87 Transmission Leak Won't Stop

[davfraz]

I have an 87 Chevy StepSide with a 405 Engine and auto transmission. I've had it in and out of the shop with a transmission leak from the rear seal. The guy at the shop tells me he has changed the seal twice. It still leaks. Anybody have an idea of what could cause that leak that changing the seal won't fix. I've about lost confidence in this mechanic. Could a driveshaft problem be damaging the seal?

[Zoomad75]

You need to inspect the condition of the slip yoke on the driveshaft. That is what the rear seal rides against. If there are any knicks or burrs to the slip yoke it will damage the rear seal. The problem may be on the end of the slip yoke when he tries to put it back into the trans, your mechanic might be accidentially tearing it then.

The rear seal is super easy to replace. Just take the drive shaft out, replace the seal and put the shaft back in. One note though, I'd make sure the rear of the truck is higher than the front when doing this job. This makes the tail end of the trans higher and minimizes the fluid loss when you pull the slip yoke out.

[Donnylee]

There also is a race on the Tailshaft I believe..... It miight be causing to much up/down movement of the output shaft and is pre-maturely wearing out the seal..... I am no tranny expert, but I would be looking for up down side to side movement of the tranny output shaft.

[bowtiehotrodder]

drive shaft out of round. and bad u-joint. does it pops when you put it in gear and take it out of gear. and the tail bushing could be worn inside the tranny

[82c10]

tell me about this 405

[davfraz]

Right! I should have said 305. See why I'm paying someone to fix my leak.

[piecesparts]

Pull the output shaft tube completely off of the truck and replace the seal that is inside the front of the tube (back of the tranny). The seal on the outer end is really nothing more than a dirt guard and the seal that is doing the real work is in the tube.

[Srubydo1986]

Just a thought isnt a 405 and 400 They just call it a 400 when its really a 405. Just a though, didnt mean to high jack good luck with the tranny.

[84slopwaggin]

A 400 is a 400 unless you bore it out .030 that then makes it a 406.

[Srubydo1986]

na i mean the pontiac 400s cause theres a 400 bb and a 400 small (guess i should make a thread about this one.)

[Jonboy]

There is also a "weep hole" of sorts in the end of the front yoke. I have heard of putting a piece of acrdboard or silicone in that hole will stop the leak.

[piecesparts]

Leave the weep hole alone. It is there to let out pressure as the yoke strokes during normal driving. Fix the leak that feeds it and then the problem is solved.

[Slonaker]

I had a problem with mine leaking from the weep hole. This fixed it.

http://www.73-87.com/7387garage/drivetrain/yokeleak.htm

When I bought a new yoke, the driveline shop recommended one without the weep hole. They said they weld them up when they work on a driveshaft with a yoke with a weep hole. I bought and used it, but I am not sure to this day that it was a good decision. The hole was probably there for a reason, like piecesparts said...

Slonaker

[86k10]

You don't need the weep hole, there is enough wear in the splines to let any pressure back, What trans are we talking about here by the way, the long shaft 350's had a sleeve on the output shaft with an o ring in it to keep oil from leaking out the weep hole and as far as I know the short shaft 350's and the 700's don't have it nor do they have a weep hole in the yoke cause it is not needed. Have your guy check to see if that is what is leaking.

[piecesparts]

Originally Posted by 86k10

You don't need the weep hole, there is enough wear in the splines to let any pressure back, What trans are we talking about here by the way, the long shaft 350's had a sleeve on the output shaft with an o ring in it to keep oil from leaking out the weep hole and as far as I know the short shaft 350's and the 700's don't have it nor do they have a weep hole in the yoke cause it is not needed. Have your guy check to see if that is what is leaking.

I am not absolutely positive about the 350s, but the 700s with a short shaft has a seall there, also. I have had that experience.

[86k10]

It's probably one of those some do some don't, I've never seen one with it. But if that's the case then I would still say just block off the weep hole.