Proper ZF gear lube


This may warrant being turned into a permanent sticky.

A friend of mine is having his gearbox overhauled by Lloyd Butfoy at RBT Transmissions right now (coincidentally, I brought it down to Lloyd's shop along with my wife's Pantera gearbox, being overhauled at the same time). Yesterday, he sent an update to the Pantera forum:



Last week I dropped by Lloyd Butfoy's shop in Anaheim, my first visit to his shop.

My ZF is with him getting a new .620 5th gear set, synchros, at least one $$ bearing and .... a new $$$$$$$$ 4:22 Ring and Pinion. Seems after about 80K miles on the box, a pinion gear tooth decided to start self destructing with a wear-related fatigue issue.

We spent at least an hour going over my ZF innards and I left with a much better understanding of the ZF, and an increased appreciation of Lloyd as a professional.

We also spent some time discussing ZF gear oil and I'd like to share what he told me.

He told me his website FAQ that called for GL4 and cautioned against using GL5 was in fact not written by him.

He confirmed our ZF is a spiral bevel style ring and pinion, not a hypoid style R&P.

He does NOT refill repaired transaxles upon their return to the owners. Just the lube used for assembly.

He feels Redline products are too slippery for proper ZF operation. NOTE: His opinion.

With the exception of some needle bearing cages, there are no yellow metals in our ZF. Lloyd has never seen any yellow metal damage in any ZF, something that in theory may occur with some of the additives found in GL5 products.

Other vendors have at times tooled and produced ZF parts. As Lloyd has all the original ZF design and tooling rights, he honestly believes such attempts by other vendors all fall short of what is truly needed in regards to quality.

The brass synchro rings offered by some vendors are sourced from a non-ZF application. While they appear to correctly match the genuine steel ZF synchos, in actual use they quickly fail. He cited a well-known individual who campaigns a track-dedicated Pantera who was destroying brass synchros in a matter of months. Of course racing provides increased wear and tear, but steel synchros never exhibit such accelerated wear. Lloyd feels the different heat-expansion properties of steel versus brass may account for the fast wear issue.

As for the $54,000 question - proper gear oil?

His words, more or less:

"If all the time everyone spends on discussing the proper gear oil was instead spent with an annual change of oil, 80w90 GL4 or GL5, then it really wouldn't matter what type or brand of oil was used."

Beyond those guidelines, Lloyd had no stated favorite oil. He said the controlled testing required to select the "best" oil is never going to happen, so he feels it is a personal choice. If it works for the owner's needs, that is good enough.

In summary:

Good ZF care = any quality GL4 or GL5 80W90 changed annually

So, is this the final word on what ZF gear oil to use?

Probably not.

But it is what Lloyd said, and that's good enough for me.



I find it interesting that Lloyd's website contains guidance that was cut and pasted from another source, and is in fact contrary to his own feelings on the matter? Since Lloyd and I have been friends for years, I won't be bashful about giving him a kick in the butt over this! :laugh:

Also FWIW, RBT's turn-around time for gearbox overhauls is in the 3-4 week range these days....

Cliff Beer

That seems like sound and practical advice to me. The important points being a) use a quality oil, and b) change it with regularity.

My uneducated impression is that the Redline products are pretty darn slippery....I know I've put in Redline and found the operating temperatures of the gearbox to have dropped significantly (tested with a very precise method called putting my hand on the side of the gearbox after a run). I have to imagine that's a positive change as heat is roughly equivalent to drag and wear. I've also noticed that the Redline products I have used improve shifting, particularly at cold...and I have to imagine that's a positive change as well.

How is it a super slippery gear oil could be a problem with brass components?


Lifetime Supporter
I have been using the Royal Purple 75/90 with a flush and fill each year. Shifting is good and if you ever have a drip it can be easier to distinguish between it and motor oil.
I could not agree more with the comments made here save to say this. Synthetics and synchronizers are not usually a good mix. Synthetic oils tend to be more slippery and do not give the needed friction for proper synchro action.

There really is no need for expensive synthetic oils in synchronizer gearboxes.

Just my .02 on this.

can someone confirm the quantity of fill in the "correct' GT40 orientation?
2.75 quarts recommended for dry transaxle. 2.5 quarts for oil changes as some oil remains in box. I overlooked this little detail last oil change on my SPF GT40 and added 2.75. It blew out the top breather and I had to drain 8oz out and all was fine
Although I come from the Miata world, we too have trans oil problems. A GL5 is just too slippery for the synchros to work. We use a synthetic Motorcraft GL4, that came from Germany. It works really well, but costs about $20.00 per Qt.

Kirby Schrader

They're mostly silver
Lifetime Supporter
2.75 quarts recommended for dry transaxle. 2.5 quarts for oil changes as some oil remains in box. I overlooked this little detail last oil change on my SPF GT40 and added 2.75. It blew out the top breather and I had to drain 8oz out and all was fine
This is interesting... A friend who has two Panteras, one he races, and I both put 4 quarts in our ZF's. Never had any of them puke.
I honestly don't remember what I put in my GT40... Time to change, methinks.



Is the annual change a time thing or usage thing. My impression is it should be changed annually regardless of how much it is or is not driven?