Installed rebuilt transmission, now grinding in 4th and 5th

[dhkemp91]

Alright I have had the car a few months and the transmission in it had no first gear. But the seller included a rebuilt transmission that he stated had 2k miles on the rebuild and he had no problems with. Finally got the new transmission in. Shifted trough all the gears sitting still. Went out for a drive and 3-5 were grinding. Decided to get some new gear oil and drain and refill the transmission. The stuff that came out was almost black... But I filled it with Lucas 75W-90 gear oil until it started to dribble out the filler hole. Went and drove again and now just 5th grinds consistently. 4th every now and then. I just don't understand why! Doesn't matter how slow I shift into 5th it grinds. Could it be air in the clutch lines? Not disengaging enough? It has a stage 5 clutch if that matters. Any help would be appreciated!!!!

[itsa300zx]

Clutch prob not disengaging enough. If you still have the stock clutch fork with the stage 5 clutch, the fork might be flexing too much. This will cause a disenaging issue, check out the Zspeed link here:

http://www.zspeedperformance.com/Nissan ... SP1005.htm

[dhkemp91]

This could be my problem even though the clutch IS disengaging enough through the first 4 gears? Do the stainless clutch lines make any difference compare to what comes OEM?

[Ace2cool]

If that's not the issue, then it's gonna be synchros.

[Shoey2]

whats the word on Redline trans and diff fluids? any noticable change on our cars?

[Ace2cool]

Yes, but if it's grinding then the damage has been done. It'll basically just be a band aid.

[dhkemp91]

So you don't believe a stronger fork and new clutch line would fix the grinding at all?

[Ace2cool]

Most likely not. Reason being, if it's not grinding in all the gears, then it's disengaging in the lower ones. Most likely have blown synchros in the trans you have now. 2nd and 4th are common to fail, but 5th not so much. Do you still have the old trans? Maybe the synchros in that one are in better shape.

[dhkemp91]

I do have the old transmission still. 4th and 5th never grinded in that one. Might end up up dropping the transmission and putting the old good synchros in the new transmission. If so ill get a heavy duty fork and chromoly pivot ball. That should fix everything.

[Shoey2]

with these cars its just easier to do upgrades and reliabilty mods while your in there anyways.

[dhkemp91]

Yeah I just didn't know about the apparent need for an upgraded fork when an upgraded clutch is installed. I can grind 3rd through 5th if I shift under load and fast. So I really don't think it's synchros.

[Ace2cool]

It's not a need. It just makes the pedal feel a bit more modular.

[dhkemp91]

I dont think i specified that my car is a 91 NA -> TT swap. I just asked the previous owner and he said the rebuilt transmission has an NA bell housing. Could this be any part of the problem at all??

[Ace2cool]

Nope. The only thing that will affect is the starter and the flywheel.