The Stovebolt Site Forums The Shop Area Engine Shop 1946 GMC 1/2 Ton - rear axles leaking

I'm fairly new to this "sport", so pardon for what may be an obvoius question. I pulled both rear wheels on the truck and both set of brake shoes are lathered with gear oil - definately not brake fluid. It looks to my untrained eye that the rear seals are shot. Is it usual that both side would be leaking? Someone suggested to me that the leaks could be the result of over filling the differential. Could the leakage be from putting the wrong weight gear oil in the differential? The brake shoe look almost new - a full 3/16" thick. Any way to salvage these oil soaked shoes?

Be sure your axle breather, located on top of the driver side of the axle, is clean. I had a plugged breather on my '51, causing a leak on the passenger side seal. I cleaned the breather, cleaned the gear oil off the drum and shoes, and four years later, no additional problems. As you drive, the differential heats up and the gear oil will be forced past your seals, if that breather is not open.

Others will tell you just replace the shoes and that may be best but I got away with cleaning with brake cleaner. (On the same truck, I had a front brake cylinder leak and cleaning the same way never got the brake fluid out of the shoes and I had to replace them).

I agree the axle seals need to go and do check to see if the unit is over full. Also If you are talking original 'torque tube' the problem can be, that trans oil is getting past the seal at the front of the torque tube and running back to the diff, you'll need an 'okie bushing' to fix that. I like to keep my diff slightly low on oil so as not to lead to the axle seal leakage. And, replace the shoes, as they are inexpensive if you shop around.

Get a manual that tells the procedure of pulling the axles. Replace the seals & brake shoes. You cannot clean all the grease out of the old linings. When they get hot it comes to the surface & causes the wheel to lock up. Very dangerous.

Pulling the axles isn't hard. Get a shop manual and it will tell you how. Getting the seals out can be fun, though. I just changed out both sides on a '51 GMC and practically had to destroy them to get them out. I used a two jawed slide hammer and a bunch of patience.

When you put the new seal in, be careful with it. I used a wood block on it with a 4 lb hammer to get it going. I've got a piece of PVC pipejoint that's just the right size to drive it in the last bit - don't know what size it is, but I got it by taking the seal into an Ace Hardware plumbing section and looking around a bit.

David Bush

Thanks for the advice. I checked the axle breather and it is plugged solid. As a mather of fact it has been soaking in solvent for about three hours and it is still clogged. I decide to check the fill level of the differential. I put a 1/2 gallon plastic ice cream container under the fill nut it to catch the drips. Well, fluid poured out and by the time it stopped the container was almost 3/4 full - that would be about 5 to 6 pints. I looked up the lube capacity of the differential in the manual and it is only 4 1/2 pints. Sure looks like I have transmission fluid coming down the torque tube big time. So JIMerit - what is an "okie bushing" that you mentioned in your reply to my last post. By the way, the oil that came out of the rear end was dirt brown in color - or maybe it is rust brown??? Any thoughs or idea would be appreciated. One more question - should the fill plug be in the upper half or lower half of the differential rear plate. Mine is positioned in the lower half. Is this correct? My next obvious step is to check the transmission fluid level. Now I think I know why the truck came with a plastic gallon of gear oil!

Jeff'z, Glad you found the problem, the 'Okie Bushing' as it's called can be found at most old truck vendors like Jim Carter's or Chevs of the 40s, both have web sites. This bushing goes in after you take the 'U' joint appart, just drives in between propeller shaft and tube and you're done. While your at it, you might want to inspect the diff inards while the cover is off, just look for broken teeth, rotten bearings etc, also feel around the bottom of the housing for metal chunks. If all looks good you just need to re-assemble the thing per the MANUAL.
Best of luck

JiMerit - thanks for defining an Okie bushing. The math in my post was a little sketchy. 3/4 of a 1/2 gallon would be 3 pints - not 6. Still a problem, but not as bad volmetically as I thought.