Muncie Won't Downshift

[mike geary]

My '65 M20 won't downshift into 2nd or 3rd. No problems at all when upshifting.
When trying to downshift, the only method that works is to cycle the shifter into first gear (clutch engaged) and then complete the downshift.

When trying to downshift normally, I encounter very solid resistance and I can hear a spinning/whining sound. Thought it might be the shifter, but it seems to be actuating the rods properly.

Is this simply a common characteristic of a worn-out tranny? Time to send $$$ to Medatronic? TIA - Mike

[Brian Monticello]

Re: Muncie Won't Downshift

When you downshift, the slider pushes against the synchro first. The synchro's job is to get the gear you want to shif INTO rotating at the proper speed. When down shifting, this happens to be faster than than it is currently spinning.

What kind of gear lube are you using? This might sound strange, but the muncie actually requires friction to "spin-up" the gear you are trying to downsift into. This friction is between the cone of the gear and the synchro. If you use a super high tech synthetic lube you run into situations where the lube is actually too slipepry to let the synchro spin-up the gear.

You should be using a GL5 spec 80w90 lube.

If that doesn't do it or if you are already using the proper lube, then your synchros are probably worn out.

brian

[mike geary]

Re: Muncie Won't Downshift

Brian:

The car is a recent acquisition and I changed the lube shortly after taking delivery. I filled it with Royal Purple synthetic, the weight was in the 85-90 range. Unfortunately, I didn't log enough miles before the change-out to draw any conclusions about the before vs. after performance.

But it wouldn't be that hard to change it to a non-synthetic to see if it helps.

These are the times that I wish I had bought that Cytech Double-Park...

Mike

[Patrick H.]

Re: Muncie Won't Downshift

Yeah, two Cytechs is even better.

I'd guess synchros as well.
I did my own M20 last year. It was much easier to rebuild than I thought it would be. Don't be afraid to try it.

Patrick

[William C.]

Re: Muncie Won't Downshift

If the clutch is releasing fully, (check by putting into reverse, ok if no grind) you have a classic case of worn blocking rings (the brass rings in the synchro assy)

[Steve D.]

Re: Muncie Won't Downshift

Mike

If you are a novice transmission hand, the Medatronics video is $25 well spent.

[Patrick H.]

Re: Muncie Won't Downshift

Even if you're not, I would say that anyone with moderate mechanical skills and some patience can rebuild a Muncie with that video.

I did mine last winter, and found it one of the more enjoyable rebuilds I've ever done on a Corvette part or assembly. I'd do one again in a second.

Patrick