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Need Help Diagnosing (clutch?) Problem?

mkory

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mkory Enthusiast

mkory

Posted
Posted

I have never been more stumped (and pissed) about something like this. Please take the time to read the whole thing and help me figure this out!!!

 

2000 4.8l manual 4x4

 

Today I was pulling into my neighborhood and when trying to upshift it wouldn't go into gear. I didn't observe any unusual sounds at all, it just won't go into gear. The truck is acting like I'm not pushing in the clutch at all. It resists going into gear and grinds if I try to force it. So I swear a lot and put it into neutral, coasting into my driveway.

 

With the truck stopped with, engine running, and trans in neutral, I push in the clutch and try to get it to go into first gear. The truck starts to roll forward because of the syncros but will not go into gear and acts like the clutch is not pushed in. So I turn off the truck. There is still fluid in the master cylinder reservoir and it's at the same level as the last time I checked it a few months ago. There is no fluid leaking or dripping from anywhere, and the clutch still feels normal when I push it in. I get under the truck and peer into the bell housing. With someone else pushing in the clutch pedal, I can see the slave cylinder move. I can also see the pressure plate move away from the flywheel. It moves away only about 1/64 of an inch, but I'm not sure what's normal.

 

So I start the engine again, truck stopped and in neutral. I put the transfer case in neutral and run through the gears. The transmission shifts into gear without using the clutch and feels the same as it does with the clutch pedal depressed, indicating to me that the engine and transmission are remaining coupled even with the clutch pedal depressed. No unusual sounds coming from the transmission, however the slight sound that does come from it freely turning changes in different gears, indicating that it's still engaging gears normally.

 

Notes: I can see the slave cylinder move and flywheel separate from the pressure plate, but the truck always acts like the pedal is not engaged, regardless of whether it is or not.

 

Does anyone have an idea what the problem might be?

hrspwr Enthusiast

hrspwr

Posted
Posted
I have never been more stumped (and pissed) about something like this. Please take the time to read the whole thing and help me figure this out!!!

 

2000 4.8l manual 4x4

 

Today I was pulling into my neighborhood and when trying to upshift it wouldn't go into gear. I didn't observe any unusual sounds at all, it just won't go into gear. The truck is acting like I'm not pushing in the clutch at all. It resists going into gear and grinds if I try to force it. So I swear a lot and put it into neutral, coasting into my driveway.

 

With the truck stopped with, engine running, and trans in neutral, I push in the clutch and try to get it to go into first gear. The truck starts to roll forward because of the syncros but will not go into gear and acts like the clutch is not pushed in. So I turn off the truck. There is still fluid in the master cylinder reservoir and it's at the same level as the last time I checked it a few months ago. There is no fluid leaking or dripping from anywhere, and the clutch still feels normal when I push it in. I get under the truck and peer into the bell housing. With someone else pushing in the clutch pedal, I can see the slave cylinder move. I can also see the pressure plate move away from the flywheel. It moves away only about 1/64 of an inch, but I'm not sure what's normal.

 

So I start the engine again, truck stopped and in neutral. I put the transfer case in neutral and run through the gears. The transmission shifts into gear without using the clutch and feels the same as it does with the clutch pedal depressed, indicating to me that the engine and transmission are remaining coupled even with the clutch pedal depressed. No unusual sounds coming from the transmission, however the slight sound that does come from it freely turning changes in different gears, indicating that it's still engaging gears normally.

 

Notes: I can see the slave cylinder move and flywheel separate from the pressure plate, but the truck always acts like the pedal is not engaged, regardless of whether it is or not.

 

Does anyone have an idea what the problem might be?

 

 

Throw out bearing or the fork is broken so it does not separate the pressure plate and flywheel?

 

Try this, this will tell you where to look first. With the truck off, put the truck in first gear and the T-Case in 2wd. Try to start the truck and see if it bumps forward.

mkory Enthusiast

mkory

Posted
  • Author
Posted

These don't have clutch forks; the slave cylinder mounts inside the bell housing. Think like an expanding donut that pushes on the throw out bearing, not a piston that pushes on a fork that pushes the throw out bearing.

 

The truck will bump forward. I don't want to try this because I don't want to cause any more problems. The syncros cause the truck to creep forward with the engine running, truck stopped, when I try to put it into first, and the tests with the transfer case in neutral confirm this.

 

I'm not sure if the throw out bearing has failed. Could it have crushed or broken apart or something? I am still seeing separation from the flywheel.

 

Can anyone else who has a manual truck tell me how much the pressure plate separates from the flywheel when the clutch is depressed?

mkory Enthusiast

mkory

Posted
  • Author
Posted

I HOPE but don't think it's air in the system, because the pedal feels the same as it always has. Hopefully someone with a 4.8l manual can come forward and observe how much separation from the flywheel they have on their truck. I can't bleed mine right now. (no fluid, car, or help at the moment)

j9304 Enthusiast

j9304

Posted
Posted

The snout on the transmission input shaft may be hung up in the pilot bushing. Had that happen on an old Farmall tractor before.

mkory Enthusiast

mkory

Posted
  • Author
Posted

I'm not ruling that out, but does that happen to our trucks? I assumed the input shaft was deep enough into the pilot bushing for this to not happen. Plus, wouldn't the trans have to become separated from the engine for this misalignment to happen?

ujtruck Enthusiast

ujtruck

Posted
Posted

according to what you post above, hydraulic part of the clutch is working,

 

but - are you sure clutch is really working ?

 

clutch pedal is not really moving the throwout bearing as much as it's supposed to

 

or your Main Shaft Synchronizer Inner, Center, and Outer Rings not doing its job

 

just my .2 cents, not a transmission expert

mkory Enthusiast

mkory

Posted
  • Author
Posted

I had a friend with an identical truck check the amount of his pressure plate off of the flywheel and it might be a little more than mine, so I will be replacing the fluid in the system tomorrow to rule out air. If the throwout bearing isn't moving as much as it should, do you know how to check the master cylinder for an internal leak? (before I have no other choice but tear the whole damn thing apart)

 

according to what you post above, hydraulic part of the clutch is working,

 

but - are you sure clutch is really working ?

 

clutch pedal is not really moving the throwout bearing as much as it's supposed to

 

or your Main Shaft Synchronizer Inner, Center, and Outer Rings not doing its job

 

just my .2 cents, not a transmission expert

 

Could you elaborate on where these are and what they do? I haven't heard of these before.

ujtruck Enthusiast

ujtruck

Posted
Posted

watch

you can learn something

 

yes, do the bleeding, get you clutch working, before you drop it

 

my old Camaro iroc-z had the same issue, you have now, all I did was replaced slave cylinder and bleed

ujtruck Enthusiast

ujtruck

Posted
Posted

HYDRAULIC CLUTCH BLEEDING

 

1. Ensure the reservoir is filled to the fill line with new hydraulic clutch fluid. Add fluid if

required. Use hydraulic clutch fluid GM P/N 12345347 (Canadian P/N 10953517).

2. Press the clutch pedal in completely to the floor panel.

3. Open the bleeder screw in order to purge the air from the system.

4. Close the bleeder and release the clutch pedal.

 

IMPORTANT: Ensure no air is drawn into the clutch system.

 

5. Repeat steps 2, 3, and 4 until all the air is out of the clutch system.

1. Check and refill the reservoir as needed while bleeding.

2. After bleeding, pump the clutch pedal several times. If clutch engagement is not

satisfactory, repeat the bleed procedure.

6. If the previous procedures are unsuccessful, perform the following steps.

1. Pump the clutch pedal very fast with full strokes for 30 seconds.

2. Stop pumping and let the air escape into the reservoir while moving the rubber pad up

and down 12 mm (0.5 in) for 30 seconds.

3. Repeat this procedure, as necessary.

mkory Enthusiast

mkory

Posted
  • Author
Posted

I bled the clutch this morning and I can see that I'm getting better disengagement, but the problem is still there. Both my truck and my friend's truck are getting about the same amount of separation; about the thickness of a match book cover.

 

The engine is still permanently coupled to the transmission, regardless of the clutch pedal, and from the looks of it the pressure plate, too.

 

Ideas?

mkory Enthusiast

mkory

Posted
  • Author
Posted

So I started it in gear with the clutch in and it broke loose. It still hangs up every few shifts, and I have to turn it off, put it in gear, and start it again in order to get going. I think I will have to have the whole thing taken apart and cleaned out/parts replaced. Does anyone in Indianapolis want to earn some money?

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