muncie problem - synchros?
Thread Starter
Team Owner
Joined: Jul 1999
Posts: 26,545
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From: Huntersville NC
muncie problem - synchros?
More and more it is getting hard to put my trans into 1st gear.(muncie M-20) It doesn't grind, it just won't go into first gear. Sometimes I can force it into gear, and then it shifts fine. If I am rolling to a stop it will usually slip into first gear if I am moving at 5 mph or less. Problem occurs only when I am stopped and in neutral. Obviously, a problem at a stop light if I can't get it into first!!
So, if I can't get it into first I can gently try to go into reverse, and it grinds, and then I can slip it into first. I'm thinking there must be a problem with my 1st gear synchro? Any thoughts? I have gone through the shifter linkage adjustment process twice, using the neutral locking tool. Not real anxious to pull out the trans and take it apart!
So, if I can't get it into first I can gently try to go into reverse, and it grinds, and then I can slip it into first. I'm thinking there must be a problem with my 1st gear synchro? Any thoughts? I have gone through the shifter linkage adjustment process twice, using the neutral locking tool. Not real anxious to pull out the trans and take it apart!
Thread Starter
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
Originally Posted by TopGunn
I know this sounds stupid but are you real sure the clutch is being disengaged all the way, the reverse gear grinding sounds suspicious along with the first gear problem.
reasonable question, but yes I am sure. Reverse gear will grind for most of us most of the time if you go directly into reverse.
Just another Corvette guy
Joined: Feb 1999
Posts: 8,518
Likes: 3,865
From: Palm Springs, CA.
The M-20 in my '70 was doing the very same thing. It was a combination of a worn shifter fork and worn shift barrel. I did the R & R, took it to my buddy's trans shop and had it overhauled for about $600.
Not too bad.
Best,
Greg
Not too bad.
Best,
Greg
Melting Slicks
Joined: Feb 2006
Posts: 3,428
Likes: 5
From: Japan
My ebay M20 did the exact same thing as soon as I installed it. Pics on the ad showed the gears and synchros to be in good shape (they were). I took it out, disassembled it and found that the 1-2 slider ("shift barrel" per Greg) and hub were junk, specifically the side of the slider that engaged first gear. I bought a complete rebuild kit from "KajunJon" in TX (input/output bearings, synchros, rollers, countershaft, seals, gaskets, and a new 1-2 slider and hub) for $230. Downloaded a PDF factory rebuild manual from eScam for $5. Only special tool required is a compound snapring plier; took me about a day to do. Problem fixed. If the synchro teeth on your first gear are badly chewed you'll probably want to consider replacing that too, but my guess is that the slider will fix the problem.As far as the grinding reverse goes, you'll likely find that the engagement teeth are chewed up as well but as long as you're careful engaging reverse you can live with that unless you require perfection...I left mine alone.
Last edited by birdsmith; Jul 9, 2006 at 11:03 PM.
Le Mans Master
Joined: Mar 2004
Posts: 7,473
Likes: 1,495
From: Little Rock AR
The clutch is not fully disengaged. This is a classic set of symptoms.
Most likely you will check the clutch and tranny linkage adjustment first. This will probably not fix it.
Then you can go ahead and replace the pressure plate, clutch disk and throwout bearing. I would resurface the flywheel and replace the pilot bushing in the end of the crank as it is fairly easy and very inexpensive.
That should take care of the problem.
I once did the clutch "remove and replace boogie" 3 times in one day with this exact same problem. The parts all looked great when out of the car and sitting on the bench BUT when I assembled the whole thing on the bench, you could see the heat warped pressure plate springs all bent up as the pressure plate was torqued down to the flywheel. Bought new clutch parts and all was well again.
-Mark.
Most likely you will check the clutch and tranny linkage adjustment first. This will probably not fix it.
Then you can go ahead and replace the pressure plate, clutch disk and throwout bearing. I would resurface the flywheel and replace the pilot bushing in the end of the crank as it is fairly easy and very inexpensive.
That should take care of the problem.
I once did the clutch "remove and replace boogie" 3 times in one day with this exact same problem. The parts all looked great when out of the car and sitting on the bench BUT when I assembled the whole thing on the bench, you could see the heat warped pressure plate springs all bent up as the pressure plate was torqued down to the flywheel. Bought new clutch parts and all was well again.
-Mark.
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Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by PRNDL
reasonable question, but yes I am sure. Reverse gear will grind for most of us most of the time if you go directly into reverse.
A couple of possibilities:
1 - (already discussed) is that the clutch is not disengaging - typically adjustment
2 - the transmission shaft is binding in the pilot bushing. Possible causes:
- Improper pilot bushing installation
- Dry installation
- Improper lubricant that has dried out/hardened and is causing the binding
Thread Starter
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
I think just about all of us will grind the gears going into reverse unless you put it in a forward gear first. I typically go from first (or second) to reverse with no grinding. I will check the clutch again but I am guessing a transmission rebuild is in my future. I just hope I can make it through the summer.
From the owners manual:
Numbers 1 - 3 are instructions on downshifting. 
From the owners manual:
4. Shifting into Reverse, when the car is stationary, is made easier if you momentarily engage another gear before selecting Reverse.
Last edited by PRNDL; Jul 10, 2006 at 05:32 PM.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Originally Posted by PRNDL
I will check the clutch again but I am guessing a transmission rebuild is in my future. I just hope I can make it through the summer.
It won't get much worse and the damage is done. So go ahead and drive it through the summer. You should be good for more miles just a little grinding going in.
I would check the clutch linkage also just to be sure.
Pull it this winter and put in a 5 speed!
Just another Corvette guy
Joined: Feb 1999
Posts: 8,518
Likes: 3,865
From: Palm Springs, CA.
Originally Posted by PRNDL
I am guessing a transmission rebuild is in my future.
And, to explain why it's not a matter of the clutch not disengaging entirely...
If this were the problem, when you did get the car into first gear you'd find the clutch engaging the second you lifted your foot a quarter of an inch off the floor and shifting from 1 to 2, 2 to 3 and 3 to 4 would be harder as well. This would be so obvious you'd have noticed right away and probably mentioned it in your first post. You said you're sure the clutch is engaging properly and I believe you.
Best,
Greg
Melting Slicks
Joined: Feb 2006
Posts: 3,428
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From: Japan
Double ditto Greg....the reason first gear goes before any of the others is that first is the only gear that is ever engaged with the car stopped, so the side of the 1-2 slider that engages the 1st gear synchro does so with the cluster gear still rotating (if you take the car out of gear and release the clutch like I do), causing greater wear on that slider. Ditto also on toddalin's M20 (IF the sliders are new!) $600 is a not-bad deal for a semi-crispy one these daze.
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,356
From: Santa Ana CA
Originally Posted by birdsmith
Double ditto Greg....the reason first gear goes before any of the others is that first is the only gear that is ever engaged with the car stopped, so the side of the 1-2 slider that engages the 1st gear synchro does so with the cluster gear still rotating (if you take the car out of gear and release the clutch like I do), causing greater wear on that slider. Ditto also on toddalin's M20 (IF the sliders are new!) $600 is a not-bad deal for a semi-crispy one these daze.
Trans gasket set
Retainer
Reverse Gear Idler
First and Reverse Gears
Reverse gears & Shaft
Pilot Bushing
Labor
Trans shifts nice. Hope this helps.
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
Originally Posted by PRNDL
reasonable question, but yes I am sure. Reverse gear will grind for most of us most of the time if you go directly into reverse.
Racer
Joined: Jan 2004
Posts: 428
Likes: 2
From: Everfrost Second Life
Originally Posted by dwncchs
Yes directly in without a pause-but Chevrolet says the test for proper disengagment is as follows--engine running-clutch out-trans in neutral-push clutch to floor-count to 12-then shift to reverse-there should be "NO" clash whatsoever-if there is- adjustment is wrong or you have clutch problems--I'm sure you checked your fluid level.There are a couple of molly additives out I would try before tearing down.
Shut the car off and see if it goes into first gear.
By the way 1st gear rings RARELY wear as well as the the 1st side of the slider because people rarely downshift into first. WHAT WILL HAPPEN -- PLEASE READ, is that if you miss a 2nd gear shift the engagement teeth on the slider's 2nd gear side can get mashed so bad on that they will prevent a 1st gear engagement since these mashed teeth now have to travel over the 1-2 hub towards first.
Paul
