I have a transmission that is sitting in my garage that I haven't used because it has problems. All the gears crunch a bit when shifting. I replaced every synchro in the trans and the result is still the same. Crunchy city.
What bothers me is that it is EVERY GEAR, I can understand if some teeth were messed up causing one gear to be a bit crunchy, but having them all crunch is driving me nuts. It has been sitting in my garage for 3 years now and I'd like to take another tackle at it.
So, what could it be?

 

You did not say is another gear box works in your car or not.
(1) The pilot bearing might be bad and is grabbing the input shaft.
(2) Alignment is bad causing the pilot bearing and input shaft to bind.
(3) The clutch pressure plate is not totally releasing the disc.
(4) The master/slave cylinders or hose is/are bad.

 

I have a working different trans with the same car. Also if I "speed shift" the problem is not present.

 

what gear oil is in it?

 

+1 on the gear oil.

I just put a newer jdm tranny in my car and ordered fresh redline oil. But I got the MTL by accident... Way too thin for our trans, have to shift slow so the syncros can get a grip.

Replaced with some reg 75w90 I had laying around. But it is too cold here in MI now for that, didn't think I would make it out of my driveway it crunched and ground so bad had to double clutch just to change gears since the fluid was curdled.

Drove it right back in the barn and mixed in a left over quart of the mtl with the heavy stuff and is better, once it warms up it is driveable.

I just ordered some neo synthetic 75w90 HD it is supposed to work well. But I can tell u the wrong fluid make a huge diff in the fd trans... I heard people say it before and I thought they were exaggerating... But no they weren't.

Good luck

 

I tried NeoSynth and "brown label"

 

Redline heavy duty shockproof oil.

Almost guaranteed to fix that issue.

 

+1 on gear oil. My FD crunched every single gear when I first bought it and would not shift at all into any gear at high rpm and I thought my tranny was toast. I flushed the fluid with Amsoil Severe gear 75W90 and everything now is perfect

 

Every high performance transmission builder I knew told me to stay away from that junk.

 

I am amazed how sensitive the fd tranny is to the fluid type... I have half a mind to try out all the popular redline/neo/amsoil/mobil one oils next summer back to back...

 

LOL, that redline crap is junk!

Neo didnt work? Amsoil or even dynojuice =)

-AzEKnightz

 

Hah.
Nope Neo nor dyno worked. I have Neo in my current trans and it is working fine.
I just hate having a transmission lying around that I can't fix =(

 

In my experience 2 things can cause all the gears to grind:

1) Using straight gear oil instead of using special manual transmission gear oil such as NEO MTF.

2) The clutch may not be disengaging completely. Possibly a broken fork?

 

For whatever reason Rx-7 transmissions are very sensitive to fluid. They love Redline, even though transmissions on other cars often don't. I have personally had Redline MT-90 solve grinding problems compared to other "decent" brands like Mobil 1.