Muncie M20 doesn't shift well when hot
 

Haven't had to post here in a long time but this one has me stumped and I'm hoping some of the gurus here have some ideas. 3 different shops around me have not been able to diagnose it. What's so odd about the situation is that it only occurs after a period of driving when everything is hot.

I've been having minor difficulties with my M20 for a while now however recently the issue started to affect me driving the car at all. At first, I was having difficulty shifting into 4th without grinding a gear and eventually some difficulties downshifting into second (I immediately thought synchros), as the car got hotter the problem went from not being able to shift quickly to having to very slowly change gears while holding the clutch to the floor. Now I'm at a point where by the time I get the car home I'm unable to shift into any gear without grinding 'em, I then have to shut the engine off and engage reverse to release the key.

But the next day, for the first 30-45 minutes, everything works. Smooth shifting for the first 20 minutes, (including 2nd and 4th) a little harder for the next 20-30 minutes, which is how I know its time to get home.

Its been acting like the clutch is out of adjustment and not fully disengaging, to that end I've tried adjusting the clutch in different ways and that does seem to change the issue but never fixes it. Last year I decided to have the clutch replaced (new Centerforce) and at first it seemed like that was the fix but the issue returned in short order. Bottom line, same problem, before and after the new clutch.

The car is a '69 350/350, mostly stock.

Plenty of room to adjust nut on clutch rod.
Had the same problem with the previous clutch that wasn't a Centerforce.
Transmission was rebuilt 10,000 miles ago so not expecting any serious wear.

:confused:

I think you have 2 separate problems. I have had both issues.

Do you have to push your clutch pedal all the way to the floor to disengage the clutch and shift gears? Is your clutch rod nut all the way at the end so there is no more room to adjust the clutch? This is a very common problem when installing a Centerforce clutch. There are several threads in the archives dealing with this issue. You probably need a longer clutch fork pivot ball to get the correct geometry for the Centerforce clutch. Alternatively, you can do what me and Bubba do and install a longer clutch rod.

Now the other problem. I have had problems mostly shifting into 1st gear and it seems to happen after the car heats up. So, like you, I start out and no problem, but then maybe later when I stop at a red light and I am sitting there in neutral and the light turns green and I can't get the shifter to move into 1st gear!!! This can be very embarrassing! But now that I think of it I haven't had that problem in a while, so maybe it cures itself. No, I think that part of your problem could be lots of different things. Might need to rebuild the trans but I will be honest and tell you I don't really have a clue.

Your transmission may be worn to some extent but, it will most certainly be shot if you keep driving it under those conditions! Having said that, I would suspect that the clutch is the problem since you notice the problem more when the car is hot. You should be able to diagnose that if you understand how the clutch interacts with the transmission. You can shift a transmission without a clutch by matching engine speed to car speed. I do not recommend that but, it will tell you if the clutch is the issue. I don't know how to explain this any better. If you can find an old guy that knows transmissions, that would be your best bet.

I'm new to the Muncie / BW Super T10 world after just having installed a BW Super T10 in my C3, but I can tell you that the gear oil I used made a big difference in the shifting of my trans.

I started out using synthetic Redline MTL which worked ok at first, but after about 20 minutes started to get hard to shift and heated the shift handle up. I parked it right away and changed the gear oil to Brad Penn Classic GL-4 and what a difference. It's quiet, smooth shifting and very cool. Others have had great luck with the Redline MTL, but not me. I guess my trans likes the thick viscous type gear oil, not the thin synthetics.

So could it be your gear oil fill? It wouldn't hurt to try some other gear lube as the least expensive option.

Gear lube is something I hadn't considered as a cause, it's a good thought and worth exploring.

I should also add that for the first five years after the rebuild I had no problems at all.

I have a similar problem. After car warms up I need to shift very slowly or double-clutch into second. I assumed it is a synchro. Will be watching this thread for insights. tks

sta-lube gl4 85w-90

If you can't get it in 1st after it's hot, you most likely have a clutch problem if the car rolls with the clutch in.
Trying different oil is cheap and sometimes helps also a very common problem is the clutch fork bending. It doesn't take much to mess up the throw.

I had grinding in my 66 M21 after I bought it. Drained and put in Redline MTL. All issues disappeared immediately! Great product! Recommend you try this before any other fix. Cheap and quick to do.
Good luck
C2Bill

The least expensive test would be to warm the car until the symptoms are dominant. Then find a level place and shut the car off. Put the car in low gear, depress the clutch and start the car. If the car begins to move with the clutch depressed; The clutch is dragging. Then all you need to do is find out why.