R66

I rebuild my M20 initially due to the reverse anti-clunk assembly at the front of the countershaft rubbing on the case. Removed it and put in new bearings and bushings, gaskets, etc.
Upon reassembly and installation, I still had a slight grinding noise like a rough bearing. 2nd disassembly, found the inside bearing surface of second gear was pitted. Replaced the 2nd gear, front and rear main shaft bearings, gaskets, etc.
After about 100 miles or so the transmission has developed a knock, very consistent (like a main bearing) 2 knocks per second with the transmission in neutral and the clutch engaged idling at 700 RPM. When the clutch is disengaged, the knock goes away as the trans mainsheet is not turning. The knock also goes away when the transmission is in any forward gear or reverse with clutch engaged (idling on a hoist). The knock is at the area of the rear bearing of the transmission. The trans is full of 80-90 wt lube.
I sent an email to the good people at AutoGear, but thinking a Muncie expert here on the forum might have run across this.
Thanks
Ron

plaidside

It sounds as if you have a broken or chipped tooth on one of the gears, input or cluster shaft.
When you say the mainshaft are you referring to the shaft that the gears ride on or the input shaft that the clutch disc rides on?
Joe

Pop Chevy

What was the end play on the cluster shaft ? Could be banging back and forth.

plaidside

I do not believe this to be the cause considering the consistency of the knock.
Joe

GTOguy

I agree with a broken or chipped tooth. BTDT. Might be able to see it pulling the side cover with the trans in-car....

wmf62

...

BUT in post #1 he says it goes away when in gear sitting with the wheels off the ground...

When the clutch is disengaged, the knock goes away as the trans mainsheet is not turning. The knock also goes away when the transmission is in any forward gear or reverse with clutch engaged (idling on a hoist). The knock is at the area of the rear bearing of the transmission. The trans is full of 80-90 wt lube.

Bill

GTOguy

Yes, forgot about that. Still, easy enough to pull the side cover and have a look for anything obvious.

plaidside

No matter what, if the noise is coming from the trans it has to come out.
Joe

R66

Sorry to have left you all hanging for a while. I had to put it on the back shelf for a while to do some civic and domestic duties.

I agree the trans has to come out again, just trying to figure out what parts to order before I rip it apart again. I also can't understand why it didn't start the knock until after 100 miles or so on the rebuild with gentle driving. :total:

Main shaft means the output shaft that the 1st, 2nd, and 3rd gears ride on.

Going to put it back up on the hoist and pull the drive shaft to assure the noise is not being tunneled from u-joints or the differential which should not be turning in neutral, but just another check. Then I'll go after the side cover and pull the engine and trans again.

I'll let you know when I find it. Might be a week or more.

Thanks

R66

Pulled the engine and transmission for the third time.
A couple of corrections to my original post:
Replaced 1st gear not second
The knock is slightly audible in all gears, but loud in neutral. Ran on the hoist again with the driveshaft removed and the throw out bearing adjusted completely back to insure not touching the pressure plate diaphragm fingers.
Upon disassembly I took measurements and found the following:Input shaft / 4th gear .030” clearance to syncro hub measured with dial indicated on end of shaft prior to disassembly. May add another oil slinger .020 thick to reduce clearance. Don’t know what it should be.

Front bearing opening in case 3.149” I.D.
Front bearing on input shaft - new 3.148” O.D. Loose fit and rocks in case opening and thus I am concerned about using it??
Front bearing on input shaft - original 3.149” O.D. Snug fit

Input shaft bearing opening for main shaft 1.813” I.D.
Main shaft bearing area 1.375” O.D.
Bearing diameters 0.218”
Calculated oil clearance 0.002”
NOTE: fine metal particles in shaft just behind the bearing area. No wear areas found to indicate where it came from.

3rd gear clearance to boss on shaft 0.013”
3rd gear oil clearance to shaft 0.002”

2nd gear clearance to boss on shaft 0.17”
2nd gear oil clearance to shaft 0.002”

1st gear clearance to bearing 0.013” Don’t know what max. is
!st gear sleeve (race) is tight to the bearing and synchronizer hub.
1st gear oil clearance to shaft 0.002”

Rear bearing to snap ring clearance 0.000” used 0.092” snap ring
New Rear bearing fit - tight on shaft and in the carrier opening.

Reverse idler gear .032” clearance at thrust washer
Reverse idler oil clearance to shaft .004” Bushings appear to be good.
Reverse idler shaft fit in case Tight fit - approx. .001 clearance
Reverse idler case surfaces thrust washer areas appear to be good with no visible wear.

Counter shaft
clearance to front thrust washer 0.017” OK GM allows 0.025” max
Counter shaft O.D. at bearing areas 0.930” No visible damage on shaft
Counter shaft I.D. at bearing areas 1.245” No visible damage on bore - May be a erroneous measurement as when the shaft is assembled and installed, there is little movement - measured approx. 0.001” movement with counter gear and shaft installed. Bearings installed with grease when measurements taken with shaft installed.
Bearings O.D. 0.125 New
Calculated oil clearance 0.065” May be erroneous
Spacers 0.071”
Shaft fits tightly at the front of the case and in at the back.

I have looked at everything for wear and gouges - nothing found.

Anyone know what the clearances should be on a Muncie M20 between gears, etc. or any manual that would provide the clearances.

Looking for any ideas. Still have it out and don't want to pull it the 4th time.

Thanks
Ron