Vacuum Modulator O-ring size - PeachParts Mercedes-Benz Forum

RML · #1 06-30-2010, 07:41 PM

On my 84 300D I was having a leak from the transmission. Actually it was a hemorrhage. It started in the winter when there was snow on the ground and at first I thought an animal had been attacked and wounded in my driveway and I was seeing its trail of blood.

Anyway, it has been a busy year and I am just now getting around to figuring this one out. I started it up and got under the car and could see the transmission fluid coming from the modulator area. I checked the modulator and it was tight, so my assumption is that it is the o-Ring, or seal as they call it in the parts section. I pulled the modulator, put the O-ring on my calipers and it appears to be 2.5 MM x 22.75 MM x 27.75 MM. Can anyone confirm this?

I am hoping to find an O-ring at the parts store or hardware store, as I don't want to order a $1.07 part and pay shipping. Neither do I want to wait for it. Has anyone had any luck with finding this part at the auto parts store or hardware store?

ah-kay · #2 06-30-2010, 07:52 PM

Have you check Harbor Freight? They sell a box of various sizes O-ring for about $7 or less. It has over 500 in there. You can take a look before you buy the whole box.

RML · #3 06-30-2010, 08:34 PM

Quote:

Originally Posted by ah-kay

Have you check Harbor Freight? They sell a box of various sizes O-ring for about $7 or less. It has over 500 in there. You can take a look before you buy the whole box.

Good idea. There is one not too far from where I am. Can I assume rubber is rubber and the material will be OK for this application?

ah-kay · #4 06-30-2010, 08:52 PM

I use them for all kind of applications, ATF, oil, water, air and never find an issue. There may be an issue with veggie oil but it will take year(s) for the problem to manifest itself. There are experts around here who can advise you but I would use it myself.

tangofox007 · #5 06-30-2010, 10:27 PM

Quote:

Originally Posted by ah-kay

There may be an issue with veggie oil but it will take year(s) for the problem to manifest itself.

If you put veggie oil in the transmission, a leaking o-ring will be the least of your worries!!!

RML · #6 06-30-2010, 11:31 PM

Quote:

Originally Posted by tangofox007

If you put veggie oil in the transmission, a leaking o-ring will be the least of your worries!!!

So you are saying that it won't be years for a problem to manifest itself if I put veggie oil in my tranny. Dang. Used fryer oil from the fast food chain is so much cheaper than transmission fluid. And all it takes is a little red food coloring to make it look the same.

ah-kay · #7 07-01-2010, 12:20 AM

Quote:

Originally Posted by ah-kay

There are experts around here who can advise you

Someone mis-interpreted my post. Don't be conceited, I was not talking about you.

Diesel911 · #8 07-01-2010, 03:07 PM

The Harbor Freight Metric O-ring kit I have has Nitrile as the material they are made of.

RML · #9 07-01-2010, 03:20 PM

I just got back from the hardware store. They had metric sized O-rings but not as big as I need in the 2.5 MM thickness. I picked up a #17, which looks like a pretty close match. It is 1-1/16 x 7/8 x 3/32. I am going to put it in now and see if it fits and if the leak stops. If it does fix the problem, I will still order one from Fastlane with my next order. It is only $1.07.

RML · #10 07-01-2010, 09:57 PM

I used the #17 O-Ring and it worked just fine. Maybe a little tight going in but I was able to tighten it down with the two bolts that hold the retainer plate for the modulator. I put a little tranny fluid on it as well to lubricate it. I do not know if "#17" is an industry standard of if that is peculiar to this manufacturer. The brand is Danco, out of PA, but the O-Ring was made in Taiwan. 1-1/16 x 7/8 x 3/32 is the size. No more leak but I will be keeping an eye on it. Now I just need to adjust the modulator to get the shifting fine tuned. It is shifting a little harsh.

tomas_maly · #11 07-01-2012, 04:00 PM

Per the advice here, I went to Harbor Freight and got the metric o-ring kit. They have a metric kit that has larger size o-rings. Unfortunately, the o-rings are a lot thicker than the OEM modulator o-ring and so the modulator either would not fit into the socket or it would leak after being tightened down. I eventually gave up and stole a modulator and o-ring unit from another car I had (with worse problems). At this point I don't want to spend more hours of trial and error with modulators that don't quite fit on for one reason or another and will just buy a set of 2 modulator o-rings, one for the donor car and one for later.