Need some input on noise

[augiep9]

I have a m20 4 speed in my c10. It was freshly rebuilt. Put the truck back on the road last August and it has been making this sound the whole time. When driving on the highway and it is decelerating between 70 and 60 it making a whining sound. When I push in the clutch it goes away but it it's still in between 70 and 60 when I release the clutch it comes back. Accelerating is fine and decelerating under 60 is fine. It's got me stumped. Any help would be much appreciated. Thanks

[HO455]

It sounds like a noisy bearing or a one of the syncros and/or gears are a little loose. There are always decisions made during a rebuild as to what parts are reusable. It could be that one of the reused parts are just slightly out of tolerance and making the noise. I'm not familiar with a m20 Is it a car transmission or do you mean SM420? If it is a truck transmission then talk to the folks at Novac. They have always be good to me plus their web site is chock full of good info.

[augiep9]

It is a car 4 speed. Thanks for the input. If what you said is accurate then it would Probly be something to do with 4th gear. If I remember right I bought all new synchros and I did buy a new gear but I can't remember what year it was. I believe the kit I bout had new bearings, synchros, and seals. Right now it's just a noise and dosnt seem to hinder performance. I guess I'll just put up with it until winter

[HO455]

My first rebuild of a SM420 had a wicked rattle in 3rd gear that over time slowly diminished. Or the rest of the truck got noisier and you couldn't hear it anymore could have been either one but at least it never got worse or failed. Good luck!