Pulling TH400 Extension Housing Advice

Starting new thread in hope for any advice.

I need to pull extension housing on rear of my 88 Xjs TH400 this Saturday.

Looks like its straightforward - remove trans mount plate, remove shield, support trans, remove rear crossbeam, disconnect driveshaft, remove yoke/flange, remove six bolts, remove extension housing.

Ive ordered new gasket (housing/trans) and new ujoint hoping to replace while still attached to differential.

Anything else? Tricks? Who has done this?!

There were reports some time back regarding worn speedo gears. The story was that the speedo drive gear, which is a great big thing surrounding a shaft back there, would get rusty. Then when you install the plastic speedo driven gear in its little carrier, in no time at all the rusty drive gear would chew all the teeth off it.

I don’t remember whether the fix was to simply clean up the rusty drive gear or to replace it in entirety. Whatever, I’d suggest you check it while you’re there.

Me thinks that this won’t be that easy to do in situ Greg.
And what about the rear U-joints? if one is bad wouldn’t the others be getting there as well?

Pull the driveshaft; only 4 more bolts after the front flange. I have changed quite a few u-joints and have NEVER attempted one with the shaft in the car.

Can i access the rear flange bolts at the differential? Or do i need to remove the plate ofvthe IRS?

Easily. From both sides.

You may run out of clearance however…

Not sure about th400, with ZF it is necessary to remove some heat shields, preferably in asbestos pieces…

I don’t recall any issues with access when I dropped the rear cage on my ‘88

OK, I guess I’ll find out. Luckily I have box delete exhaust pipes, no more huge mufflers there, so I hope I have more clearance than normal.

I will also make sure to mark yokes/driveshaft for alignment. When I reattach yoke to transmission shaft, I assume I need to get it perfect on the splines so it aligns with driveshaft yoke? Is there a trick to this? Or do I just need to keep lifting driveshaft up to see if the 4 bolts align, and keep re-inserting yoke until perfect?

The yoke (output shaft flange) doesn’t care. It’s the U joints on the drive-shaft that need to be lined up. I go with the general idea that if I have a vibration-free car before I dismantle something in the drive train, then assembling everything in the same relative positions as before will give a good result!

True. I guess I could install yoke onto transmission however I want, and then put it in Neutral so I can turn it to line up.

BTW, is yoke American and flange British?

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Heck, IDK. I speak both languages!

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The way things work on an XJ-S, the drive shaft bolts to a flat flange at both ends. I’d call that a flange. The way it works on some cars, though, is that the U-joint cross itself is attached to a cradle with a pair if U-bolts, and that’s what you remove to get the drive shaft out. That cradle is what I call a “yoke”.

Might be just me, though.


And further complicated by the slip yoke used on almost all US cars until the 2000s- internal splined to slide directly on the output shaft of the transmission or transfer case. Used to allow length to change with suspension movement; British almost universally accomplished this with a splined area in the shaft itself.

OK, makes sense. The only driveshaft I’ve ever taken out was on my Jeep CJ7. Piece of cake, tons of room, didn’t even need jackstands. I think it had yokes.

Should be interesting on the XJ-S in comparison!

Think I’ll rent something to press ujoints though.

Question, when I remove driveshaft from output shaft flange, does the flange simply slide off the shaft inside the housing, or is it bolted to the end of the shaft?

I believe it is bolted. Which is weird, so many cars have a yoke that simply slides out of the back of the tranny, eliminating the need for the slip joint in the middle of the drive shaft.

OK. So does that mean when I turn that bolt, the flange will turn with it? I’ll need someway to hold the flange so I can get enough force? I also assume this is a high torque bolt. I couldn’t find any mention of ft lbs on this bolt in my ROM book.

Put the transmission in “Park.”

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90 minutes into it, all ready to remove driveshaft. Easy work so far, just tedious.

I did have to remove exhaust, but ive got some new over axle pipes and mufflers being shipped, so will just leave it on jackstands an extra week.

Gotta go borrow a big pipe, those four flange bolts for driveshaft are on tight, all i trust is my 12 point box wrench, and i need some leverage!

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Ok, stuck

Got driveshaft off, and removed bolt holding flange onto transmission spline. But flange will not come off. I tried tapping it with hammer, but i don’t want to hit it too hard? Do i need a puller?

Ok, got it off. Crow bar loosened it.

Got the extension housing off! Total time 3 hours. Phew. That’s enough for today