The Stovebolt Site Forums The Shop Area Driveline SM420 loud noises over 1200 rpm!

1948 Loadmaster 235ci, & SM420. I have some crazy load noises, sounds like someone is trying to get a geared item to mesh with another geared item while they are moving!
It does not start until I'm over 1200rpm, and it seems to be more apparent in 4th, then 3rd, then 2nd.
I had the tranny gone thru when I rebuilt the motor, and it only has 100 miles on it since being reinstalled.
I will not have a chance to pull it until next week, I am just wondering if anyone has a idea or theory what might be going on.
Thanks

the old crashbox 4 speeds always get noisy - something missed when it was "gone thru"? only opening it up might reveal some wear marks or dings to show where the problem is, otherwise it's a guess - bad bearings? broken retainer clip someplace?

Bill

Did a pilot bushing get installed in the back of the crankshaft?

Next week when I get a chance I will be pulling it out, and opening it up, in the mean time I am just curious. The kit that was installed when it was "gone thru" was new gaskets and bearings. I have driven 100 miles since the tranny was rebuilt and the noise/symptoms just made themselves known last week, I am hoping it is nothing to major, but I am prepared for anything.
Don I don't remember if I installed a pilot bushing or not. Without would it have functioned normally for the last 100 miles? I am pretty sure I have the 6:17 rear end, so the top speed I have reached/sustained is 45-48 mph.
Thanks, Curt

when something goes wrong after recent work, pretty safe bet something about that work was substandard, quite possibly parts .... could even be something about the clutch/throw out bearing, front trans bearing retainer ... did you renew the clutch on re-assembly?

if you had the flywheel resurfaced the bushing would have been removed .... OTOH, if it wasn't and you you didn't replace it, the old one should still be in place, and likely well worn, which may have contributed to failure of a poor quality replacement input bearing

Bill

I agree with you Bill, I am thinking work, or parts.
My machinist resurfaced the flywheel, I will have to ask him about the bushing, but I don't know why He would have not replaced it. The pressure plate was serviced, and clutch and throw out bearing replaced, at the same time as the motor/tranny rebuild.

Since it gets louder the faster you go, it leads me to believe it is in the back of the transmission instead of the clutch or input shaft. You might want to take the rear bearing retainer off and look around. If everything looks good, you might want to take the top cover off of the transmission and look around, but I think you are going to wind up pulling the transmission and going back to the guy who went through it in the first place.

I know this is a long shot, but make sure the starter return spring is attached correctly.

Here is a little video with sound I made this morning. I rev up to 1200rpm in 2nd, 3rd, then 4th. I will be pulling the tranny early next week.

I'd be grabbing some wrenches RIGHT NOW, not driving it or even running the engine. Something that noisy can end up with hand-grenaded gears and a case in several pieces. You've used up all your luck already if the transmission is still in one piece.
Jerry

It looks like it does it with our without driving which shoots my theory of the back of the transmission. It could be anything. I agree with Jerry. Don't even start the motor. It sounds bad.

wow, agree with above, stop abusing whatever has come loose and tear it down, sounds like replacing some gears is in your future

Bill

That was the last run it will make, I wanted to record the sound for the guy who 'went thru' the transmission.

A noise that bad should be easy to find, when you get back into it. Sounds like something big is banging around.

This week I unhooked the driveline from the tranny to try and isolate my problem. I ran thru all four gears, up to 2000rpm, no noise. So I started examining my driveline (all three U-joints where replaced 100 miles ago) there was forward/back play in the yoke that connects to the pinion shaft. Then I noticed the pinion shaft nut which is supposed to be 160-280ft lbs, was finger tight!
Today I tightened the nut, and installed a cotter pin, which was not used by the last person who worked on it, and went for a short drive through the neighborhood. So far No Noise!
If you have a Big Bolt it would not hurt to check and make sure you have a cotter pin installed.

Glad you found it. Good fix!