Another loose 5th gear 5MT question

[heiche]

I've got my 5MT apart on the bench due to an annoying issue where 5th gear would grind unless very gently selected.

 

To a lesser degree, there were these issues as well: some grinding/whirring noises in neutral (not TOB), and reverse gear was getting harder to engage.

 

I figured the input shaft nut had backed off and was loose. I was half correct. The nut was still very well staked in place and obviously had NOT backed off. However, once unstaked, it virtually spun off with no effort. Once the 5th gear hub/synchro/drive gear were pulled off, it was apparent that there was some wear in between them that caused them to be loose (too much clearance between them). So I think this is why the nut wasn't tight, although it hadn't backed off.

 

Does this make any sense to anyone? I'd like to replace the affected parts, but I'm concerned that this might happen again if there was something else that caused it. Please let me know, thanks!

[heiche]

answering my question for future searchers... It seems the wear was initially caused by the outer needle bearing journal inside the 5th drive gear.

 

Looking at the picture in my first post, you can see the lines where the needle bearings rested. I initially figured that was just caked on oil from where I parked it. However, after cleaning it out it became quite obvious that those were actual grooves in the surface! (see pic below) Spinning the gear with the bearing installed on the shaft makes a horrible grinding/whining noise. What could have caused the needle bearing to create those (relatively) large indents? The rest of this post has my assumptions... I have to assume it was rust. When I bought my car it was a non-runner that had sat for a couple of years. Perhaps it had condensation in the tailhousing (getting in via bad shift rod seal?) So you've got water, you've got iron, you've got a couple of years to get some nice rust going. And so the grooves were created.

 

Fast forward to last spring when I got my non-runner running. Wow, what and odd whining noise it makes when I let off the clutch! That was the grooves making noise as they passed over the needle bearing when 5th gear rotates in place unselected. This vibration caused wear to accelerate, wobbling 5th gear a bit, and soon causing wear to the side of the gear where it faces the hub.

 

Eventually 5th gear just became very sloppy, causing poor engagement issues like grinding, and the whining noises continued at various pitches depending on the selected gear, except 5th itself when it is locked in place. The nut never backed off.

 

Anyway... I've spent way too much time/effort obsessing about this. I'll just replace all parts involved and be on my way

[heiche]

Just updating this post for closure... Finally got the car back on the road (it hibernates for the winter) and the transmission is perfect at the moment. No more unusual whirring/whining, and 5th now engages smoothly without grinding.

 

What was replaced to fix the issue above: 5th gear parts: drive gear, needle bearing and race, sleeve/hub, synchro.

 

What was replaced while i was in there: both input bearings, center diff bearings, input shaft nut and washer, all seals, sti short throw shifter (no longer gold colored btw, now silver), uncle BAC's cocktail

[Max Capacity]

Glad to hear you got it running well.

 

Sorry I just found this thread. I know my tranny guy is pretty picky about replacing the basic things you did wheneven the tranny it apart.

[xt2005bonbon]

heiche my friend! Reviving this old thread...

 

I carefully read your second post in this thread, and I wonder if I am suffering from the same type of whining/whirring you've described. Although I do not have any issue with 5th gear as you described. Here is a link to my thread below. You're welcome to post if you've got any idea or good insights .

 

http://legacygt.com/forums/showthread.php/engine-rpm-related-vibration-felt-shifter-changing-gears-263917.html?p=5670029#post5670029