"Clunk" after gear change and gas

It could be a lot of things including the thrust bearing in the engine is gone and the crank is moving around.

If that is what is happening, in a Pantera this is even a worse case scenario because of the very close clearances within the bellhouse to the clutch assembly.

If the clunk is happening in relation to engaging and releasing the clutch, bet on it and if you let it go any further, you could be looking at a minimal $7,000 to rebuild the ZF, plus a clutch, plus a bell house (if you can find one) plus the labor for all of this.

You may luck out and it might just be the U joints on the axle shafts but you need to put the car on a lift, run it in gear, and watch what is happening.

If they are really bad, you might be able to feel them loose by hand without running the car.

The original u joints were notorious for early failure. As early as 30 or 40 thousand miles.

I wish you the best of luck on this one.

Don't think it's anything catastrophic as all the bell housing components have been replaced, as well as the engine rebuilt. Now the question of if it's all been put together right. (sigh)

U-joints are easy to periodically check. Look down on each u-joint end-cap; is there a shiny circle (also known as the 'ring of death') around the visible edge of a cap? This comes from the cap beginning to rotate in the yoke due to incipient seizure of the tiny needle bearings inside. This is more difficult to see on the outboard u-joints but it can be done with jackstands and a light; outboard joints fail, too.

Got pretty logo-covers glued over the u-joint yokes so you can't see the cap-ends? Another way to check is to reach in with a finger, and run it around the inner part of the u-joint cross where it touches the yoke. If your finger comes out red mixed with grease, that's rust from rapidly rusting high carbon steel from failed needle bearings. Check ALL 4 legs of ALL 4 u-joints.

Rotating caps will thrash out the required press fit in the yokes, trashing the entire halfshaft in a short time. There are no replacement halfshaft parts and cannibalization does not often work. If ignored, a failing u-joint will eventually break, freeing one end of the halfshaft to flail around like a 10-lb war-club and smash things- like your ZF cases. Fixing this takes removal from the car followed by complete tear-down followed by TIG-welding and remachining. I've redone several such ZF cases. New u-joints are 50X cheaper.

Another thing that makes noise a sensitive driver might notice: the lower a-arm studs run in bronze bushings (2 in each upright) that may not have been greased since DeTomaso assembled your car. They wear egg-shaped and engaging the clutch makes the end(s) of the stud(s) visibly move and make a little noise. The motion or sound is not much but as I said, some drivers are VERY attuned to changes in their machine (which is good!)

Finally, ring and pinion differential gears, and transmission gears do wear out after many miles of hard use.... One easy driving So-Cal owner I know has WORN OUT two ZFs (but then, he has over 250,000 miles on his beloved Pantera.)

To add to above, I'd ensure that all halfshaft bolts are tight. (Assume you've checked already but happened to me once). Good luck, curious what you eventually find.

Ok, after reading this I had to check the u-joints... Is this the infamous "ring of death"?

Yikes! Change 'em...quick!

Alright, sure will! About time anyway to clean up that whole area.

Definitely change them before driving the car again.

i have a new set on ebay if interested, mike.....

I think I have identified the problem as the shifter shaft going into the side box. There is play between it and the bronze bushing. I think when getting on the gas after a shift, the rod is clunking against the bushing. I'd guess it to be about .006. I tried to shim it with some brass sheet, but it obviously slides back and forth with the rod until it comes out.

Has anybody replaced this bushing? It looks unfriendly to do. It doesn't seem to be dangerous to leave it alone, but it's annoying.

Nobody has replaced this bushing??

I have replaced lots of them. They are available from RBT and they are a PITA to remove!!

Ron

I found that if you take a tap, don't remember the size at the moment and thread it in and let it bottom on the crank, keep threading it in until the bushing is out.

So the box has to come off. Just remove that large nut holding the linkage together?

Take out the two small rubber plugs on the bottom of the shift box to allow you to have access to the two 5mm grub screws holding the shift rod to the linkage. Next,slide the rod out. With the trans in Neutral,gently pry the linkage towards you to allow the first piece of linkage to come free. Remove the 19mm nut, linkage and keyway from cross shaft. remove three 13mm bolts and one 6mm Allen bolt securing the shift box to the trans. Remove shift box paying attention to the shims between the box and the front section of the case.( where the 6mm Allen bolt went through.)
Easy enough?


Ron

Okay thank you.