synthetic tranny and diff fluid choices

RodneyWright · **Posted:** Thu Jan 15, 2009 11:50 am

OK, I know I’ll open up a can of worms here, but I want to replace the current tranny and diff fluid in the GT with some upgraded synthetic. There’s a lot of stuff on the market, but I was thinking about either redline or royal purple. Any comments on either of these or is there something else I should consider.

Michael Westerfield · **Posted:** Thu Jan 15, 2009 12:14 pm

Haha, you are already gonna start modding it! Once you get that fluid out of there you will notice you need some 3.73 or 4.10s. It's a disease!

Graham Jagger · **Joined:** Fri Aug 29, 2003 12:53 am **Posts:** 1718

I've had really good results with the RP. Including oil analysis from Blackstone Labs to back it up. Ran it in the 1st Z06 and running it in the current one.

RP 5w-30 oil. Lasted a few track events, ax events, and almost 6K street miles. So roughly 8K miles on it. It still passes the test at Blackstone Labs. Could go 10K miles on it easily.

RP Synthetic Power Steering fluid. I have no issues with foaming etc which happens in some Vettes that are tracked.

RP Synchromax trans fluid. This is a D4 type auto trans fluid used in newer manual transmissions. It has additives to help the synchros and will not destroy them. I noticed the car shifted smoother with it. I get not trans overtemp warnings like a lot of C5s on track get. It just seems to run cooler.

RP Max Gear Diff fluid, 75w-90. No GM slip additive required.

I've used RedLine and Mobil1 fluids end to end before and they are ok too. Just prefer the RP and now it is really easy to find.

RobLupella · **Posted:** Thu Jan 15, 2009 1:03 pm

Graham Jagger wrote:

I've had really good results with the RP. Including oil analysis from Blackstone Labs to back it up. Ran it in the 1st Z06 and running it in the current one.

RP 5w-30 oil. Lasted a few track events, ax events, and almost 6K street miles. So roughly 8K miles on it. It still passes the test at Blackstone Labs. Could go 10K miles on it easily.

RP Synthetic Power Steering fluid. I have no issues with foaming etc which happens in some Vettes that are tracked.

RP Synchromax trans fluid. This is a D4 type auto trans fluid used in newer manual transmissions. It has additives to help the synchros and will not destroy them. I noticed the car shifted smoother with it. I get not trans overtemp warnings like a lot of C5s on track get. It just seems to run cooler.

RP Max Gear Diff fluid, 75w-90. No GM slip additive required.

I've used RedLine and Mobil1 fluids end to end before and they are ok too. Just prefer the RP and now it is really easy to find.

User is not an employee or RP or its subsidiaries, affiliates, or family. This is a non-compensated endorsement. :wink:

Dustin Fredrickson · **Posted:** Thu Jan 15, 2009 2:01 pm

I've run Redline in most my cars with good results. Didn't work too well in the Subaru with blown syncro's, though. The Miata shifted better with the Redline fluid. It does "wear out" a bit though - I had replaced the clutch and decided to re-replace the tranny fluid while I was doing it, and while the Redline in there was only about a year old, the new stuff did feel better.

Not sure what weight your tranny uses, but if it's a common diff fluid like 75W-90, be careful to get stuff without the LSD friction modifiers (which tend to make the syncros work less than optimally). Redline carries both a 75W-90 and 75W-90NS for this reason.

RodneyWright · **Posted:** Thu Jan 15, 2009 2:16 pm

Michael Westerfield wrote:

Haha, you are already gonna start modding it! Once you get that fluid out of there you will notice you need some 3.73 or 4.10s. It's a disease!

simple mods, simple mods.....

I really like the way the car is out of the box. Not seeing where I need to make any changes right now other than wheels/tire and brake pads.

George Bright · **Posted:** Thu Jan 15, 2009 2:29 pm

RodneyWright wrote:

Not seeing where I need to make any changes right now other than wheels/tire and brake pads.

Ryan started this way too. :lol:

Ryan Holton · **Posted:** Thu Jan 15, 2009 2:32 pm

George Bright wrote:

RodneyWright wrote:

Not seeing where I need to make any changes right now other than wheels/tire and brake pads.

Ryan started this way too. :lol:

We all do.

Wes Eargle · **Joined:** Mon Oct 27, 2003 9:47 am **Posts:** 3683

RodneyWright wrote:

OK, I know I’ll open up a can of worms here, but I want to replace the current tranny and diff fluid in the GT with some upgraded synthetic. There’s a lot of stuff on the market, but I was thinking about either redline or royal purple. Any comments on either of these or is there something else I should consider.

Carolina Mustangs sells Redline.

If you want a real mod, grab a set of Magnaflows. :twisted:

RodneyWright · **Posted:** Thu Jan 15, 2009 10:31 pm

jakepressley wrote:

I'd aviod changing gearing before tracking it and getting a baseline.

These guys are just busting my chops on the mod stuff

. Trust me, no diff gearing change for me. Besides, that would throw me out of stock class.

DickRasmussen · **Posted:** Thu Jan 15, 2009 10:44 pm

RodneyWright wrote:

OK, I know I’ll open up a can of worms here, but I want to replace the current tranny and diff fluid in the GT with some upgraded synthetic. There’s a lot of stuff on the market, but I was thinking about either redline or royal purple. Any comments on either of these or is there something else I should consider.

Ask Sam Strano. I do understand from Sam that the diff clutches in the SN197's are different from the earlier ones (longer lasting) but that the shop manual no longer permits "packing them tight". I think this is good news since SERIOUS autocrossers needed to constantly reshim the older diff clutch packs.

FYI I think the diff factory fill is synthetic.

Kevin Hoff · **Posted:** Thu Jan 15, 2009 10:54 pm

Dustin Fredrickson wrote:

I've run Redline in most my cars with good results. Didn't work too well in the Subaru with blown syncro's, though. The Miata shifted better with the Redline fluid. It does "wear out" a bit though - I had replaced the clutch and decided to re-replace the tranny fluid while I was doing it, and while the Redline in there was only about a year old, the new stuff did feel better.

If you still have the Redline in the Subaru I'd suggest Motul Gear 300. It worked very well for me in the old WRX, notably smoother and easier action than stock but no grinding, unlike Redline.

--Kevin H.

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