My SM465 constantly makes noise.

[Rodent]

I picked up a '76 K20 that was literally at the crusher. Truck runs good, but the damn transmission constantly makes a high pitched grinding whirring noise. In neutral, in gear, clutch in or out. I've driven it and it doesn't hang in gear or pop out under load and shifts pretty good. This noise is consistent with engine speed.

I've tried different transfer case positions, held pressure on the shifter to the side. The only thing I haven't done is coast with the engine off.

Any ideas? The previous owner was a old man in poor health on a fixed income. he couldn't afford a power steering cap. He tied bags over the pump and wired the ignition with Romex. Supposedly when it started making this noise he sent it to the scrapper.

[greg64]

Okay, given your good tests, I'm thinking it's the input shaft bearings. Consistent with engine speed rules out the output side. Clutch up/down rules out throw out bearing.

Is the fluid level okay?

[jetmech85]

Clutch in would eliminate every thing except crankshaft pilot bearing/bushing and throwout bearing. Clutch out would eliminate that. ???? Improper clutch adjustment could cause the throwout bearing to turn constantly and be noisy if it is failing. Any pedal free play? All return springs installed on the clutch linkage?

[Bigstevex4]

He has covered everything else did drain oil. That's a must get pieces chucks shiny stuff ah as long as its not in a pile. And these are not quiet trans to start with. there truck trans.

[Rodent]

Haven't checked the fluid level. I have my CDLs so I'm used to noisy transmissions, but this one just sounds sorta ill.

[86c20]

i have a sm465 with over 350k in a wrecker it makes alot of noise all the time only time it dont is when its loaded and my foot is in it. as long as you have good fluid run it i have never seen a trans take so much hard use and not mess up. not even real truck trans take that abuse that that one has and still work lol

[tucsonjwt]

I would not rule out the clutch and input shaft bearing. SM465 is a crude transmission but I am told it usually holds together for a long time. I just had my clutch replaced along with the input shaft bearing and an input shaft repair sleeve and the clutch fork retaining clip was broken off and caused some noise - not like what you describe but worn clutches can generate a lot of noise in the transmission area.