GM Synchromesh transmission fluid question (Page 3/4)
theogre DEC 27, 12:19 AM
When stick trans is making noise just @ idle & out of gear...

Is very likely input shaft has bearings are "bad" or out of adjustment if can be adjusted @ all & oil type won't help much if any.

Many FWD GM sticks don't actually use crank pilot bushing/bearing often makes more problems because nothing but bearings in the trans centers the clutch disk & loads related to that.

Can also be iffy Throw Out Bearing as Hydro Clutches nearly always have the TOB touching the pressure plate "arms." Is Why This system have no clutch adjustment.
Vintage-Nut DEC 27, 10:22 AM

quote
fierogt28: This is the correct oil as pictured.



Yes - GM / ACDelco Synchromesh Transmission Fluid
Canada GM / ACDelco number is 89021808
USA GM number is 88900333 or ACDelco 10-4006

Different Numbers - SAME Fluid!

USA Photo of GM / ACDelco Synchromesh Transmission Fluid

[This message has been edited by Vintage-Nut (edited 12-27-2023).]

Vintage-Nut DEC 27, 01:01 PM

quote
Patrick:
Is it (Royal Purple Synchromax) thicker than the others?



GM Synchromesh Transmission Fluid is SAE 75W-80
Royal Purple Synchromax Fluid is 75W-90

"Synchromax is formulated with Royal Purple’s synthetic, proprietary Synerlecadditive technology, offering improved shift quality over a wide temperature range and
reduced gear noise."

[This message has been edited by Vintage-Nut (edited 12-27-2023).]

Patrick DEC 27, 04:46 PM

quote
Originally posted by Vintage-Nut:

GM Synchromesh Transmission Fluid is SAE 75W-80
Royal Purple Synchromax Fluid is 75W-90



Thanks for the info!
cyrus88 DEC 27, 06:54 PM

quote
Originally posted by Vintage-Nut:

Royal Purple Synchromax Fluid is 75W-90




I don't know where you got that from, but Royal Purple does not specify. Royal Purple states: "Royal Purple® Synchromax® is recommended for manual transmissions that specify an automatic transmission fluid or other light-viscosity oil."

Anything that requires 75W-90, RP recommends their MAX GEAR 75W-90.

[This message has been edited by cyrus88 (edited 12-27-2023).]

Patrick DEC 27, 08:34 PM

quote
Originally posted by cyrus88:

I don't know where you got that from, but Royal Purple does not specify.



Damn, why does this need to be so difficult.

Interesting that none*of the GM Synchromesh part numbers posted above are mentioned in Royal Purple's cross-reference Here.

[EDIT]*Incorrect

[This message has been edited by Patrick (edited 12-27-2023).]

La fiera DEC 27, 08:45 PM
Since I installed the Getrag in my Fiero I've only used Synchromesh (Pennzoil brand) and it shifts like a hot knife in butter, very smooth and never clunky whether I'm at full swing or just putting around. I do have an aftermarket Quaife limited slip in it.

No need for additive with this design.
Patrick DEC 27, 08:58 PM

quote
Originally posted by La fiera:

Since I installed the Getrag in my Fiero I've only used Synchromesh (Pennzoil brand) and it shifts like a hot knife in butter, very smooth and never clunky whether I'm at full swing or just putting around.



My Formula's Getrag shifts smooth as well (with I believe, synthetic 10w30)... but that's never been my issue. It's that damn rattle while out of gear with the clutch out. Do you have the rattle?

I've mentioned this before, years ago... but my Getrag never had the rattle until I let someone drive my Formula at autocross. They were unfamiliar with the car, and did several high rev 3rd gear launches off the line... and that's all it took for the damn Getrag rattle to manifest itself.

[This message has been edited by Patrick (edited 12-27-2023).]

FormulaGT DEC 27, 11:17 PM

quote
Originally posted by Patrick:

Damn, why does this need to be so difficult.

Interesting that none of the GM Synchromesh part numbers posted above are mentioned in Royal Purple's cross-reference Here.



GM part # 12345349 I posted earlier crosses over to RP Synchromax on page 2 of link you provided.
Patrick DEC 27, 11:27 PM

quote
Originally posted by FormulaGT:

GM part # 12345349 I posted earlier crosses over to RP Synchromax on page 2 of link you provided.



Ah, sorry... I was using the updated GM part numbers listed later in the thread. Thanks. At least now we have confirmation that Royal Purple Synchromax is indeed suitable to use in place of GM / ACDelco Synchromesh Transmission Fluid.