M-20 Transmission noise

[David D.]

I took my '64 327/300 4-speed out for a ride yesterday. I've had this car for 28 years, and this is the first time I experienced a grinding noise when shifting into 4th gear (normal driving). I was able to avoid the noise if I shifted from 2nd to 4th, but when shifting from 3rd to 4th, it would occassionally grind. I also noticed a slight roughness/vibration when letting the clutch out after downshifting from 4th to 3rd.

I checked the shift linkage adjustment and the clutch adjustment free-play, and all is OK. It sounds like the transmission needs to come out for some work, correct? I put a new clutch in about 20 years ago, so I remember how much "fun" that job was.

[William C.]

Re: M-20 Transmission noise

First I'd check for any clutch drag, on a seldom driven car, corrosion on the flyeheel facr can create a slight dragn and if the trans is a wide ration, the 3-4 shift requires the mosteffort fron the synchro's. I'd raise the rpm and slip the clutch a couple of times and see if it doesn't stringhten out on it's own.

[Tom S.]

Re: M-20 Transmission noise

I agree with Bill try slipping the clutch a couple times and see if it doesn't clear up. I would almost bet that it will.Tom

[Edward J.]

Re: M-20 Transmission noise

David, I would try maybe a fluid change if the fluids been in there for all the years, maybe a syth. gear oil change.The 80w90 fluid tends to get like molasses after alot of years. maybe even drop the fluid to a 75w90. its alittle thinner when cold.

[David D.]

Re: M-20 Transmission noise

I took the car out again and performed the clutch slipping a few times. I still get the occassional grinding going from 3rd to 4th. It doesn't happen with the first few shifts (cold fluid), but as the trans warms up, it happens every so often.
The other thing that is repeatable every time is when downshifting from 4th to 3rd, just before the clutch is fully engaged, I feel a roughness in the driveline that was never there before. I can repeat this by disengaging and then engaging the clutch numerous times while coasting (around 40 MPH or so). This leads me to believe I have something going on in the 3rd and 4th gear area of the trans.

[Gary R.]

Re: M-20 Transmission noise

Does it pop out of gear if you load up the engine and let off?

[David D.]

Re: M-20 Transmission noise

Gary - no, it stays in 4th gear properly under all conditions.

[John D.]

Re: M-20 Transmission noise

Gary - no, it stays in 4th gear properly under all conditions.

Hello dave

I had a similar problem on a Chevelle years ago that went away when I replaced the 3-4 synchro assembly.
Maybe you should write a PRTS on it (kidding)....You (Moraine) and I (Linden) worked together years ago....

best regards

john

[Michael G.]

Re: M-20 Transmission noise

David,

You don't say or maybe don't know how many miles that are on the transmission. Parts wear out, could be that simple. Possibly a worn out slider or syncro or could be both. Engagement teeth on the aforementioned components do wear which can or could lead to the conditions you've described.

[David D.]

Re: M-20 Transmission noise

Thank you to all that have replied. Hi John - hope you are doing well.

I will work on taking the trans out of the car to take a look inside.

Dave