Grinding downshifting from 4th to 3rd & reverse - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 07-01-2019, 07:40 AM Thread Starter
 
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Grinding downshifting from 4th to 3rd & reverse

I just installed a new McLeod 11" disc and flywheel along with a rebuilt transmission. The car seems to shift fine, except downshifting from 4th to 3rd and occasionally going into reverse - grinding in both cases. Any guidance on whether this is clutch, throw out bearing, or bad syncros?? I did not install the transmission and am not sure what throw out bearing was used. Thanks in advance

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #2 of 3 (permalink) Old 07-01-2019, 05:23 PM
 
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always go into first b 4 going into reverse

what lube is in it ?

who adjusted the linkage .?? original shifter and linkage >?

4th to 3rd is strange . if you come to a stop or really slow down is it easier to go inti 3rd>>??

is the clutch adkusted correctly for clutch ingage/release height??
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post #3 of 3 (permalink) Old 07-01-2019, 06:17 PM
 
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Originally Posted by cij911 View Post
I just installed a new McLeod 11" disc and flywheel along with a rebuilt transmission. The car seems to shift fine, except downshifting from 4th to 3rd and occasionally going into reverse - grinding in both cases. Any guidance on whether this is clutch, throw out bearing, or bad syncros?? I did not install the transmission and am not sure what throw out bearing was used. Thanks in advance
Assuming you know all your linkage is factory and correct........

Most likely you are not getting a "clean" release of the clutch disc - this would be my first thing to check. Requires an adjustment. Your pressure plate/disc combo should have included directions which will tell you how much "air gap" is needed between the disc and flywheel. Takes 2 people to check - one to push the pedal to the floor, the other to insert a feeler gauge via the inspection cover on the bottom of the bellhousing. I have never gone to this extreme, I just adjust the rod a little more and test drive. If it improves, but not 100%, adjust a little more.

I first used the McLeod set-up on my last 400CI build. They included the wrong throw out bearing length. Mine would not allow the clutch to release enough so putting into 1st gear was a clash and the pedal was way down at the floor. Installed the longer bearing and it worked.

I had another issue at the same time. I installed a generic aftermarket one-size-fits-all clutch fork. Bad choice over the correct factory fork. Wrong angle/length and the fingers that held the throw out bearing were wrong & too long. Had to install a longer clutch fork pivot into the bell housing. This also helped........until the day the clutch fork fingers overshot the throw out bearing at high RPM breaking off the collar and sending it into my pressure plate/clutch and took it out. Purchases a correct Pontiac fork and all was good with the next clutch set-up, except............

I purchased new flywheel-to-crank bolts. Did not pay attention to what I ordered nor thought much about it. Thought there was only 1 size of bolts. The ones I purchased were for an automatic which has a thicker head. The stick trans flywheel requires a thinner head so it does not stick up so high. End result - bolt heads were too tall and hitting the clutch disc springs. It always had a "strange" sound that I was not familiar with whenever I let out the clutch. I attributed it to the carbon fiber disc material vs the "typical" friction clutch material I was used to using. Wrong bolts.

Did you align the shift linkages at the shifter using an alignment pin? If the alignment was not done, your shift linkages at the shift forks on the side of the trans may be off and not in the exact "neutral" position they need to be to shift smoothly. Your shop manual should show you this and how to line it all up using a pin.

Make sure you have the correct transmission fill and fluid. Newer trans use the thinner ATF stuff and the older trans will use a gear oil. Why I mention this is on the old truck I am working on I drained the trans fluid. It was much thinner than gear oil and gave the gear oil that came out a red tint. So I figure someone who was not familiar with these older vehicles simply added some ATF to top it off thinking that all manual transmissions got the ATF. I refilled it with the correct gear oil and the trans sounds quieter and is required for these older type transmissions which were designed for the heavier gear oil.

I would check these things first before looking at the trans as a problem.
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