TTAC Commentator thetopdog writes:
I drive a 2006 Corvette Coupe (45k) with the 6-Speed manual. The past few months I’ve noticed that most of the time I try to make the 1-2 shift at high RPM, I get really terrible grinding coming from the tranny. It only happens at high RPM (5000+) and it doesn’t happen every time, but it happens enough for it to be a concern. If I clutch in, let the revs drop a little, then throw it into 2nd, there’s usually no problem.
I have the CAGS (1-4 skip shift) eliminator installed. I had the dealership replace the clutch packs under warranty. Apparently they screwed up because my entire clutch stopped working, leaving me stranded. After getting it flat-bedded to the dealership, I was told the entire clutch system was contaminated and the seals were destroyed. I’m not entirely sure what they did after, but they fixed it somehow (probably flushed the system and replaced the seals?). I also had a transmission leak (what a quality car, huh?) last fall that was also fixed under (extended) warranty.
I haven’t checked the fluid level in the master cylinder recently, is it something I can do myself? I’m thinking this might have to do with worn synchros, but is there another possible solution? I’ve heard that changing your clutch fluid can help (apparently GM Synchromesh fluid is good for this?). If not, is there any solution short of a brand new tranny?
One more thing, what exactly is going on when the tranny is grinding? Is the grinding itself going to lead to severe damage if I’m not careful?
Sajeev answers:
Holy loaded question, Batman! I simply cannot supply TTAC’s snarkiness with this much content. Much like your Chevy dealer (whose actions raises several read flags) consider me overwhelmed by your Corvette.
First and most importantly, yes, change the clutch fluid regularly. From my experiences with an aggressively driven Z06, the fluid needs replacement rather frequently. So do it. The clutch reservoir is adjacent to the brake master cylinder, on a metal bracket: the easy way to replace fluid is with a syringe via the reservoir. But don’t suck the reservoir dry, lest you get air in the system. Just drain it to low, refill with brake fluid, actuate the clutch to circulate…and repeat about three more times.
If fresh clutch fluid doesn’t cure it, switch to synchromesh tranny fluid. Frank Williams pinged me on this, and sent me these relevant links: Here and here and here and (drum roll) here.
And your last question: this explains how synchros work. Using that reference, the grinding sound you hear is the “gear” not engaging the “collar” smoothly. If a fluid change(s) doesn’t help, you might have a worn gear, collar, synchro or some combination of the three. Which means you need a modest transmission rebuild: there are plenty of Corvette savvy rebuilders (outside of a GM service department) eager to help you there.
Having driven a well-sorted ‘Vette, I’ve got to say, it will be well worth it. Get ready to fall in love all over again.
[Send your technical queries to mehta@ttac.com]
Having owned an ’05 and an ’08 (both 4 speeds), AND having all the usual problems with the clutch & tranny that too many others report in the two big Corvette forums, I will have to say that Sajeev is just about right on with his advice.
Especially the clutch fluid. Many owners do this every time with their scheduled oil changes. Use a turkey baster to drain the resvoir.
And when it’s out of the factory warrantee, never EVER return to that dealer’s service department. The horror stories of their so-called “Corvette Certified Technician Specialists” are rampant.
I highly doubt it has anything to do with the clutch fluid. If you had trouble shifting into all gears then that would indicate a possible clutch problem.
Is this God’s way of saying you should have bought an automatic transmission?
I think both Sajeev and thetopdog are both confused about how things work, in this case.
Clutch fluid is part of the operating suystem for the clutch. I think in Corvettes it has to be brake fluid, because the reservoir is shared with the brakes. In any cae, I am sure it is NOT synchromesh trans fluid! All this affects is the transmission of the mortion of the clutch pedal to the clutch release mechanism.
The synchromesh fluid belong inside the transmission, to lubricate and cushion the trans internal parts, gears, synchros, etc. It won’t do anything for the clutch.
The clutch disc problems are a mechanical problem, perhaps caused by the erratic operqtion of the clutch master/slave cylinder mechanisms.
In any case, I think it’s going to take a pro to figure this out completely.
However, DO NOT put gear oil in the clutch master cyl reservoir or you will have even worse problems.
Bob
Thanks to Sajeev, and thanks in advance to all the guys who are willing to help me out in this thread
One more thing I forgot to mention. I have no idea if this is related or not, but sometimes when I push the clutch pedal down when shifting, I feel a “buzzing” or vibration from the clutch pedal. Most of the times I don’t feel it, but once in a while the clutch pedal will buzz and vibrate pretty badly when I push it in. Any ideas if this is a related problem?
DO NOT put synchromesh fluid in your clutch master cylinder!! Use brake fluid, petroleum based fluid will ruin the seals!
If I clutch in, let the revs drop a little, then throw it into 2nd, there’s usually no problem.
That sounds to me like a “normal” shift.
What are you doing when it grinds?
Ummmm, Sajeev? (Raising hand) I have a follow up question?
I am not a mechanic but have done some of my own work over the years. I did a clutch on a 58 F-100 many years ago… In your discussion about the clutch fluid…how does the new fluid replace the old fluid down the line to the slave cylinder? Isn’t bleeding necessary to ensure everything gets new fluid?
Me: If fresh clutch fluid doesn’t cure it, switch to synchromesh tranny fluid.
Oops, so that didn’t come out right. I meant to say…
“If fresh clutch fluid doesn’t cure it, switch the TRANNY fluid to synchromesh.”
relton,
Not to put words in his mouth, but I believe Mr. Mehta was suggesting using synchromesh fluid in the TRANSMISSION, not in lieu of hydraulic clutch fluid.
Bottom line, IMO…the dealer replaced the clutch…they most likely need to adjust the linkage, as it might not be allowing full clutch disengagement. Take it back!
Ralph, pushing the clutch in and out circulates the fluid on a C6. Seen it with my own eyes. Drain and fill the reservoir, push clutch 10-20 times and the fluid is brown again. So you lather, rinse and repeat.
I am not saying this method is better than bleeding, but I don’t have a lift in my garage and Corvettes are too low to the ground.
I am not a mechanic but have done some of my own work over the years. I did a clutch on a 58 F-100 many years ago… In your discussion about the clutch fluid…how does the new fluid replace the old fluid down the line to the slave cylinder? Isn’t bleeding necessary to ensure everything gets new fluid?
There’s really nothing special about clutch or brake fluid. Any non-compressible fluid would work, even water. But brake fluid (which is used as clutch fluid) is formulated for a high boiling point and to absorb water to prevent the lines and cylinders from corroding from the inside. Over time, the fluid eventually reaches its limit to absorb moisture and then you are at risk for corrosion problems.
The fluid never goes ‘bad’ per se, it just becomes water saturated and that’s what you’re trying to prevent. Replacing the fluid in the reservoir supplies fresh fluid and eventually the entire system will equilibrate. It’s not as good as replacing all the fluid, but it’s much easier, and it still provides enough fresh fluid to solve any normal moisture capacity problems.
I think two different fluid systems are being talked about here, but the response was not sufficiently clear to make this obvious to some :
1) the clutch master cylinder. actuates the clutch & would tend to be an issue in all gears, not just a single shift. however, the speed with which the shift needs to be executed in a 1-2 shift in order to maintain acceleration would mean that it was the shortest shift time, so perhaps clutch actuation is part of the problem.
2) the transmission itself. if a specific synchro/gear was going bad, using a different fluid might help mask the problem.
I thought I had a similar problem with an old International pickup. (Well, it was a nearly new 1964 pickup when I had the problem.) I thought that the first gear synchros were gone because it had a tendency to grind when I shifted into first the first time when I started the truck. I discovered though that if I pumped the clutch pedal a couple of times the problem was “fixed”. Therefore the culprit was the clutch hydraulic cylinder.
Of course the reason I thought the problem only affected first gear was that I never tried to shift directly into any other gear when I first started the truck.
The occasional vibration in your pedal could be due to the fact that the dealer may not have replaced your throwout bearing and/or pilot bushing when they replaced your clutch. It sounds like they did a shoddy job, so I wouldn’t trust that they replaced the bearing like they’re supposed to. It could also be a symptom of not having the proper pressure in your clutch hydraulic system, either due to old fluid, water in your fluid or air in the system. I would do things in this order, going to each one if the one before didn’t take care of the problem:
1. Change your clutch fluid and bleed the system thoroughly.
2. Change your transmission oil. Do some research to find the best oil for your Corvette. Oils are not created equal and what’s good in one car is not necessarily good in another. Syncromesh may be a good choice, but do the research.
3. Redo the clutch job, do it yourself or get a mechanic with good references. Basically drop the tranny, change the throwout bearing and pilot bushing if they look worn, and put it back together making sure it’s aligned properly. You should break in your clutch for about 100 miles or so before doing any high rev shifts.
4. None of that worked? Then it’s the transmission. Either rebuild or get a replacement.
The first think you got to do is,
go to “HURST” and buy a new shifter and linkage.
It will turn your crappy shifter into butter.
If you ever have to bleed a hydraulic clutch, check out this video for a helpful tip.