Hot Rod Forum banner
1 - 5 of 5 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter · #1 ·
Hey guys I'm new to the whole transmission rebuilding thing (the inside of a transmission always seemed scarier than inside a motor but I've finally decided to give it a shot lol!!!) I'm working on a 400 transmission out of an '86 Chevy 1 ton van, and I've run into a little bit of a problem. Everything has gone together pretty well but but I have a massive leak in the forward drum when I check it with compressed air :( . I took it back apart and the lip seals were not nicked or torn. So I put it back together, even more slowly and carefully lol, figuring maybe I'd rolled one of the lip seals (though the piston turned freely). Not surprisingly, I got it back together and it still leaks. Using 30 psi of air with the forward drum setting on the pump, I can put my hand over the middle of the drum and feel compressed air blowing out! It's almost like it doesn't even have any seals in it at all. The piston doesn't even try to move! I tried to make sure and match up the lip seals with the old ones that came out (though the transmission had been rebuilt at some time in the past but I don't know who did it or how well it worked). So what do you think? Could it be the check ball in the drum that's stuck? Wouldn't I hear/feel air blowing out the back of the drum if that was the case? Please help! I'm no expert at all but I've read alot of posts about rebuilding 400's (JakeShoe rocks!) and I have the Ron Sessions book, but I just don't understand how it can leak so bad (BTW the piston and drum looked good, I didn't see any gouges or noticable wear).
Thanks!!!!
 

·
More for Less Racer
Joined
·
20,942 Posts
I could be wrong and it is a different drum, I haven't been in a 400 in a while, but there are 2 seals on the piston and one on the drum? Did you forget the one on the drum itself? Hopefully one of the pro's will see this a give a definative answer.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #3 ·
Man I wish that was it lol. I wouldn't be surprised if I did something like that but I put the 2 seals on the piston with the lips facing away from the springs and put the one in the middle of the drum with the lip facing the other way (towards the springs). I'm sure I'm overlooking something that simple though :embarrass Thanks for the fast reply!!
 

·
Administrator
Joined
·
10,122 Posts
Forward drum.... only two seals will work fine if they are on the piston... center seal in the drum , not that important.


Steel piston or aluminum?

Metal sealing rings or teflon like material?

Are you sure you have the correct hole for air checking when using the pump assembly?

Welcome to Hotrodders... there is no need to put "please help" in the thread title here. Very helpful bunch of guys here
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #5 ·
Thanks for the replies guys! I think (or at least hope) I panicked over nothing. I disassembled it all again, rechecked the lip seals and their orientation, and reassembled. (The fact that I managed to take it apart and assemble so many times without tearing them is nothing short of a miracle lol). I think one of my problems was with my air gun. Using a very good one this time lol, again with 30 psi, the piston pumps up and holds. The hissing I heard (which was really worrying me) is coming from the center of the input shaft (probably out of an oiling passage?) If I put my finger over the hole, no more hissing, and no more feeling of air coming from the center of the piston area!! So does this sound right? Also I had checked the thickness of the steels that I took out before the rebuild and just replaced with the same. But I wasn't happy with the clearance between the top friction and direct clutch hub, so this time I put a thinner steel in and now have .041 of clearance. Also this time before air checking, I put it together without the forward clutch hub in and I can see the clutches applying. Sorry for being so long-winded lol but everywhere I read said if you hear air it's bad, but it seems like where I hear it from is not around the lip seals.
Thanks again !!!!
 
1 - 5 of 5 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top