AX15 woes... help me think through this.

I've been wrestling with this problem for a couple months now and I'm getting close to having enough time to pull the trans back out for further inspection.

The problem:

3rd won't let me in. If I attempt a push for 3rd it makes no audible noise or physical grind UNTIL I attempt to release the clutch "in" that gear. If I'm sitting still and shift for third, as I let the clutch out slowly, you'll see the shifter punch back ever so slightly and you'll see the shifter vibrate as if the syncro sleeve is skipping across the teeth on the 3rd gear's mating teeth.


What I've done or tried:

Full transmission rebuild (all new bearings, new blocking rings, and seals), New Hurst shifter (at this point just to be sure the shifter isn't related), Amsoil 75W-90 GL-4 new transmission fluid.

Other potentially useful information: There are no other issues with the transmission, every gear engages quietly and without grinding; even reverse isn't that bad. The clutch seems fine as it never has a problem disengaging or slipping at hwy speeds. If I can get the third gear to "catch" it will remain in without popping out but its likely to be quite audible if I attempt it.

Here is a picture of the transmission I took when it was apart. The 3-4 syncro sleeve is under the fork on the left side of the first picture. When I shift for 3rd the sleeve moves towards the intermediate plate via the shift fork. As you can see there is no damage to the mating teeth, and I replaced that blocking ring, as well as the rest of them, when I rebuilt the transmission. Does the discoloration on the 3-4 shift fork mean anything ya think?





There are only 4 components that could be related to this symptom as I see it. The syncro sleeve, the blocking ring, the shift fork, and the 3rd gear with its braking surface for the blocking ring. I would assume if the blocking ring wasn't braking on the gearing I would have an audible grind when ever I attempted the shift, not as I release the clutch; correct (there was no change in symptoms when I changed the 3rd gear blocking ring)? Any advice would be helpful. There are only so many parts here to replace and I'm sure eventually the problem will be cured by throwing replacement parts at it but help me pick the correct one. Thoughts? Ideas? Comments? :dunno:

When you reassembled the trans, did you put the correct blocks into the block ring? There were some that were different lengths than others. IIRC, The ones for 1-4 were the same length, but I think 5th had ones that were the same length on one side, shorter on the other. If you put the short ones in that block ring, I could maybe see it happening.

Either that, or it sounds like the shift rail isn't being moved far enough for some TBD reason.

When you shift it on the work bench, how does it feel? Did you check everything with the cases apart before you buttoned it all up?

asp said:

When you reassembled the trans, did you put the correct blocks into the block ring? There were some that were different lengths than others. IIRC, The ones for 1-4 were the same length, but I think 5th had ones that were the same length on one side, shorter on the other. If you put the short ones in that block ring, I could maybe see it happening.

Either that, or it sounds like the shift rail isn't being moved far enough for some TBD reason.

When you shift it on the work bench, how does it feel? Did you check everything with the cases apart before you buttoned it all up?

Click to expand...

Are you referring to the 3 inserts within the syncro collars? If so, yes. I made sure not to reverse any of them and even installed them back exactly as I removed them; just to be redundant. I also disassembled each syncro collar assembly one at a time, as so not to mix up the inserts. One thing to add is that the symptoms of the third gear was my original motivator to "rebuild" the transmission. The exact same symptoms were present after the rebuild.

Your second guess is exactly what led me to purchase the Hurst shifter. My hypothesis was that maybe the pivot bushing had worn enough to allow the shifter to drop slightly and potentially remove some throw length. I've already replaced the "cup" bushing at the end of the shifter before doing the overhaul and that made no difference.

Before reinstalling the transmission I did bench shift it while manually rotating the input shaft. The engagements felt fine and the change in ratio was as expected from each gear. I checked as much as you could check before buttoning it back up but everything is quite the "select" fit and won't really let you screw up too much.

bump bump? Any other thoughts before I go and buy what will surely prove to be unnecessary replacement parts...

For those who stumble across this thread later, maybe I can help you out. After a dead end on information and a direction to go in, I sourced out a transmission parts company, that is conveniently local enough for me, and decided to throw money at it. The company's name is Southern Gear and the staff is quite knowledgeable of the components in question. Now I wouldn't call up there and request someone to explain how the components works, or ask what's wrong with your transmission. I get the feeling people know what they need when they call this place. I got the number from an old man who runs a heavy duty truck repair shop down the road.

Either the case, the components I bought were the 3-4 shift fork, 3-4 syncro sleeve, and 3rd gear/hub unit (~$178.00). My thought was replace everything related to the area. Once the parts showed up, and I took them out for a look, it was apparent what I had missed. See I inspected the shift forks when I removed them during the rebuild, and noted the parallel machined edges, but didn't realize how wide, or how tight to the collar it was supposed to be. Once I looked back on my pictures, it was apparent what I had missed.

Here is the two forks side by side. You can see how much more narrow the old one is than the new. I'm not sure what caused it but it's definitely the problem.





Hindsight says the heat discoloration should have been an indicator but I was reassured by two "respected" opinions that it was normal and not an indication of a problem. I should have known better when the other one wasn't discolored. Oh well, such as life. Third gear is back, and the guys down at Southern Gear said they'll take back the parts I didn't need; which is really nice. That shift fork is only $34 bucks.... Sucks I had to take it down/apart twice, but at least I know that EVERYTHING is in perfect working order.

I just was thinking about this and came to check up on it. Good to know and I'm glad you got it fixed.

That looks like "my shifter is an armrest" type wear.