Has anyone here had a problem with really aggressive shifting on the stock tranny and 6th gear locking out? I've now had this happen to me twice and can't figure out why it's happening. It does eventually let me shift into the gear after a few minutes of driving afterwards and attempting to get it in. What could be causing this?

 

It's got single cone synchro's on 6th. You are 3X stock power level. You will end up breaking it.

 

I think 6th is basically an "overdrive" gear. It would have to be one helluva fast track to get out of 5th (at stock power, which is what the tranny was designed for).

I have heard of people cryo treating the OEM brass synchro's and gears before... Not sure exactly HOW much benefit that would produce at those power levels.

John

 

I'm not aggressive shifting into 6th. It's just that after racing and going through 1st - 4th or 5th gears, I'm slowing the car down on the road and go to putting it into 6th and it's locked out.

What could be causing this if I'm not even using this gear in racing?

 

Dude, the synchro is hosed.

 

But the car and tranny only has 12,500 miles and after 6th gear finally lets me in, it works just fine like it always has. Even with the aggressive shifting in all the other gears, I haven't had this problem with them. But with no aggressive shifting into 6th, it happens to it. That's what I don't understand.

 

Yea I agree. You may want someone to check out that synchro

 

If that's really all it could be then I guess I'll have to have the synchro checked out. Thanks

 

You are applying 600hp through a gear and synchro designed to hold 240.

NA cars that are tracked heavily will damage the 5/6th synchro's because they only have a single cone synchro. The synchro has to speed up the gear before the fork can move the gear's sleeve over and lock into the 6th. You are asking a tiny piece of brass to speed up the next gear at high speed, all while transmitting 3X the power the car originally made.

The rest of the trans uses double cone synchro's on 1st, 3rd, and 4th, and a triple cone synchro on 2nd.

 

You are likely grinding a bit when you shift from 4th to 5th. Slow that shift down just a bit so it doesnt grind.

The damage done by grinding into 5th is what causes the difficulty getting into 6th.

There is a thread on this from like 5 years back with pictures etc.

Let just say it becomes obvious what happens when you actually are holding the damaged parts in your hand.