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PTO tech in chitchat

472man

Well-known member
Joined
Jul 17, 2020
Member Number
2316
Messages
47
Loc
Idaho
I'm working on my 1951 Chevy dump truck that has a PTO problem... I think. The truck has an sm420 and a Chelsea PTO with an idler gear that turns all the time the countershaft turns. The problem is as soon as the clutch is let out a grinding noise starts. I put in a rebuilt transmission, no better. I put new bearings in the PTO,no better. I took the PTO off ran the truck and the noise is gone. I checked that the PTO was correct and it doesn't have any obvious bad wear patterns. I used an extra gasket to increase backlash and the noise is the same. The noise is loud enough I don't want to drive it, anyone ever dealt with something like this before?
 
Is the pto disengaged fully? PTO will make some noise while engaged or working.
 
It is fully disengaged, but the noise is the same when it is engaged
 
Wow. We had one of these a while back, I think it was 55 or so and it wasn’t exactly road worthy. All I remember was the weird lever for the pto had to be just right for it to work and/or make noise. That’s all I got. :homer: I miss that old truck. :(
 
Pictures of setup? maybe a video with sound? I have a similar truck but unfortunately the engine is seized up.
 
Have books for ordering PTO'S can lookup what a PTO for your application is part number wise and can look up on web the average cost.
 
Normally shimming involved to get your clearances correct on PTOs for Fuller transmissions. The shimming varies with different model transmissions.
I would think yours would be the same.

A manual for both trans. and PTO should help. Google?
 
I found that a 5p-208 gear is what Chelsea called for and that is what's in it. I will try to figure out a video of the noise it makes
 
IGT said:
Normally shimming involved to get your clearances correct on PTOs for Fuller transmissions. The shimming varies with different model transmissions.
I would think yours would be the same.

A manual for both trans. and PTO should help. Google?
Click to expand...

The info I found for the PTO says to use gasket to adjust backlash. The range was .012-.025 if I remember right and it did fall in the top end of that range with the standard gasket
 
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photo17978.jpg
 
In the video it sounds like the gear is just riding on the trans gear. My 70 c60 has a similar chelsea pto. It was real finicky to set up after I had the trans rebuilt. I ended up getting a used takeoff from Vandhaugs. Look on there for a used one. I didn’t pay that much for it and it runs so quiet and smooth I was blown away.
 
The PTO driveshaft is unhooked since I keep taking it out anyway and the output side.of the PTO is definitely not turning
 
Re listening to your video and your last comment the gears aren't engaging. Are you sure it's the right pto for the direction it's facing? I put one on a sm465 and it seems like one for the left or right side of the transmission output shaft facing the same direction (rearward) had different part numbers.
 
that a sliding gear one or one with a dog clutch?

point is, just because it ain't spinning the output don't mean the input gear ain't spinning
sounds to me like not enough backlash, but like any internet diag, you kinda gotta be there fingerfucking the parts to actually notice what's bad
 
M92PV4U said:
Re listening to your video and your last comment the gears aren't engaging. Are you sure it's the right pto for the direction it's facing? I put one on a sm465 and it seems like one for the left or right side of the transmission output shaft facing the same direction (rearward) had different part numbers.
Click to expand...

The sm420 only has one PTO port. The PTO has a sliding gear inside it that engages. So the countershaft gear of the tranny and the 1st gear of the PTO are always spinning whenever the clutch is engaged.
 
cool now can you measure backlash? there's gotta be a way to get in there and rock the PTO's input gear back and forth while it is installed
betting on it being preloaded hard, causing the gear to run loud
 
[486 said:
;n96780]cool now can you measure backlash? there's gotta be a way to get in there and rock the PTO's input gear back and forth while it is installed
betting on it being preloaded hard, causing the gear to run loud
Click to expand...

I don't have the right tools but if it looks like I need more backlash I will see if the local China freight has a dial indicator long enough to reach down through the top cover. Thanks everyone for the help!
 
Loosen the mounting bolts to increase the backlash and see if it gets any quieter.

If if not I have a sm420/pto in good condition out of a ‘53 I might part with :flipoff2:
 
you don't really need an indicator, you just need to be able to see in there to rock the gear and eyeball it
 
[486 said:
;n96868]you don't really need an indicator, you just need to be able to see in there to rock the gear and eyeball it
Click to expand...

I think I have some.machined washers, would it work to loosen the bolts stick some washers in to space it out,tighten it up and see if it helps?
 
[486 said:
;n96885]you'll lose all your oil but yeah sure
Click to expand...

Shouldn't hurt it to let the clutch out for a second with no oil in it?
 
it's fine so long as it ain't bone dry, you know drained and let sit for weeks
 
[486 said:
;n96893]it's fine so long as it ain't bone dry, you know drained and let sit for weeks
Click to expand...

It has gear lube now so it should be good. I will give that a try tomorrow and report back
 
472man said:
The info I found for the PTO says to use gasket to adjust backlash. The range was .012-.025 if I remember right and it did fall in the top end of that range with the standard gasket
Click to expand...

I would get some gasket material in the .012 thickness and make a gasket. If it still grumbles add another .012.

Do you have anything to measure accurately your gaskets thickness?
 
IGT said:
I would get some gasket material in the .012 thickness and make a gasket. If it still grumbles add another .012.

Do you have anything to measure accurately your gaskets thickness?
Click to expand...

I found some .030 metal shim material stuffed that in with the existing gasket and tightened everything thing up and the noise is still the same. The gaskets come in .010 and .020. Should I shim it out further?
 
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