Posted by Zachary Gooch on February 10, 1998 at 21:05:06:
The tranny in my '68 WM300 has a horrible 4th gear noise.
It has the stock New Process 4-speed. When lugging at
low speeds or partially letting off the throttle at
highway speeds, it makes a thrashing, grinding sound. The
tranny was opened up a few weeks ago, and 3rd and 4th synchros
out of an identical tranny were swapped in. Everything else
was in excellent shape internally. The clutch is brand new, and
everything else inclusing the front and rear ends and the
tranfer case have been properly gone through and fixed. All the
u-joints are fine and none of the driveshafts are loose. It
runs fine in every other gear. Any help diagnosing this
problem would be greatly appreciated!