Technical Muncie M20, is my clutch not releasing?

Hi everyone.

I currently am fighting an issue with getting my car into gear. First I will state it is a Chevy Big Block with Muncie M20 and hurst shifter. I initially started the car on jack stands to see if it would go through the gears which it would, but I also noticed with the clutch in the wheels would rotate. I would hit the brake, stop them, and let of the brake and watch them continue to spin again. I pushed the car out for the first time in three years to make a few trips up and down my driveway a few hours later. I initially found it very hard to get the car into reverse, grinding but eventually going in. I backed the car down the drive, went for first, no such luck. Same with second, I however was able to catch third and went with it. The clutch felt normal, made no noise and the car pulled up the driveway and I didnt feel it pulling me at idle with the pedal in. I backed down again, grinding reverse, and stopped to find a foward gear, which I absolutely couldn't find a single one this time. I shut the car off and instantly was able to put the car into a gear. To me I figured there wasnt enough freeplay in the clutch and it was dragging as I should have noticed earlier with the wheels still turning on the stands, and made the only adjustment I could with the modified stock 56 chevy clutch rod that was in my car when it had a small block, moving it one hole closer to the front of the car, allowing me to have about an inch and a half of free play. I got back in the car, started it and was able to put the car into reverse with no problem at all, no grinding what so ever. But yet again I couldn't grab a single foward gear. I shut the car off, stuck it in gear, started it and pulled it in for the night.

What I'm really wondering, is if it's my clutch, my pilot bushing, or my worn out shift linkage giving me fits. The transmission really was a pain to get on the back of the engine, I had to pull it on using the bolts part of the way, initially I figured it was maybe because I dont have a clutch alignment tool. Maybe the pilot bushing was too small for the m20? I know the engine was hooked to an automatic before I got it, and I didn't change the pilot bushing. I also am running a Lakewood scattershield with out a blocksaver plate and wonder if that could cause issue. Lastly, I wonder if it's just the worn out Hurst Shifter, which I'm not even sure has the correct shift linkage rods, and I know there are a few worn bushings in there somewhere, because this thing bench shifts like crap.

Just a looking for honest opinions and suggestions. Thanks.

 

take it all apart and post pictures, maybe we can see what's wrong.

We'd only be guessing..but if you had to force the transmission into the clutch, you could have easily damaged something.

btw, not having free play usually makes the clutch slip, which is the opposite problem from not releasing

also the linkage angles could have been wrong

 

Thanks Squirrel, my plan is to take it all apart as I have a firewall to dress up anyways, but that will come when I have the spare time. I will however post some photos of my linkage tomorrow. From what I can tell it looks like it may be all together wrong when comparing it to other photos. Like I said, it has always difficult to shift on the bench.

 

Years ago when doing a 4 speed swap into an early Camaro I learned the hard way that there are different height throwout bearings. If you put in a short one and you need a tall one, it might exhibit the symptoms you mention...just not enough clutch action to fully disengage.

 

My first thought was the TOB being incorrect. How much motion do you have at the fork? Somewhere close to 1" should be fine. Any slop in the linkage anywhere will hurt your required motion. If you have any adjustment in the rod at the fork, give that a try. You may need to extend the rod, rig something up temporarily to test it out in the driveway. You have a non-stock bellhousing so the geometry is different from a stock set up. Is the fork pivot adjustable?

 

Sounds like the linkage needs adjustment to me. If you take it apart, check the input shaft bushing for correct size and depth. Find a dial indicator and check that the bellhousing is centered on the crankshaft.

 

FWIW, I have an M20 that was fitted in my Nova several years back . None of the clutch linkage is proper, pushrod out of a truck of some year, etc etc and I have similar issues. While mine will go into all gears and shift ok, the pedal has to be BURIED to the floor to get it into first once warmed up.

 

It sounds like you have a number of possibilities here. For starters your mention of having to draw the trans to the bell housing with the bolts is not good. Not having an alignment tool is a red flag for a number of reasons. If you had the trans hanging there but not slipped in all the way it could be easy to bend the disc. A three finger pp only needs a release gap of .050-.060 and a diaphragm even less, .030-.040. If you bent the disc it might be dragging and causing your non release issue.
Another possibility is if the disc was off center because you could not align it you may have scored the pilot bushing forcing things together. A damaged or tight bushing can drag the input shaft keep the disc spinning (maybe not continuously, but enough to cause your troubles) and it could be difficult to shift into gear.
Chevy aluminum bells don’t have a hole in the bottom to check your release gap but if you can determine where it should be you could hole saw a 5/8” hole in the bell to use. If you have the old cast iron two piece bell then you’re in luck- check the gap and rule that out. If not enough gap then adjust the clutch linkage.
Have you checked and adjusted the shifter? Was it a complete shifter/ linkage or was it cobbled together?
One last thing, if you have the sintered bronze pilot bushing don’t use any Lubri-Plate or other grease on it. The bushing is porous and oil impregnated and the grease can seal the pores causing it to run dry.

 

I had a similar problem (it kept going out of adjustment and I would readjust and it would be fine...for awhile), I finally sucked it up and just put a new clutch/pressure plate/throw out bearing in it, and so far so good. Good luck!! I hope your solution is less expensive than mine.

 

Need to pull it apart to inspect anyway, if the engine was born with an automatic there was no pilot bushing.

 

Everything's been covered, one thing to do is have someone SLOWLY push the clutch pedal in as you watch from under the car, the same with the shifter action.
Oh yeh, you may need to put gussets on the levers of the clutch cross shaft (Z-bar) pivot, movement there could eat up some of your needed travel.

 

If you put it on a flat surface. Put it in first, step on the clutch, start the engine, does it start moving? If it does, it's not releasing.
What style bellhousing do you have. If its a full circle, use a cut off wheel on a grinder to cut a slot in line with the disc/flywheel face to measure the released gap. We do it on all of our race cars.

 

Will it shift with the engine not running? If it does it’s a clutch problem.

 

It's a lakewood blowproof bellhousing so checking the release gap will not be possible. My first intention for today was to check the shifter as it was something I was given and seems like it was just cobbled together. I will take some photographs today while working on it.

 

I will check the freeplay at the fork, I know there is a little bit of slop in the linkage but I didnt have any problems with it when running a small block and 3 speed. I have two places I can connect the rod to the fork, one gives more freeplay and the other gives more disengagement. I think it needs to be somewhere in the middle.

 

Yes, it will shift while not running.

 

Last night when I couldn't get it into gear I shut it down and did exactly that. Once with my linkage setup with less freeplay and once with about 2" of freeplay as those are the only two adjustments I have. With less freeplay and more clutch disengagement I was able to find a few gears with the car running, but I think the clutch was dragging with the pedal depressed, spinning the input shaft, which is why reverse would grind. I never did notice the car pulling itself with the clutch in, but I did notice the wheels spinning with the clutch in while I had it up on jack stands. With it adjusted for more freeplay and less disengagement it took the grinding out of reverse but then I couldn't get it into any foward gear until I shut the car off. I shut it off, put it in gear, and pulled it in the garage and then went in to do some research.

 

"Maybe the pilot bushing was too small for the m20? I know the engine was hooked to an automatic before I got it, and I didn't change the pilot bushing".

What pilot bushing? GM Automatics don't use a pilot bushing. That could be problem if there is no pilot bushing in the crankshaft.

 

I had the same issue once. pilot bushing was "jambed" on the input shaft. so it sounds like the Crank shaft is turning the input shaft.

 

Don't think this has been mentioned yet but aftermarket scattershields aren't always concentric to the crank. If it's off center the disc will be tilted and if excessive could need more throw to disengage or possibly cause pilot bushing to bind too.

 

News to me, although it definitely had a pilot bushing in the back of the crank, but also a flex plate.

 

Engine and trans out, a friend and I are going to tear this thing apart after dinner and get some pictures on here asap.

 

I read you have 1 1/2" free play in the clutch pedal? That's about right, BUT adjust to zero if you can just for a test to see if the symptoms go away before tearing it all apart. Report back.

 

Ah shit!

 

Haha, just about two hours too late. The nice thing about my situation is that my dad has a 57 with 327 and Tex Racing Super T-10. I went out and felt his clutch pedal and I noticed he has hardly any freeplay. I had my friend put Dad's car in gear and push the clutch in while I turned the driveshaft, then we went out to my car and did the same thing and that's when I heard a horrid screeching noise as I spun the shaft while it was in gear. It functioned, but that noise is what prompted me to pull it all out...

 

Smoothy, I've been trying to figure out a way to word this without coming across like a know-it-all or a smart-azz and I can't. I was a GM dealer parts counterman from 1970-2017, over the years all car lines, medium duty trucks and just a touch of the old heavy duty (Brigadier, Titan 90, the big boys) and I can't recall any Powerglides, Turbo Hydromatics, Tempest two speed, S.T.300 having a pilot bushing, if I'm wrong please correct me. Sounds like that engine or at least the crankshaft has been "around the block" a bit, pilot bushing and a flex plate.

Chevy used for many years a Bronze bushing, P/N 3754587, later replaced by a needle bearing encased in a spacer, while the part number escapes me that part was originally used in the 6.2/6.5L Diesels. Again to my knowledge the pilot hole is the same for any manual transmission input shaft that GM has used since 1955 whether it be Saginaw, Muncie, Borg-Warner. The outer diameter of the sleeve that fits into the end of the crankshaft, well there are at least a few different diameters, Pontiac for one. Off the subject, Pontiac used a ball bearing for their engines but that was too large for Chevrolet engines.

 

I would bet you are correct in stating that the crank has been around the block. I can't imagine that you're wrong about no chevy ever coming with a pilot bushing if equipped with an automatic with your experience, all I know is that I dont know that much about automatics, or transmissions in general. But it still makes no sense to me as to why it would have a flexplate and a pilot bushing, unless it was once used with a manual transmission application.

 

Yep, that crank saw a stick at one time. Converters register with the big nub on the front and only seat in the larger O.D. before the pilot bore.

 

Usually a pilot bushing is in the crank far enough so that it will not contact the end of the torque converter when an automatic transmission is used. In fact it was not uncommon "back in the day" to see a service replacement crankshaft come in from GM with a bushing installed.

 

Just now wondering if you have the disc in backwards?