blctalon

I've been doing some work on my 78 lately. I got the new rear end installed along with new trailing arms, bearings, strut rods, suspension etc.

When I first got the car and drove it home and placed it in the shop, knowing it needed some work. Among other things, after letting it set a over night and returning to work on the car the next day, I noticed transmission fluid all over the floor. Tried tightening to bolts a little with no luck. Dropped the pan to change the filter and have a peek and it looked like I found the problem. The front passenger side of the pan had an ever so slight bend in it which I thought was making it not seal up properly. In addition, I noticed the fluid was infact dripping from this area of the pan. It appeared to be coming out of the gasket-tranny or gasket-pan surface. I installed a new pan and after a month or so of doing other work to the car, decided to add the oil and drive it around to break in the differential.

When I parked the car everything appeared normal. I returned the next morning to go to work and saw the beloved transmission fluid all over the floor again. I rolled underneath the car and it appears to be leaking in the same freaking place-front right corner of the pan area.

I looked closely at the transmission mounting surface when I removed the pan and it looked fine. The only thing I can think of is a hair line crack or something I didn't notice. What do you think? So far I've used 2 new gaskets and torqued the bolts like the manual says. I'm really getting tired of cleaning oil off my shop floor!

bobs77vet

tightening up the pans just makes things worse...they only get tightened to like 100 inch lbs after that the gaskets split and leak

marshrat99

I'll get flamed but here's what I ended up having to do to stop my tranny leak after replacing the gasket 3 times.

I took the pan off. Put a straight edge on the gasket contact surfaces and found several places that were irregular. So I ever so gingerly nudged the irregular places back in line using piece of flat bar stock and a hammer. I checked the tranny surface but couldn't find any problems.

Lastly (here come the flames), I got a new gasket and spread a thin film of Permatex #2 on one side and place this side down onto the top of the tranny pan to "stick" the gasket to the pan. When the Permatex had set up for @30min, I put another thin coat of Permatex on the top of the gasket and installed the pan onto the tranny using just a socket and extension but no ratchet installed. IE, used the socket and extention like a screw driver with my hands. This prevented over tightening.

I've driven all summer with the latest gasket and so far no more leaks.

BTW, my friend has begun restoring a 72 Nova and his tranny leaks like you wouldn't believe. I keep telling him that his tranny must have come out of a Vette.

blctalon

Amazing how inefficient a drain hole can be on your transmission pan. Mine didn't start draining properly until I had all but 2 bolts off. Ok, so the pan is off and I'm underneath with a straight edge. The mounting surface is very close to being flat. I didn't measure it with a caliper but if I had to guess I'd say it's only about .001-.003 inches from being flat on that corner. I would like to think the gasket would make up for this slight imperfection along with a little pan flex. I do not see any cracks either. I'm kind of stuck at this point as I don't see any uneven surfaces to pound down with the hammer. I think what I'm going to do is get some sealant and a new seal and stick it all together and let it dry then see what happens.

If it continues to leak then followed by

comp

have you looked at the shift lever o-ring and the kick-down cable o-ring really good ????

DR.Jay

Try the o-rings. Also I have been using Gray RTV on transmission pan gaskets for 10yrs. Use Gray Only. Gray Prematex is specificaly designed for aluminum. If you use Permatex eliminate the gasket. The Permatex Gray has been used as a replacement for transmission pan gaskets by Jasper for as long as I have been doing business with them.

joe78

I went through this crap for months changed pans, I dont know how many times.I would drive it park it everything looked great come out in the mourning and trans fluid on the floor.I changed the speedometer cable at one some time and put in a new bullet, to save time here it came down to this the o-ring that came with it was a bit undersized found out it was that all the time it sure looked like it was the pan since there was no trace around the bullet.This may help check it out.

c3 in hawaii

I went through the same problem, the o-ring in my kick down cable was cracked along with the casing, replaced the kick down cable which came with a new o-ring... never leaked again

comp

if you ask a question ,you have to check back in

jimvette999

IMO, the problem people have locating leaks is partially because the fluid level rises after the engine is shut off. The torque converter partially empties itself through the pump raising the level 2-3 inches. These leaks are best located by running car till hot, jacking car up (both ends), wiping everything down carefully and coming back hours later and trace the leak to its source. A leaky front pump o-ring is often the cause of the leaks thought to be pan gasket, shifter seal, dip stick seal, detent cable etc. The fluid will sometimes travel around and follow edges and fool you into thinking it's from someplace it's not. I used to rebuild transmissions for a living and this was the procedure we used successfully to locate leaks.
As far as pan leaks go, we had the best luck flattening the pan rails back out , using cork gaskets, no sealer, properly torqued to 15ft.lbs. in a criss cross pattern in two passes.

Jim

blctalon

Sorry I haven't posted back, I've been busy. After I replaced the transmission pan gasket (for what I think will be the last time) and parked the car after driving it, I found no initial leaks. I put the drip pan under it just in case to stop from having to sop up fluid. I checked back a couple hours later and still couldn't see any leaks. Went out the next morning I found some oil dribbling around the same spot. I'm pretty confident it's not the pan gasket now and I think it might be an O ring or boot thingy you guys are talking about. It almost looks like it's running out in the area where the dipstick tube goes in.

I'm not too familiar with these older transmissions but is the kickdown cable the one that bolts into the transmission right below the 2 fluid lines? I'm thinking this is the culprit although I can't seem to catch it in action. I don't think it's the speedo o-ring as that is on the opposite side of the tranny on the tailshaft and the leak is around the from right passenger side of the vehicle. Anywho, thanks guys. I'll probably jump more into it this weekend as I have some tests to finish up this week. I'll post back what I find.

Ryan

comp

do them all

blctalon

Arg, now that I've recovered from my sickening hangover I can make the follow post on what I found.

I ended up driving the vette and letting it leak into a pan one more time just to try and pin point where the fluid was coming from. Of course, it took literally hours after the car shutoff to start leaking, so I went to it the next afternoon. Upon closer examination the fluid appeared to be leaking out of the dipstick tube where it goes into the transmission. I removed the hold down bolt and popped the dipstick tube up and found a rather crappy little o-ring. I plucked it off and put a #11 plumbing oil ring on there, reinstalled and went for a drive.

When I looked at the car this morning it appeared no oil leaked out from my weekend drive. I'm going to drive it again and watch the area at least one more time, but I think I got the leak fixed at this point.

marshrat99

Those little ole leaks are freeking frustrating but once you get them fixed then you get a great feeling of accomplishment.

Edzred72

Exactly the problem I chased with my 77, but it was the F***ing speed-o gear leaking. One thicker plumbers O-ring fixed that SOB...
Eddie

Vette Gator

Is there a place that lists all the O-rings for a TH350? My car is up on jack stands right now and I was hoping to fix my leak(s) by starting with these. I would like to buy all the O-rings first and just do them all at once rather than taking them off and then trying to find ones that match.