Leaking tranny fluid near the modulator - PeachParts Mercedes-Benz Forum

RML · #1 01-06-2010, 09:55 PM

I noticed I was leaking transmission fluid, so I did the tranny service with a new pan gasket and new filter. I cleaned everything up under there so I could tell where it is coming from if the pan gasket did not solve the problem. As soon as I refilled the tranny with fluid, I could see a drip, and it looks like it is coming from above the pan gasket on the left side near the modulator. Any ideas what is there that would leak? I really cannot get a good look at it and may take it down to my indy and get the car up on the lift to have a better look. I sure would like to have an idea about what is going on before I take in. I am thinking that maybe it is the modulator O ring. I had the modulator out to inspect it a few months ago and it did not appear that there was any problem with the modulator or the O ring. I put it back in and believe I got it nice and snug. At least as snug as one can get with an allen wrench in that little space.

johnjzjz · #2 01-06-2010, 10:17 PM

good guess modulator O Ring is the place i would do next - jz

micalk · #3 01-06-2010, 11:08 PM

O-ring

a flat spot could be the culprit. wouldn't be easily identifiable, wouldn't cause a fast leak. how old was the O-ring? Anything more than a year or two and it's cheaper to simply replace it rather than worry about it.

RML · #4 01-06-2010, 11:38 PM

Quote:

Originally Posted by micalk

O-ring

a flat spot could be the culprit. wouldn't be easily identifiable, wouldn't cause a fast leak. how old was the O-ring? Anything more than a year or two and it's cheaper to simply replace it rather than worry about it.

This is a fast leak. The PO had a rebuilt transmission installed in 1997, about 100K miles ago. I don't see any repairs in the records to the vacuum modulator since then, so I am assuming the O-Ring is the age of the tranny.

Is there any thing else around that area that could be leaking? I am pretty new to tranny service so am just learning about what the possible issues are.

RML · #5 02-01-2010, 06:18 PM

I was talking to a friend last week who has a friend at the MB dealer in town who is a mechanic there. He said he would pick his brain about my tranny leak. I saw him again today and he reported back that the mechanic thinks it may be a transmission cooler line leak.

I am pretty much a novice when it comes to transmissions. Does the cooler line enter on top of the transmission? Do I have to drop the tranny to service it?

One thing I have discovered is that the leak happens when it is running more so than when not running. I filled it last week and when I pulled out of the garage, there was a large red puddle, just like it was pouring right through. Seemed way too much to be an O ring.

I tried to find a picture or a diagram of the tranny but haven't found anything useful. If anyone can point me to a good diagram or picture I think it would help.

Thanks for any input.

SD Blue · #6 02-01-2010, 06:49 PM

I haven't crawled under there and specifically looked at the tranny cooler lines lately, but I do remember a left side cooler line. What I don't recall is where it attaches to the transmission. If near the modulator, it certainly could be a culprit. It is easily traced by following the cooler lines, checking especially at the clamps. What happens is the rubber in the clamps for the cooler lines deteriates and results in metal-to-metal wear and the sidewall starts to seep. Some have reported "fuel hose" fixes but when this happened on mine, I had to replace the entire hard line portion (cost ~$50/ea). Definitely install new rubber-protected clamps.

Diesel911 · #7 02-01-2010, 11:09 PM

I have read that when you Pull the Modulator the Plastic Modulator almost always breaks.
If you intend to change the O-ring and need to get your car on the road right away it might be nice to have that Plastic Pin in hand incase the Old one breaks.

Diesel911 · #8 02-01-2010, 11:22 PM

There is a Seller on eBay selling non-turbo pistons at $290 a set of 5. When I ask him last year what country Right Way Industrial was in (the company that makes the pistons); he said Taiwan.
In the sellers ad he said he would ship anywere overseas for $35.

RML · #9 02-01-2010, 11:25 PM

Quote:

Originally Posted by Diesel911

I have read that when you Pull the Modulator the Plastic Modulator almost always breaks.
If you intend to change the O-ring and need to get your car on the road right away it might be nice to have that Plastic Pin in hand in case the Old one breaks.

I did pull it out to test it before. I read about how you need to pull it straight out or you can break it. It is not really all that delicate; you just have to be careful. I have been driving my 85 while I figure out what is wrong with the 84, so getting it back on the road right away is fortunately not a big issue.

I am wondering if the ones that break are the original modulators that have never been changed. I suppose that plastic pin can get brittle. My transmission was replaced at some point by a previous owner and I am assuming the modulator is not the original.

Thanks for the input.