Why Won't This Thing Stay In Reverse?

JuiceMan · 05-13-2002, 06:45 PM

Ok ever since I purchased my 69 (5-speed) I have had problems with the transmission staying in reverse.

All of the forward gears work excellent and I never have no problems with them. However when I shift into reverse just as soon as I apply any throttle the car will move backward about 1 foot then the gearshift will "fly" right back into neutral while making a loud grining noise on it's way back. The only way I can back the car up is if I hold constant pressure on the shifter and give the car very little gas. I'm not talking about light pressure either. More like pushing almost as hard as I can.

However even when I hold the car in gear it has to be dead level ground or it will jump out of gear again. Any incline and I can forget going anywhere in reverse.

This problem really bugs me. My local shop said the transmission needs rebuilt however I am having a hard time admitting to that considering the price of a rebuild

I have checked my shift coupler's adjustment and replaced all bushings and this didn't help any.

Anyone know exactly what could be causing this? I don't think reverse has synchronizers so iw ouldn't assume it's that. Other than a bad gear anyone know what else could cause this? Could bad transmission or motor mounts cause this even though all the forward gears work correctly?

Thanks,
Dustin

JuiceMan · 05-14-2002, 06:44 AM

Anyone have any ideas?

JuiceMan · 05-14-2002, 05:50 PM

TTT->

Jim Sims · 05-14-2002, 06:35 PM

Okay Dustin, Looking at the factory shop manual cross-section for a 901 tranmsission I would venture to say your 1st/reverse gear detent system (a ball or round ended plug that engages notches in a selector shift rod to help hold a gear engaged) is worn out or missing or put together wrong. This could mean a worn ball, plug, selector shift rod or weak spring. It could also mean the detent system was not reassembled correctly (or parts left out) during past transmission work. It appears part of the 1st/reverse detent system (a ball and spring) is accessible from underneath the car without disassembling the transmission. It appears to be under a hex head cap screw on the bottom of the transmission on the passenger side of the intermediate plate. I also suppose this screw could have also just come out (and the ball and spring then fell out) but I would suspect then the transmission oil would have also leaked out. If none of this means anything to you I suggest you consult a mechanic who knows 901 transmissions. Part of this tranmsission is shown in 101 projects. Good luck, Jim

JuiceMan · 05-15-2002, 05:27 AM

Actually Jim that was very helpful. I'm going to have to get myself a shop manual it looks like. However just knowing part of what COULD BE wrong is accesible without removing the trans helps

Thanks I'm getting under there to take a look.

Jim Sims · 05-15-2002, 06:24 AM

Dustin,

I did some additional consideration of your reverse gear problem The reverse gears are straight cut so they don't inherently have an axial thrust pushing them out of mesh when under load but if they're worn (somewhat rounded) this could be happening. Although, unless abused or run at the edge of meshing for a long time, reverse gears shouldn't see that much wear. Your problem could be a combination of worn gears, a worn shift fork and an weak reverse detent spring. These parts alone will be around $500 if they need replacing. However, one can replace these items by dropping the transmission and removing the front cover; one doesn't have to get into the core of the transmission. See the first gear synchro repair project in 101 projects. If you have to go in and do this I'd recommend refurbishing the first gear synchro system while your'e in there (another $200 in parts?).

However, if you're lucky there may be a much easier fix! Given the fact that the hex head screw that gives access to the reverse detent spring and ball is on the bottom of the transmission it may have been mistaken by a previous owner or uninformed mechanic for the transmission's drain plug. It may have been unscrewed and the spring and ball lost or they were reinstalled backwards (spring first, then ball, who knows!). The spring could also be weak due to creep over time. The nominal free length (no load on it) of this spring is 29.2 mm and the minimum free lenghth is 28.2 mm. If it is shorter than 28.2 mm it should be replaced; given your problem I'd get a new one period. Also get a new ball. If this is your problem this fix will save you a $1000. Good luck, Jim

john walker's workshop · 05-15-2002, 06:51 AM

my guess is the straight cut engaging teeth on both reverse gear and the 1st/rev operating sleeve are worn at an angle, which would pop it out of gear under slight load. the gear oil is probably quite metallic looking. they don't have 100% engagement when set up, more like 80%. easy fix, with the eng/trans out. just pull the trans nosecone.

michel richard · 05-15-2002, 08:31 AM

Had the exact same problem years and years ago, in a beetle. I was not even close to doing any wrenching at the time, so I don't know what the actual problem was.
I do remember that the trany had to be opened (D'oh) and some gears changed.
HTH
Michel