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OK I finally gave up on gaskets and used Loctite red RTV to seal my transmission pan. I am happy to report no leaks where before it was drippping a pint per week (at least).

So now, I can see my other leaks. I've got a good one at the rear seal, and a lot coming out of the speedo cable at the transmission.

I can use some advice on tackling these two leaks. Is the rear seal as easy as dropping the drive shaft, popping the old seal, and tapping a new one in there?

And I have seen a lot of threads about the speedo gear. Do you have to remove the whole thing to get to the seals? Or is there a seal just for where the cable threads on the housing? Any advice is always greatly appreciated.
 

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I need to do some leak work on my Th400 but other things are ahead of it. I don't really know how to do the things you mentioned but I can recommend Cliff Ruggles' book on rebuilding TH400's. It is better than my shop manual and has loads of photos and easy to understand text. It will show you how to do the seals.You can get it in book stores or directly from Cliff at :

Cliffs High Performance Quadrajets :: GM Turbo 400 Transmissions

If you get it from Cliff, you can call on him for advice!!
 

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OK I finally gave up on gaskets and used Loctite red RTV to seal my transmission pan. I am happy to report no leaks where before it was drippping a pint per week (at least).

So now, I can see my other leaks. I've got a good one at the rear seal, and a lot coming out of the speedo cable at the transmission.

I can use some advice on tackling these two leaks. Is the rear seal as easy as dropping the drive shaft, popping the old seal, and tapping a new one in there?

And I have seen a lot of threads about the speedo gear. Do you have to remove the whole thing to get to the seals? Or is there a seal just for where the cable threads on the housing? Any advice is always greatly appreciated.
Speedo Gear; there are 2 gaskets, one is a large O ring the other a cup seal where the cable enters the gear housing. Either or could be leaking. Mine was leaking where the cable goes into the gear. I replaced the seals 2x could not get it to stop dripping. Finally I ordered a new gear housing from Ames. It's identical to the OEM one except for the GM stamping. That stopped the leaking. Why it began is beyond me. To replace the O ring you need to remove the gear housing, to replace the cup seal you can unscrew the cable from the gear housing.
 

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Discussion Starter #4
Thanks. I got the 2 selas on order from Ames. I'm going to put new U-joints in there and I am going to take a look at the Rear seal with the yoke out.
 
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