I need some tips and tricks for getting a trans pan gasket to seal

[CSFJ]

Ok, in the last decade and a half that I've owned only manual transmission vehicles, I seem to have lost my touch for getting a transmission pan to seal.

I recently picked up an '88 silverado with a 700r4 trans. The truck had been parked for several years after the trans had been rebuilt, has about 6k on the rebuild according to the invoice for the work. Since I began driving it, it developed a leak. So, I figured since it had been setting so long, I would throw in a new filter and gasket.

Now the old gasket was cork and the new one is rubber, so I installed it with no sealant. Now the leak is worse. Bad enough that I began to suspect the input shaft seal on the trans. Checked that tonight after work. Dry as a bone, so that's good.

Now in years past I never had this problem, but as I have said, I seem to have lost the touch. I would like to stay away from using just sealant, as this truck is going to be a parts chaser and see regular driving duties, so it will get regular filter and fluid changes on the trans and I don't want to scrape sealant off every time.

I've checked Fluid Lockers website along with Fel-Pro and Cometic. Fluid locker is the only one that offered trans gaskets, but not for the 700r4.

So, should I abandon the rubber gasket and go back to the cork? What have you guys used, and what worked or didn't?

 

[chengny]

Here is my trick for installing (and re-using) rubber gaskets - anywhere except with Perma-dry oil pan gaskets. Always works and saves $$:


Take your pan back down empty out any remaining ATF and wipe dry with a rag. Then using paper towels and acetone or gasoline, degrease the entire inside surface. Pay special attention to the flange face - the surface where the gasket will eventually seat and seal. When you have removed all traces of oil from the flange, apply a thin coat of red (high temp) RTV silicone sealant. The use of silicone is more about stability than sealing, so you only need to use enough that it acts as an adhesive not a sealer.

Let the silicone dry and get a little tacky. While it's drying, I'll explain why you are probably getting leaks. Provided you have cleaned the flange faces until they are completely clear of all old gasket material - and the pan is not warped enough to prevent it from making total contact - the problem is the rubber itself. Rubber gaskets seal great - when properly made up. The problem with using rubber - especially if one is used to cork gaskets - is, quite often the joint gets over tightened.

With cork it's easy; the gasket is compressed until the bolt is hard to turn - then you stop. Not true with rubber. When rubber gaskets are compressed during the torquing process (and this is especially true when the distance across the sealing surface is thin, as in the case of a transmission pan gasket) they have a tendency to "walk". IOW, as the joint is clamped tightly together - and the rubber is squeezed between the flanges - it can be forced out of position. So, instead of remaining in the area that it supposed to be sealing, it ends up bulging out on either one side or another.

The trick to avoiding this is to secure it in place with an adhesive. Always apply the adhesive only to the surface of the part that can be removed. That way - in the future - if the joint ever needs to be opened, the gasket will stay with the removable piece. When it comes time for reassembly the gasket will be already in place and ready to to install.

Okay, by now the silicon should be tacky. Clean any oil that may be on the gasket with acetone or gasoline. Put the gasket on the pan flange and carefully position it. Use a few of the pan bolts to help. As the gasket holes line up with the holes in the pan, drop a bolt in every 3 or 4th hole. Obviously they will be pointing the wrong way but they will be coming out. They're just to keep the gasket in place while the silicone dries and forms a bond between the gasket and pan. Let it dry for a couple of hours.

While it's setting up, go to the hardware store and get the appropriate number of lock washers (16 for a 700R4?) - in the correct size - for the pan bolts. This is kind of important if you are not used to working with rubber gaskets. They will help you resist the urge to crank down on the bolts when making up the pan to the casing. The locking action of the washer will allow you to use less torque than if they were not there. And you won't walk away wondering if the bolt will back out and cause the pan to leak. As a side note: Perma-dry rubber gaskets come with compression limiting spacers built into the rubber. Each hole has a plastic ring around it that prevents the gasket from being squeezed out by excessive clamping force.

That's it, remove your locating bolts, raise the pan into position (Bonus: because it is now glued in place, no more struggling with lining up the gasket or having it fall into the pan) and start the bolts/lock washers. When they are all finger tight, tighten the joint up in 3 stages using as close to a criss-cross pattern as you can devise. The final torque value should be about 8 ft-lbs maximum. Even though the gasket is glued in place it can still be squeezed out of position by over tightening the bolts. The lock washers will hold the bolts and keep the flanges tightly together.

 

[CSFJ]

I'll give this a shot this weekend. I had the suspicion that the gasket may have walked. When I first installed it, the bolt holes in the gasket were snug enough to hold all the bolts in when I put the pan up. The only spec I could find for torque was 120 in. lbs. so I snugged them by hand with a short grip on the ratchet. After it kept dripping, I went back and snugged the bolts again, with the same short grip on the ratchet. I was thinking about using thread lock this time, but I'll give the lock washers a try.

 

[firebane]

Also make 100% sure your pan flange is straight. When I was putting the pan back onto my truck I laid it on a flat surface and it was so warped that I had to buy a new one.

$50 at Napa for a new pan with a drain plug.

 

[CSFJ]

Yeah, already planned on ckecking the flange against a flat surface. Though, I do like the idea of a drain plug too.

 

[MadOgre]

I find that as long as both mating surfaces are completely clean and dry that I have no problems. I prefer the rubber gaskets.

The trick is to evenly tighten the bolts so that the gasket is firmly snug against both mating surfaces before torqueing to specs.

I will tighten all by hand and then use my 1/4" ratchet to snug them up and then go to my torque wrench to finish the job.

Also I believe the correct Toque specs is 13-14 ft lbs

But I cant stress enough that both mating surfaces need to be squeaky clean. Often a razor blade is needed if replacing a cork gasket.

 

[CSFJ]

I had both surfaces nice and clean when I replaced it, but did not think to check the pan flange for level.

 

[MadOgre]

Your screwed if its bent. But B&M has pans with drain plugs for around $50 on summit and there chrome too. I paid $55 cdn for a deep sump chrome pan with the filter extension for my 700R4.

Its about the same amount for a TH400 and TH350

 

[MadOgre]

They are stamped steel and work great!

 

[bucket]

A rubber gasket with a steel core would be great, but I don't think anyone makes one for a 700r4. But when using the thin floppy rubber gaskets, I smear on a very light coat of yellow weatherstrip adhesive. Works well when all surfaces are clean.

With aftermarket cast aluminum pans, you don't have to worry about warping the pan flange. Just tighten the bolts and call it good.

 

[CSFJ]

I've got a new pan and gasket coming from Summit. Found one of their stamped steel pans with a drain plug for $20, and a Fel-Pro pan gasket. Both shipped for less than $30. Should be here tomorrow. Don't know if I'll get it installed tomorrow or Saturday, but I'll post up the results.

 

[PrairieDrifter]

YESS! Yellow super weather strip adhesive works awesome.

 

[CSFJ]

I'll try to find some of the yellow w/s adhesive to have on hand. Is it just a generic, or is it made by 3M or one of the other big name companies?

 

[PrairieDrifter]

I usually get the 3m brand just because I like 3m but I'm sure there's plenty of other brands

 

[CSFJ]

This damn truck can kiss the fattest part of my ass. Looks like I'll try nothing but adhesive tomorrow. I am not happy at the moment.