Gearbox Noise

[pakiwi]

I have a 1973 RWA. PO had clutch seize from lack of driving and had this replaced. Car has done 18,000 miles total.
Ever since I have had the car, changing in and out of 3rd gear, I get a grinding noise. From 2nd to 3rd and from 4th down to 3rd. If I take my time changing, and using a gentle touch, I can get into and out of 3rd without a problem.
If I idle in Neutral, go from 2nd to 1st to start, sometimes it seems that 2nd is locked out. I disengage the clutch, then re engage and it goes in smoothly.
Fluid has been changed twice and level is good.
Any other recommendations.
I have a Datsun tranny sitting on the shelf, but that is on the winter list.
Thanks for any assistance.
Allan

 

[walshja]

When I had a leak (still do) in my clutch master cylinder, I got some air in the system, and I had all the same symptoms you are having.

since you have changed the fluid twice, is it possible you could have gotten some air in your hydraulic system?

just a though

 

[pakiwi]

Sorry,
I guess I wasn't too clear.
I have changed gearbox fluid twice and have not changed Clutch fluid.
Allan

 

[Jim_Gruber]

Bleed the clutch, bleed the clutch!!!

 

[jvandyke]

wouldn't worn synchros do that?

 

[jhorton3]

That's the exact same problem I have with my gearbox, same gear, same symptoms. I've changed fluid in transmission and bled the clutch system. The problem I fear is in the synchro on the 3rd gear set. Changing to a heavier gear oil helped some, but not enough. Sometimes I can double-clutch when downshifting and not get the gear grind, but it's rare.

I'm saving my pennies for a transmission rebuild sometime in the future.

 

[jvandyke]

I have those symptoms too and while it could be insufficient clutch bleed, I've bleed every which way you can imagine including fitting a speed bleeder on the slave. I swapped gear boxes when I got the car because of no oil in it and I think I lost a needle bearing. I did not have the grind before but who knows. I did have to put a nut behind the slave push rod to "lengthen it" maybe I should try even more length? I suspect that the release bearing maybe be the one for a 1275 but I don't know what effect that would have, although I do now have a 7/8" bore master acting on the slave. I need to rebuild my now "spare" box and get ready to swap when I no longer have a choice to wait. My old box looked great (synchros and such, but then again so did the one I put in, don't know if I could ID a worn synchro to save my life though.

If you let the rpms drop a bit between shifts are things smoother?

 

[CraigCootsona]

How new are the master and slave cylinder? Either being pitted or worn could do it. I'm not sure if you have an adjustable linkage between the pedal and the master, or between the slave and clutch arm but that's another place to look. You could try pumping the pedal a few times then engage gears and see if it improves. That could indicate air in the lines.

 

[JPSmit]

I have a Datsun tranny sitting on the shelf, but that is on the winter list.
Thanks for any assistance.
Allan

I think this is the point others have missed

1. heavier oil
2. check clutch
3. turn up stereo
4. put in datsun tranny this winter

 

[pakiwi]

John Peter,
You sound like my father. Sorry. He always told me its a 35 year old car, what do you expect. I was guessing most likely 3rd syncro as a heavier oil and when its cold, it is not as evident, also when the revs have dropped it slides nicely into gear.
I had read that most of the problems occur with 1st and reverse, rather than 3rd and with the occasional problem at stop, thought it may be Clutch adjustment or air leak.
Thanks,
Allan

 

[JPSmit]

John Peter,
You sound like my father. Sorry.

actually what really frightens me is when I sound like my father.

 

[Jimmy74]

Oh the hours I've spent chasing these tranny problems down! Here are some problems I've encountered, most of which reduces the distance the clutch plate travels when the pedal is depressed, causes dragging and a balky transmission:

1. Hose to slave cylinder. Bulges and reduces throw, or colapses internally preventing complete disengagement (burned clutch plate follows).
2. Wear in the holes the master and slave clevis pins set into.
3. Leaking master, slave or both.
4. Air in the hydraulic line.
5. Slop in the clutch fork pivot point (worn bushing).
6. Bent clutch fork.
7. Excessive play in the main input shaft (at the bearing).
8. Squashed out rear suspension (changes angles/distance of tranny yolk to diff. resulting in gear pop out on rough terrain).
9. Excessive wear on shaft/bearings of laygear.
10. Bad pilot bushing (causing drag).
11. Idle speeds over 1000 exacerbate issues.
13. Floor mat holding clutch pedal 1/4 " off the travel stop.

This isn't an engineered diagnosis, just experience. I wish you luck, and hope you don't need to show the light of day to the inside of the bell housing/tranny too often.

If your taking the slave on and off, you can cut the end off the top bolt hole ear of the slave changing the hole into a slot. It mounts and dismounts real easy that way (you can leave the bolt loosened in the tranny, because clearance against the frame rail is a !@#$).

 

[BugEyeBear]

10. Bad pilot bushing (causing drag).

I pulled & rebuilt a trans that was grinding when downshifting. I ASSUMED it MUST be the synchros.
Reinstalled the newly rebuilt trans, only to discover it STILL was grinding when downshifting.
Turned out it was caused by a worn pilot bushing.
This worn bushing causes the trans input shaft to drag & spin at a higher speed than usual (the input shaft would usually drop in RPM once the clutch is depressed, but if the pilot bush is worn the input shaft tends to match the crankshaft speed even when the clutch is depressed).
On the 2nd installation I replaced the pilot bushing and everything worked GREAT! :thumbsup:
Bushing only cost a few $$!

Moral of the story: Do it right the 1st time.
2nd Moral: Try replacing the inexpensive parts 1st!

Good Luck!
-Bear-