I have a 1985 190D with a 5 cyl, 2.5L non-turbo diesel. With the shift lever in drive, the automatic transmission quickly skips through 1st, 2nd, and 3rd gear and is in 4th gear by the time the vehicle reaches 5 mph. As you can imagine, this makes for some pretty poor 0-60 times. If I manually select the gears (2,3, Drive) the transmission shifts reasonably smooth and the car is sluggish, but driveable.

Some history on the car: I bought the vehicle from a friend who had a transmission overhaul a year and a half before I made the purchase. The tranny worked fine for him for the first year, and then suddenly experienced the problem I described. I’ve been driving the vehicle for almost a year manually shifting it (feel free to scold me...) and have checked the following things:

Fluid: Clean, proper level, no sign of degradation

Control cable: freely moves and returns when actuated from under the hood. When I had the tranny pan off, I checked the motion of the valve that the cable operates, and it moved freely and through it’s full range.

Vac Pressure: I disconnected the hose at the transmission and connected a gauge with a long enough extension hose so that I could read the gauge while driving. At idle I measured 10 inches of vacuum. As the vehicle accelerated from a stop, the vac would go to zero, and then increase to 10-12 inches as the top end of 2nd gear was reached (remember I can’t manually select 1st gear). After manually shifting into 3rd, the vacuum would drop to 0 and climb to 10 or 12 at the top end and so on. After parking the car and shutting down the engine, the vacuum dropped to 0 after about 30 seconds.

One more thing, the tranny has recently been contaminated with water (much after the shift problem started). Here is an excerpt from my post elsewhere on this forum:

Back in March I discovered my transmission fluid was the color of a strawberry milkshake. I replaced the radiator with a new one, drained the tranny and torque converter and flushed the system. Everything was fine for a couple months and then the tranny started acting up again. Yup, more water contamination. We have a pretty good analytical lab at work so I gave a sample of the fluid to a friend and he ran a couple tests on it. He found 2.5-3% contamination of WATER. No sign of antifreeze.

“t walgaumuth” and “old deis” suggested I take a look at the top of the tranny for a missing or defective vent. While I have the tranny dropped, I might as well attempt to fix the shift problem. Any suggestions you might have will be appreciated.

I'm nearly ready to drop the tranny. Everything is disconnected except the dipstick tube, and a few bolts on the housing. I can feel the vent on the top of the tranny, but can't tell yet if it is responsible for the water contamination.

Any suggestions regarding the shifting problem described in my previous post would be appreciated!

Sounds like whoever had the tranny apart may have forgot something! The bowden cable you mentioned seems to work, but where internally does the linkage continue? Is there a clip missing, or what? Just a thought and hope you can fix it without costing a fortune, or new tranny! Good luck.......BB

try 1) temporarily disconnecting the vacuum to the modulator and 2) adjust the cable from the throttle to be tighter so it's just under a little tension at idle.

Both of these adjustments should tend to delay the shifts. If that doesn't work, welcome to the club nobody really wants to join .

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

The cable appears to actuate the valve, so all the clips and linkages seem to be in place. While I had the pan off, I had someone actuate the throttle from the engine compartment as I watched the valve. It traveled through its full throw. I didn't tighten the cable to see if that made any difference. I guess I'll have to do that once everything is back together.

I did run the car with the vacuum hose removed from the transmission, without any noticeable change. Looking through the posts and Steve Brotherton’s article
http://www.babcox.com/editorial/ic/ic20242.htm
it appears as if the vacuum values are acceptable. I don’t know if the vacuum modulator on the tranny is using this vacuum “signal” properly.

How does the transmission know when to shift? From what I’ve read, the bowden cable and the vacuum line is there just to control the feel of each shift point, i.e. make it firmer or softer. Is there a master mechanism that tells the tranny it’s time to shift? A governor? A valve? Electrical signal from the connector on the side of the tranny?

Thanks for your continued help.
Paul
member: MB bad tranny club

Well, after quite a struggle, the tranny is out. Nothing stands out as a potential location for water entry- the transmission vent is intact. I disconnected the bowden cable from the tranny and it looks like this could be a potential leak spot. The o-ring was in pretty sad shape and there was pink fluid caught up in the grooves around the housing.
I also disassembled the vacuum modulator and it looks like it saw a little bit of heat sometime in the past. The housing appears to be slightly melted and the o-ring was as hard as a rock, another likely leak point. I've never found burned fluid, but it's possible the modulator could have been damaged before the last rebuild and never replaced.

I have a hard time believing such a large amount of water could enter from these spots, remember I found 2.5-3% water in the fluid. This is about 4 oz. More than what I would expect to leak around a bad o-ring exposed to no pressure. What do you think?

I'm still in serious need of advice regarding the shift problem that I described in my first post. Where are all the transmission specialists on the forum?!?

Does anyone know where I can find a shop manual for this transmission? I've been told that tech info is only available on microfiche.

My mechanic completely disassembled the tranny and gave me a box of parts to take to the Mercedes dealership and find replacements. One of the parts in the box was a plastic gear that drives the governor. It seems as if the person who rebuilt the tranny for the previous owner didn't properly engage the tabs on this gear and damaged it upon re-assembly.

The new parts were installed in my transmission and the valves were inspected and cleaned up where necessary and I'm back on the road. I was able to adjust the shift timing and firmness and now have acceptable performance. It's no race car, but what you might expect from 93 hp.

Oh yeah, and no signs of water entering the housing. The bowden cable and modulator housing were replaced, both of which were suspected leak points.

Thanks for your suggestions,
Paul