Occasional gear grind

[dimsum]

Finally got the engine running somewhat decently, but the gears grind when I shift. I have a 5-speed transmission mated to an L24.

 

While I had the engine out, I had the transmission rebuilt. The mechanic said the synchros looked fine, so he only replaced all the bearings.

 

Now, when I shift, the gears will grind about 40 to 50% of the time (either upshifting or downshifting). When I shift either way, it is at a relatively low RPM (<3500).

 

I think that double-clutching helps a bit, but I'm not sure. I also replaced the clutch hydraulic fluid, but that did not help any.

 

Before I started the car up this past March, it had been sitting for about a year.

 

My guess is that the clutch cylinders are bad and need to be replaced, but I wanted to get a second opinion from this group.

[Pop N Wood]

Having the clutch not fully disengage can cause such a problem.

 

What all have you changed since the trans last worked right? Is it all stock stuff, or an aftermarket clutch? What type of transmission fluid are you running and when was the last time you changed it? Does it make a difference if the car/trans is fully warmed up or cold?

[dimsum]

Having the clutch not fully disengage can cause such a problem.

 

What all have you changed since the trans last worked right? Is it all stock stuff, or an aftermarket clutch? What type of transmission fluid are you running and when was the last time you changed it? Does it make a difference if the car/trans is fully warmed up or cold?

 

I'm using the same clutch that was in the car before (Centerforce street clutch). I also have a Fidanza aluminum flywheel.

 

I'm running Redline MTL 70W80 transmission oil, just changed.

 

I do not know if hot or cold makes a difference. I'll try and check that out when I get a chance.

[Zmanco]

I had a similar issue with the guy who rebuilt my 5 speed. In my case the syncros were gone for 2nd and 3rd gear. After the rebuild they were still poor. It also popped out of gear in reverse. He claimed he had put new syncros in. In any event, while he fixed the reverse issue he must have done something else because the syncros are better now. I still have to granny shift on the 2-3 upshift if I take it to redline though.

 

There's another guy who specializes in rebuilding Datsun Roadster transmissions far north of me. The next time I change the clutch and have the tranny out I'm going to take it to him and see what he can do.

 

But first you need to confirm that the clutch is properly disengaging. Are you sure you don't still have air in the lines? What about putting it into 1st gear when the engine is idling and the car is stopped? Does it take more effort than it used to? If so, then the focus should remain on the clutch. If it's the same as before, then I'd focus on the tranny.

 

I suspect you'll probably have to pull it again. I feel your pain

[dimsum]

I suspect you'll probably have to pull it again. I feel your pain

 

Ugh...that's what I was hoping I could avoid. I'm planning on changing out the clutch cylinders first to see if that solves the problem. That will force me to bleed the lines again, this time making sure I don't have any air left in them.

 

Thanks for the recommendations.

[dimsum]

One friend mentioned that the transmission fluid might be causing the problem. He had a Toyota AE86 whose tranny would grind when he used synthetic transmission oil. He suggested trying some regular oil to see if it gets rid of the problem.