Rear transmission leak- 1939 Ford

[Chris]

Hey guys, I have a 1939 Ford three speed that I put in my 34 Ford. I went through it myself and it shifts excellent. It is leaking out of the back, seems like under where the rear trans mount bolts up to the case. I pulled the mount off, could not pin-point the leak but used some sealer around the two shafts and put it back together. It is still leaking...pretty good leak (leaves a small puddle after a couple days). With the trans saddle I cannot see directly up to the back of the trans to see the leak, but it runs down the back of the case, then down the bottom and drips off the drain plug onto the ground. Is there anything else back there that could be leaking? It is definitely gear oil and not grease or anything. The mount, and under the mount, are bone dry. I'm guessing it's the shafts...any other thoughts?

Thanks guys.

[4t7flat]

Yep, those shafts leak,the more wear ,the more they leak. Several people make shafts with O-ring grooves. Check out PLAINJANE38 on E-bay,he sells lots of custom parts for early Ford transmissions.

[OLLIN]

Right there where the torque tube Bells out and where the ujoint is.. i found a guy that was selling rubber hose that you glue and make a complete o ring..instead of the cork seal. You could probably make it yourself though

[Ole don]

The pin that holds the reverse idler shaft may leak.

[F&J]

The pin that holds the reverse idler shaft may leak.

Several people make shafts with O-ring grooves.

Clean with carb spray and air, then watch for a leak there.


Very common on Model A, and the local A motor/trans shop will not put one together without the o-ring shafts.

[Fortyfordguy]

We do not use the o rings on the shafts. Typically they get rolled or cut during installation. Plus you've now cut a groove in the shaft, potentially weakening the steel. Also, the shafts do not wear at the ends where they sit in the case bores. Remember, the shafts are stationary.

We have the advantage of working with totally clean & dry gearbox castings, so sealing up the shaft ends is a simple matter of a final wipe with brake clean and spreading RTV sealer around the shaft ends.

Going a step further, we clean the hole for the lockpin with the cleaner on a Q-tip. Inject some RTV into one end of the opening, smear some on the lockpin, and tap the pin into place. Let it sit overnight before finishing up the job and adding any gear oil.

When you install the trans, you'll be making a connection to the torque tube (if closed drive). Use a thin layer of RTV on clean parts before adding the gaskets. The gasket sets come with a length of cork for use as a seal at the rear opening of the split cap assy. Some guys have tried using some oil resistant rubber tubing instead. I don't know how well this works.

We've done MANY trannies and found these things to help control the leakage. Stay away from synthetic gear oil.....it seems to find the tiny openings easily on its way to your garage floor.

[Kiwi 4d]

It doesn't appear your roadster has a radical rake. But if it does have you checked the diff and transmission oil levels? Could it be the diff oil working up to the front along the torque tube overfilling the transmission. I had this problem in a 32 3w .took me a while to work out why the transmission leaked so much from the rear. Till I checked fluid levels and there was way too much in the transmission .and a very low diff.

[rockabillybassman]

Originally Posted by Kiwi 4d

It doesn't appear your roadster has a radical rake. But if it does have you checked the diff and transmission oil levels? Could it be the diff oil working up to the front along the torque tube overfilling the transmission. I had this problem in a 32 3w .took me a while to work out why the transmission leaked so much from the rear. Till I checked fluid levels and there was way too much in the transmission .and a very low diff.

I rectified that by using a rear main trans bearing that is closed. Combined with a new grease seal at the forward end of the torque tube, and one of those rubber tube seals in the bell keeps it all dry.

[alchemy]

I think no matter how much you glue up the idler shafts (front will leak as well as the rear), it's gonna find a way out. When I rebuilt a trans a year ago I followed VanPelt's advice, cleaning completely, using sealant, and waiting overnight for it to set. Still leaks like it had a quarter inch hole back there.

But it just matches the engine and the rearend.

[3wLarry]

sounds like you're in good hands Chris...love this place

[F&J]

We do not use the o rings on the shafts. Typically they get rolled or cut during installation. Plus you've now cut a groove in the shaft, potentially weakening the steel. Also, the shafts do not wear at the ends where they sit in the case bores. Remember, the shafts are stationary.

Yes, I know the shaft does not rotate, but filty oil, mixed with debris, and the contant micro-movement that does indeed, occur to that shaft, does make the leak worse, because they do get sloppier. If henry put a retainer that kept the pin locked as solid as a bolted or tapered connection, there would be no micro movement there, and no wear.

Cad/LaS used cork seals on their grooved shafts, as this is a potential leak point(as there was no technology for O-rings), . Cad/LaS shafts never break due to the groove.

[F&J]

Chris, if you do decide it does need o-rings, and you are worried about the seals getting cut: Borrow some lathe time, and make one of those sleeve type ring compressors like race guys use...only tiny

It is just a short mild steel sleeve, tapered inside, polished bore, with perfectly flat face to sit against the trans case. The output ID will be barely big enough for the new shaft, and the input ID will be enough to let the un-compressed O-ring to be able to start in the hole.

[40FordGuy]

We used to apply the "hardening type" "Permatex" on them,...after thoroughly cleaning shafts and case. Speaking of the case,....if an earlier trans failure occured, that's where the case cracks, when debris gets between gear teeth...Always closely inspect those.

4TTRUK