View Full Version : Trans leak, anybody know anything about it??

04-19-07, 05:26 PM
Fluid is very, very slowly coming out where the driveshaft goes into the transmission. Right now it is just a drop every once in a while. Is this a hard/expensive fix and what is involved?

Thanks guys.

04-19-07, 09:22 PM
Your trans tailshaft extension has a worn seal. Jack up your rear axle and support it on jack stands under the axle tubes. Drop your drive shaft. Catch the fluid which may come out of the extension. If you have the rear high enough that the trans is level, fluid loss should be no more than a quart.
Unbolt the trans mount from the cross member and the trans mount from the transmission. Raise the trans, it should have enough clearance to remove the mount. Unbolt the extension from the trans body. You should be able to remove the extension. You may have to tap it with a hammer to loosen it.
There maybe some more fluid loss when the extension come off.
Replace the seal.
Check the drive shaft input piece for wear

04-04-08, 02:26 PM
What about the 1979 Brougham 6.0, atf oil comes out throu the hole in the bottom near the converter (between engine and tranny). Hot to fix it?

04-04-08, 07:27 PM
I'm going to disagree with deville33. It's not the seal between the tailshaft and the trans case, it is the seal IN the tailshaft that seals around the driveshaft itself. Once you drop the DS (mark the end where it bolts so you put it back the same way to maintain balance), use a large flat blade screwdriver to carefully pry out the old seal. A new one is less than ten bucks. Pay attention to which way goes IN. Tap it home with a hammer, gently, making sure it doesn't get cocked to one side too deep. Lube the slip yoke with a little ATF, slide the DS back in, and bolt it up.

PKi, you have a 425, not the 6.0 368 in that 79. Your problem is a leaking front pump seal. You need to drop the trans, remove the converter, remove the front pump and reseal. My 81 leaks there, too. I'll fix it this summer...

04-05-08, 12:16 PM
I have to correct my profile, the VIN says it's 1980 and 368/6.0.

Is there a seal to change and where to buy online?

04-05-08, 06:42 PM
Cool, it's definitely the 368 if it's an 80. Front pump seal is available at any parts place. So cheap, you probably want to get it local.

rockauto.com has it:

BCA/NATIONAL Part # 6712NA {Oil Seal / Acrylates / Shaft Size=1.875" Housing Bore=2.758" Outer Diameter=2.762" Width=0.425"}
GMC THM350, THM350C, THM400 3 Spd. Automatic Transmission



04-11-08, 04:57 AM
OK, many thanks, i have found where to buy it. Are there other sealings or parts i shound change when the transmission is dropped?