AX15 Reverse Shifting Issues

[MDotson90]

Hi to all, 

Hoping to get a little guidance!

I recently completed a rebuild of the AX15 with a master rebuild kit which was uneventful. When it was completed and bench tested, it shifted rather smoothly into all gears, except reverse. It took a few tries each time, but the reverse gear would engage and the output shaft would spin in the opposite direction with no issues once it's engaged. 

Having read a lot about difficult shifting just after a rebuild, we thought little of it and installed it in the car. Now, we are still having the same issue, but worse. The transmission won't at all shift into reverse, and feels as if something is blocking it. There's no grinding or partial engagement of the reverse idler gear whatsoever. Even with all but the most extreme force, it still feels like there's a hard stop just in front of the reverse range. We managed to force it into reverse (luck?) maybe twice since it's been installed in the car, and it moves the car beautifully backwards with no noise, clunking, grinding, or popping, but as soon as it's returned to neutral, the same issue occurs again. 

We took it out for a test drive and let things get nice and warm, and it shifts wonderfully into all 5 forward gears, but the reverse is still absent. 

Any ideas what could be going on? Do I have to drop the transmission? The shifter isn't binding on/hitting the body or console as we've removed all that and it had no difference. ? Here's a video of the issue. Thanks in advance for any advice.

InShot_20180312_025446985.mp4

[Moses Ludel]

MDotson90...It sounds like you've tried shifting after rotating the reverse gear.  Reverse in a non-synchromesh gear will sometimes require slight movement for engagement, though this is unlikely.  You can fiddle with letting the clutch out in neutral, then depressing the clutch pedal and trying the reverse shift again.  If that allows smooth/easy reverse engagement, the issue may resolve.  Unlikely.

More likely, the detent pins, balls and springs are not aligned properly or mixed/swapped in their positions.  This could cause the reverse rail to hang up.  A reverse rail out of rotation or a reverse fork bind for any reason could also be an issue.  You share that when you have been able to get into reverse, all works well without noise.  That would indicate proper gear alignment and a shift that allows full engagement of reverse once the rail can move.

This sounds like a restriction at the reverse rail, which can occur when springs, ball and pins are either not in proper sequence or hanging up the rail(s).  Also be sure there is nothing in the shift mechanism (tower parts) preventing the reverse rail engagement.

Let us know what you find.  If this narrows to the reverse rail movement and detent/shift pin/spring obstruction, there is minor access to some parts through the outer rail plugs.  If the issue is on the inside of the transmission between the rail(s) and detent bores, you will need to remove and at least partially disassemble the unit.

If you took photos of your assembly work, try to determine whether the pins/springs and balls became mixed at the reverse rail detent.

Moses