DSR

What are the normal wear areas on a '65 M20 mainshaft?
Do you get wear on the mainshaft shoulder where 2nd & 3rd gear make contact?


Do you get wear on the sides of the shoulder maked in red? Is there a thurst clearance spec. for 2nd & 3rd. gear?

pop23235

I’ve seen very few with measurable wear, but a few gall under 2nd gear. What wear I’ve observed is load bearing area, not thrust area.

DSR

I ask because the trans I took out of my car was having 2nd gear problems. I took off the side cover and mearsured 0.035" gap between 2nd. gear and the shoulder on the mainshaft, and only 0.011" between 3rd gear and the shoulder. 2nd gear seems loose with lots of play on the mainshaft.
The 2nd gear problem was after 50,000 miles on my rebuild I broke 2 teeth off second gear. The counter gear looked ok to me, so I replaced 2nd gear, bearings, bushing, thrust washers, etc.
7000 miles later I broke 2 teeth off the counter gear in the 2nd gear postion. Maybe the counter gear should have been replaced the first time?
But when I took the side cover off this time I noticed that 2nd gear looked loose, like it has too much thrust clearance (0.035").
Now I'm thinking maybe 2nd gear is jumping around too much and causing damage.
What do you think?

pop23235

I’m sure there are rebuilders on here that can answer your dilemma. There’s a great reference book by Paul _______( can’t recall ) that you should read. My guess if your breaking teeth, your transmission may not be clearing gears, ie still not free from one gear as you shift to second. I’d be concerned with wear on the internal shift levers and side plate combs as well as external levers. Of course there are other punishing ways to break teeth, but if on the quarter mile, you’d already know why. My guess is radial wear would yield abnormal gear noise. There’s a good bit of tolerance for axial misalignment for the gear teeth, but radial wear should show up as excessive looseness from drive to coast.

PS: If I had broken a gear, would not reassemble without checking that the mainshaft did not bend.

DSR

I do have Paul Cangialosi's book Muncie 4- speed. But I'm not sure what caused the breakage. I never thought about a bent mainshaft??
The trans always ran smooth no vibrations and shifted nice, no clashing of gears for 50,000 miles. Then driving up the road slowly one day 2 teeth break off 2nd gear.

Donald #31176

You may want to contact forum member Tom Parsons (aka) DzAuto. He has plenty of experience with Muncies.