Pulling TH400 Extension Housing Advice

XJ-S
21

Anybody else doing this in the future and searching archives, ill list steps while its still in my head:

Mine is 1988 XJS with TH400

  1. remove exhaust pipes from end of downpipes to beginning of over axle pipes
  2. remove transmission mount. Everything. Of course leave two bolt/nuts that go into trans pan.
  3. remove rear left/right side heat Shields (philips screws)
  4. remove huge shield covering driveshaft (4 philips screws)
  5. get big piece of wood and support transmission under pan with floor jack. Raise it just a little to clear crossbeam.
  6. Unbolt crossbeam (6 bolts plus 2 more)
  7. mark driveshaft with paint so you know how to align when you put it back in (this would be great time to have both ujoints replaced…i did)
  8. remove four bolt/nuts from driveshaft at differential flange. Lower rear of driveshaft gently
  9. remove four nuts from driveshaft at transmission (put car in neutral so you can spin driveshaft around to expose top nuts) , remove entire driveshaft
  10. remove big bolt holding flange to transmission shaft, remove flange (may need to tap with hammer and crowbar to loosen off)
  11. remove 6 bolts holding extension housing on
  12. remove extension housing

Youll need a new gasket for housing/transmission. Standard th400 part, easy to find. 6 holes.

Total time, about three hours.

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22

One strange thing…

The new gasket i got that goes between transmission and extension housing is paper, and it says do NOT use RTV sealant.

But i can tell that it previously had no gasket, but did have black RTV sealant which ive peeled off.

Is this how GM used to do it? Or did a PO already get in there (i doubt it) and not use gasket?

24

Never done it but I guess it’s either or? It must be a very thin gasket no?
Signs of leaks with the RTV sealant?
AFAIK tight tolerance assemblies prefer not to use gaskets but sealant.

25

AFAIK the tail housing was installed originally with a paper gasket and no sealer, torque 23 lbs. If the surfaces are not marred of pitted, then no sealer required. With that said, for peace of mind, I would apply a gasket dressing ( no RTV) to hold the gasket in place during reassemble. Make sure the mating surface are clean and any transmission oil is controlled, and not dripping onto the mating surface. Good luck.

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26

Gasket dressing used with paper gasket, used anti-seize on bolts, so backed off torque to 20 ftlbs.

So glad I took photo before removing flange, as you can see, it is not flush with end of shaft. A hammer and block of wood is all that’s needed to seat. Don’t forget, bolts for driveshaft need to go in first. Put bolt back in with blue thread locker and 70 ftlbs.

IMG_20210620_094528224
IMG_20210620_0945282243024×4032 2.49 MB

IMG_20210620_094721589_HDR
IMG_20210620_094721589_HDR3024×4032 1.97 MB

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