I started an engine build project a few months back. I am at the reassembly part, and thought that while the motor is out, it might be wise to clean up and safety wire my ZF.

So I got parts from RBT (gaskets, seals, bolts, advice) and my buddy helped me tear into it.

Here's what I found.

I tried to convince my wife that by building my new motor, I actually saved us about $10K. Unfortunately, she was not buying it.

I am very glad to report that there is no damage inside - but I am guessing that on the first hard acceleration with my new motor, I would have been singing the blues.....

Rocky

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Three heads were on the bottom, and 4 came off as we were disassembling the differential carrier.

No - I haven't put anything on it (yet). Not sure, but I think I am just going to go with the cast finish.

Case finishing suggestions appreciated.

Regards -

Rocky
JFB, stock ring gear bolts have been breaking since the Pantera was still in production. We THINK its because the stock ZF bolts are ISO gr-10.8 (about gr-8 SAE) and are too hard and brittle for the job. U.S gr-5 bolts are much tougher and more ductile, which is what's needed with impact stresses like the ring gear experiences.

In addition, the stock bolts are serrated under the heads to 'dig in' and act as locks, but the surface of the ring gear is too hard for that to happen, so the serrations only act as surface-area reductions that contribute to loosening. SAE bolts are not serrated and most have drilled heads for aircraft safety wire as a further deterrent to loosening.

Since 911 Porsches use the same ZF-design differential, their second- generation ring gear bolts are not serrated under the heads and are often drilled for safety wire. You can take one of your stock ZF bolts to a race shop in Germany and ask them what they think. They will likely have spares to fit.
quote:
How did you get your case looking so spick and span? It looks fantastic!

Yes, do tell, how'd you get your ZF case looking so brand new? I tried aluminum cleaner, oven cleaner, scrubbing, and even bead blasting, but nothing got it looking like new, so I finally painted it with Eastwood Alumablast paint.

So, what's your secret?
Based on the input from the GT-40 forum, I had the ZF media blasted at a local shop. After that, I masked and painted the two sidecovers, and the tail cone.

GT-40 Forum - Cleaning ZFs

I sealed all of the holes up with "Gorilla Tape". I made a big cardboard cover for the front and taped that all up as well.

Tranny was bead blasted with 80-120 grit, ~75 psi. Shop was instructed to not blast from the front.

One of the reasons to get into the case (above and beyond the safety wiring) was to ensure that none of the "beads" had gotten into the seals.


Rocky
quote:
In addition, the stock bolts are serrated under the heads to 'dig in' and act as locks, but the surface of the ring gear is too hard for that to happen, so the serrations only act as surface-area reductions that contribute to loosening.


Once loose, the bolts begin to back out. Once out far enough they will impact some internal ZF surface and be snapped off. Maybe they then drop harmlessly into the pan, or they drop into the gears and ....

I know of one new owner who upon his first ZF fluid change heard a "PLOP" hit the drain pan. It was one bolt head. Fishing with a stiff wire, he started probing the ZF and soon had all ten bolt heads and 3-5 sections of bolt threads.

The ZF had been shifting fine and made no noises.

I know of one well-known vendor who dismisses the need to safety-wire the ZF. He told me this in a face-to-face conversation, not some second hand rumor.

Don't believe it.
quote:
thanks for the education...that sure looks like something I would like to see first hand.

does the bolt body have a solid section that would act like a fitted dowels when threaded into the dif hsg cpl?


Stock bolts only have a very short unthreaded section at the top. The first time I SAW this happen was at a 'Vegas Fun Rally in the '80s. A couple had just driven in from Los Angeles, when he was told to move his Pantera from in front of the host Hotel. He started it and popped it into reverse. A bolt-head caught in the R/P gear-mesh and got spit out at high velocity. It cracked the cast aluminum ZF bottom cover in pieces, dumping the whole load of lube for all to see. Not a proud moment...

Steve Wilkinson had towed a restored show car for display that year, and just happened to have a spare ZF lower cover in his truck's tool box. It wasn't cheap and the swap in the hotel parking lot was messy, but they had help and drove their Pantera home that year, instead of 'enjoying' a 300 mile tow-truck ride.

Safety Wire Is Your Friend!

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