Muncie M21 Whine

[John R.]

The M21 in my 67 coupe has developed a whine in both second and third gear at lower speeds. The whine tends to go away at higher rpms and is not evident when the transmission is cold. Is it time to pull and rebuild the transmission?

[Werner R.]

Re: Muncie M21 Whine

i think the whine needs to be discussed with an expert on trannies. who knows with the info given. for instance, a whine that is only in one gear [second] and that goes away with rpm was what i had on my trannie. it was due to a slight rubing of the teeth on the gear of the primary with the gear on the countershaft. not a big deal, but slightly worrisome. talk to an expert to make sure you don't have a rebuild looming.

[Donald O.]

Re: Muncie M21 Whine

John,
Do the obvious first.
Have you checked the trans lube level?
Don

[Tom P.]

Re: Muncie M21 Whine

I agree, check the fluid level first. If it is full, and this is a whine which has developed recently, then yes, it is probably rebuild time.
If it is NOT full, and you fill it, and the whine goes away, then it may be OK.
If it is NOT full, and you fill it, and the whine DOES NOT go away, then it possibly has been worn excessively, and may need a rebuild.
UNFORTUNATELY, the only sure fire way to know, is to tear it down. I've been building Muncies for almost 35yrs, and I haven't seen any which couldn't be saved---------------except those which were exploded behind a killer BB.

[John R.]

Re: Muncie M21 Whine

I don't want mine to explode as it has all the right numbers on the case. I started to check the level this morning but the filler plug (square head on the passenger side?) is really in there tight. I'm afraid to really torque it as I don't want to damage anything. Any suggestions?

[William P.]

Re: Muncie M21 Whine

Most of the time a tight plug can be "Warmed" with a propane torch, then place a candle next to the plug/thread area, and let the wax melt into the threads, freeing up the plug. I have found that most manual transmissions that get quieter the higher gear you shift into, is mostly caused by a bad rear output bearing.