Cant stop that 3rd gear grind!

[rsx858]

Ok so this season, prolly back in june, i blow up a transmission (that was obviously on its way out) while shifting into 3rd. I take the thing to a very reputable builder who takes the thing apart and upon seeing the utter destruction that was my transmission, he starts fresh by rebuilding a tranny off a donor. Sure enough my new transmission with all fresh parts makes a healthly grind at high rpm going into 3rd gear ESPECIALLY on downshifts. long story short i take it back, synchro damaged, new build, and still more gind. Take it back, synchro damaged, new build with a brand new synchro and gear, and yet it still grinds!.

Now i know nothing about transmissions but the guy doing the work has a great reputation. What possible defects could be causing this grind? For reference I am a religious heel-toer, I have made sure that i have been getting the clutch all the way to the floor, i have tried double clutching but with no better results, and the only way i can get it not to grind on the downshift is when i move the shift lever very slow and not apply much force. -resulting in a much slower shift

Thanks for your help!

[Black91n/aRX-7]

What fluid are you running? That has a big impact on shifting.

[rsx858]

I usually run redline mt 90 and recently have tried using both mt90 and royal purple 75 90 so far fluids have had no difference in preventing the grind

[Z3_GoCar]

Redline/RP should both be up to the task. How's your shift linkage? Any worn shifter bushings? How about motor and trans mounts? Are they tired, soft, and cracked? How about the motor? Do you have a worn thrush bearing? The grinding is only a symptom of something else worn, something that you hadn't yet changed. Good luck.

[joeg]

How is your clutch??

[seckerich]

Check your pilot bearing and inspect the input shaft on the trans. No good to heel and toe if the shaft is still spinning with the crank. Check the shifter bushings to see if there is free play and the gear is only partially selected. Is the clutch disengaging right at the floor or about half way down? All else fails send it to someone who knows the tricks to make these work well in race conditions if your previous builder does street trannies.

PS If that is your car in ITS trim in your avitar you need a real limited slip too!!

[lateapex911]

I bet thre smoke is from a lock up going into turn 3 off the banking at NHIS....

[rsx858]

I bet thre smoke is from a lock up going into turn 3 off the banking at NHIS....
[/b]

U guessed it :D

When the tranny went up the first time the clutch went with it. I had a new racingbeat sprung 4 puck installed. after the later rebuilds, i was told that the clutch had broken in very nicely.

I realize now there are a bunch of things im going to have to check here. Whats the story on the shift linkage? Like i said i really know nothing about transmissions. Iv heard people attribute the linkage to alot of problems, i assume at a minimum ill be having to drop the tranny to inspect anything.

[Conover]

There is not a whole lot of linkage on those transmissions, what there is is inside the transmission, about the only thing you can check is the bushing where the shift lever goes in. It really sounds like you are outrunning the synchro to me, like either you have friction modifier in the oil, or the brass is worn out, or something like that.

[Chris Wire]

I wouldn't rule out a bent shift fork either...