ck_1la@yahoo.com

I have a 2008 C6 LS3 w/ Z51 package and about 47k miles. Transmission is a 6-Speed Manual.

I have two questions. Any advice woudl be greatly appreciated:

ONE:
When I shift gears from: 2>3 (just started having issues today – 6 Sept.), 3>4, 4>5 and 5>6 and the RPM is ABOVE 6250 RPM it seems like I lose power and the car slows and there is no acceleration - then suddenly the clutch or transmission (I am not sure as I am not an expert) seems to grab and take hold.

After what seems like a 1.5 to 3 second delay, after I have released the clutch, it seems to grab and then climb back to the RPM it should be at and then speed starts to increase again. This only happens when the RPM are above 6250 and I am driving the car “hard” (and leaving a Mustang, Camaro SS or Mercedes AMG 63 – which can hold its own against my lowly LS3 I might add - in the dust).

Any thoughts on what might be wrong and what is the best way to diagnose the problem without wasting money? (I am of course taking it easy from here on out – as a clutch job costs $1700 I am told – that is with tax and tip included).

TWO:
I trust that the clutch is also considered a “maintenance item” and NOT covered under GM’s 100k Drive-train Policy. If you know anything about this and or how to get it covered under Warranty, I would appreciate that too.

Thanks in advance – CK. (Houston, Texas – where Corvettes don’t like the heat!)

SUB VETTE

Are you saying the RPM stays above 5000 but the car speed decreases after the clutch has engaged? If so, your clutch is definitely slipping or is not fully engaged.

JCtx

First, edit your post because you said '500RPM' initially. Later you said 5000, which assume is correct.
Second, to know if your clutch is slipping, perform a very easy test: With the tranny in 5th gear and rpm at 2K rpm (after a few seconds in gear), floor the throttle and watch the tach. If revs go up without forward thrust, it's confirmed you need a new clutch. Otherwise the problem is with the hydraulic system, which includes the master and slave cylinders. Report your findings.

By the way, a more common problem when shifting at high rpm is clutch pedal stuck to the floor due to either master or slave cylinder failure, attributed to never changing clutch fluid. If you haven't done it, remember to do that when your issue is solved. And if clutch has to come out, install a remote bleeder, to do the job right. Otherwise you're stuck with the half-a$$ method of just replacing the reservoir's fluid whenever it gets dark (not the same). Good luck.

Joe_G

I suggest you do this low cost maintenance item and see if it helps:

http://rangeracceleration.com/Clutch_Care.html

SUB VETTE

The Ranger Method is well worth doing as a first step.

ck_1la@yahoo.com

Thanks for the advice/info.

ck_1la@yahoo.com

I will do as you have suggested. (I also edited my post to say 5000 RPM - thanks). I very much appreciate your writing back. This forum seems like a good place to ask and answer questions about all things Corvette.

I will report my findings later today.

ck_1la@yahoo.com

Thank you very much. I have saved the link to my e-mail and will go to my mechanic's (he is also my friend, so I get good rates) shop in Houston this weekend and have him go through the Ranger steps with me (so I can also learn).

ck_1la@yahoo.com

Much appreciated. Another fellow has also suggested the same thing.

ck_1la@yahoo.com

I have tried what you suggested; I placed the gear in 5th, at 1950-2050 RPM and floored it. Also tried the same in 6th. It pulled in both gears IMMEDIATELY - full power - no issues whatsoever.

The problem only happens when I am ABOVE 5000 RPM. I am not sure if the clutch pedal is staying stuck to the floor or what - but perhaps I should change the clutch fluid? Or do you believe the issue may be more serious? (I know I am going to have to do something soon, hopefully preventative. What I am trying to avoid is paying big bucks$$$ for them to take it apart and then finding out I just needed the clutch fluid changed...I digress.)

Thanks in advance.

ck_1la@yahoo.com

Thanks for your question - I appreciate your reply very much!

My answer is this: When shifting into gear and then releasing the clutch pedal (and the release of the pedal into the new gear occurs when ABOVE 5000 RPM's ONLY) the car loses speed (almost as if in neutral) but the RPM's stay up (as my foot is still on the gas pedal) and then it seems to grab after 1.5 to 3 seconds and then pull forward and continue accelerating.

What do you think?

DOUG @ ECS

That is just one of the many items we address with our mail order tunes, or tunes performed here. The car is programmed to drop timing upon the clutch pedal being pressed as a tq management device.

Not a bad idea for longevity and clutch life, not so good on performance, especially if you have since replaced your clutch with something like the Mantic single or twin from ECS.

Joe_G

Did you add 4.10 gears to this car?

There is a secondary acceleration based rev limiter that often comes into play when you add 4.10 gears.

Before you do anything else please do the clutch fluid maintenance and report back.

SUB VETTE

This is confusing. Either the clutch pedal is stuck to the floor or it isn't As mentioned above, dirty clutch fluid can cause the stuck condition, that's why it's important to try the Ranger Method for correction. But you need to be more clear about the clutch pedal position.

ck_1la@yahoo.com

Thanks Doug. I do believe that there is a device in the Corvette CPU that makes the RPM drop lower in order to get into gear at very high RPM - say 6200 RPM+. My clutch works perfectly fine otherwise and only has this issue at very high RPM.

Joe_G

I don't think your issue is a rev limiter issue...I'd do the clutch fluid swap today, it's super easy (just don't get it on your paint) and try it.

I suspect your problem will be cured and you're only investing $3 and about 10 minutes to try.

ck_1la@yahoo.com

It is not stuck to the floor. I shall have the clutch fluid checked. I do believe that GM has installed a limiter that drops the RPMs when one tries to go into gear at too high of an RPM. This is to prolong the life of the clutch (or so I have been told).
Thanks for your reply(ies).

SUB VETTE

Exceeding the red line RPM will cause a fuel line shutdown to prevent over reving.

Joe_G

There is no rev limiter at 5000 rpm, except for the acceleration based rev limiter and since he doesn't have gears or turbos he's not going to hit that one.

There is, on some cars I understand (I'm pretty sure Z06's, didn't know about coupes but maybe newer ones have it) a rev limiter that kicks in if the clutch pedal isn't all the way up. There is a clutch pedal switch at the top and the bottom. If the clutch switch isn't all the way up your cruise control won't work.

I've never had trouble with this switch based rev limiter nor have I seen it in any tuning I've done, but I have heard stories from reliable folks (Ranger) that it exists.

I suspect the OP's pedal isn't coming all the way up after a high rpm shift. Proper fluid maintenance should fix this.

I wish he'd do it and post up. I would like to see this be solved for him.

JCtx

Nope; just one (at least on '12 cars). BUT it's a lot better than 2 ... so the rest of your statement could be true (I don't know). It's a rheostat switch, so it can actually 'know' exactly where the clutch pedal is, not only top and bottom. Don't understand why GM put it on the Vette, since it doesn't have 'hill assist'. Two switches would have been cheaper IMO. How do I know? By accident, since I also thought there were 2, like in most other manual cars without hill-assist. I was going to bypass the 'deep' switch so I could start the car without having to depress the clutch pedal, but found the rheostat instead, so aborted the project.