LouieM

I had my 1967’s born-with M20 Muncie rebuilt earlier this year and have since put 1,500 miles on it, from cruising to autocrossing. The main reason for getting it rebuilt was that the 3-4 synchro was shot. The rebuild was done by the regular mechanic I’ve used off and on for several years, a guy who has run his own Corvette specialty repair shop for about 30 years and is well regarded and highly reputable. He knows Sting Rays inside and out and has rebuilt countless Muncies.

The tranny hasn’t felt right since the rebuild, which included internal parts from Auto Gear and a new shift linkage. The mechanic originally filled the rebuilt tranny with synthetic lube, but shortly after that I had him drain that and refill with Sta Lube GL4 85W90. The main problem (which happened with both the synthetic and dino oil) is that frequently the shifter on the console becomes frozen in one position. This happens most often when I back out of my garage, after which I can’t get the shift lever into any other gear. Just pulling the lever rearward to get out of reverse can feel like I’m moving it through semi-frozen molasses. The shifter feels solidly cemented in place once in neutral; no amount of effort will move it from the neutral into any other gear, although sometimes I can force it back into reverse if I push hard enough. While frozen in neutral I can take my foot off the clutch and the engine stays running, so it really is in neutral. Strangely, sometimes when I turn the engine off I can then easily shift into any gear.

The mechanic has readjusted the linkage under the car twice; the first time didn't do much, the second adjustment lasted a few hundred miles. I should say that the tranny had this same problem before it got rebuilt and re-linkaged, and that this shifting problem had begun to rear its ugly head over the previous year or so.

So, before I take my ’67 back into the shop, I’d like to get the benefit of anyone advice who’s had the same or a similar problem.

Desert Nomad

I'm no transmission specialist but wondering how the clutch adjustment is. A dragging clutch would certainly make it difficult to get in gear or out I would suspect. On the other hand, it would probably grind like hell when moving into reverse which was not mentioned, so I guess that's not the case. Just sounds like the gears are not moving freely on the shaft inside. Keep us posted.

DansYellow66

I agree - it sounds like a clutch that isn't adjusted to release fully, possibly complicated by a shifter, neutral gate adjustment issue too. Is this a stock Muncie shifter or a Hurst shifter? I doubt the initial fill with synthetic lube caused any issues to develop.

R66

If it grinds going into reverse with the engine running and clutch disengaged, clutch adjustment or replacement is in order. If it does not grind going into reverse clutch has to be disengaging. Does it have a pilot bushing or bearing in the back of the crank?
Have you tried putting into 1st gear with the engine shut off and then start the engine with the clutch disengaged?
Not an expert, but the more things you try will help the experts help you.
Maybe drop Autogear people a line or call them for help.

LouieM

The shifter is stock, not a Hurst. The mechanic and I both thought to loosen the clutch takeup, but it made no difference.

LouieM

The pilot bushing is nonmagnetic bronze. The Centerforce II clutch already in the car was left in place owing to minimal wear. The car starts with the clutch disengaged and in first gear. I believe the mechanic has already called Auto Gear and everyone is mystified. The tranny shifting is heavy and somewhat notchy, almost like a Tremec 5-speed, but the parts are all new, so...

DUB

OK...

IF when you DO NOT have the engine running...does the shfiter shift the transmission through all gears smoothly????

If it does...and you get in it any gear....keep it in gear and with friend pushing on your car...press in on the clutch slowly and see when it allows the car to move due to the clutch releasing.

If the above scenarios work and the clutch is releasing....then...

Put the transmission in neutral....and crank the engine. Then try to put it in gear. IF when you try to get it in gear and it is like you are hitting a wall and the shifter won't move into the gate...your problem is in the pilot bushing NOT allowing the input shaft to spin freely....thus allowing the internals of the transmission to be able to shift.


Which is IF your shifter works great when the engine is OFF...but not working with the engine running...it is the input shaft...or I would place about 99% probability that that is what the problem is.....because I have dealt with pilot bearing binding the input shaft....but usually that occurs right after the transmission was installed.....but it is possible. even though your have 1500 miles on it.

DUB

MikeM

LouieM

Thanks very much for your analysis DUB. I appreciate your wealth of experience. I'll have a chance to follow your advice this coming week. I have a question: The pilot bushing and input shaft were not changed during this rebuild. As I mention above, this shifting problem also sometimes happened before the rebuild when the tranny/pilot bushing had been in the car several years. Does this still ad up to a possible pilot bushing/input shaft problem?

Lou

GTOguy

I'll add that loosening the clutch linkage is liable to compound your problem, not help it. You need to take OUT some free-play so that the clutch has a better chance of dis-engaging.

DUB

Lou,

IF what I wrote in my past post fits the scenario...then I guess it can. BUT...keep in mind ...it also depends on what is going on internally in the transmission in regards to the recent rebuild. My comment in my past post was dealing with a transmission that was know to be good.

By no means am I the guru of clutches and shifting issues. But from what I have seen and found and repaired in the past 30 years. I feel that when the shifter does not go into gear when the engine is running....but WILL when the engine is NOT running...it has to do with the input shaft and pilot bushing.

This is also assuming that the clutch disc is OK and and the clutch works correctly when the engine is off....and that internal transmission parts are correct.

You know that it is not going to fix itself and the chances that it has to come back out is probable. Which it seems you are no opposed to do.

TRUST ME..I have been where you are at...and like I say at my shop. "It is what it is". After trying other methods to do a repair that all fail...time to get tools out and take parts back off.

DUB

R66

Pulled the muncie from R66 due to a slight rubbing noise and hard to get in gear. The anti-clunk device and spring rivets worn off. Removed the anti-clunk device and spun the bearings and gears. (didn't remove the gears from the main shaft. Seemed good.
Still had the rubbing noise. Removed the trans and found the internal bearing surface on the 1st gear was black and pitted (Bubba got me). Replaced it with another 1st gear from my old stock along with bearings and etc.: ack:
Had a knock like a main bearing. 1st gear from a 65 muncie is smaller in diameter (about 3/64") than a 66. Back out and back together for the 3rd time with a new first gear (thanks to Bob at Performance Transmission that knows his Pooop ) Now better than any Muncie I have rebuilt or owned.

If the mechanic didn't check everything, including the pilot bearing, he didn't do his job.
In my case, if the 1st gear had welded it's self to the shaft, I am going for a ride no matter what gear i'm in. Did he inspect all of the gears?
Everyone is human, and the guys running the shops have to get it out to make a living. They can screw up once in a while and doesn't mean he is a bad mechanic.
Pull the trans and find out what the problem is, it will only get worse.

LouieM

DUB,
I was pulled away from this situation by family obligations, but now I’m back to it. I just tried your method on my 67 a few minutes ago with a friend.

Yes, with the engine turned off the shifter goes into all gears. BTW I would not call the shift action “smooth,” it feels more like a 5-speed Tremec but at least it goes into all gears with no trouble. If a friend then pushes on the car while I slowly release the clutch, the car moves forward.

After that, I started the engine this morning in neutral, and then I was able to shift into any gear with the engine still running. At times in the past, however, when the shifter wouldn’t move into any gear with the engine running, as soon as I turned the engine off I could move the shifter into any gear. So, turning the engine off basically freed up the shifter. This problem with the shifter is intermittent; doesn't happen every time I use the car.

Any more thoughts? Or is it simply time to leave my car at the mechanic’s. He always stands behind his work, so if the tranny has to come out, so be it. This is still a mystery to me, since the problem is intermittent, the tranny has 1500 miles on it, and the main shaft, clutch and pilot bushing weren’t changed.

Lou

DUB

Thank you for your feedback.

I seriously doubt that your pilot bushing is the problem because you can get the shifter to engage when the engine is running.

You may still have issues internally such as the sliders, synchronizers, etc.

Let the guy who did it go back into it and inspect it.

YES...if you shifter linkage and shifting plates on the shifter have a lot of free-play in them...that can cause part of the problem. The linkages and plates where the shift linkage attach to the shifter needs to only be able to slide front to rear and not have any wobble in them.

DUB

plaidside

Since this condition existed before your rebuild I would identify what parts are still in the transmission after the rebuild and inspect them.
Did your mechanic change the slides when he did the rebuild? If the original sliders were used with the hubs then either the slides are binding on the hubs or the teeth of the slides are worn causing the non engagement.
Joe

C2 Hot Cam Guy

Sound like a lot of it is shifter adj & clutch

LouieM

The new linkage has been thoroughly gone over, twice. The sliders were replaced. The mechanic has been in touch with Autogear. I'm stumped at this point, but after Thanksgiving I'll drop the car off and hope it starts acting up while the mechanic is driving it. What a frustrating situation.

DUB

PLEASE excuse me if I seem a bit.....uhhhh....condescending.

I have seen cars that people told me the linkage was installed right...but when I slide under the car it is missing the special 'G' clips and there is a lot of slop on the rods.

So I can only assume that your is RIGHT. And I an sure it more than likely is...so hopefully the guy will find the problem.

DUB

LouieM

OP here. I didn't have a chance to get the Muncie attended to before the Thanksgiving and Christmas bombs hit. Then it started raining a lot here in northern Calif.

But, last week I was driving around town and the "Stuck in Neutral" thing happened several times in a row, as follows: Pull up to red light; push in clutch pedal and put shifter into Neutral; take foot off clutch pedal. When light turns green, push in clutch pedal and TRY to put shifter in First. Shifter won't go into First or any gear, including Reverse. After several attempts to put shifter into ANY gear, I turned off the engine (keeping the clutch pedal pushed down), upon which the shifter instantly went into First, Second, Third, Fourth and Reverse one after the other. This happened several times in a few minutes, so it is a big, fat clue to what is wrong with the rebuilt Muncie. Unfortunately, I don't know how to interpret this clue.

After getting stuck in Neutral several times, as described above, the Muncie shifter worked fine the rest of the day, which included a 50-mile drive with several stops.

Anyone have a clue about what is happening with this M20?

Lou

Railroadman

Why do you shift into neutral and take your foot off the clutch at every red light? If you are able to downshift when approaching one (I did not read back through the posts to see if you can) it seems going into first as speed decreases and leaving it there until green would solve the symptom if not the problem itself.

BTW - stay away from that damn dam!