When your A/v8 goes CLUNK?

First some back ground:

I have a model A coupe on a 32 frame with a 41 ford rear end, torque tube, 39 ford trans, 8ba motor.

I built this thing a couple years ago, and have had mostly
trouble free driving for the last 18,000 miles. It has been great.

However, the current problem:

After coming to a complete stop,
when I let out the clutch in first gear I hear a fairly loud
Clunk, just as the car starts to move.

I cannot get it to do it everytime.
and I have put up on jack stands and tried to repeat it
but I can't get it to make the sound.

I am suspecting the rear end, maybe to much lash?
could the rear wear it self out, or pinion coming loose?

But the sound doesn't sound like it is that far away.
It seems like around the driveline where it attaches to the
u-joint tranny area.

A couple of questions, how much lash should a banjo have
and I mean how far should the tire move back and forth, as
a very crude measurement?
When I compare it to my other cars it doesn't seem to be that different, but the other cars are all 50 years old.

If it was the rear end, why would it only be at stop and first, because it doesn't happen in reverse.

Mostly I am looking for advice as to where to look, have you ever dealt with this?

Could it be tranny, or driveline? I can't figure out how it could be but, maybe.

thanks for any help.

 

I've seen some REALLY worn out universal joints...check that?
maybe check to make sure the axle nuts are super tight? how about all suspension points? anything that might be worn or sticking?

good luck
Zach

 

Try turning the engine by wrench on the crank nut; then you can listen at different places inside car by trans, under car, wheels on and off ground. U joint would be a logical suspect--and a really obnoxious job to change.
Crank nut turner tech for tight engine compsrtment: Get appropriate short 1/2" drive socket (7/8 on 8BA?), little Sears adapter that allows you to turn socket with 3/4" flat wrench, and sears ratchet box wrench.

 

I usually go with the "Trial by Fire" method- do a big, roasty burnout and see what falls off....If nothing, keep driving. But buckle up. You don't want to be stupid, ya know.

 

Dave, the backlash is checked at the pinion, useing a dial indicator. I set all ring & pinions at .005 to .008., and i try to get .005 on new gear sets. The turning torque on the pinion wth new bearings is 25 inch pounds, to get the corect bearing pre-load.

If the pinion nuts came loose, you would have major gear whine, and get loader the faster the car went.

From what your saying, i would be looking from the u-joint to the coupler at the pinion. Also how was this driveshaft shortened? is it a 37-48 solid shaft, or 33-34 tube. If the shaft was just cut, and the coupler welded, it could be broke there.