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- Dec 20, 2020
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I did a few polls in Corvette groups to see what fluids are commonly being used in ZF6 transmissions. Below is a list of the fluids people seem to be commonly using, their Viscosity at 100c and Pour Point. Lots of people are using Amsoil - which is waaaaay thinner than the 10w60 what ZFdoc Bill Boudreau prefers.
ZF6 Fluids from 2003:
Just sharing some info with some of you guys that may be interested or if some of you aren't on the ZR-1 Net. There was a posting last week on the ZR-1 net from Bill Boudreau (ZF-Doc) which most of us know he very knowledgeable on the ZF transmissions for our cars. He stated that he prefers the synthetics over the factory petroleum fill during the discussion. But (DO NOT USE Mobil-1 in the ZF’s) when the discussion came up on fluids for the ZF 6-speed. Also mentioned was Redline fluids, which is a very good fluid too. Yes RedLine fluid!
Here’s are the copies of the posting from the ZR-1 net:
Bill Boudreau wrote:
Hey Folks,
Mobil-1 oil, when used in the ZF S6-40 transmission, may cause slight/gradual development of glazing of the synchronizer's phosphor-bronze binding surface. Five out of six ZF S6-40 transmissions that I rebuilt that previously had Mobil-1 5w-30 oil in them had some degree of glazing of some or most of the synchronizer phosphor-bronze lining surfaces. As the percentage of glazed surface area increases on any given synchronizer ring, the ability of that synchronizer to bind efficiently also becomes reduced. Gradually over time, this condition may lead to increased shifting effort especially in the more frequently used gears.
I prefer the Castrol TWS 10w-60 (BMW P/N 07510009420 - M5 engine oil) for use in the ZF S6-40 transmission over the factory fill (GM P/N 1052931).
Other lubricants which work well in the ZF S6-40 transmission are RedLine Manual Transmission Lubricant (MTL) and RedLine Light Shock-Proof Transmission Lubricant (Green Martian Blood).
Don't forget to check/maintain the clutch hydraulic system to ensure optimal shifting performance of your ZF S6-40 transmission.
See Ya,
Bill Boudreau [email protected]
ZR51 Performance http://www.zfdoc.com
5612 E. Almeda Court
Cave Creek, AZ 85331
(602) 319-6575
Hib Halverson Wrote:
RedLine Light Shock-Proof Transmission Lubricant (Green Martian Blood).
Bill may remember the ZF out of my ratty old Malibu that we rebuilt back in early 2000. It had been run on Red Line Light Shockproof for quite some time. I'll let Bill describe the condition of the parts in that gearbox.
cYa
Hib Halverson
Bill Boudreau Wrote:
I was very impressed with how little wear had occurred in Hib's ZF S6-40 transmission. I would have to rate the RedLine Light Shock-Proof Transmission Lubricant as being excellent for use in the ZF S6-40 transmission.
Oh yeah.... it looks like Martian Blue Blood ... not green... my bad.
See Ya,
Bill Boudreau [email protected]
ZR51 Performance http://www.zfdoc.com
5612 E. Almeda Court
Cave Creek, AZ 85331
(602) 319-6575
Hib Halverson Wrote:
Bill and I are working on getting together to tear-down a second ZF that's, also, been run on Light Shockproof for a number of years. I'm sure once he and I finish that job we'll both have something to say about it.
In the meantime, I've had some private emails asking about where to get the Light. The best idea is to call Red Line Oil and either ask if they'll sell you some direct or ask them for the name of a retailer in your area. Keep in mind that very few of Red Line's dealers stock Shockproof lubricants. Info from Red Line can be had by calling (800) 624-7958.
Also, Light Shockproof is suggested only for ZFs in aggressively driven street cars or race cars. I would not use it in a ZF that sees mostly normal or easy driving. Also, I would not use Shockproof in a trans that sees a lot of operation in very cold weather. In either of those cases, I'd use Red Line MTL.
Both of these lubricants cost less than the Castrol 10W60 and can go far longer before lubricant changes.
There is a lot of interesting technical information about the Shockproof lubricants on Red Line's web site.
cYa
Hib Halverson
ZF6 Info from Hib Halverson in 2002:
There are six distinct versions of the ZF S6-40.
First, there L98/LT1/LT4 transmissions and LT5 transmissions. The difference is the LT5 uses an input shaft that is about 1/2-in. longer and a clutch housing that is about 1/2 inch taller. The reason for this is that the LT5 cylinder case is about half-an-inch shorter than the small-block V8 and for the LT5/ZF combination to fit in the powertrain mounts of the C4, something had to get a little longer so GM designed a longer input shaft and a different clutch housing.
Second, there are early ZFs (89-93.5), with an input torque rating of 450 lb/ft, and late ZFs (93.5-96), with a 400 lb/ft. rating. This is a significant difference as the helix angle on the gears is different. This was done to make the transmission quieter. The original ZF was developed with the LT5 Turbo project in mind. When the turbo project was killed, there was no need for such a high input torque rating. With all the complaints about gear rattle in neutral and first gear growl, GM decided to increase the helix angle to quiet the trans. Of course, increasing the helix angle, decreased the strength of the gears, hence the lower input torque rating.
Third, there are ZFs with reverse lockout (89-94) and ZFs with the so-called "crash-through" reverse (95-96). With the 95-96 gearboxes there's no reverse lockout to pull up. Reverse is "protected" with a higher effort detent in the reverse gate.
There are other minor differences and the best source for information on those is Bill Boudreau at ZR51 Performance, a ZF rebuilder. Ph: (602) 319-6575 email: [email protected].
| V@100c | Pour Point | |
| Castrol 10w60 (ZFDoc #1) | 22.7 | -39 |
| Redline Lightweight Shockproof (ZFDoc #2) | 17.1 | No data |
| Amsoil | 10.1 | -48 |
| Valvoline | 8.8 | -42 |
| Royal Purple | 7.5 | -51 |
| Penzoil | 9.08 | -45 |
| Mobil 1 5w30 (ZFDoc “Not Recommended”) | 10.75 | -42 |
| AC Delco | No data | No data |
ZF6 Fluids from 2003:
Just sharing some info with some of you guys that may be interested or if some of you aren't on the ZR-1 Net. There was a posting last week on the ZR-1 net from Bill Boudreau (ZF-Doc) which most of us know he very knowledgeable on the ZF transmissions for our cars. He stated that he prefers the synthetics over the factory petroleum fill during the discussion. But (DO NOT USE Mobil-1 in the ZF’s) when the discussion came up on fluids for the ZF 6-speed. Also mentioned was Redline fluids, which is a very good fluid too. Yes RedLine fluid!
Here’s are the copies of the posting from the ZR-1 net:
Bill Boudreau wrote:
Hey Folks,
Mobil-1 oil, when used in the ZF S6-40 transmission, may cause slight/gradual development of glazing of the synchronizer's phosphor-bronze binding surface. Five out of six ZF S6-40 transmissions that I rebuilt that previously had Mobil-1 5w-30 oil in them had some degree of glazing of some or most of the synchronizer phosphor-bronze lining surfaces. As the percentage of glazed surface area increases on any given synchronizer ring, the ability of that synchronizer to bind efficiently also becomes reduced. Gradually over time, this condition may lead to increased shifting effort especially in the more frequently used gears.
I prefer the Castrol TWS 10w-60 (BMW P/N 07510009420 - M5 engine oil) for use in the ZF S6-40 transmission over the factory fill (GM P/N 1052931).
Other lubricants which work well in the ZF S6-40 transmission are RedLine Manual Transmission Lubricant (MTL) and RedLine Light Shock-Proof Transmission Lubricant (Green Martian Blood).
Don't forget to check/maintain the clutch hydraulic system to ensure optimal shifting performance of your ZF S6-40 transmission.
See Ya,
Bill Boudreau [email protected]
ZR51 Performance http://www.zfdoc.com
5612 E. Almeda Court
Cave Creek, AZ 85331
(602) 319-6575
Hib Halverson Wrote:
RedLine Light Shock-Proof Transmission Lubricant (Green Martian Blood).
Bill may remember the ZF out of my ratty old Malibu that we rebuilt back in early 2000. It had been run on Red Line Light Shockproof for quite some time. I'll let Bill describe the condition of the parts in that gearbox.
cYa
Hib Halverson
Bill Boudreau Wrote:
I was very impressed with how little wear had occurred in Hib's ZF S6-40 transmission. I would have to rate the RedLine Light Shock-Proof Transmission Lubricant as being excellent for use in the ZF S6-40 transmission.
Oh yeah.... it looks like Martian Blue Blood ... not green... my bad.
See Ya,
Bill Boudreau [email protected]
ZR51 Performance http://www.zfdoc.com
5612 E. Almeda Court
Cave Creek, AZ 85331
(602) 319-6575
Hib Halverson Wrote:
Bill and I are working on getting together to tear-down a second ZF that's, also, been run on Light Shockproof for a number of years. I'm sure once he and I finish that job we'll both have something to say about it.
In the meantime, I've had some private emails asking about where to get the Light. The best idea is to call Red Line Oil and either ask if they'll sell you some direct or ask them for the name of a retailer in your area. Keep in mind that very few of Red Line's dealers stock Shockproof lubricants. Info from Red Line can be had by calling (800) 624-7958.
Also, Light Shockproof is suggested only for ZFs in aggressively driven street cars or race cars. I would not use it in a ZF that sees mostly normal or easy driving. Also, I would not use Shockproof in a trans that sees a lot of operation in very cold weather. In either of those cases, I'd use Red Line MTL.
Both of these lubricants cost less than the Castrol 10W60 and can go far longer before lubricant changes.
There is a lot of interesting technical information about the Shockproof lubricants on Red Line's web site.
cYa
Hib Halverson
ZF6 Info from Hib Halverson in 2002:
There are six distinct versions of the ZF S6-40.
First, there L98/LT1/LT4 transmissions and LT5 transmissions. The difference is the LT5 uses an input shaft that is about 1/2-in. longer and a clutch housing that is about 1/2 inch taller. The reason for this is that the LT5 cylinder case is about half-an-inch shorter than the small-block V8 and for the LT5/ZF combination to fit in the powertrain mounts of the C4, something had to get a little longer so GM designed a longer input shaft and a different clutch housing.
Second, there are early ZFs (89-93.5), with an input torque rating of 450 lb/ft, and late ZFs (93.5-96), with a 400 lb/ft. rating. This is a significant difference as the helix angle on the gears is different. This was done to make the transmission quieter. The original ZF was developed with the LT5 Turbo project in mind. When the turbo project was killed, there was no need for such a high input torque rating. With all the complaints about gear rattle in neutral and first gear growl, GM decided to increase the helix angle to quiet the trans. Of course, increasing the helix angle, decreased the strength of the gears, hence the lower input torque rating.
Third, there are ZFs with reverse lockout (89-94) and ZFs with the so-called "crash-through" reverse (95-96). With the 95-96 gearboxes there's no reverse lockout to pull up. Reverse is "protected" with a higher effort detent in the reverse gate.
There are other minor differences and the best source for information on those is Bill Boudreau at ZR51 Performance, a ZF rebuilder. Ph: (602) 319-6575 email: [email protected].
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