C-4 ZF-6 Oil

[Mike B.]

I'm preparing to replace the oil in my C-4 manual transmission. Reports are that the original GM oil, part number 1052931 is hard to come by. Some have recommended Castrol Synthetic Formula TWS 10W60 (also available from BMW with part number 0751009420).

Can someone chime in with expert advice?

Thank you.

[Duke W.]

Re: C-4 ZF-6 Oil

Does the owner's manual list anything other than the GM part number - like a specification for an industry standard ATF or gear oil?

Duke

[Mike B.]

Re: C-4 ZF-6 Oil

Duke,

I'll check the manual but from other sources I believe that the factory fill is 5W-30.

Since I wrote this post, I found out some related information. You might find it interesting if not informative. I was surprised to find the recommended change interval to be around 10-12,000 miles.

Mike

TRANSMISSION OIL (status) - Vascular flow of oil through the porous Phosphorus-bronze (Pb) material of each synchronizer is essential for effective British Thermal Unit (BTU) heat exchange occurrence. Frequent transmission oil changes (15K-30K miles) will ensure lower Pb particle levels suspended in the oil. The ZF S6-40 6-speed transmission is lubricated by engine type oil. Manufacturer recommendations specify the use of GM P/N 1052931 (5w-30) or BMW P/N 07510009420 (10w-60) oil.
Approximate oil capacity of the ZF S6-40 is 2.2 quarts.
FYI - the BMW 10w-60 oil is fully-synthetic and is used in the BMW M5 engine.

(Q.) I just bought, at the local BMW dealership, 3 liters of the Castrol TWS 10W60 oil. I was surprised to see that it is motor oil. Not being a lubrication engineer myself, who did the investigation and determination that this product is compatible with and good for our ZF transmissions? Jim – Grand Sport Registry

(A.) Jim, the C4 Corvette ZF S6-40 6-speed transmission uses engine oil for lubrication. I was told by Jeff Henning, Warranty Administrator of ZF Industries North America, that Engineering of ZF Industries in Germany determined that the BMW imported Castrol (RS superceded by TWS) 10W-60 oil was the recommended alternative to the (GM P/N 1052931) factory-fill oil for use in the ZF S6-40 transmission. In effort to verify ZF Industries alternative lubricant recommendation, we ran our own test series on the BMW imported Castrol TWS 10W-60 oil. Independent testing of the transmission oil samples was sub-contracted out to CTC Analytical Services. The test series went as follows:
Spectrographic analysis indicated that it is has full synthetic composition.
After 2 hours of operation, approximately 100 miles, oil sample analysis tests indicated that the viscosity rating was reduced from 60 down to a 43 level. No need to worry, this is a normal occurrence for this heavier type of oil. I attribute this to microscopic-level lubricant-strand t******* through operational loading where all of the oil contents has been passed through gear pressure-loading regions at least a few times.
At 200 miles, the viscosity level stabilized at a 42 level viscosity since the 100 mile oil analysis test results.
At 5000 miles, the oil analysis test results indicated a 40 level viscosity.
The test-transmission was completely disassembled and checked for wear. There were no signs of carbon film like experienced with the factory-fill oil. The phosphor-bronze lined synchronizers had no glazing and experienced an average mass loss of approximately 4% based on reserve-wear-range mass equivalency between 0.062"(new) and 0.048"(spent)
gap wear/mass measurements.
At 10,000 miles, the oil analysis test results indicated a 39 level viscosity.
At 12,500 miles, the oil analysis test results indicated a 37 level viscosity.
At 15,000 miles, the oil analysis test results indicated a 34 level viscosity.
The test-transmission was again completely disassembled and checked for wear. There were no signs of carbon film like experienced with the factory-fill 30 oil. The phosphor-bronze lined synchronizers had no glazing and experienced an average mass loss of approximately 17% based on reserve-wear-range mass equivalency between 0.062"(new) and 0.048"(spent) gap wear/mass measurements.
At 15,000 miles the oil had enough phosphor-bronze particles suspended
in it that deposits began building up inside of the synchronizer sliding
sleeves from the normal centrifuge-like rotational occurrence.
In Conclusion, until someone invents a copper magnet, we recommend that the ZF S6-40 6-speed transmission oil be changed at 10,000 - 12,000 mile intervals so as to minimize the amount of deposits of the suspended spent synchronizer material from collecting in critical component contact surface areas.