The Stovebolt Site Forums The Shop Area Engine Shop SM 420 noises in 3rd/4th

Groaning is the word I'm describing here.

I took the 66 out to the filling station for the first time and then proceeded to get some more actual road experience. Due to a groaning noise, I recently drained and refilled the trans. w/new fluid, it still groans. However, I aptly determined that it only does it in 3rd and 4th gears. Are one of the gears common to 3rd and 4th gear? I think I'm in for a trans. rebuild. Hey, that's better than an engine rebuild, right?

Prior to this (before a trans. fluid chg.) I thought it sounded like it was dry, hence the drain, clean and refill. This seemed to not make much of a difference. It still groans.

Rance

PS: Good news from this run down the road is that I think my rpm's at 60 will be OK for a while. Maybe not a Big Grin ( ) but at least a smily ( ).

I'm working on the same setup as yours, but with an SM465 and a 292. How does she pull? I can't wait to get her done over the winter. Sorry I can't help you with your problem, by the way.

jay

I would think that if you had a bearing or gear problem, it would quiet down in 4th gear. Do you have a PTO drive on your trans?. I had one that would just scream the faster you would go. Good luck with it,
Scott

Jay, It seems to pull just fine. Granny gear could probably pull a stump, just like they say.

Scott, there's just a PTO cover plate, no PTO.

At first I was sortof bummed because it sounded kinda like a couple of rods were knockin in the engine. Then I determined that it only happened in 3rd/4th. Is there one of the gears or maybe a shaft that comes into play for only 3rd/4th gear?

Rance

3rd. is a "reduction", with the power being transmitted through the cluster gear, then to the output shaft. 4th. is direct drive, straight through the trans. It's unlikely that anything in the transmission, except possibly the output shaft bearing, could be involved. That one is under a cover plate, just ahead of the flange that connects to the driveshaft.

If you have a 2-piece driveline, the center carrier bearing could be making the noise, or the pinion bearings in the rear axle could transmit sounds forward, giving the impression the noise is from the transmission. Have someone ride in the bed on a test drive, and see if they can get a different perspective on the noise. Check the universal joints, too!
Jerry

sounds like a normal old trans to me they get noisy when they get a lot of miles on them.fill it with MYSTIC JT-7 and drive it.

I had both the input and output shaft show wear in the bearing shaft surface and no replacements available .... to me at least. Seems like all the 4 wheelers have scrounged all those 420 bits.
gooday
jim

Im not tryin to second guess anyone or you,,,but if its in just the higher gears,,, and uhhhhh dunno what groaning is,,,but are ya sure its your transmission...??? drive line noises can uhhhhhh (what do i wanna say) reverbrate,,or come from other things,,??? uhhhhh if its just higher speeds,,could be your rear end,,,,or driveline (carrier?) or depending on whats original or replaced... driveline noises can be hard to diagnose sometimes.. lotta things involved.. like angularity of components... (with swapped modifications typically)... one good way to tell if its the transmission itself is feel the gearshift... if you feel that noise directly through the gearshift,,then it is probably the transmission...if not...its something else...another test is,,,if its drivline itself, such as angularity,,,or balance,,or a slip yoke out of time,,,is typically drivlines vibrate or make noise in harmonics...and it seems a drivline vibration will change at speed,,,or acceleration or deceleration,,ive noticed it worst for some reason at about 45 mph.....
LOL..hmmmm now i read hotrod posted some of this.. heheh so i wasted my breath again.....hehehe

I agree with fatweed. I had a strong whine that I thought was coming from the tranny when I put a load on it in 4th gear. When I swapped my diff for a taller rear end, I put in a new bearing, adjusted the pinion/ring gear and there was no more sound. Even a vibration from the rear end can be transmitted through the gearshift.