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48 GMC 1 ton clutch sticks and will not disengage


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48 GMC 1 ton clutch sticks and will not disengage

Hello from an Ex Marine in Pensacola Fl.

My grandfathers 1948 GMC 1 ton truck is hard to drive because the clutch will not disengage easily. I start it with clutch in and in a high gear because it wants to pull hard then pops the clutch loose and I can shift it [ still wants to grind ]

if I go to neutral I can not put it back in any gear while running so I turn the engine off and put it in gear before starting and it will take off with clutch pressed in if in 1st or 2nd gear.

I have to hit the brake for the clutch to pop loose after it pulls the 270 CI engine down hard.

driving it I have to let off the gas and wait a second or two for the engine to drag before the clutch will pop loose and I can shift.

it sticks but other wise a very strong smooth clutch.

Thanks Semper Fi 0311 71-78

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Guest BillP

I had that same thing on a Cadillac. If you can get it running in neutral and are able to then put in gear, try this: First, set the hand brake and/or push down on the brake pedal firmly so the car won't move. Put it in any gear and with the engine running, let the clutch out very slowly until it begins to slow the engine. Maybe give it a little gas so the engine doesn't bog too much. Allow the clutch to rub, or nearly engage like this for a minute or so. Don't use a lot of engine speed or do this too long or you'll build up too much heat and glaze the clutch or hot-spot the flywheel. That should do it. This happens because the truck sat too long without being used and the humidity fused the disc to the flywheel and or pressure plate. In the future, try blocking the clutch to the floor or use the truck more. If this doesn't work you'll have to replace the clutch, not a huge job, but this is certainly easier. PS, nice looking truck, Jarhead. (Navy, 67-70)

Edited by BillP (see edit history)
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Thanks for the replies

If the truck is running it is impossible to put it into gear because pushing the clutch to the floor dos not disengage the clutch.

I have to start the truck in 1st gear or reverse and it starts moving as soon as the starter is pressed just as if the clutch is not pushed in at all.

then I hit the brakes and just before the engine dies the clutch brakes loose and I can quickly shift to another gear with a little grind. It did set for 18 years in the weather before I could get it.

I have been driving it like this for 3 years and it gets no better by driving it so it is time to do something before I mess up the transmission besides being hard on the starter.

I am 100% disabled so it will have to go to a garage and I am unsure what parts I may need. If anyone knows of a place I can buy a new pressure plate or clutch kit please let me know as I can not find this clutch anywhere. I think this is a 250 series truck . it is for sure a 1 ton with a 270 CI engine.

Thanks again

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You don't have the classic frozen clutch situation. It sounds like your clutch is dragging. Could be bent or maladjusted linkage, throw out/pilot bearing problems, Disc or pressure plate problems. If the linkage/adjustment checks out OK I'm afraid your next option is clutch and throw out/pilot bearing replacement. It's very likely your local NAPA store can get your parts............Bob

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You don't have the classic frozen clutch situation. It sounds like your clutch is dragging. Could be bent or maladjusted linkage, throw out/pilot bearing problems, Disc or pressure plate problems. If the linkage/adjustment checks out OK I'm afraid your next option is clutch and throw out/pilot bearing replacement. It's very likely your local NAPA store can get your parts............Bob

I think this may be an adjustment of the linkage. How much free play do you have. You should have no more then 3/4". John Hanson

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I think this may be an adjustment of the linkage. How much free play do you have. You should have no more then 3/4". John Hanson

This is what i adjusted today . I adjusted the linkage where the clutch barely engages at the very end of the travel.

I might add that this old truck only has 64,000 original miles and the engine is virgin so all linkage is very tight and showing no wear at all.

having made this adjustment I still have the same problem. once I was able to rev the engine and put the transmission into high gear from neutral with just a little grind. normally I have to turn the engine off , put it in gear and start the engine which will give a little forward movement before the clutch brakes loose.

shifting must be done quickly because if I am in neutral I can not put it into any gear without turning the engine off.

This old truck was always well maintained and garaged but when My granddad died the family fought over the truck and the winner of the fight just parked the truck outdoors where it set for 18 years and deteriorated until it was about to be junked . that sucked because I tried to buy it for all that time and was always had my offers declined.

It was in terrible condition when I got it and with a lot of work I got it running but this problem is the same now as then. I would really like to buy a complete new clutch but can not find one . this old truck means a lot to me , here is the original bill of sell . It is a model FC253 if anyone can help me find clutch kit.

Thanks everyone for your help

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Large trucks often have a multi plate clutch. They have a habit of dragging and not releasing as you describe. So the factory put a brake on the clutch that engages when you push the pedal all the way to the floor. In other words you have to push the pedal down all the way, hard, to completely release the clutch.

They can also get gummed up with oil, dirt, rust etc over the years. If there is an access plate under the bellhousing it can help to spray Brake Kleen spray into the clutch.

The idea of propping the clutch pedal down when the truck is out of commission for more than a month, is a good idea to prevent it sticking.

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use2b

I checked my Hollander Interchange and it shows that 47 thru first series 55 Chevy and GMC used the same clutch assembly. A 9 1/8 inch for standard and a 10 inch for heavy duty. NAPA stores have both. Pull yours and check the diameter of the disc and order the correct size clutch set from NAPA, $169. Also check RockAuto.com under Chevrolet Truck 3600 (1 ton) and see if they have one cheaper.

P.S. Hollander shows FC250 series has 228 cubic inch engine

Edited by Bob Call (see edit history)
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Thanks Rusty and Bob , I guess I will just have to take it to the shop and have them pull it apart to make sure what clutch I need.

the problem is it will be setting out in the weather until it is put back together but I can cover it up with a tarp and car cover.

it will have ether a 10 3/4" or 11" clutch because it has the optional engine that year which is for sure a 270 CI.

has an oil pump instead of dippers , oil filter cartridge and holds 11 quarts of oil.

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Nice truck . I'm no Chevy guy, but your motor is still a splasher( dippers). The pump is used to get the oil from the sump to the troughs and top end. The pressure fed didn't come in till 52 or 53, I think. Trucks were first.

This is not a fix but have you tried double clutching when shifting?

Good luck.

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I would say from the described symptoms, this is a disc delamination problem. A broken part of the disc will over-ride the disc and there's not enough clearance left for the pressure plate to release. Hence the "break loose" effect.

Robert!!! Good to cya. Got the

Buick going after new fuel tank and complete new wiring cowl-forward. Have ordered new motor mounts. Then, onto the brakes.

John

images link 47 Buick Super

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Edited by jbell7 (see edit history)
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Fixed it!

Thanks for all the advice and realizing I was going to have to put it in the shop and then have the parts rebuilt I did something crazy.

had nothing to loose so I sprayed 1/2 can of WD40 into the clutch while it was running and the other half in with the clutch broken loose with a stick holding it disengaged.

yea it slipped quiet a bit at first but after 3 days of driving it and a 50 mile trip to a car meet it is almost like a new clutch now.

I am sure it would slip with a ton loaded on it but all I carry is 2 dogs so all is good.

Thanks again

Edited by use2b (see edit history)
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