What is the best ZF transmission oil to use in a 1974 Pantera?

Here is a list of the currently available gear oils that match RBT's recommendation. This isn't an exhaustive list. I'm sure there are others but these are the ones I know of. There may also be GL-5 gear oils that are OK (eg. Redline 75W-90NS) but because Lloyd Butfoy says to use GL-4 gear oils, that's what I've listed here. Gear oils that say GL-4+ or GL-4/GL-5 are just GL-5 oils. Lloyd also recommends changing your gear oil annually, regardless of mileage driven, due to condensation forming inside the case. In fact, the less you drive your Pantera the more important this is.   

Conventional (mineral based):

PennGrade Classic GL-4, 80W-90

Driven Racing Oils, GL-4, 80W-90

Richmond Gear, GL-4, 80W-90

VP Racing Classic, GL-4, 80W-90

Synthetic:

Redline MT-90, GL-4, 75W-90

Pennzoil Platinum, GL-4, 75W-90

Amsoil, GL-4, 75W-90, Manual Transmission and Transaxle Gear Lube

Motorcraft (Ford) XT-M5-QS, GL-4, 75W-90, Full Synthetic Manual Transmission Fluid

Note: a ZF Transaxle is more likely to develop leaks when using synthetic gear oil. If you're using synthetic oil and you do develop a leak, it doesn't necessarily mean that you have a bad seal or gasket. Synthetic oil is just better at finding a way out than mineral based gear lube! Lloyd Butfoy tells me that even brand new, freshly sealed, ZFs sometimes leak when filled with synthetic oil.

Castrol Axle Limited Slip 80W-90 API GL-5 (Former 80W-90 Hypoy C)

Dump that Redline shockproof, I used it in my formula Atlantic Hewland gearbox when I first got it and was destroying gears every outing, since I switched to Lucas oil I have had virtually no issues.

I know beat a dead horse, but I thought I would add these attachments with sources noted in red. Funny the actual Pantera Owners Manual lists GL-5 for the trans, then there is the Pantera Technical Service Bulletins and the Pantera Technical Information. When EP (Extreme Pressure) is mentioned I read elsewhere that GL-5 is a higher EP than GL-4 but maybe both are applicable when the manual states "EP".

Keep in mind, our gearbox manufacturer’s recommendation is to use 80W-90 GL-4 mineral based oil. Roy Butfoy always kept a drum of Castrol 80W-90 GL-4 in his shop. They have updated their recommendations to allow 75W-90 GL-4 synthetic. Unfortunately, GL-4 gear oils are becoming increasingly more difficult to find. If you decide to use a GL-5 gear oil, mineral based or synthetic, just make sure it specifically states it’s designed to be used in manual transmissions and transaxles. GL-5 gear oils that are designed specifically to be used in differentials are likely too slippery to allow the ZF’s synchros to work properly.

Steve:  Any user feedback on the VP GL-4 gear oil that you started using?

thanks, Lee

Hi Lee,

VP GL-4 Classic is working well.  At one point Lloyd at RBT wrote that GL-4 works best with out synchronizer rings.  I'm not sure if I can feel better shifting but this gear oil seems to be working correctly.  As others have mentioned, it is important to change the transaxle oil annually.

Thanks, Steve

Thanks Steve.  Yes, I do an annual change and was thinking of moving to the VP and hence my asking.  Lee

Is the annual change based on what is considered a normal amount of driving? I don't put many miles on my car per year. What is it about the oil that drives the annual replacement?

One of the characteristics of the ZF is, condensation tends to form inside the case. The less you drive your Pantera, the greater a problem this becomes. Water, air and steel bearings, gears, etc. don't coexist well together. This is the reason to change gear oil annually. This is also the reason that your brand new, spare ZF, that's been sitting in a crate, untouched for 40 years, is probably junk by now.

In your red Owners Manual, DeTomaso and ZF say to drain & replace the lube at 3000 mile intervals. Many Panteras have gone their whole 50+ existence on the same factory lube! And almost none have ever had the second shift detent re-greased!  But removing it works best.

Marlin mentioned it but  the Pantera gear-change system actually has TWO separate shift detents. One is buried inside the ZF and the other is part of the shift-stick assembly in the cabin. Having two detents often causes shift problems. Total removal of the cabin detent frees up shifting on any Pantera, and for a change, the job is easy. D. Quella used to do it free on all the cars he worked on.

Take off the chromed gate and the trim piece (4 metric screws). This exposes the top of the shift mechanism. The shift stick is in a die-cast aluminum housing. Behind the shift stick is a 1" OD snap-ring covering a hole in the housing. Remove the snap ring; inside is a spring on top of a vertical sliding piston. Tease the upside down piston out with a strong magnet, a finger or other tool. It will be caked with ancient dried grease. On the bottom of the piston is a small protruding tip: that is the detent which engages the shift rod going back to the ZF. Bag the piston & spring and put on a shelf somewhere for the next owner.

Close up the hole left when the piston was removed (I used a wine-bottle cork-Chianti, of course!) You're done- replace the trim and shift gate and try your new smooth shifting Pantera- all done while sitting comfortably in the drivers seat and without draining & replacing the brand of ZF lube. But the old lube in your ZF still needs replacing at least yearly!

Note- the above fix and the tach repair in another post today on this Site, were both subjects of our Pantera in illustrated print articles to be found in long-past POCA Newsletters. There are now over 600 such tech articles archived.