Help with 4-speed trouble-shooting (2 Viewers)

[Adax]

Here's the diagnosis and update.

Last weekend I found someone with three 4-speeds for sale. Interestingly one of them had the exact same problem mine does. I bought one of the other ones that shifts fine and the shafts turn as expected in each gear - but has broken input side mounting flanges I later discovered. I then began tearing into both of them. I've probably pulled and installed the input shaft 10 times.

The problem is the input and output shaft binding together as I suspected, but not for the reason I suspected. The roller bearings are fine and there is no rust in the mating.

I found when pulling the input shaft that after hitting the bearing once to drive it out, everything spun as it should - problem solved. But the bearings are positioned by the end plates which pushes the input shaft bearing back into the case enough to cause the binding again. I swapped in my known good input shaft and have the same problem. I then installed the input shaft without the 4th gear synchro ring on a hunch and surprise it works fine when fully seated.

So, the problem is that the input/output shaft clearance is too tight which causes the 4th gear synchro ring to engage the 4th gear synchro cone, essentially locking it into 4th gear. This also explains why I could turn the shafts 2-3 degrees independently before they locked up as there is that much play between the ring and the 3 keys that locate it.

I can find no way to adjust this clearance. The bearings are positioned into the case by the two end plates and the shafts are positioned in the bearings without room for adjustment. Are there shims in the output shaft somewhere that I can change to increase the clearance so that the synchro does not engage?

The problem exists with both of my input shafts and synchros so the problem is either with the case or the output shaft somewhere.

Thanks for all the help.
Alan

 

[Pin_Head]

I don't know that this clearance is adjustable on the H42 and I don't have my FSM in front of me to check. I would suspect that the bearings aren't fully seated on the shafts or their is a piece of dirt between the bearing and the shaft seat, or possibly the 3-4 synchro assembly isn't assembled properly. Maybe the bearing retainer O-rings are too thin?

 

[Adax]

FIXED

After thinking about it overnight I came to the conclusion that the output shaft must be positioned too far into the housing - meaning that the output shaft bearing is not seated all the way onto the shaft. I measured this as shown below, comparing my bad tranny to my good one.

The blue arrow points to the output shaft flange on which be bearing is seated. The red arrow points to the inner bearing race. On my good tranny, the bearing sits 1.97 mm above the flange. On my bad tranny, the bearing sits 3.21 mm above the flange, proving my theory. Ideally the shaft should be removed and the bearing re-seated but since I don't have a puller that large, I placed a brass drift on the input end of the output shaft and hit it several times with my BFH. Remeasuring I found a 2.00 mm step. Replaced the input shaft and everything works fine.

Since I have two trannys with this problem, I suspect it is somewhat common. I found both without an associated transfer case. The two good trannys I found were with their transfer cases. I believe someone separated the trannys from the T-cases by hammering on the output shaft to drive it out of the T-case, thereby unseating the bearing a few mm and causing the 4th gear synchro to bind.

Mystery solved. Hope this helps someone else out in the future.