Fluid for a carbon syncro'd manual that clashes when cold??

[CJK440]

Specifically a T-56 in a C5 corvette. 3&4 clash when cold. Just got the car and the few times I drove it it was 20's out her in New england (getting it home and inspections). Was thinking of a fluid swap to kick the can on a rebuild and maybe trying Type F as it was claimed it grabbed better in a slushbox and are carbon lined syncro much different? But went down a rabbit hole on here about Type F in an MT and still trying to decide on what to try.

I assume I would want to make sure I choose something non synth with a low viscosity when cold? What do you recommend to breathe a little more lift into a tired T-56?

 

[4wheeldog]

Redline MT90 is the best I have found for allowing synchros to work as fast as you can shift.

 

[zfasts03]

These T56 transmission call for Dexron 3 or 4.

Even when new they clash gears in the cold. This transmission does not like the cold. The whole car (2003 Z06) I have does not like the cold at all. The suspensions squeaks, the interior creeks and rattles, the tires (summer tires) don't grip and the tranny is a mess until warm.

I am running Amsoil ATF sig series red cap, with slight improvement over factory fill. I think Redline D4 ATF might be the favorite according to the forums when reading years ago.

 

[MolaKule]

These T56 transmission call for Dexron 3 or 4.

Even when new they clash gears in the cold. This transmission does not like the cold. The whole car (2003 Z06) I have does not like the cold at all. The suspensions squeaks, the interior creeks and rattles, the tires (summer tires) don't grip and the tranny is a mess until warm.

I am running Amsoil ATF sig series red cap, with slight improvement over factory fill. I think Redline D4 ATF might be the favorite according to the forums when reading years ago.

Updated List of Manual Transmission Fluids May 30th

NOTE: This list is only a “summary” list of MTFs available in the MTF Lubricant Market and only available in US auto parts stores and US Import outlets. It is not an endorsement nor a critique of any one fluid, nor is it implied that any one fluid will cure problems in MTs that have design problems or those that have excessive wear. Viscosities listed are at 100C and rounded up.

B. The next higher viscosity MTF would be the 7.0 to 7.6 cSt@100C versions(SAE 70W75) (About the same viscosity as the original DexronIII/Merc)

1. Royal Purple's Synchromax
2. Ravenol MTF-2
3. Honda MTF
4. VW part number G052512A2
5. GM Manual Transmission and Transfer Case Fluid
6. BMW (Pentosin MTF 2) MTF-LT-1, 2 ,3
7. Tutelo (Petronus, Italy, Product Code 1402)
8. Penrite Pro Gear 70W75 (Australia)
9. FUCHS Titan Sintofluid FE 75W Manual Transmission Oil. GL-4 75W Gear Oil
10. Redline Power Steering Fluid
11. RAVENOL STF
12. HPL Manual Transmission Life 75W75 7.1 cSt

Thread 'Updated List of MTFs'

May 30, 2024

Updated List of Manual Transmission Fluids Updated May 30th, 2025

NOTE: This list is only a “summary” list of MTFs available in the MTF Lubricant Market and only available in US auto parts stores and US Import outlets. It is not an endorsement nor a critique of any one fluid, nor is it implied that any one fluid will cure problems in MTs that have design problems or those that have excessive wear. Viscosities listed are at 100C and rounded up.

A.These MTL fluids are closest to a Kinematic Viscosity of 6.X cSt@100C (About the same viscosity as Dexron VI ATF) LV MTF's:

1. HPL Manual...

• MolaKule
• Replies: 0
• Forum: ATF, Differential, Trans, Brakes, P/S

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[MolaKule]

These T56 transmission call for Dexron 3 or 4.

I have never seen a Dexron 4 or IV; better check again.

No Dexron III ATF has at least a GL-4 protection rating, which is the minimum GL-4 protection rating for MTFs.

 

[zfasts03]

sorry, yes Dexron III.

 

[Saturnguy]

Mobil 1 black label, 112980

https://www.mobil.com/en/lubricants...s/our-products/products/mobil-1-synthetic-atf

 

[Overfill]

I have never seen a Dexron 4 or IV; better check again.

There's no Dexron III ATF that has a GL-4 protection rating, which is the minimum protection rating for MTFs.

What is the performance shortcoming for Dexron and Mercon fluids from meeting GL-4? I tried to comb through the afton handbook, but its not clear since they don't list GL-1/2/3/4/5 testing criteria in the same likeness as specifications. I am befuddled because I just noticed that Mercon V spec has to pass FZG stage 11

 

[MolaKule]

What is the performance shortcoming for Dexron and Mercon fluids from meeting GL-4? I tried to comb through the afton handbook, but its not clear since they don't list GL-1/2/3/4/5 testing criteria in the same likeness as specifications. I am befuddled because I just noticed that Mercon V spec has to pass FZG stage 11.

Does a FZG stage 11 pass alone constitute a GL-4 rating?

 

[RooflessVW]

Honda MTF is always my go-to. Cheap and always shifts smoothly.

 

[Overfill]

Does a FZG stage 11 pass alone constitute a GL-4 rating?

Like I said, I don't know what testing and performance criteria frame a GL-4 rating.

 

[Overfill]

 

[Saturnguy]

Couple of choices

Mobil 1, 112980 at Rock Auto…
https://www.rockauto.com/en/parts/mobil,112980,transmission+fluid,11387

https://www.mobil.com/en/lubricants...s/our-products/products/mobil-1-synthetic-atf

Also TES-295, now TES-668, slightly higher viscosity…
https://www.allisontransmission.com/aftermarket-and-channel/parts-and-service/on-highway-fluids