4spd fluid?
Premium Supporting Vendor
Joined: Aug 2001
Posts: 5,364
Likes: 38
From: King George VA
Appreciate that you made the leap of faith to synthetics, but I'd still recommend a fluid such as the AMSOIL Manual Syncromesh Transmission Fluid (5w30) (product code MTFQT) mentioned above. Right viscosity for your tranny, but also with the right additives. Engine oils have additives that tranny fluid doesn't need to combat the combustion byproducts in the engine oil, and it has other additives that help combat the high shear forces found in a tranny.
Although I'm lurking down here, my 02 Z06 and my 06 CTS-V (both Tremec six speeds) came with factory fill Dexron III, a mineral oil basestock ATF. I've been running synthetic ATF in both for years.
As an indication of why I think synthetics outperform mineral oil based fluids, compare the rapid shear down low of grade on the factory fill in my CTS-V to the shear stability of the AMSOIL ATF I replaced it with:
2006 Cadillac CTS-V Used Oil Analysis Dexron III vs AMSOIL ATF Transmission Fluid
__________________
C66 Racing #66 NASA ST2, SCCA T2
AMSOIL Dealer (Forum Vendor)
AMSOIL Preferred Customer Program (Members buy at Wholesale - a savings of about 25%)
C66 Racing #66 NASA ST2, SCCA T2
AMSOIL Dealer (Forum Vendor)
AMSOIL Preferred Customer Program (Members buy at Wholesale - a savings of about 25%)
CF Community Team
Joined: Oct 2004
Posts: 19,341
Likes: 5,232
From: Cape Cod, Mass.
2025 C6 of the Year Finalist - Unmodified
2025 C8 Z06/7/E-Ray of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
2021 C8 of the Year Finalist Unmodified
2020 Corvette of the Year Finalist (performance mods)
2019 C1 of Year Winner (performance mods)
2017 Corvette of the Year Finalist
2016 C2 of Year
2015 C3 of Year Finalist
That's right guys. These 'new fangeled' things could be a pig-in-a-poke. I mean, microwave ovens, cell phones...they could give you cancer, right? My gosh, using synthetic oils is like playing with fire 
. Of course, about every manufacturer of a well-made vehicle puts synthetic oils in now. The others would too [because they know they are that much better], but they're savin' money. Well, stick with your 38 year-old experience and the rest of us will live in the 21st century.
. Of course, about every manufacturer of a well-made vehicle puts synthetic oils in now. The others would too [because they know they are that much better], but they're savin' money. Well, stick with your 38 year-old experience and the rest of us will live in the 21st century.
I'm really not resistant at all to new technologies. I use synthetics in my C5 and C6 because they were designed for it. I'll stick with what has proven to be reliable for me and many others in my older Corvettes.I am not trying to impose my beliefs on anyone. I simply responded to the OP question and gave him my well tested opinion of 38 years in duration. If you want to use synthetics it won't bother me. I even run an IPOD in my new Vette
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Okie-dokie. But, engines haven't been designed to be compatible with synthetic oil. Synthetic oils were designed to be better lubricants for all engines. Once the formula for synthetic oil was developed and proved to be so much better than organic oil (for engine life..thus, for warranty reduction) most all manufacturers jumped on the 'bandwagon'--so they could SAVE MONEY on their warranty claims. {Gee. Not a purely altruistic purpose in their madness.} Anyway, except for not having an adequate level of zinc needed for a few high-load, flat-tappet engines, synthetics are good for just about any mechanical device requiring oil. There are companies even adding the zinc so old farts like us can use it in their high compression, high performance, high revving 38 year old Chevy engines.
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
Jeff, thanks for the refresh!
My guess "copper" was close, but wrong..
That issue as I recall, is the potential problem with using sythetic oil in an old muncie. I don't know what brass parts are used inside a muncie and I don't know what "problems" are caused by the oil. It might take a long time for the brass to do whatever it does.
This additional additive can cause problems with yellow metals like brass or bronze.
That issue as I recall, is the potential problem with using sythetic oil in an old muncie. I don't know what brass parts are used inside a muncie and I don't know what "problems" are caused by the oil. It might take a long time for the brass to do whatever it does.
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
A little clarification: The issue has nothing to do with mineral based vs. syhthetic fluids. It has to do with the specification. GL-4 spec is for synchro transmissions with yellow metals. GL-5 is for hypoid gears and has a higher sulpher content. My understanding is the high sulpher content can be harmful to the yellow metals. The opposite is true also, do not use GL-4 in applications requiring GL-5 spec fluids.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
George Solich, chief engineer at www.autogear.net, who designed the Autogear Muncies with the Supercase, etc, says to NOT use synthetics in Muncies. The synchros simply do not behave as designed and can hurt shifting performance. He recommends a 80w-90 mineral gear oil with the MT-1 sub-spec which he says is good for the yellow parts. Valvoline fits the bill:
http://www.valvoline.com/products/co...il/gear-oil/61
This is a GL-5 spec'd gear oil. Years ago, GL-5 was thought to corrode yellow parts at twice the normal rate. The modern GL-5 recipes addressed that problem and are now a recommended replacement for GL-4 which is largely unavailable. Google "API-GL4 and API-GL5" for more info about cross compatibility.
Also, if you wish to speak to George Solich give him a call,..good guy:
www.autogear.net
http://www.valvoline.com/products/co...il/gear-oil/61
This is a GL-5 spec'd gear oil. Years ago, GL-5 was thought to corrode yellow parts at twice the normal rate. The modern GL-5 recipes addressed that problem and are now a recommended replacement for GL-4 which is largely unavailable. Google "API-GL4 and API-GL5" for more info about cross compatibility.
Also, if you wish to speak to George Solich give him a call,..good guy:
www.autogear.net
Last edited by 73, Dark Blue 454; Jun 29, 2009 at 06:37 PM.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I'll tell ya another fact- the design requirement had NOTHING to do with lubrication.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
ok, gotit, so it is the GL-5 additives (sulpher?) that is bad for the brass parts (aka yellow metal), but that would be the old GL-5 spec. The new GL-5 spec is ok. Taking all that into consideration, I think I am going to use 100% pure virgin olive oil in my transmission.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Man, the immense knowledge around here is just staggering.... 
Synthetic oils have been around since the early 1940's. They were invented by Germans for use in Panzer tanks because the hardware just wouldn't survive with organic oil products. All engine/tranny manufacturers would have switched over years ago...but the cost difference was too great. Since the 1980's...when the Japanese started developing very small, powerful, hot running engines, synthetic oils have been the saviour of many auto warranty programs. Now that synthetics have proved their value, designers are building engines that can push the limits of metal-on-metal action; thus, the Z06 engines [et al]. That doesn't mean that older engines can't use synthetics "because they weren't designed for it"
; in fact, those engines will be much better off...live longer, run cooler, use less fuel, yada, yada. Oh well, we shouldn't let facts get in the way of someone else's "knowledge".
Synthetic oils have been around since the early 1940's. They were invented by Germans for use in Panzer tanks because the hardware just wouldn't survive with organic oil products. All engine/tranny manufacturers would have switched over years ago...but the cost difference was too great. Since the 1980's...when the Japanese started developing very small, powerful, hot running engines, synthetic oils have been the saviour of many auto warranty programs. Now that synthetics have proved their value, designers are building engines that can push the limits of metal-on-metal action; thus, the Z06 engines [et al]. That doesn't mean that older engines can't use synthetics "because they weren't designed for it"
; in fact, those engines will be much better off...live longer, run cooler, use less fuel, yada, yada. Oh well, we shouldn't let facts get in the way of someone else's "knowledge".
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
7T1vette. Synthetics are generally better lubricants than petro-based oils; nobody has argued otherwise. But in some applications, the very properties that makes synthetics better (more slippery) is the reason mineral lube is often the recommendation. For our old Muncie transmissions, mineral lube is recommended to ensure proper operation of the synchros. Again, the Chief Engineer at Autogear says to not use synthetics in a Muncie because it could hurt shifting performance. Trust me. George knows what he's doing.
For our old differentials, Eaton, Auburn, and Dana/Spicer, the three giants in the industry, all recommend AGAINST the use of synthetics for their limited slip carriers.
http://www.eaton.com/EatonCom/Produc.../FAQ/CT_128414
http://www.auburngear.com/aftermarke...6pagesize%3d20
(click on "limited slip" above then scroll to "Important Lubrication Note")
http://www2.dana.com/pdf/5323.pdf
(See top of page 3 above)
So, to say carte blanche, that synthetics should be used in place of mineral based petro lube in all cases, would be very poor advice.
For our old differentials, Eaton, Auburn, and Dana/Spicer, the three giants in the industry, all recommend AGAINST the use of synthetics for their limited slip carriers.
http://www.eaton.com/EatonCom/Produc.../FAQ/CT_128414
http://www.auburngear.com/aftermarke...6pagesize%3d20
(click on "limited slip" above then scroll to "Important Lubrication Note")
http://www2.dana.com/pdf/5323.pdf
(See top of page 3 above)
So, to say carte blanche, that synthetics should be used in place of mineral based petro lube in all cases, would be very poor advice.
Last edited by 73, Dark Blue 454; Jun 30, 2009 at 03:52 PM.
Thread Starter
Melting Slicks
Joined: Jan 2006
Posts: 3,028
Likes: 2
From: North NJ
Melting Slicks
Joined: Aug 2005
Posts: 2,359
Likes: 15
From: Confusion
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
according to my user manual pg 66 capacities:
4spd trans 2 1/2 pts US, 2 pts Imperial, but it doesn't say how much synthetic oil to put in.
and 2 pts is a quart... so I am guessing a bit more than 1 quart.
4spd trans 2 1/2 pts US, 2 pts Imperial, but it doesn't say how much synthetic oil to put in.
and 2 pts is a quart... so I am guessing a bit more than 1 quart.
Intermediate
Joined: Jan 2009
Posts: 42
Likes: 0
From: NJ
I used syn 75/90 syn gear oil (Mobil 1 in my case, but I would not hesitate to use any good quality name brand in its place) in my M-20. Improved the shifting in my opinion and was the correct weight.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
I agree Amsol has a GL-4 with "MT-1" rating meaning it is for gearboxes. There are many lubes out there that will not work well with our brass synchro tramsmissions. Adding 25% Lucas oil stabilizer works well too.
