69 Muncie M-20 Question

[Brad H.]

All,
My 69 427 Muncie M-20 doesn't shift as smoothly as I think it should. The clutch is adjusted correctly and is fairly new. The shifter linkage is adjusted correctly and the shifter is rebuilt. The transmission seems to hang just a bit on any kind of aggressive shifting and some at normal shifting as well. The only thing I did not have rebuilt during restoration of the car was the transmission - it was just resealed. I have driven several C-2s with M-21 transmissions and they shift like butter. Is the not so great shift a normal issue with the M-20 or is it likely the sincronizers? Any thoughts would be greatly appreciated to help make the decision to pull it and have it rebuilt. It is quiet however.
Thanks very much,
Brad

[Richard H.]

Re: 69 Muncie M-20 Question

Brad, did the trans seem to operate better before your restoration? The thing that raises my eyebrow is you say the clutch is fairly new. I just last night read an interesting old thread over at the CF concerning clutch kits. This was about C1s, but ended up talking C2/C3s where Lars had actually tested the travel required on the pressure plate to engage/disengage the clutch disc, and the one he tested could not fully disengage the disc within the stock linkage adjustments. Here's the link; he posted on #20: http://www.corvetteforum.com/forums/...ver-shaft.html Not saying that's the problem, but it might be a possibility. I'd hate to see you spend the money on a rebuild of the tranny, and still have the same problem.

Rich

[Joe L.]

Re: 69 Muncie M-20 Question

Brad, did the trans seem to operate better before your restoration? The thing that raises my eyebrow is you say the clutch is fairly new. I just last night read an interesting old thread over at the CF concerning clutch kits. This was about C1s, but ended up talking C2/C3s where Lars had actually tested the travel required on the pressure plate to engage/disengage the clutch disc, and the one he tested could not fully disengage the disc within the stock linkage adjustments. Here's the link; he posted on #20: http://www.corvetteforum.com/forums/...ver-shaft.html Not saying that's the problem, but it might be a possibility. I'd hate to see you spend the money on a rebuild of the tranny, and still have the same problem.

Rich

Rich--------


Yes, full clutch disengagement is a problem with C2 and C3 Corvettes. I have found that if the clutch is adjusted with the amount of free play specified in the service manual, there will not be full disengagement at full deflection of the pedal (i.e. on the floorboard). There needs to be minimal free play in order to achieve full disengagement at full deflection.

This problem is compounded if the flywheel has been surfaced and that's one of the reasons I don't recommend the use of a surfaced flywheel for a Corvette.

[Joe L.]

Re: 69 Muncie M-20 Question

All,
My 69 427 Muncie M-20 doesn't shift as smoothly as I think it should. The clutch is adjusted correctly and is fairly new. The shifter linkage is adjusted correctly and the shifter is rebuilt. The transmission seems to hang just a bit on any kind of aggressive shifting and some at normal shifting as well. The only thing I did not have rebuilt during restoration of the car was the transmission - it was just resealed. I have driven several C-2s with M-21 transmissions and they shift like butter. Is the not so great shift a normal issue with the M-20 or is it likely the sincronizers? Any thoughts would be greatly appreciated to help make the decision to pull it and have it rebuilt. It is quiet however.
Thanks very much,
Brad

Brad------


One more possibility: if the linkage was rebuilt with some of the parts replaced, I've found that to be a big problem which can cause just the problems you're experiencing. Rather than rebuild a shifter, I recommend going with a complete new shifter assembly.

[Larry M.]

Re: 69 Muncie M-20 Question

Brad:

What lube are you running in the transmission?? This could have an impact on shifts, particularly with cold/cool fluid.

Larry

[Mark E.]

Re: 69 Muncie M-20 Question

Brad,

Your thread caught my eye because I have a similar issue with my '70 M20. Before I removed the bellcrank and pushrod for cleaning and replacement of pivot parts and bellhousing boot, third gear would sometimes crunch during careful, deliberate up-shifts. After reassembly, third gear is fine but now fourth gear sometimes crunches. The clutch was adjusted to specs before and after disassembly of the linkage.

Until now, I suspected tired synchros and 100k miles of use.

Joe's post has encouraged me to readjust the linkage. It sounds like more engagement with less free play than spec might be worth a try.

[John L.]

Re: 69 Muncie M-20 Question

Brad
another indication of this common problem that Joe & Richard describe is grinding, hard/slow shift into reverse where you have to have the pedal flat on the floor.

[Brad H.]

Re: 69 Muncie M-20 Question

Thanks to everyone for the ideas. I did add some clutch pedal adjustment to make sure the clutch was disengaging but I can't be 100% positive it is totally disengaging. I bought the car with the original engine rebuilt and a new design clutch. Engine rebuild paper work reveals about 3000 miles has been put on the engine/ clutch assy since. Engine runs perfectly but I believe the clutch/transmission had the not perfectly smooth shift issue from the git go. I do have the mild grind/hang shifting in to reverse as well.
Joe, I know you have a 69. Most of the Corvette retailers offer new shifters. Any idea if any of them are any good?
I really appreciate all the input. This car has 63,000 original miles on it. Is that where you guys think synchronizers would begin to wear out? I suppose both the shifter and synchronizers could both be the cause.
Brad

[Joe L.]

Re: 69 Muncie M-20 Question

Thanks to everyone for the ideas. I did add some clutch pedal adjustment to make sure the clutch was disengaging but I can't be 100% positive it is totally disengaging. I bought the car with the original engine rebuilt and a new design clutch. Engine rebuild paper work reveals about 3000 miles has been put on the engine/ clutch assy since. Engine runs perfectly but I believe the clutch/transmission had the not perfectly smooth shift issue from the git go. I do have the mild grind/hang shifting in to reverse as well.
Joe, I know you have a 69. Most of the Corvette retailers offer new shifters. Any idea if any of them are any good?
I really appreciate all the input. This car has 63,000 original miles on it. Is that where you guys think synchronizers would begin to wear out? I suppose both the shifter and synchronizers could both be the cause.
Brad

Brad-------


My M-20 transmission had 200,000 miles on it when I took it out of the car and it had never been apart. The transmission still shifted perfectly at that time. Of course, I drove it pretty mildly it's entire life. If a car had been "beaten", I'm sure the transmission life would be drastically shortened.

The reproduction shifters I have seen all appear virtually identical to the originals. I have not used one or had any experience with one, so I can't speak from experience, though. You could look for NOS if you wish. It was GM #3960609.

By the way, are you sure this car really has 63,000 original miles? These old speedometers "reset" to zero at 100,000 miles and there's no way to know how many times that occurred in the life of the car. Mine reads 00000.0 right now and the speedometer has never been tampered with. But, the car has 200,000 miles on it (exactly!).

[Jerry W.]

Re: 69 Muncie M-20 Question

Joe...Just curious..How did you your car into storage with Zero Zero Miles ?

[Gary R.]

Re: 69 Muncie M-20 Question

Hey Brad
Good to see you back here. How is that diff working out?

One thing that caught my eye was the fact you said there is a new(er) clutch. I wonder if it could be a centerforce clutch? These were one of the "have to have" parts floating among the various forums about 8-10 years ago, along with a rack or jeep steering box, side pipes, TT wheels. The problem is they are not bolt in parts. The Geometry is off and the pedal throw is way out. The fix was to get an adjustable ball stud to set the correct length, then weld it together. Many guys bought this type of clutch and had fits with it, pulling the trans out to reset the ball stud. I don't know if that is your issue but something to think about.

The trans should shift as easy as your other Muncies, there should be no difference between M20-M21-M22 as far as shifting. If the sliders, hubs, and or brass blockers are worn you would have that problem. It may also pop out of gear.

Find anymore WWII planes?

Gary

[Patrick H.]

Re: 69 Muncie M-20 Question

Joe...Just curious..How did you your car into storage with Zero Zero Miles ?

He drove it around the neighborhood just enough to get it there exactly.
True story.

[Joe L.]

Re: 69 Muncie M-20 Question

Joe...Just curious..How did you your car into storage with Zero Zero Miles ?

Jerry------

I knew I was going to put it in the garage for some work and it was getting close to 200,000 miles, having gone around once in about 1976. So, I drove it until it got close. Then, I drove it up and down the street until it got to exactly to 00000 and then backed it into the garage (where it, unfortunately, still remains).

DSCN3243.jpgDSCN3244.jpg

[Brad H.]

Re: 69 Muncie M-20 Question

Hey Gary,
Good to hear from you! I actually sold that car in favor of the convertible 427 I have now. That diff did great though! You know, I think the clutch may be a center force unit! I can't remember for sure, so I'll drop the bell housing cover and see. You may have hit the nail on the head. Do you have a recommendation on a good clutch that won't cause these problems?
We've finally gotten out of the WWII fighter restoration business for multiple reasons, most of all cost. I'm building an aerobatic experimental airplane now. Thanks for your help as always!
Brad

[Jerry W.]

Re: 69 Muncie M-20 Question

Joe..What a great story....With all of the crap in the news today....It brought a big smile to my face...Thanks for what you do here.