I think I remember the owners manuals having recommended speed ranges for the various gears or am I mistaken ?
Short version wink
I have a customer with a 67 belevedere,
It has a stock smogger era 440, a 4 speed and 3.23 rear end gears with excessive backlash.
the car developed a noise ( which I first noted and made him aware of spank spank)
It is a knocking noise that appears to be coming from the transmission area.
The D/shaft has been checked, new u joints etc. It sounded like a cluster gear oscillating back and forth in the case. I pulled the trans and SURPRISE the front thrust washer cluster just flat wasn't there. Back together and all seemed well.

He called a few days later and said the noise was still there. I rode around with him for an hour and he could not reproduce the noise except for one time when he was down to10-15 MPH in 3rd gear. I told him to put it in first and the noise stopped.

I believe the remaining noise is the excess play in the R/E slopping back and forth due to his gear choice EDIT: and resonating up the D/shaft. I forgot to mention this noise appears only in a "NO LOAD" condition, IE: no accel or deccel but in between and at low RPM /Speeds using 2nd or 3rd gear

He seems to think it is OK to putz around at 15-20 MPH in 2nd or 3rd gear. Doing the RPM calculations at those speeds he is barely above idle speed, but I cannot convince him he should be using 1st gear at those speeds.
Any help is greatly appreciated

FYI: at 15mph with 3:23 RE gears
Transmission
Gear / ratio------ RPM w 25”Tire --------RPM w 26"

1st = 2.66:1---------- 1732 -------------------1665
2nd = 1.91:1--------- 1243 -------------------1195
3rd = 1.39:1------------905 ------------------- 870
4th = 1.0:1 ------------ 651 --------------------625

Grabbing at straws here: One other thing I have not verified is the "Phasing" of the U-Joints. The shaft was new a few years back and was done by a shop we normally use. If the phasing was slightly off I do not know if that could cause this issue ? No vibrations at higher speeds
TIA beer


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Last edited by TJP; 07/31/21 01:34 PM.
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