View Full Version : Jeep transmission overhaul...should I get a good grade?

08-12-2011, 01:18 AM
My welding instructor had a problem with his Jeep a couple weeks ago. The transmission had locked in fourth gear. He asked me if I would take it apart and fix it. I've never worked on the insides of a transmission before, so I jumped on it. It's an AX15, for those in the know.

I got it all apart, and found a broken snap ring had destroyed the synchronizer on fourth gear. He decided to replace all the synchronizers, and got all the parts. I reassembled the transmission, and he had it reinstalled.

It drove fine for several miles, then it wouldn't go into second any more. All the other gears continued to work OK. Bummer!! I feared I'd never hear the end of this.

He had it removed and took it apart, and he couldn't find anything wrong except some small burrs on the little rectangular blocks that drive the synchronizer rings. Those parts were reused. He's not sure if that's the problem, so he's discussing the issue with his Jeeping buddies.

I told him I still wanted a passing grade on transmission repair, since the transmission has five speeds and four of them work OK. Throw in a bonus for reverse working, and that's a solid B+ in my book. :D

08-12-2011, 01:39 AM
That AX15 sounds like a Borg-Warner T-5.

We used to have a lot of them fail when the owners used the wrong oil in them. A T-5 is loaded front & rear with tapered roller bearings on the mainshaft. The thrust bearing in the middle is a Torrington roller thrust bearing. Using the wrong oil usually causes this bearing to burn up, and weld the input & output shaft together....fourth gear.

Yes, on most of the transmissions, with the exception of the old antique gearboxes, burrs on the blocking ring guides can prevent shifting.
You get a "C" for not replacing the blocking rings and guides.

A.K. Boomer
08-12-2011, 09:21 AM
burrs are most likely not your problem - if it worked once it will most likely keep on working and actually get better if it were "burrs" of any sort.

I would put a high emphasis on checking out the de-tent locking system - it's a series of spring loaded balls and elongated rounded end pins that only allow for one gear to be engaged at a time and they also keep the shifting forks in a designated area, I would also check for a broken roll pin on one of the shafts that hold the shifting forks.

I just replaced the lead main bearing in my del sol yesterday and took it out late last night for a severe spanking and all is well, tannies are allot of work to get in and out and it pays to double check everything - I also use locktite on internal bolts and such, that being said I did not inspect the de-tent mechanisms at all due to the trans shifting perfectly before I tore it down - my only concern with it was the lead main and I had it diagnosed before removal due to the growling getting worse the closer I got to first gear, it could also have been the counter-shaft bearing on that end but very unlikely due to it being a massive roller bearing.
A good rule of thumb I use with transmissions or any other kind of labor and parts intensive repair is "verify"
anotherwords it's not good enough to just replace parts and have it work again, verify where things went wrong esp with shifting problemo's --- why did 4th gear lock up in the first place? was this broken snap ring retaining the part? or is it related to something else? If you don't find it - it don't go back together...
I suspect your 2nd gear lock-out problemo is directly related to the 4th gear lock up - this is just too coincidental, the shifting rails and there carefully orchestrated "one at a time" engagement is suspect and at the very least needs a going over with a fine tooth comb...

08-12-2011, 10:21 AM
Oops, I probably should have mentioned that the transmission WILL go into second gear when the Jeep is stopped, with the engine running or not. But it won't go into second when the Jeep is moving.

I think that rules out the detent balls and shift rails. I'm confident he and his Jeeping buddies will figure out what's wrong.

My part was to put everything in its proper place, not to make expert evaluations of things I've had zero previous experience with. I'm just glad I didn't make some bone-headed NOOB mistake putting it back together.

08-12-2011, 03:30 PM
It sounds like the second gear blocking ring is bad or the taper the blocking ring goes against is worn or both are worn and need replaced.

08-12-2011, 03:36 PM
It sounds like the second gear blocking ring is bad or the taper the blocking ring goes against is worn or both are worn and need replaced.
+1. The ring is not turning free on the cone shaped part of the gear

08-12-2011, 05:05 PM
I won't get a chance to look at it until next Tuesday. We were playing with it Thursday, and everything seems to move like it should. That's when we noticed the tiny burrs.

He's got some friends with a lot of experience on this sort of thing, so it's probably just a matter of getting one of them to check it over.

08-12-2011, 05:45 PM
Make sure that it has the right oil in it. That ring works merely on friction.

08-12-2011, 10:32 PM
If the blocking ring goes all the way on the second gear taper then it won't do it's job. It has to stop the gear from turning so it can engage the dogs on the gear.