clutch hydraulic cylinder problems

[CaseyR]

My 94 C2500 is going on 280,000 miles. Duriing the 60,000 or so miles that I have had it, I have gone through five clutch master cylinders and two slave cylinders. The truck has an aftermarket solid flywheel. The local Chevy dealer mechanic said that the problem was that the clutch disk is too strong. Doesn't feel that bad to me - tried driving a 3500 and the clutch felt much stronger. Had the clutch disk and pressure plate, plus other incidentals, replaced (no place to work to do it myself). The owner of the shop said the new pressure plate would be softer but it feels stiffer to me. Blew out the clutch master cylinder soon after getting the new clutch.

I am getting to be an expert on driving the truck in traffic with no clutch. Probably will not have any sychros after a few more bouts of clutchless stop and go freeway driving.

The problem each time is that the hydraulic fluid is forced out around the "O" ring where the line enters the cylinder. The cylinder itself appears to be fine otherwise. When it first happened, about 600 miles from home but within walking distance to a Chevy dealer, the dealer did not have the cylinder so I tried replacing the line and the "O" ring. Lasted about a day. Tried two "O" rings - lasted another day. When I finally got the new clutch master cylinder, it lasted for about 10,000 miles. Haven't tried replacing just the "O" rings since, but am tempted to try it - except that they are rather hard to obtain.

I am certainly getting to be good at swapping out clutch cylinders. Even made myself a little device from a small "C" clamp to push out the roll pin on the slave cylinder. I would be more than happy to give up my little hobby of replacing the cylinders, however, and find a more permanent solution. Not only is driving clutchless somewhat inconvenient, the cylinders are now more than $70 each at the local Shucks.

It appears that there is no heavier duty cylinders available. Short of having a couple of heavy duty hydraulic cylinders fabricated at the local hydraulic shop for a small fortune, does anyone have any suggestions as to possible solutions? It is almost enough to drive a dedicated stick shifter to a slush box...

Thanks

[Hubert]

I think you have the external slave, arm/fork, pivot ball mechanical mechanism.

Did the clutch fork or arm get replaced with new clutch and pressure plate?
Also did the pivot ball in the bell housing get replaced?

Clutch disengaging force comes from strength of pressure plate + frictional losses to articulate the mechanisms (clutch arm pivot).

I don't think there are many options for heavy duty pressure plates?? Some people make different discs but p/p is limited by weak master/slave and space limitations. What did you replace it with? If GM part or similar its a Luk and they are not real heavy or hard to disengage.

From reading some other posts its probably the clutch arm/fork and pivot ball is worn and adding significant resistance to the mechanism. My 97 master cylinder is a plastic little dingy thing. You can see it flex when you have some one push in the clutch. I don't think they stand up to much heavier actuation forces.

I had a 78 manual transmission/ clutch that kept breaking the all mechanical push rod mechanism even with new clutch/pp/throwout brg. Looking back now it was probably the pivot ball/arm was also worn out.

[Turbo Al]

Hurbert has given you the correct info, replace the pivot ball, throwout arm/fork. Unfortunately this means pulling the trans I believe. Also when bleeding the slave be very careful with the bleed screw -- if you tighten it too much you will split the cyl.
Your cluch pedal is probably really hard to push more than half way. There is a grease fitting on the throw out arm/pivot ball joint.

Al

[CaseyR]

Yes, the 94s have the external slave cylinder right next to the exhaust pipe.
The throwout bearing release fork was replaced, the pivot apparently was not. I had pulled out the tranny earlier and the pivot felt as smooth as the proverbial baby's butt, it was pretty dry, but I lubed it as much as I dared. I suppose I might try replacing the pivot as a last resort. It requires pulling the tranny but I might be able to finess replacing it without pulling the bell housing. I don't know what brand of pressure plate was used, the work was not done at a dealer. When I get my shop built this summer I will be able to tear it down completely but I need the truck to get the materials to build the shop.

When the "O" ring blows out there is almost no noticeable resistance to pushing down the clutch pedal, so at least that lets me know that the pedal assembly is not screwed up.

[tehillah1]

I'm glad to see some info here on this little piece of product. I just got back from a two hour stint under my '94 about 3 miles from the summit of Loveland Pass...probably up around 10,000+ ft. It was a balmy 3 degrees out. In trying to ascertain why my pressure plate had suddenly disappeared while towing a car back home from Summit County. Turns out the black plastic line running from the clutch master cylinder down to the slave had somehow gotten up against something hot (exhaust manifold?) and there was a hole burned in it bigger than the i.d. on the line. Has anyone done a retrofit on this set up to ensure that this plastic is not in harms way from the heat at the back of the engine? I was going to go up Monday and do a temp fix on it to get the two vehicles home but after reading this post it seem my slave may be fried as well...I'll have to go armed for bear with a new slave and the necessary pieces for the temp as well...

[Hubert]

I have not done anything better than OE replacement. On the later trucks 97+ its an internal slave cylinder. My hydraulic line was near the crossover but does not look like it will touch or really close to manifold either.

Have heard that really high EGT's can boil out accumilated water in brake fluid / hydraulic fluid of hydraulic clutch line and has caused a few problems. Slower driving high EGT (long slow grade or stop and go traffic) it gets really hot under manifolds and near exhaust. I had some melted wire loom near my starter.

Only thing I have ever heard is I read one guy on another site refitted a metal master cylinder out of a bigger 2-1/2 ton GM truck. I don't know specifics of that swap. I would not think its a bolt up thing.

Might wrap line with the foil backed high temperature tape. Or some type of high temp sleeving.

Good luck and post something if you find a good idea.

[HH]

Check the fork pivot ball. It may feel smooth, but may still be worn down. Also verify you are using the correct height throwout bearing. If you are using an aftermarket clutch and PP, you must reatin the stock location of the pivot arm to get the proper lever arm advantage.

[tehillah1]

I think your diagnosis of the cause may have been a factor, Hubert, though I'm still not convinced that the plastic tubing didn't come into contact with some very hot metal...I went up and replaced the slave and the line from the master to slave and got some clutch back (couldn't do a full bleed since I forgot my allen wrenches) but then couldn't get the truck to start in the sub-zero, low battery charged, thin air at 10,000 feet. She'd almost bite and get going but then I'd lose cranking power from the batteries. I'm towing the truck home tomorrow and will work over the frozen repairs, rerouting the tubing and bleeding out the cylinder. It's time for some gauges and as soon as the weather warms up the cooling upgrades. I found a dual thermostat housing from a '98 for $30 here locally so with a new 130 gpm water pump, a couple of new thermostats, a new upper radiator hose and maybe a fan upgrade I can hopefully lower those egt's and start towing correctly. Thanks for the info y'all provide here.

[Bnave95]

a new upper radiator hose

The lower hose is more important at this time also. What a pain to change when all is together. You'll be doing some clearence grinding where the duel stat housing will hit the belt tenchen.

[tehillah1]

I had to drag the truck down off of the mountain to get it running...for some reason my glowplug idiot light is not coming on any more after all the cold start attempts...maybe the controller has given up the ghost.
I attempted to get the clutch system bled out yesterday only to have it fail to engage at all. Seems like the new slave cylinder has gone south in the attempt. I'm getting plenty of pedal push to the cylinder (it'll push fluid and air) but no clutch engagement. I had a bit when I started but now I can't get any clutch action at all. I hope I don't have to tear it down to the clutch arm to fix this issue, but I guess I'll do as I have to...next step is to make sure there's enough pressure from the master cylinder, then double back on the slave. It wouldn't be the first time I've had a new part fail at installation.
Any ideas on why the glow plug light would quit?

[Bnave95]

Any ideas on why the glow plug light would quit?
__________________
Fuse OK?

[tehillah1]

I checked the fuse...it's ok. I'm not entirely clear where the glow plug controller is...is it on the back, driver side of the engine, two leads on it? I'm waiting for the snow to quit so I can give another round of attention to the clutch hydraulics and then see what's going on with the glow plug circuitry.

[jeffscarstrucks]

CaseyR, You are going through exacly what I did for some time until I finally took heed of the advice I found here. Go buy a shift fork and ball BEFORE you take the bell housing off so you will be ready! I had a hard time believing it until I saw the ball starting to push out of the back side of the fork because it was worn nearly all the way through! I went through all the other things but this was the problem I should have looked for first! My bud at the GM dealer said "o sure we sell these all the time"...duh. Good Luck and keep us posted, JEFF

[Bnave95]

I checked the fuse...it's ok. I'm not entirely clear where the glow plug controller is...is it on the back, driver side of the engine, two leads on it? I'm waiting for the snow to quit so I can give another round of attention to the clutch hydraulics and then see what's going on with the glow plug circuitry.
The 94 are some what difference than my 95. The glow control should be near the rear on the firewall. Heavy gauge wire from the under hood fuse block. Check where the wires go from the glow plugs to the controller.
It may have failed though I would make sure your wiring is good. A little cleaning,also when was the last time you did a good cleaning on the grounds?

[tehillah1]

Bnave95,
I bought this truck back in late November and haven't put many miles on it nor have I spent a whole lot of time under the hood, until recently. I've replaced the water pump, a job I'll re-do this spring with some cooling upgrades. I did replace most of the wiring between the batteries, starter and alternator because they were looking pretty poor. I used heavier gauge wire for everything and grounded everything to the block. I'll check out the connections on the controller this weekend and see if a good cleaning solves the problem. Thanks for the input...I'll keep you posted to what I find.

[Bnave95]

I'll keep you posted to what I find.


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