[J.T.]

I have just rebuilt my Muncie m-21 from a '70 GTO and found a slight rubbing noise while accelerating in 1st gear. I was told that the front idler gear my be walking back and rubbing the 1st speed gear. I removed the trans and removed the side cover. The idler gear and 1st speed gear have plenty of clearance.



But what I did find was with the 1-2 slider pushed back It just touches the front idler gear.



The rear idler gear was replaced because the teeth were a bit chewed up. now if I put the old rear idler gear back in, the front gear and the slider clear by .001"-.002". I would think this is still not enough. There seems to be no end play in the idler gears to shim them back away from the slider.

Dose anyone know what I should be looking at to correct this?

Thanks, JT

[Held for Ransom]

Looks like your slider is installed backwards. I believe the bevel should face rearward on the 1-2 gears.

[J.T.]

That is the way it was when it came apart.



Was it wrong then too?

JT

[Bruce Meyer]

Its backwards. Both sliders bevels face forward.

[Held for Ransom]

Alright, went to other computer. While I remembered the bevel part being the 1-2, I was wrong on the install. You have it correct. If changing the front idler moves its positioning, maybe that idler is bad. Or the case.

[Bruce Meyer]

Wow. I just looked at the exploded view of one in an old Chiltons manual and it shows both bevels facing forward. WTF?

[J.T.]

Held for Ransom-

Thanks for the pic confirming the slider.

I don't think the case is worn because .018" between the front idler gear and the front thrust washer.

Any Idea on how much room should be between the slider and 1st speed gear when the slider is back in 1st gear?

JT

[squidtone]

JT,
I just got done today putting my Muncie M20 back together. (bad gears, got a whole new set of Autogear M22 "Rock crusher" wide ratio gears) Here are some things I learned while doing this whole job:

Your slider is correct. The bevels on the sliders face away from each other, so the 1st-2nd slider bevel faces toward the back.

Muncies are infamous for the reverse idler coming into contact with the slider when in first gear. Some folks actually make a larger bevel on each tooth on the reverse idler gear with a bench grinder. That may be drastic....

The rotation of the countergear should always tend to force the idler gear toward the back of the case. While you do have some endplay on that idler gear, is the reverse idler shaft able to seat all the way into the tail housing? Is there gunk in the shaft bore or roll pin slots preventing the shaft from moving back far enough for that extra few thousandths of clearance? If the shaft can go back a wee bit more, it may be enough for clearance.

the other thing that occurs to me is that maybe the slider doesn't have to move all the way against the helical teeth...it only needs to engage the engagement teeth...can you adjust your shifter stops (if you have them)?

Dave

[J.T.]

Dave,

I'm glad you chimed in. Your website was one of my sources of reference.

I thought about cutting the bevel on the front idler gear but as you said, as a last resort.

The tail housing is clean and the idler pin sits in deep enough so the locking pin is inside the tail housing. the rear thrust washer sits flat against the housing.

It seems to me that the slider is stopped by the detent lever in the side cover. If I were to adjust out the amount of travel with the shifter stops (that I did install) the gear would not lock in place. Wouldn't?

JT

[squidtone]

Yes, that's very true and I thought the same thing: the detent arms in the shift cover would/should prevent the fork from "shifting" the slider over too far. So I agree that maybe the shifter stops would have no real effect.
The only other thing I've seen is maybe lower quality sliders can wobble around and make contact with the reverse idler.
The 5speeds guy (Paul C I think) has a video that shows the difference in lower quality and higher quality sliders. The higher quality sliders fit tighter on the hubs and can't wobble as much.
I bought torqlok sliders (not from 5speeds co.) but I don't know who made them and if there are different levels of tolerance. They do wobble a bit, and from my first ride last night with the "new to me" trans, I swear I can hear an occasional noise in neutral. Everything is new, but it's not GM new, it's a hodgepodge of new parts from Italy, china, USA...who knows.
I guess I'm fortunate that I don't get that contact in first gear, but the trans does need to break in. ( As an aside, the rock crusher gear set from Autogear is very nice and sounds good too. That rebuild I did on my website was with the original gears that were horribly worn. My inexperienced eye did not see this the first time around, so I re-did the whole thing this past week with new gears)
So, slider quality is something to consider I guess.
Dave

[J.T.]

I bit the bullet and cut the bevel a little more on the front idler gear. I would estimate I took off about .050". It looks much better.



Trans will go in next week. Can't wait for a test drive.

JT