Transmission: Replace Output Shaft

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In Sept 2007, about 20' into a hard launch I heard a loud bang under my '91 Stealth. The car would still move under its own power, but would slip with too much throttle. I learned later that the weak 18-spine output shaft between the tranny and xfer case had broken. Torque could no longer be sent to rear wheels. The car could move because the VCU (viscous coupling unit) was sending torque to the front wheels. Too much throttle though, and it would slip. Note: do NOT drive your car in these conditions. I was lucky and did not burn up the VCU, but easily could have.

After quick research it appeared that I had three options:

  1. Replace with stock
  2. Upgrade to 25-spline xfer case
  3. Upgrade to 300m shaft
I decided on #3 and set about more researching to see if I could do it myself.

Compare original to 300m

Compare Mark Williams 300m version (top) -to- broken original (bottom).

My first step was to check out the shop manual to see how everything worked,

CrossSection showing break

I also read thru the description in -->

I was convinced after reading all this (seeing that the tranny would have to be opened up), that this was a job for professionals only, but then found a 3SI thread by AbsurdParadox:

Output shaft replacement without tranny pull: EASY -->

Two how-to sites to check out first:

AbsurdParadox's tips, with some EDITS and photos:

Fig.4 Lugs/Webs to pull on
Fig.6 Substitute Punch
Fig.7 Moving cluster to remove VCU
Fig.8 Removing Shaft from transaxle
  1. You do NOT need to remove anything suspension or drive train related other than the transfer case cover and the passenger side wheel.
  2. To get that allen bolt out that sits in your input shaft, you can use a crowbar to hold the flywheel in place through that access hole on the front (of the car) side of the tranny. EDIT(Impact wrench works great also).
  3. Before pulling the tranny cover off, remove the the little plate that holds the the three balls and sprins in. This will make removing the cover easier. You may want to place a towel under the tranny when you pull the tranny cover, so you don't lose the balls if they fall (mine didn't).
  4. You will probably have to hammer the cover off a bit. Take it easy, and use some soft wood or soemthing to wedge in one side while you hammer on the other to provide some better leverage for you.
    EDIT(A slide-hammer worked very well for me. There are three "webs" Fig 4. on the cover that can be hooked by the slide-hammer. Simply rotate around the cover pulling it out evenly, a few taps at each web, then move on to next one. As a gap starts forming between cover and case, just keep it even all around, by pulling where the gap is the smallest.)
  5. Once you think you have the cover's dowels disconnected, the input shaft is still probably holding it on. Stick the allen head bolt back in the shaft and give it a few taps to free it from the cover.
    EDIT(this was not necessary when using the slide hammer, the cover pulled from the input shaft by the impact of hammer, for me anyway)
  6. Since you didn't remove anything suspension related, you can NOT remove the super long bolt at the lower left corner of the case (its too long to clear the A-arm). Just swivel the case cover on this bolt. #:EDIT(or use a jack to raise the wheel hub, the bolt will then pass under it)
    EDIT (I could not find a punch to push the VCU pins in, so used a small screw, held by needle nose, worked great! Fig.6 Also, I found the easiest way to rotate the VCU was to turn the wheel hub)
  7. You may have to pry the gear that hangs over the VCU to get it to clear so the VCU cap can come off. At first I was prying on the gear, but Internexus (Sean) realized we can just stick something in the end of that shaft and pry that way. EDIT(the slide hammer shaft worked perfect for this Fig 7.)
    EDIT (don't panic if the shaft appears to be blocked by brake rotor Fig.8, simply turn the steering wheel all the way to right, and then there is clearance )
  8. Don't be too worried about pushing the pins in the VCU cap too far in. You have a long way to go before they'll fall out.
  9. Use some RTV when reassembling.
  10. Tighten everything up evenly when putting the case cover back on!
EDIT Torque values which may be of interest:
Transaxle case bolts - 18 ft. lbs
Input shaft allen key bolt - 12mm hex = 70 ftlbs, 7mm hex = 25 ftlbs
Two bolts that hold the cover plate with the springs and balls underneath - 7.5 ft lbs

EDIT Recommended reading is a post by Bret Brinkmann, with warnings, and some tips.

Fig.9 Compare Old to New

The spines on the old shaft were heavily worn as can be seen in Fig.9 . . . Unfortunately, the mating piece in the transfer case had equally worn splines, so had to be replaced. I did that myself, but could not have done it without a BIG press. It took a lot of force to remove the gear from the spool/coupler.