Muncie Syncro or ThrowOut Problem?
Thread Starter
Melting Slicks
Joined: Nov 2006
Posts: 2,618
Likes: 149
From: Anaheim California
Muncie Syncro or ThrowOut Problem?
My Muncie M20 in my '61 will start grinding and chattering when going into first gear after the car has been driven and warmed up. The grinding and chattering can be felt through the shifter. The problem is intermitent but seems to happen more often when the engine is heated up and run hard. Does this appear to be a syncro problem or throwout bearing going bad? I would think a throwout bearing would constantly make noise. Any ideas, please chime in. Thanks
Race Director
Joined: Jun 2006
Posts: 17,901
Likes: 751
From: Inverness FL
St. Jude Donor '07
most likely the synchros. when it does it , you can tell the difference by shifting into neutral and then pushing the clutch in and out several times. if it does it in neutral, then it is the throwout bearing. if it does it when you try to shift from neutral to any gear (except reverse), then it is synchros.
BUT, instead of synchros, it could be that your clutch needs adjusting because it may not be fully releasing the clutch disc and therefore causing the synchros to try to match the gear/synchronizer speeds while there is still power from the engine.
Bill
BUT, instead of synchros, it could be that your clutch needs adjusting because it may not be fully releasing the clutch disc and therefore causing the synchros to try to match the gear/synchronizer speeds while there is still power from the engine.
Bill
Pro
Joined: Mar 2007
Posts: 500
Likes: 3
From: Huntington Conn
Are you using any type of synthetic gear oil?
If so, get it out of there.
That could be your only problem.
I know I am going to hear from those who will disagree here, if so, just ask any other volume rebuilder of our ol' boxes!
The synthetics are "to slippery" for our poor old muncies that are not designed for that product, there needs to be enough drag between the synchro ring and the gear to slow the gear movement enough to smoothly engage, the older the trans, the more polished the synchro taper on the gear gets do to age and use, the more sensitive it is.
Stick with a quality brand of 75-90 W petroleum base gear oil
STAY AWAY from bargain chain store brands, no matter what the bottle reads as far as specs met. They have poor anti foam properties,
without going into it you can imagine what happens if your oil foams up!
If so, get it out of there.
That could be your only problem.
I know I am going to hear from those who will disagree here, if so, just ask any other volume rebuilder of our ol' boxes!
The synthetics are "to slippery" for our poor old muncies that are not designed for that product, there needs to be enough drag between the synchro ring and the gear to slow the gear movement enough to smoothly engage, the older the trans, the more polished the synchro taper on the gear gets do to age and use, the more sensitive it is.
Stick with a quality brand of 75-90 W petroleum base gear oil
STAY AWAY from bargain chain store brands, no matter what the bottle reads as far as specs met. They have poor anti foam properties,
without going into it you can imagine what happens if your oil foams up!
Pro
Joined: Jul 2008
Posts: 622
Likes: 24
From: Clermont Florida
If the clutch is not releasing, it will be difficult to get it in any gear, while running, but not moving, once the problem starts. When you have trouble going into first, try going into reverse, straight from neutral, after holding the clutch in for about 5 seconds. If it grinds, go into a forward gear, then without releasing the clutch, shift to neutral for 2 seconds, and then try reverse. If it grinds at all, the clutch is not releasing.
A bad throwout bearing should make noise whenever you push on the pedal, even in neutral.
If only first gear grinds or gives you problems engaging, when stopped, the problem will be a synchronizer.
A low oil issue could cause a problem shifting, so check the level in the trans, to be sure.
I have run synthetic trans fluid without problems, but you never know. I would think, however, that if it could be too slippery for the synchros, that you would have a shifting problem with all forward gears.
Rich
A bad throwout bearing should make noise whenever you push on the pedal, even in neutral.
If only first gear grinds or gives you problems engaging, when stopped, the problem will be a synchronizer.
A low oil issue could cause a problem shifting, so check the level in the trans, to be sure.
I have run synthetic trans fluid without problems, but you never know. I would think, however, that if it could be too slippery for the synchros, that you would have a shifting problem with all forward gears.
Rich
Le Mans Master
Joined: Sep 2008
Posts: 5,662
Likes: 2,344
From: Lake Minnetonka, Mn
2018 C1 of Year Finalist
If heat appears to be the overriding issue, I would check and or change the fluid. The syn oil can be a problem, as someone already suggested, because of its ability to be too slippery and the synchro cannot perform its duty as a cone clutch in slowing the gear down.
If your throwout bearing was a problem, it should be a problem in all gears.
If your throwout bearing was a problem, it should be a problem in all gears.
