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Cheap Jon
11-12-2012, 06:12 PM
My 2005 Chevrolet half ton Silverado 4 wheel drive with 5 speed manual transmission has a clutch problem. The clutch starts to engage when the peddle is about 1" to 2" off the floor. The dealer wants to replace the master and slave cyls.,I feel that the problem is with the master cyl. because the fluid level in the master cyl. is not low,and there is not any leakage that I can see. Replacing the slave cyl. requires that the transmission be removed. I may do this myself, any advice will be appreciated.

Jon

winchman
11-12-2012, 07:33 PM
I'm pretty sure your truck has a concentric slave cylinder, which fits around the input shaft of the transmission. I've never heard anything good about them, but most of the manufacturers have gone to them for weight and cost savings.

They live in a horrible environment with heat and abrasive dust. The piston has a large diameter to length ratio, which makes it easy for it to get cocked in the bore. When that happens, the pedal will come up, but the clutch won't be engaged. In some installations, it's a long arduous procedure to get the air out of the system.

Some service manuals call for it to be replaced whenever the transmission is removed, even if it's not yet causing any problems.

It's truly a design from hell.

Guido
11-12-2012, 07:37 PM
Truly hell designed systems in a GM product?--get Saltmine in here.

--G

torchroadster
11-12-2012, 07:39 PM
Have you tried bleeding it? I don't know about this specific application but it's worth a shot if it hasn't been done yet. Fully flush all the old fluid.

JCHannum
11-12-2012, 07:44 PM
Not a GM, but I went through a similar problem with a 1990 Ford P/U with the pancake slave cylinder. Went through all the gyrations to avoid changing the slave cylinder with no joy. You might as well bite the bullet and replace it and the clutch and pressure plate as well.

winchman
11-12-2012, 07:46 PM
Other than the fact that it starts to engage when the pedal is 1-2" off the floor, what's wrong with it? That seems about normal IIRC from my days with manual transmissions.

justanengineer
11-12-2012, 09:37 PM
Your dealer is a knucklehead. There was a recall on the master cylinders in the early - mid 2000s due to poor (lack thereof) adjustment/design causing this issue. My brother bought his 2006 Sierra new and his was replaced free. My Dad's 2003(?) or 04(?) Silverado was bought used from a dealer after the state of PA returned it due to clutch "problems," but the dealer decided not to "fix" it as there wasnt really a problem. Dad has been driving it without issue on the original MC for about four years now, and from the few times Ive driven it I can say its a PITA downshifting sometimes, but given a heavy left foot its not too terrible.

winchman
11-13-2012, 04:32 AM
"The clutch starts to engage when the peddle is about 1" to 2" off the floor."

Let's be sure of the terminology here. A clutch "starts to engage" when it begins to transmit power (while slipping) to the transmission, and the clutch should be fully engaged (no slippage) when your foot is removed from the pedal. It starts to disengage (slip) as you press down on the pedal, and it should be fully disengaged (no contact between the pressure plate and disc) when the pedal is almost all the way to the floor.

It's a fairly common for people to use the terms in the opposite manner, thinking the pedal is the clutch when it's really the clutch RELEASE mechanism. If you think of the automotive clutch as a normally-on switch, the pedal is a momentary push button to open the circuit.

kendall
11-13-2012, 06:30 AM
They live in a horrible environment with heat and abrasive dust. The piston has a large diameter to length ratio, which makes it easy for it to get cocked in the bore. When that happens, the pedal will come up, but the clutch won't be engaged. In some installations, it's a long arduous procedure to get the air out of the system.

Some service manuals call for it to be replaced whenever the transmission is removed, even if it's not yet causing any problems.

It's truly a design from hell.

Not a bad design, just good advice to change it when you have the transmission out. Considering the reason the average manual transmission has to come out is for a clutch change, it's sensible to change the throw-out,slave and pilot bearing.

CCWKen
11-13-2012, 02:47 PM
The master cylinder (or any hydraulic cylinder for that matter) doesn't have to be dripping externally to be "leaking". Worn cups or seals will just allow the fluid to bypass. It happens a lot with brake master cylinders. You can feel it if you hold your foot on the brake pedal--The pedal slowly goes to the floor. So the absence of an external leak is not confirmation of a good cylinder.

danlb
11-13-2012, 02:55 PM
Is it just me, or do the mechanics just not know how to isolate troubles?

Instead of replacing both, why not plug the line and look for leak down of the master cylinder, then check the pressure exerted. If the master is OK, then look at the slave

It drives me crazy to have to pay for parts that are not broken AND pay for the time to replace them until they finally find the problem.

Dan

browne92
11-13-2012, 08:13 PM
It drives me crazy to have to pay for parts that are not broken AND pay for the time to replace them until they finally find the problem.

Dan

In electronics, we refered to this as 'shotgunning'. Keep replacing parts till it works. Like you, I'm opposed to it. But this thing is a 2005. Mileage could easily exceed 100K. If this is the first time to replace the clutch, I'd replace it from hell till breakfast.

J. Randall
11-13-2012, 10:29 PM
My 2005 Chevrolet half ton Silverado 4 wheel drive with 5 speed manual transmission has a clutch problem. The clutch starts to engage when the peddle is about 1" to 2" off the floor. The dealer wants to replace the master and slave cyls.,I feel that the problem is with the master cyl. because the fluid level in the master cyl. is not low,and there is not any leakage that I can see. Replacing the slave cyl. requires that the transmission be removed. I may do this myself, any advice will be appreciated.

Jon

Assuming you have your terminology right, what is it you don't like about it starting to engage at about 2" up off the floor, sounds about right to me. As long as it engages and doesn't slip, and then shifts and disengages alright, I am having trouble seeing your problem.
James

Cheap Jon
11-14-2012, 12:32 AM
The clutch is actualy starting to engage right off the floor, if you do not hold the pedel down all the way you can feel the truck move when it is started. I have been looking on the web for info on any recalls on the master cyl. but no luck. The dealer wants $525 to relplace the master cyl. and $1200 for both. I have a rebuilt one on order fo $50. The truck has 59447 miles on it.

Jon

winchman
11-14-2012, 06:18 AM
If it's starting to engage right off the floor, and it's not fully disengaging with the pedal all the way to the floor, there are several things you can do to isolate the problem.

Of course, the first thing is to be sure it's got plenty of fluid.

Then check for any obvious leaks. If it's using fluid, it's got to go somewhere, and it doesn't evaporate quickly. Look on the bottom of the bell housing and at the end of the master cylinder under the dash. Also check the flexible line to be sure it's not swelling when you use the clutch.

Next is to bleed the system. It only takes a little pocket of air to keep the clutch from fully disengaging when you press the pedal down. A pressure bleeding tool may make it easier. The routing of the line on some vehicles makes this process especially difficult.