Help me understand my Tranny!

[ayalar007]

Hello all, I know its been a while since I have posted anything here, but to be honest, the ol girl has been running great and my time latley has not allowed me to post anything.

Latley the old girl's tranny has been slipping from 3rd to 4th only when cold. After it warms up, it shifts beautifully. I read a couple of posts from other members that were experiencing the same thing, but the responses were all different. Some say that the tranny was on its way out, others suggested that a fluid change would resolve the issue.

My question is, what casues that tranny to slip? I have adjusted the bowden cable and the shifts between 1st to 2nd and 2nd to 3rd and crisp and nice. I have adjusted the vac modulator, and I have (what I beleive) is a nice shift quality, not too harsh not too soft. Also, why would a fluid and filter change correct a slipping tranny. My fluid was changed about 2 years ago. Should I change it again? And if I do, do I have to remove the fluid in the converter too??? My tranny was serviced then (2yrs ago) and had a valve body rebuilt, had the B2 piston replaced and had the vac modulator changed to the updated version. This was done by an indy in Miami that is well known for his knowledge of Mercedes' trannys. Before I go to him, I want to make sure I understand what's happening.

All help in this matter is greatly appreciated!

[ayalar007]

can anyone chime in?

[pawoSD]

A fluid and filter change can correct a problem like this because if the filter is somewhat (or completely) clogged with junk then the fluid flow levels fall dramatically, and the pressure and amount of fluid needed to activate the pistons during a shift just isn't there, so it will slip. I'd try the filter and fluid change first, it may solve the problem.

[ayalar007]

pawoSD,

Thank you so much for your response. I guess if anything, a fluid change is much more cost effective than an overhaul anyway. My question then is, do I also have to change the fluid in the converter, and if so, How does one do that?

[Breckman99]

You may also try adjusting the firmness of those shifts, if you keep letting it slip like that it could cause it to fail sooner than if you hadent adjusted. Use the SEARCH and you will find all kinds of information.

Try searching for
transmission vacuum modulator adjustments
bowden cable

transmission 722.xxx

[speace]

Try searching on "K1 spring kit" and see if that fits your symptom.
Some describe the problem shifting from 2-3 others say 3-4. These cars don't start out in first so some count them as 3-speeds...

My 87 300E and my 92 400E flared on upshift to high gear only when cold. I lived with it on the 87 and had the 92 tranny rebuilt at about 200k miles. After rebuilding, it would still occasionally do it and they adjusted the bowden cable to make the problem go away.

I think the K1 spring kit would have fixed my 87 and delayed the overhaul of my 92 if I had known about it at the time.

[ayalar007]

Thank you all for all your input. I have read all of your responses carefully and appreciate all of your thoughts. As far as the adjustment on the modualtor goes, I have read the threads here and I have adjusted the modulator in the past, and I have the modualtor at the point where if I stiffen the shift anymore, it would be unbearable. You see my tranny had the K1 spring kit replaced and it now starts on 1st gear. When the tranny is cold the 1st to 2nd shift is very harsh. If I stiffen the shift quality anymore, my mounts are going to suffer. Once the tranny is at normal operating temp, the 1st to 2nd shift is crisp and on the money and the 3rd to 4th shifts beautifully also. This is where I am completely puzzled. Why does the tranny act up only when its cold and behaves the way it should when warm?

[Pete Burton]

Your description of shift character is similar to the one I have experienced recently, except my problem has been the 2-3 shift. Cold would flare worse and worse, and once it got warm it was fine. After trying nearly everything I could think of, including replacing the valve body with a rebuilt unit, I pulled the trans and I am disassembling it now. I believe that these units eventually wear the clutch packs so the travel to engage becomes greater and greater. When cold, the trans fluid takes longer to fill the volume necessary to engage the clutch and you experience slip. With a warmer fluid, it takes less time and manages to engage the clutches enough. I expect that with new friction discs it will engage much quicker cold or hot. That's the hope anyway.

[ayalar007]

Pete,

Thanks for your great info. I was hoping it did not have to come to that, but I fear that this is the only solution. Im going to try the fluid replacment anyway just to see what happens. Im wondering if trying a synthetic fluid would help the cause or make matters worse. Anyone??

[Pete Burton]

Originally Posted by ayalar007

Im wondering if trying a synthetic fluid would help the cause or make matters worse. Anyone??

I was hoping it would help me, and maybe it did for a little while, but in the end I still ended up pulling it after it would no longer shift into 3rd.

[ayalar007]

In other words, the longer I wait the worst it'll get. Maybe I should just bite the bullet, and go ahead with a rebuild

[Pete Burton]

Well, to make a long story short, I rebuilt my transmission and I've been driving it for a few days. I found several problems with it during disassembly. Between 2 transmissions, a rebuild kit, a few parts from the dealer and a rebuilt and tested valve body, I made a great shifting transmission. I bought the valve body first, and after trying that made no difference, I took the trans apart. I spent about $500 total, but $200 was for the valve body that I didn't really need. Now I have a good, spare valve body. In order to justify replacing it, I'll have to find a cherry SD that needs a trans rebuild. Dang

[rs899]

Pete-

Nudge- nudge.

C'mon . We need a rebuild guide on here somewhere. I need a pathfinder before I want to mess with a total rebuild of my 300D's 722.315.

Rick

[Pete Burton]

As I mentioned to Brian, one thing seriously holding me back is almost total lack of photo editing/computer file management abilities. I use computers for a number of things at work, primarily designing automated machinery. On my to do list is getting some software and knowledge so I can put together pictorals on stuff, like how I made and used a tool to compress the lip seal on the B3 piston with a 3 liter soda bottle (for a net savings of $252.23, I figure). Any good advice I get will indeed nudge me along. I took about 200 digital pictures.