86 AX5 5th gear issues

[dzlmnche]

Guessing a lot of you are on the "All Things Comanche" FB group where I already posted this, but figured I'd post here too...

 

86 2wd I just swapped a 4cyl Mercedes diesel in. I did not drive the truck at all before the swap, but I suspect this issue is unrelated.

 

Rumbling only present in 5th gear, fades in and out roughly ounce or twice a second. I had initially suspected tire balance, but I believe I have isolated it to 5th gear specifically, regardless of road speed.

 

I see lots of talk about c clips falling off and either causing partial engagement of gears that damages teeth or a complete loss of 5th gear. As I kept reading, I came across a couple people saying earlier AX5s used a crimp style lock nut to hold 5th. Can't get a whole lot earlier than 86 so my question is... is it likely that my transmission has the nut rather than clip? Are the 5th gear issues mostly isolated to the later AX5s with the c clips? I suppose its possible the gears are damaged, but seems less likely to me on a stock 4cyl 2wd truck if they never became only partially engaged.

 

I found my slip yoke wobbling more than what seems acceptable to me with a leaking seal, so I ordered a bushing and seal and plan to pull the rear extension housing to replace both of those parts. I will inspect 5th at that point.

[eaglescout526]

I say replace the seal and bushing first. Then test for your rumbling. I had that issue before and the extension got too hot and wore out both the bushing and case to where you could not put a bushing in and have it stay in place. Course that was due to no oil in the rear extension. 

 

But you may have found your problem with the wobbling yoke

[dzlmnche]

I say replace the seal and bushing first. Then test for your rumbling. I had that issue before and the extension got too hot and wore out both the bushing and case to where you could not put a bushing in and have it stay in place. Course that was due to no oil in the rear extension. 
 
But you may have found your problem with the wobbling yoke

Are you saying you had a sort of rhythmic rumbling that was due to a bad output slip yoke bushing?

[eaglescout526]

It was a combo of some things. Poly bushings, not changing the oil in the tranny after first owning it, but some of it was due to the bushing and case being worn out and was causing the rumbling. It wasn’t noticeable for me when I had vibrations galore but if IIRC I would occasionally hear and feel a drone or rumble from fifth, but that was a while ago. That transmission grenaded itself. 

 

But do do inspect the fifth gear as a precaution since you’ll be in there

[dzlmnche]

5th looked perfect. I put two small tack welds between the snap ring and 5th gear so it can’t come off.

 

Bushing and seal replaced. The slip yoke has some wear too, but it is much tighter now and drives noticeably smoother. May replace the slip yoke at some point.

 

I was having vibration issues from the diesel swap and had no headliner so it was really hard to tell if the issue was isolated to 5th while being shaken in an echo chamber. Got a headliner in and vibration issue sorted and it became more clear that the issue was not isolated to 5th gear.

[eaglescout526]

Awesome! 

Side note. I did replace my slip yoke prior to the trans blowing up and it fit really snug with new case, bushing and seal and still does to this day.