1985 300TD Losing Torque on Hill

[kekovach]

My 300TD is seriously losing torque when I go uphill. It's a pretty steep hill, but it kind of feels like the car is failing to shift. It's an automatic, and I can hear (and see) the RPMs go up up up, but no corresponding increase in torque.

Is my transmission dead? I hope not.

[kekovach]

Sorry to dredge this one back up, but I've got more information now! I'm wondering if my transmission is dead, or if it's simply acting up. Tell me if this sounds familiar:

Again, Mercedes 300 Turbo, 1985.

Starting cold, the transmission works OK. No problems shifting beyond the minor hesitation you expect for an automatic of its age. After not driving for very long (basically until the engine warms up) The car fails to shift. So the transmission is functioning, but only during the first five minutes of the cars operation when started cold. If I shut it off and crank it again, I get the same problem. I don't have to wait though, if the engine is already warmed up. The transmission just won't go.

The transmission fluid is still red, and doesn't appear dirty. The mechanic who checked it said it was a little low when we brought it into the shop, but not "alarmingly low"

Is this familiar to anyone? The shop we took it to says "transmission has gone south." They're not a shop that works on
transmissions ordinarily. They specialize in diesels, but won't do anything with a transmission except a replace. They don't have a specific diagnosis for it, just that "something is wrong." They're very competent when it comes to diesels, and a great bunch of guys, but I don't want to spend 1200 dollars replacing something that isn't genuinely broken. If there are odds that it's a vacuum issue, or some sort of valve or belt or chain or whatever, I'd rather take a stab at it myself, or have someone who knows transmissions better take a stab at it than just blindly fork over the cash for a used or rebuilt transmission that might or might not be good anyways. That coupled with the fact that I have absolutely no cash makes it a fairly frustrating situation.

Thoughts?

[LUVMBDiesels]

If you put it in L can you start?
Can you manually shift it from L to S to D and have it go through the gears?

[rrgrassi]

How many miles on it?

Did it sit for 6-mos to a year prior to purchase?

I had a Pontiac Bonneville ragtop that had the 455HD and the TH400 slushbox. It did the same thing. Cold was fine, warmed up, forget it. Turned out to be all the seals had dried up and shrank. Cold oil filled the gaps, warm oil went right past them. Ended up having the tranny rebuilt, as the car did sit for a year before I bought it. I do not have it anymore though... One of 3750 made. Sold it because I had to. Job loss back in 2001.

[Brian Carlton]

When was the filter last changed?

[kekovach]

The transmission filter? I don't know. It was a recent purchase, and we hadn't gotten it to the shop yet to have all that stuff checked (fuel filter, oil, tran. filter, etc...)

I could see maybe the seals drying out, but the car ran a full month (driving every day or every other day, and one or two long trips) before this problem turned up.

[Brian Carlton]

Originally Posted by kekovach

I could see maybe the seals drying out, but the car ran a full month (driving every day or every other day, and one or two long trips) before this problem turned up.

How do you know whether or not the vehicle ran 22 years before this problem turned up?

[kekovach]

Originally Posted by Brian Carlton

How do you know whether or not the vehicle ran 22 years before this problem turned up?

I don't. I know the vehicle ran when I bought it used, a little over a month ago, and I know it ran for a month before this problem came about, and it came about suddenly.

[Brian Carlton]

Originally Posted by kekovach

I don't. I know the vehicle ran when I bought it used, a little over a month ago, and I know it ran for a month before this problem came about, and it came about suddenly.

Since you don't know if the vehicle ran for 22 years with the same transmission filter, the fact that it ran for the single month that you purchased it is irrelevant..........don't you think?

[kerry]

Is the transmission slipping or are you just feeling less torque? If the latter, try changing your fuel filter and cleaning out the banjo bolt.

[kekovach]

Oh, no, what I was saying was regarding the seals. If the seals were all dried out from sitting idle, and that was causing the failure due to the leakage of hot oil but not cold, wouldn't that failure have shown up immediately rather than after a month?

It looks as though the transmission filter might be easy to change myself? There seems to be a few threads about it.

I guess this a common symptom of a dirty filter?


Thank you so much for the advice.

[kekovach]

Originally Posted by kerry edwards

Is the transmission slipping or are you just feeling less torque? If the latter, try changing your fuel filter and cleaning out the banjo bolt.

Losing torque I guess was a bad choice of words. I'm pretty sure the transmission is actually slipping. It's still in the hands of the shop, so I can't take it out and try to shift manually. The shop is only a few miles up the road, and the decision I'm trying to make now is, do I go up to the shop, scoot the car home in first gear and try the simple stuff (filter, fluid, modulator valve? etc...) or do I just bite the bullet and fork over 1200 bucks for a new tranny.

[my123ca]

Originally Posted by kekovach

The car fails to shift. So the transmission is functioning, but only during the first five minutes of the cars operation when started cold. If I shut it off and crank it again, I get the same problem. I don't have to wait though, if the engine is already warmed up. The transmission just won't go.



Thoughts?

Do you mean the car wont move or just wont shift to 2nd or 3rd? If it is the latter, our cars have a temp switch valve that directs vacuum to the tranny. Maybe the switch is not working or is stuck. Also change filters(Tranny and Fuel) and clean the banjo bolts as others have suggested. The banjo bolt in our cars has some input to the vacuum system. Our transmisions are quite tough. Ive lost transmission fluid twice while running and its still working great. Try to find something less costly before condemming the tranny.

[kekovach]

Would that be the "modulator valve?" I've heard that thrown around a bit when talking to folks. I understand it to be problematic at times, and need adjustment to get proper transmission performance.

Yes, you have it right. Car will move, and even shift fine, but won't shift up when warm.