kdm123

So here's what happened..

I have a '03 ZO6 that I've done about a dozen track events with. The car has only 30K miles on it. I drive it mostly at Willow Springs, which means I don't use 1st, 2nd, or 6th gear. I only upshift once or twice into 4th. I've never had a problem with the 4th gear synchro, but it suddenly went from working fine to being completely gone. This happened while racing, but I don't remember any really bad upshifts.

The tranny shop tells me the 4th gear synchro is broken. They also say that 5th and 6th gears are very bad, which is weird because I never use 6th except on the freeway. Again, the car has only 30K miles.

Are T56's inherently weak? I don't really do any hard shifts except a few times where I've shifted from second to third.

They want $2500 for the repairs. Is it better just to buy a beefed up aftermarket/rebuild tranny? Summit Racing sells a rebuilt T56 for $3000.

froggy47

You have an M12 transmission unless it's been changed along the way.

They are usually very strong when shifted properly.

IIWM since it's already failed I would go with a "built" one from one of the forum vendors, shouldn't cost much more.

tmtraylor

It's toast... Sell it to me for scrap. Just kidding!!

They have a reputation for being pretty strong and with a few tweaks super strong.

I suggest calling RPM or RKT and talk with them. For the money you have been quoted you may be able have yours rebuilt and beefed up.

Good luck!

drivinhard

The "weak" spot is typical the stamped synchro keys that sit between the inner/outer hub. However, I say weak because in my opinion what makes this problem come to light, along with the fork and fork pad issues, is the stock clutches and hydraulics. They can have release issues, even if you think they are working fine, they can still have release issues. If the clutch isn't 100% releasing instantaneously, you are going to have problems. You can pretty much expect to have trans issues at some point, using a stock type clutch with factory hydraulics.

Get a really good aftermarket clutch and hydraulics in the car, and you're going to protect your trans. QM makes a really trick 7.25" unit that is very, very street friendly (in terms of engagement/chatter). Unless you are literally sitting in 2 hrs of traffic everyday, I would run this clutch on the street (in suburbs or more rural area).

Also if you track a lot and plan to keep your 3.42 stock differential, consider switching to M6 ratios if you end up buying a rebuilt unit. The 2.66 first gear transmissions are much better for road racing as they have a tighter gear spacing.

kdm123

What does an aftermarket hydraulic slave cylinder and clutch cost? Thanks for your reply.

SunnydayDILYSI

I'm parting out a 2002 Z06 and would give a great deal on the tranny. 79,000 miles, but never had any issues and shifts smooth.

fatbillybob

Zo6 box is bullet proof. Even the guys who went from 2012 scca T1 rules to gt2 rules are not breaking the boxes and lot of that racing is at wsir. Im running T2 from T1 racing and often at wsir plus all the local tracks and no issues.

heavyzee

I would send it to tick. And get a tranny cooler. Heat is the enemy at the track

0Anthony @ LGMotorsports

Couple things....

1. check your clutch. I know everyone says their clutch is fine but if it is draging or not releasing all the way that is going to play a role in wearing on the syncro's. Same thing with bearing drag on the torque tube

2. Road racing...they will need to be rebuilt. Most HPDE guys are not going to go through them like we did but we had to do syncro's on the Challenge cars roughly every 4-5 races or they would start to stick during shifts.

3. Heat is a bad thing. Make sure you have good fluid in it, it isn't low, and it isn't getting hot. If it is, get a cooler setup on it. Personally I think we have a pretty good setup.

4. I see no reason why you can't rebuild what you have. RPM Transmissions does really good work and we use them for a lot of our builds too. While you are in there get new shift fork bushings, solid keys and polish the gear set. You will end up with a better, stronger unit, than just buying a reman unit from Summit or Jegs.

VGLNTE1

they are tough as nails, but the stock synchros are not. Call RPM and get a level 4 trans with all new stuff for less than a new stock one. they are the best in the business. Mine went on me last year on the track. Couldn't get it out of 4th gear. Some keyway let go and fell. I also do not use other gears more than some, but they all work together. After 10 years of drag racing and road racing it finally needed upgraded at 85000 miles. They are great trans

SouthernSon

Do you have a cooler? If so, how are the lines routed - above the vent on the tranny or below?

Whis9

Interested also

SouthernSon

Yes, a common problem that others seem to overlook from time to time. Also, while filling the system one needs to make sure the return line is pumping and full before filling the tranny to level. Several trannys have met their demise from low fluid level. It can be a messy job but the fill level of oil has to be full WITH lines and cooler filled, too. Plenty of fluid has been lost due to vent overflowing from incorrect mounting.

J.R.

Another vote for RPM Transmissions.

In over 10 years of road racing Corvettes I have never broken an RPM trans. Note that RWHP was from 350-450. I also maintained these with rebuilds every 150 hrs and using GM synchromesh fluid with a trans cooler. These were all stage 4 or stage 5 builds. A good clutch setup is important. I ran a quartermaster dual with rally discs.

I first started out using stock MM6's and quickly found out that the cost of an RPM was by far more cost efficient than the cost of removing and fixing stock transmissions.

Phoenix64

kdm123

I do have a trans and diff cooler, but they were installed after I had already done about 6 months of track days with it. I will check with the rebuilder if there are any signs of heat damage or oil starvation.
It's weird that 6th gear was worn as well considering that I only use that gear on the freeway

JeremyGSU

I went through this last year. '04 Z with 32k on it and about 23 track days, mostly at Sebring. No coolers except for an oil cooler.

The transmission was just getting extremely notchy and hard to shift into the gears. I thought the clutch was bad and ordered a new Monster clutch and RPM transmission at the same time. When they pulled everything my stock clutch was fine and the transmission was bad.

They didn't find any bents keys but said it just "quit working".

Not really sure what that means but either way a new tranny was required.