jonessw20

Finally got my c5 z06 to the track last week and was having a lot of trouble with the shifting. Up shifts into 4th had to be done insanely slow. If I went to shift into 4th I would have to hold it there for a second or two with pressure before it would finally pop in. It didnt grind or anything, just had to wait for it to click in. I tried short shifting but had little change. Also downshifting into 3rd wasnt the greatest. If i got my heel toe just right it would usually go in fine. But not every time. It was killing my braking zones because some times it would take a few attempts to get into gear and i was basically planning to have trouble and id give myself alittle extra time by braking a bit early. That was more of an issue on the main straight though and was coming from being about topped out in 4th. The shorter straights i had much more consistent downshifting to 3rd but still would get locked out occasionally. Also, off track going into any gear was a pain and the whole trip home shifting was terrible. Took way more effort to get into any gear. Reverse was especially painful. Id have to put it into a forward gear first some times and then i could barely get it to push into reverse. With the car off it goes into all gears with ease.

I was going to wait to make this post because I wanted to go through some of the basic troubleshooting first and havent had time. But today I went to move the car and it went into reverse with little effort and went into all other gears much better. I didnt drive it on the road yet but I was shocked at how much better it was. Im assuming its a heat related issue because of this?

More info on the car. Its an 02 with 61,000 miles. Pretty sure stock clutch. Previous owner had a tick master cylinder installed. I wasnt happy with the shifting since i purchased it. I went through all the basic stuff. Shifter alignment, swapped fluid from what i was told was mobil 1 to redline d4, washer mod on the detent, adjusted the tick master, installed a mgw shifter(tested one on another car and loved the feel of the throw). It seemed like every time i did one of these common fixes the shifting would feel better but it never really lasted or seemed a bit inconsistent on the street.

Hoping thats a good enough description to get some good feedback on what is most likely the issue. If any other info is needed let me know. From my searching it sounds like the stock clutch could very well be the problem. Im hoping the trans is ok and id really like to not have the downtime and have to spend the money for a rebuild at this time.

jonessw20

Here is a video of my fast lap if interested. I was short shifting before turn 4 just so i didnt have to deal with it while taking the corner, its a full throttle turn. I think that was hurting my time a bit. The shift to 4th on the first straight is basically right at the finish line so it isnt shown. Time spent getting into 4th out of turn 5 left me with little extra acceleration but trying to ride 3rd out just didnt seem right.

Other then the shifting issues this car was amazing on track. Even on the cheap undersized federal tires that cost 533 shipped to my door. I really cant wait to get this issue sorted and get some tires with real grip on and see what it can do.

fatbillybob

I have only raced my C5Z. It was a streetcar for a very short number of miles. I bought it new. What I noticed was the 1st symptom of poor shifts was actually going into R. This was even worse hot off the track or hot from one session to the next after an inter session cooldown beg-int-adv group so maybe an 1.5 hours.

I would bleed the ckutch with my remote bleeder. It would get better but I would need to bleed the clutch after every race day. Finally, one day I could not make the high RPM shift and my race day was over. To get back into the trailer I had to engine off clutch in select 1st and start the car and roll the car on the lift gate. Diagnosis was worn clutch disc. When I took the clutch disc out it was below the wear limit. Simple fix new clutch disc. Then many races later same symptoms take clutch out below wear limit.

Conclusion: My car gives me plenty of warning with increasing difficult shifts. It always starts with R being hard to select 1st. Then 4-3. By then I know I'm on borrowed time.

I don't know how to diagnose a synchro problem until you make sure the clutch plate thickness is within the proper spec.

Hope that helps give you some ideas.

Hi Volts Z06

Obviously the advice from fatbillybob is the first place to look. If you find that the clutch is OK you might want to check your motor mounts. I’ve had clutch problems which were the result of bad motor mounts as they induce stress on the input shaft which bends slightly. The resulting misalignment will destroy clutch disks and pilot bearings eventually.

fatbillybob

How can you check for bad motor or trans mounts? I don't know a way. Do they time out?

Hi Volts Z06

In my case I was using poly mounts and the heat from the headers had deteriorated the polyethylene. Stock motor mounts are filled with a goo (high viscosity oil?) that you can see leaking from the mounts.

Trans mount should be pretty easy to visibly inspect on a lift.

jonessw20

Yeah this does sound alot like what im dealing with. It seems odd though that the clutch disc being worn would cause such an issue. I would think that it would cause slipping rather then a lock out condition. I think im just going to go ahead and get a new clutch on the way and start dropping everything out. Your description along with a few others ive found is enough to make me think that it is the cause. Plus it will be good to get the remote bleeder installed while im in there. Guessing it will be a solid 2 or 3 weeks before I have it done but I will report back what I find.

jonessw20

Ive wondered what effect the motor mounts would have on shifting. I know in my MR2 with the midengine it made a huge difference in shifting when upgrading mounts. But the stress is distributed alittle different in that configuration. I have visually inspected them in the past though and I see no signs of leakage and they appear to be in good shape. I assumed as long as they are not leaking they should be ok?

fatbillybob

I work on a lift and I don't see anything that would indicate failing mounts. The motor is tied to the torque tube. Shifter is bolted to TT. TT is bolted to transmission. So I'm thinking mounts would have less of an issue than the typical car. But good mounts are important for good race function.

Miguel S

I was also having shifting issues from 3 to 4 and in addition I also had a torque tube rattle (similar to the sound when you turn off the engine with the clutch out and in neutral). It was from a broken motor mount (it was barely leaking on the cradle side so it was hard to tell). I am assuming that they alignment of the torque tube is fairly tight, so by loosing one of the 3 mounting points it allows an odd bending moment in the system. Just thought I would offer this point to consider.

Miguel

fatbillybob

Well I guess you have proved the TT to trans to motor is not stiff enough. Mounts have to be good. Thanks for posting!

Hi Volts Z06

I can't tell you how many people told me I was wrong when I said my motor mounts killed my clutch. It was in-fact the rep for Mantic who swore to me there was driveline misalignment when he saw the rivets ripped out of my dual disk clutch. I really didn't believe it myself until I went to reinstall the clutch and couldnt get the input shaft to engage the clutch. I finally jacked the back of the motor up and it slide right in. That lead me to check the motor mounts and I found them melted on the back side (under heat wrap no less) so the motor was leaning back putting pressure on the input shaft.

As a side note- we just installed AMT's new motor mounts on my re-build and I have to say these things are AMAZING. Aside from looking pretty- they should last forever. If you haven't seen them- check out Mark's post here: https://www.corvetteforum.com/forums...otorsport.html

Miguel S

Mine also melted under the wrap on the sub frame side so you would be hard pressed to see it from under the car. I also replaced mine with AMT's and I have no problems now. Solid product for sure.

Miguel

96GS#007

Past experience is that the C5 Z06 needs a real cooler for the transmission fluid. Your post seems to imply the issue gets worse with time and therefore heat.

I’d add a cooler before I start worrying about other stuff.

crimlwC6

I've raced for 5 years in Phoenix without a tranny cooler. If I had the cash laying around, I would get one but I think your problem is clutch related. Track days, especially at a quick pace, are brutal on stock clutches. Do the ranger method, you probably have several track days (or perhaps many more) left, budget for a clutch upgrade. Do the torque tube bushings at the sametime and check the mount for the transaxle for play. I've had stock ls1 clutch, light flywheel with Spec 3+ clutch and now stock zo6 clutch. The 3rd to 4th on stock is always slow and...deliberate. Light flywheel and beefy clutch are fun on track

jonessw20

I think the heat buildup throughout the day made things worse. But I was having issues from the start of the day and i had trailered to the track so temps were definitely not too high in the beginning.

I got some time tonight to mess around with it. The lock nuts for the tick master cylinder adjustment were not tight. Its possible that it had twisted a bit. I made some adjustments and took it for a cruise. It smoothed out the shifts a bit. Still had the pause from 3rd to 4th. Just didnt seem quite as bad. The downshift from 5th to 4th is probably as smooth as it could possibly be. Upshift from 4th to 5th feels fantastic. 3rd to 2nd feels good. It just seems that the 3rd to 4th and downshifts from 4th to 3rd are the worst. Ive already done the ranger method a few times but I might try and do an actual bleed of the system. Ive read a few people were able to successfully make it happen with out a remote bleeder. If I can get the car by for this season that would be ideal for sure. Then I can think about sending the trans in for a refresh as well.

jonessw20

Last night I worked on the car a bit and I think i definitely have the issue figured out. I started out with bleeding the system. It appeared that the fluid was very fresh. I think when the previous owner swapped the master out they actually did a proper bleed of the system. Then I moved on to checking the slave cylinder travel. Started out at 3/8'" which I think is proper spec. With the clutch pedal depressed the disc did not spin freely though. I noticed that it still appeared to be compressed between the pressure plate and the flywheel. I spun the motor around to inspect the clutch all the way around and actually could see a gap on most of the disc. It turned out that at one of 3 points on the pressure plate, it is not fully releasing. With slight pressure from a pry bar I could create a gap and spin the clutch disc freely. After removing the pry bar it would continue to spin freely for about 2 turns and then go back to being too tight. I decided to try making an adjustment with the tick master. I was able to increase the travel of the slave cylinder to max of 1/2" but unfortunately this was not enough and it is still dragging at the one point. Time to start pulling her apart.

Videos show where it is and isnt releasing. One spot that I pry it has alot of travel because its not really releasing. The spot with no movement is released and the gap is visible.

fatbillybob

Sounds like what I said before worn disc. It is possible you got some broke pressure plate fingers. That will cause point grabing

jonessw20

fatbillybob

Cool Beans! I have seen the fingers break but not the meat of the ring. You diagnosis of the single catchy spot was the give away which is why my post above yours also says pressure plate fingers. Good thing it did not blow up and leave you stranded at the track. It is really lame to have to go home on a flatbed.