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How much interference for a clutch throw out bearing?

Jonnyhook

Plastic
Joined
Sep 17, 2022
Hey folks. I am fixing an old dump truck and the throw out bearing has become a challenge. The previous bearing totally failed and messed up the cast iron collar that it was mounted on. This part has been discontinued and I’ve looked everywhere to replace it but that isn’t going to happen. So my plan is to machine off the screwed up part and bore into the collar, then press fit a bushing in to replace the damaged area. I have ordered a new thrust bearing that matches what was originally on there, but I have no way to tell how the bearing was installed. I assume it was press fit, but how much interference would I want? The bushing will be steel and the shaft is 1.75” so the inner race of the bearing will be just over 2”. Would I still shoot for the typical .001 per inch, for .002 of interference? I will do .002 for the bushing, I am just not sure if that’s also the answer for a thrust bearing. Thanks.
 
Its apparently a push type clutch throwout.........not familiar with GMCs ,but it would be a Lipe or Lipe Rollway clutch in most old trucks.............note this is completely different from the Spicer Angle Spring type clutch that pulls ......anyhoo,a light press fit 001 would be plenty..............you odnt want the throwout ball bearing loose ,or it will rattle against the throwout levers.in the clutch cover.
 
I m certain if you got on an old truck forum in the US,someone would have the part................i recently found a guy a throwout for a 1942 Federal with a Spicer gearbox .........this guy is rebuilding a 1942 truck from a complete ruin ,it has a 850cu in flathead Hercules motor.
 
I m certain if you got on an old truck forum in the US,someone would have the part................i recently found a guy a throwout for a 1942 Federal with a Spicer gearbox .........this guy is rebuilding a 1942 truck from a complete ruin ,it has a 850cu in flathead Hercules motor.
Agree. It’s out there somewhere. But at this point considering I can fix it, it’s not worth any more time.
 
Its apparently a push type clutch throwout.........not familiar with GMCs ,but it would be a Lipe or Lipe Rollway clutch in most old trucks.............note this is completely different from the Spicer Angle Spring type clutch that pulls ......anyhoo,a light press fit 001 would be plenty..............you odnt want the throwout ball bearing loose ,or it will rattle against the throwout levers.in the clutch cover.
Ok, .001 then. Any use in a retaining compound like loctite 620?
 
I’ve tried Napa and have a friend there who has been looking everywhere but can’t find it, and he can usually find just about anything. I’ve tried Fisher auto parts. I’ve contacted the GM dealer and got old part numbers. I’ve run them through fleet cross and searched for all the cross referenced numbers. I’ve searched eBay, Amazon, and basically google at length many times. I’ve called many bearing suppliers. While I’m sure one is out there somewhere sitting on a dusty shelf, I’ve decided I will just fix what I have.
 
Medium duty trucks are a pain in the ass to get parts for, pickups no problem, heavy trucks no problem.

Yep. And GM medium duty trucks "top Kicks" are the fucking worst. I have made tons of parts for these turds over the years. I've made new front hubs, new steering shafts, modified tie rods and steering boxes from other trucks to fit. And we're talking 10 year old trucks from the 2010's! Not some old junker. GM just flat doesn't support them and they change shit every year or two. Wrecking yards know this and charge a fortune for parts. Like a front axle is $2500 and they won't part it out so when your idiot driver's crunch the hub cover on a curb and all the oil leaks out you can either buy an entire $2500 front axle that "should fit" plus pay the shop to change it or you can pay a shop like mine $1500 to make you a new hub from scratch and just pay the shop to change the hub.

I would shoot for a standard press fit of .002" for a 2" ID bearing. If it presses on easy then press it off and put some green loctite on it.

On a steel bushing with an 1/8" wall I might go heavier than a .002" press. Depends on surface finishes, how sturdy the cast iron part is that you can press against, etc, but that wall thickness sleeve will stretch a lot so you can make it real tight and it'll still go on easy enough.
 
If you install a coupling on an electric motor of, say, 5000HP using .001" per inch of shaft diameter it will transmit all 5000HP forever and give no trouble.
 
they usually never fit too tight. most are just spring clipped to the clutch fork and is super loose along the tube is slides on. just needs to be enough to hold it onto the shift fork. and with so much clutch dirt in there they have pretty loose tolerances to slide on.
the bearing assembly pressed in should have right on tolerance or 0.001 press fit.
 
I thought about this yesterday, I replaced the throwout bearings on my little Komatsu dozer. THey are about 4" OD, and the collar they sit in is .002 undersize. as is the "fingers" bushing that goes in the OD. Simply greasing up the bearing before pressing it in, my press never registered over 2 tons of pressure on the install. NO need for loctite on mine as the say its assembled prevents them from ever coming out or moving around.
hope this helps
 








 
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