67 L36 4th gear grind when hot

[Lawrence S.]

I have searched the posts and have seen a few similar issues to mine but nothing conclusive that I could find. Thought I would throw this out there and see if anyone has any ideas.

When I drive the car more than say ten miles and casually shift into 4th I get a fine grind. I can feel it in the shifter but it is not loud in the tranny.

A few facts: The clutch releases very close to the floorboard I have tried to adjust the clutch so it does not release so close to the floor, but no luck. The clutch and pressure plate are LUK products. Nothing fancy just as close to OEM as I could find. As I recall the flywheel was original and I had it turned. I have read that this could be the problem? By turning the flywheel the geometry is changed too far out of spec? Should had just installed a new flywheel?
The car has 71K miles on it and the tranny has not been rebuilt to my knowledge. The tranny shifts great in all gears otherwise. It just seems when it gets hot things are not working quite as well.

Thanks guys!

Lawrence

[Stephen L.]

Re: 67 L36 4th gear grind when hot

Do you have excessive pedal travel at the top before the clutch begins to disengage? Are you out of adjustment on the clutch rod? After driving/heat up of the clutch components things expand enough to result in a slightly engaged clutch possibly causing your problem. Did tthis problem exist before you replaced the clutch? Did you install the throwout bearing correctly (with the "tangs" in the groove) or is the bearing clipped on the clutch arm?

[Lawrence S.]

Re: 67 L36 4th gear grind when hot

Stephen,

Yes there is excessive travel at the top of the pedal prior to engagement. IIRC yes issue was same prior to clutch replacement.
Thanks for the pics! This may be the issue. Will check it out.

[Lawrence S.]

Re: 67 L36 4th gear grind when hot

One more point, I am out of adjustment on the clutch rod.

[Leif A.]

Re: 67 L36 4th gear grind when hot

With excessive play at the top of the pedal and being out of clutch rod adjustment...have you checked to be sure you have the little rubber bumper installed on the clutch pedal assembly?? Without that in place the clutch pedal will return to a much higher level than normal and not allow you to adjust the clutch rod effectively. That small little piece can make a BIG difference.

[David M.]

Re: 67 L36 4th gear grind when hot

Check the bell crank and fork ball pockets for excessive wear. Gota keep this assembly well lubed to prevent wear.

[Lawrence S.]

Re: 67 L36 4th gear grind when hot

The rubber bumper is there.

Will check the bell crank and fork ball pockets for excessive wear

[David M.]

Re: 67 L36 4th gear grind when hot

Should check the shift gate alignment as well. The rods may need a little adjusting.
Get the clutch right first, Then adjust the rods,

[Owen L.]

Re: 67 L36 4th gear grind when hot

Just making a wild comment for those more knowledgeable: Could this have anything to do with a worn synchro ring in the trans?

[Bill B.]

Re: 67 L36 4th gear grind when hot

Owen,

My first thought on this as well, as the OP indicated specifically mentioning a 4th gear grind. If a pilot bearing/throw-out bearing/clutch/adj issue, I would have suspected the other three gears to be somewhat grinding as well. Also would have expected severe grinding when going into reverse from neutral if it was any other issue, as I believe reverse gear has no synchro.

[Chuck G.]

Re: 67 L36 4th gear grind when hot

Just making a wild comment for those more knowledgeable: Could this have anything to do with a worn synchro ring in the trans?

I had a similar problem with the 1967 Muncie wide ratio trans in my 56 Chevy hot rod. Whether I shifted "hard and fast" or "slow and easy", it would grind going into 4 th gear.

I pulled the trans and had it rebuilt. New synchros and new sliders... No more grinding.

[David M.]

Re: 67 L36 4th gear grind when hot

I had a similar problem with the 1967 Muncie wide ratio trans in my 56 Chevy hot rod. Whether I shifted "hard and fast" or "slow and easy", it would grind going into 4 th gear.

I pulled the trans and had it rebuilt. New synchros and new sliders... No more grinding.

Id agree after the simple trouble shooting steps are resolved before moving to the more complex.

[Mike T.]

Re: 67 L36 4th gear grind when hot

Lawrence - Could you fill in some of the blanks for us, it would help to know a few more details. You did mention the car has 71K miles on it and I got the impression that the clutch is relatively new, yes? If so, about how many miles on it and besides the clutch disengaging close to the floor which seems to have been an issue for a long time, about how long has this 4th gear grind been noticeable? Back to the clutch replacement, did you do this or have someone do it? Just trying to see the big picture.

[Lawrence S.]

Re: 67 L36 4th gear grind when hot

The clutch has approx 5K miles on it. Yes has always had this issue since the new clutch. I did the replacement with help. Keep in mind it will not grind until after the car has been driven say 25-40 miles and as of lately starts grinding in the 25 mile range.
i am going to check the clutch fork/TO bearing attachment next.
Thanks for all the replies guys.

Lawrence

[Stephen L.]

Re: 67 L36 4th gear grind when hot

Lawrence, any update on your clutch issue/gear grinding?