rja

Lately, I've been running into issues shifting my car when driving on the track. I had the pressure plate go -- one of the rivets clamping the diaphragm spring failed -- and has been replaced w/ 4.0 parts. Also replaced the slave cyl because it was damp.

Still, seeing some issues, esp. when pulling 3->4 briskly. After a few track days, I've observed that the problems only start to occur when things start to heat up. I.e., it's hot out and / or I start pushing the car harder. (I usually take it easy the first couple sessions and then build speed throughout the day, and never any issues during these sessions.)

At this point, I'm pretty convinced I need to get some add'l cooling back to the gear box. Anybody else w/ similar experiences to support (or discredit) this?

Thanks,

-Roland.

mooty

I think ur synchro is dead or about to die

Jamie_GT3

When I discussed with Matt (guards) he said most of the heat in our trannies comes from the stock diff slipping. Do you have an upgraded diff?

I've noticed that my 4.0 pressure plate gets a little sticky when hot and to get the car out of gear I have to rev just a touch. Mainly notice it running errands around town coming to a stop...

rja

Hi Jamie, yes, rear diff upgraded w/ Guard. Mooty, yes, could be synchro but it always shifts fine on street and even on track unless really pushing it (again, heat into system). I can slow my shifts down a just little bit (but still quick) and she'll go right on in every time. So, not so sure a bad syncro. If bad, I'd expect always bad but hard to really know how thermal expansion might affects it.

AudiOn19s

what fluid are you running? I noticed mine was a little sticky when hot on the factory fill switching to Delvac made that condition better but the trade off is it's a touch notchy when cold (if cold is an issue where you are from).

I've since moved to the Millers oil in my tranny and find it has the same cold characteristics of the factory fill and none of the sticky stuff when hot. Best of both worlds if you ask me.

p.s. there's already a tranny cooler on the stock box, not sure if maybe a cup cooler is bigger and would work better?

Mvez

I assume you are using the non LS version?

mooty

that's how synchro dies.
first onlly balks when hot, like track type of driving. you can't duplicate it on street.
if you keep driving it, it gets worse and worse.
now i am assuming ( big assumption ) it's the synchro issue. it could be totally something else.

but everytime i had the symptom you mentioned, it 's synchro.

stevecolletti

What engine/trans mounts are you using? Somewhere here, I read that shifting can be an issue when the engine/trans mounts get tired. I'm pretty sure that thread also said it wasn't a problem on the street.

Jamie_GT3

^^^ this, went back and re read and you said 3-4th shifts. I'm assuming most are on corner exit with the car laterally loaded? Maybe engine/tranny mounts? Hoping it's not a synchro, but not unheard of...

997gt3north

the 3rd-4th shift seems to indicate a problem somewhere

if you said 2nd-3rd then that is well know under side load

can't say i've ever heard of a 3rd to 4th problem unless the tranny needed a partial re-build of some kind

if you think about a street geared track car, then the 3rd to 4th shift is the one that is repeated over and over and over

as Mooty said - synchro wear is very likely the answer


how old is the car? how many miles on the tranny? is this a one car owner car? do you know the track miles history? etc, etc?

GTgears

I'm going to say that there's not a cooling issue. Keep in mind that your gearbox is very similar to the 996 Cup gearbox. We used to run those at Daytona, and endurance races all over the world without overheating. It is a motorsports based gearbox and amply cooled.

I am going to go with the people who are saying you are getting close to due for a rebuild. This assumes two things.
1. You are changing your gear oil frequently enough (every half a dozen track days+/-).
2. You aren't using a super slippery gear oil like Redline MT that is known to get too slick when really hot.

If you rule out 1 and 2, then I'm going with the start saving for a rebuild because you have worn out your 3rd gear synchro.

Regards,

Matt

Izzone

+1 or the 4.0 clutch / pp is worn out....they don't last long

rja

Thanks for all the replies.

I have urethane inserts in the tranny mounts and cup cables. No issues w/ 2->3. Problems I'm seeing are on fast pull from 3->4 when accelerating down the straight. It doesn't happen often but I am seeing issues from time to time where I never did last year. As mentioned, if I make the shift more purposeful then never a problem. Always in heat of a moment ....

It's been about 8-9 track days since last changing the gearbox oil. I'll need to check w/ Cantrell to see what they used but I assume OEM stuff else we would have had a discussion about it.

Matt, assuming it's a synchro (and I'm not making any assumptions that it is right now) is this something that can be readily repaired on my gearbox. The car has 14k miles on it (and 16-20 track days) so what I am going to assume is that a rebuild is unnecessary. Also, if a bad syncro then I also assume that there should be some metal in the oil to help confirm. Yes?

Thanks much,

-Roland.

996FLT6

U should be changing gear oil once every track weekend just for cheap insurance. What gear oil are u using? I would start with that 1st before opening up the tranny. Mike

rja

Matt, thanks very much for taking the time to talk today. Very helpful. I'm going ask Cantrell to change out the gear oil as a long shot it might help, and monitor closely. Should the problem continue or get progressively worse, I'll ask Cantrell to change out the syncros. Thanks again for taking the time.