C5 LS7

My 99 FRC is leaking oil from between the rear end and the tranny. A car shop said they thought the tranny was leaking from the rear seal. I purchased a new rear end recently and it looks to me that the rear end fluid runs from the rear end into the space between the rear end and the tranny, if that is true then the leak is a bad seal between the rear end and the tranny???? What do you guys think? More info: this leak started when I started drifting the car. Please help

Rick

ragtopws6

First, is it leaking externally? You are saying the diff fluid is leaking and not the trans fluid? There are 2 seals on the end of the transmission (one to keep the trans fluid in the trans and the other to keep the diff fluid in the diff) and between the two, there is a small cavity where it is drilled out to the bottom as a drain hole. If you are seeing diff fluid on the bottom, then I would guess you need to replace the diff seal. Other leak might be where the trans seals the diff (big o-ring). I would clean the area and take it for a short drive and see where the leak is coming from.

broke again

I am having the same exact problem in the exact same location. Started to really leak after dyno session (about 12-13 pulls).

bumble-z

Is the fluid red? If the tranny is manual, it would be leaking @ the large rubber o ring. If it's a auto, it could be the large o ring or the seal that is in the seal plate. Either way, you have to pull the rear diff. "13 pulls, on a dyno session" ????

jrmotorsports55

I'm having the same problem, tranny fluid on bottom of back of tranny. Looks to be coming from the small hole in the bottom of the tranny. Just had the car apart to replace all of the diff o rings, so not sure what is leaking.

Jason

ragtopws6

OK, this pictures shows the 2 seals on the end of the trans. The black seal inside is the trans seal. The brown seal on the outside is the diff seal (to put it correctly, it keep the diff fluid from entering the trans). There is a small hole in between the seals and is vented outside (bottom of the trans).



Another angle to see the inner seal.



This picture shows the outter o-ring seal that seals the trans and the diff together.

jrmotorsports55

Those pics help.

Thanks,

Jason

LT70ZR91

My fluid is from the transmission. How hard is it to change the black trans seal?

C5 LS7

Yes, its red. Tranny is manual.

sperkins

I had the exact same problem just a few months back. Fixed it with super strength black silicone from Advance Auto Parts.
Cost - about $10

ragtopws6

The trans/diff has to be removed from the vehicle; the transmission has to be seperated from the diff; the tailshaft housing has to be removed from the transmission; THEN, you can punch the seal from the back side (careful not to damage the red seal).

0MrPickles

anyone have the part number of the "outer-O-ring" ?

Thanks!
Michael

Bill Curlee

Theres NO seal between the differential and the tranny that keeps the differential fluid inside the differential. The differential fluid fills the space between the differential and the transmission. If you have fluid leaking at the joint between the differential and the transmission, it has to be differential fluid.

The LARGE black O ring seal on the outside of the transmission flange is whats leaking.

IF,,,you actually have red transmission fluid at that joint, it has to be leaking from somewhere else and running down to that area. Wipe EVERYTHING down and see if that helps pinpoint the leak. If the trans seal was bad there would be differential fluid in the trans or trans fluid in the diff.

Check the fluid lever in the tranny and make sure that its not over full.

0MrPickles

hey Bill,

Its DEFINITELY transmission fluid. Smells like feet!

I've been told what the problem is, I just want to get the part and need the number

Chevy dealer can't understand what I'm describing.

Dope

If your large outer o-ring is leaking (or missing), you can easily seal this by using some RTV as mentioned above. If you're lazy like me, all you have to do is jack the rear of the car up, clean the outside of the transmission and diff about 1/2" in each direction from the seam, and then smear RTV on the bottom half of the two components where they meet. Make sense? You're basically sealing it from the outside instead of the o-ring that seals from the inside. It looks ugly but who cares, you can't see it unless you take the car apart.

I had this problem when I changed out my tranny, I actually forgot the big outer o-ring. Starting leaking shortly after, I cleaned it on the outside and smeared the high-temp RTV all over the circumference of the seam where the tranny and diff join. It stayed that way for about 3 years until I got a new rear end, whereupon I finally added the missing o-ring. It never leaked and I had a full diff. Sure is a lot easier than dropping the exhaust, rear subframe, pulling the rear diff, etc...

Dope

ragtopws6

The GM part # you need is 12369456. That is the large O ring that is on the back side of the tailshaft housing and that seals between the trans and the diff.

0MrPickles

Thanks! ordered and picked up the part yesterday. Going to be a fun weekend!

SaberD

its pretty common for the rear extension housing gasket to fail. this happened to me.

bumble-z

O Ring, or gasket? What did you do for repair? Thanks.

SaberD

its a gasket. i didnt have a garage at the time so i had to take it to a professional. didnt do any research about what needed to be done since i wasnt doing it myself.