 3rd"...

If I floor it when it's disengaged, it will temporarily drop back into second (basically if I trigger kickdown), otherwise I have to move the selector back to 2 to bring it back into gear.

This does point to K1, if I'm reading the manual correctly. I'm thinking maybe I freed up the sticky 2-3 command valves, and then screwed up the K1 somehow on reassembly. No K1 actuation seems like it would mean no output in 3 or 4.

 

New (used) valve body from 928intl is on its way. I will also throw in a K1 spring kit before bolting it in.

Probably send my existing VB off for a rebuild just to have a spare that's "good to go" when it comes rebuild time.

Fingers crossed this will restore drivability for now.

 

I will have to add that when I cleaned the valve body on my nephew's car, I also installed a shift kit. I am not sure which piece restored the 3-4 gears, but something did. I cleaned the VB, installed shift kit, and changed the oil/filter. I also added Trans-X, but it has been in there all along due to the TC seal leaking. The Trans-X seals it up for me for a band-aid fix until I completely rebuild it.

 

Just for the datapoint- your nephew's '85 starts in first gear on part throttle roll off from being stopped, correct?

Regarding trajectory for the trans' in general, I recall at least one thread where band adjustments were recommended. I don't recall any threads about anyone actually doing that and when I've checked around asking to have mine checked, no shops would actually to it. So at least with B2, it makes me wonder whether wear is occurring that could be corrected with proper maintenance (given that different pins are available to make the adjustment) extending the functionality, instead of progressively deteriorating to failure over time with no adjustment. Seems like this isn't B2, though.

 

Yes, the '85 would start in 1st, upshift to 2nd and stay there. It now upshifts all the way to 4th.

When my B2 band broke on my S4, I lost all forward gears (reverse was fine). I don't think this would cause only losing 3-4.

 

When I measures my bands when they were out I found no measurable wear on the B1 or B2 bands. Also almost no wear on the k1 or K2 drums. Just the problems with the k1 and k2 clutches I stated above.