Which oil in the gearbox ?

[Lassieman]

Hello!
I was going to change the oil in my ZF gearbox 1991.
Have seen that many prefer Castrol TWS 10W60.
Is it true that the (engine oil) works well?

Best regards
Lasse

[PhillipsLT5]

thats it, sold in liters at bmw dealer

[scottfab]

I use Havoline 10w30 which was reportedly what GM shipped them with.

[VetteMed]

There's varying opinions on which fluid to use, but the BMW oil seems to be the favorite. I've been running it for a few years now and have no complaints. It should be changed out every 1 year or 12K miles, as its viscosity does degrade.

[mike100]

I'm running a thinner GM Synchromesh clone with good results and easier shifts.

[EV2DEMON]

I don't know, but mine got worse with Pennzoil synchromesh.

Looks like I'll bite the bullet and drop the cash for the BMW stuff.

[Paul Workman]

Bill Boudreau @ ZFdoc.com recommends the Castrol TWS 10W-60 for the new ZF (that replaced the original one that locked up on me while cruising at 70 mph).

According to Bill, locking up is a problem not uncommon with the ZF - especially on a few of the 94-95 transmissions. This, according to what Bill told me, it is due to insuficient lubrication of the reverse gear where it spins on a shaft shared with 6th grear. He went on to tell me that as part of his transmission "blue printing" he routinely opens up the oil galleries that feed oil to that reverse gear. He recommends the procedure, but if I opted to forgo it to save a little money, he said to BE SURE TO USE THE CASTROL TWS. (I had him open the galleries and I use the TWS. That's my story an I'm stickin' toit!)

Oh, the ZF that froze up on me had 42,000 on it is all. I can't say what it had in it - oil wise - I bought that LT1 Vette with 38,000 mi. I suppose it would be reasonable to guess iit had the original oil in it.

One other thing is to check to be sure the oil level is full. It is easy to forget, so it's part of my annual get ready for spring driving season routine.

P.

[Coupe89]

Just changed mine last month and used Castrol TWS 10W60.

[Hib Halverson]

I've done a lot of research over the years on the ZF S6-40.

First, be careful using GM's "synchromesh fluid". It was not intended for use in the ZF and it's viscosity may be too low for good durability.

The Castrol 10W60 is an acceptable choice but while Bill the ZF Doc likes it, that lube needs to be changed frequently.

The transmission lubricant used by GM for the portion of the ZF development which was done with transmissions in road racing cars was Red Line MTL.

I use Red Line Light Shockproof in my ZF and have been using it since '97. I change it every 36,000-40,000 miles. Periodic oil analysis shows excellent durability. Shift effort is reduced. It's calcium EP additive package has a positive effect on gear rattle, too.

For a number of years, I had a second ZF behind a 400 SBV8 in an old Chevelle which I also lubricated with Red Line Light Shockproof. Back about 1999, I took it over to Phoenix and had Bill take it apart and inspect the parts. They exhibited a very low level of wear, however, Bill has never been enamored with Light Shockproof because of its gel-based formula and it's color, a sort of "baby blue". Bill always calls it "Martian Blood".

Admittedly, Red Line suggests it be used in race only applications but for many years I've had excellent results with it in the S6-40 along with other manual transmissions such as the NV3500 five-speed and the Richmond six-speed.

[mike100]

Originally Posted by Hib Halverson

The transmission lubricant used by GM for the portion of the ZF development which was done with transmissions in road racing cars was Red Line MTL.

I've used Redline MTL in the past in a T5 with good results and I would probably use it in my ZF if I had 3 bottles laying in front of me.

Currently, I'm running Amsoil synchromesh as it allows 3rd gear to go into mesh a LOT easier than with the Castrol. I'm willing to change the fluid a little more frequently so as to not let it thin out the viscosity too much, but one fluid I'm contemplating is the Ford fully synthetic manual transmission oil. It is a 75w-90 (which is roughly a 40w engine equivalent). I feel this might fall in between the Castrol 60w and the Amsoil 30w. It is definitely thicker in my mustang transmission and I have run both the Amsoil and the Ford lube in it.