Transmission Fluids

[MrStip14]

Evening gentlemen,

Im looking to replace my transmission fluid and do not know what to get. I’m torn between OEM and AC Delco synchromesh. I’ve seen people saying they like synchromesh and it helps stop the 2nd gear grind. It occasionally happens to me. Just seem to shift too fast sometimes.

It worries me a bit not using OEM since the diff is in the transmission. I believe Amsoil synchromesh won’t work with the diff.

Wondering what you guys think?

Sponsored

 

[crepr12]

OEM...jmho

 

[bvanlieu]

Honda MTL is pretty well formulated, even 30 years ago. I will be sticking with OEM when the time comes. If that was not available, I would look at Redline mostly from past experience where it has worked in multiple vehicles for me, which IIRC is simply Redline MTL vs -85 or -90

 

[Frenzal]

I've used the AC Delco stuff (but you need to get the Synchromesh friction modified version) in my old 6-6 Accord, and still use it in my S2000.

I would be worried to use in the Integra with the LSD just because I'm not sure it is OK with LSD. But for now, I don't have any shifting problems on my Integra, so in my case, I'll just use the OE MT fluid.

 

[bvanlieu]

Its a helical (gear based) LSD, so just MTL. modifiers are for clutch based ones to provide necessary friction for engagement.

 

[stanleywinthrop]

"I believe Amsoil synchromesh won’t work with the diff."

I've put close to 100,000 miles on Honda LSD transmissions filled with Amsoil synchromesh, with nary a problem. I'm not necessarily arguing that Amsoil is better than Delco or any of the other brands mentioned in this thread, but it absolutely does not harm Honda transmissions.

 

[Spart]

Its a helical (gear based) LSD, so just MTL. modifiers are for clutch based ones to provide necessary friction for engagement.

Bingo. No secret sauce for this LSD.

The CTR folks have been having good success with AC Delco Synchromesh 10-4014. Has resolved issues for some with second gear grind, 3rd gear popout, and 4th/5th gear lockout issues. It's a common enough swap that you'll find kits for sale at dedicated Honda shops, for example: https://dc5rparts.com/products/ac-delco-synchromesh-transmission-fluid-kit

The GM Synchromesh fluid has been well-regarded for decades, and if it's the right viscosity range for your trans (it is close enough for ours) it's usually a good option.

And for those who still somehow have anxiety over using non-OEM fluid: the owner's manual literally states that if Honda MTF is not available, that you can use SAE 0W-20 or 5W-20 motor oil temporarily. (Note that 5W-20 motor oil is equivalent-ish to 70W/75W gear oil, which is what Honda MTF is.)

Now like it mentions, you want a fluid with additives for a manual trans (which Synchromesh, Redline, and other MT fluids have!) but it isn't the end of the world to not use the exact OEM-branded spec in this particular trans.

GM Synchromesh isn't the only equivalent replacement fluid that could be good in these cars, any MTF in the 70W, 75W, 75W-80 (or close) range that is GL-4 should be a viable option. Redline MTL is a 75W-80 that's pretty good, and I use Redline MT-90 in my Tacoma (which is a 75W-90.) If you go heavier (such as 75W-90) just be aware that the cold weather characteristics might change. But if it's always warm where you live or you track the car, heavier might be fine.

 

[Spart]

Some more context around manual transmission gear oils. Here are the kinematic viscosities (in centistokes/cSt or mm2/s) of Honda MTF and other 70W, 75W, 75W-80, 75W-85, and 75W-90 GL-4 MT gear oils:

Honda MTF (Approximately 70W but not listed as such)
7.265 cSt @ 100°C*
30.70 cSt @ 40°C

* Note that I found a VOA on BITOG from 2022 that measured the viscosity @ 100°C as being 6.96 cSt. Honda MTF has been through three formulations, so it's possible this number of 7.265 cSt @ 100°C is from an older formulation. Honda doesn't publish this data anywhere that I can find.

BG Syncro Shift II (75W-75 GL-4)
7.11 cSt @ 100°C
37.85 cSt @ 40°C

Castrol Syntrans FE 75W
6.3 cSt @ 100°C
32.2 cSt @ 40°C

Pentosin FFL-3 (BMW MTF-LT-5 equivalent)
7 cSt @ 100°C
34.7 cSt @ 40°C

Pentosin FFL-4 (75W-80 GL-4 and BMW MTF-LT-1/2 equivalent)
7 cSt @ 100°C
34.7 cSt @ 40°C

ACDelco Synchromesh 10-4014 (no weight specified, but close to 75W-80)
10.05 cSt @ 100°C
50 cSt @ 40°C

Motul Gear Power FE 75W
5.8 cSt @ 100°C
30.7 cSt @ 40°C

Motul Motylgear 75W-80
10.1 cSt @ 100°C
58.8 cSt @ 40°C

Motul Motylgear 75W-85
12.6 cSt @ 100°C
82.6 cSt @ 40°C

Motul Motylgear 75W-90
14.2 cSt @ 100°C
85.4 cSt @ 100°C

Redline MT-LV (70W/75W GL-4)
6.3 cSt @ 100°C
29.9 cSt @ 40°C

Redline MTL (75W-80 GL-4)
10.4 cSt @ 100°C
50.8 cSt @ 40°C

Redline MT-85 (75W-85 GL-4)
12 cSt @ 100°C
62 cSt @ 40°C

Redline MT-90 (75W-90 GL-4)
15.5 cSt @ 100°C
82 cSt @ 40°C

Royal Purple Synchromax
7.5 cSt @ 100°C
39 cSt @ 40°C

Amsoil "5W-30" Manual Synchromesh Transmission Fluid (note this is like a 75W-80 gear oil, no clue why they use the motor oil weight.)
10.1 cSt @ 100°C
49.4 cSt @ 40°C

Amsoil 75W-90 Manual Transmission & Transaxle Gear Lube
14.0 cSt @ 100°C
80.3 cSt @ 40°C

You will note that ALL of the 75W-90's in my list have significantly higher viscosity than Honda MTF, around double.

Honda MTF seems closest to Redline MT-LV, BG Syncro Shift II, Royal Purple Synchromax, Castrol Syntrans FE 75W, and Pentosin FFL-3/4.

Viscosity is not the only thing that matters for shift feel with a manual trans, though it can make a big difference in cold climates. Friction modifiers will alter the synchro feel, which is most of what you're feeling through the shifter. This is why what feels "right" in every gearbox will be subjective and oil from one brand won't feel the same as equivalent weight oil from another brand.

Climate and use also matters. If you live somewhere that doesn't really get winter, or you track your car, 75W-90 might be the ticket. But if you want like for like with OE, I would stick to 70W, 75W, or 75W-80 oils and pick your favorite based on friction modifiers (shift feel.)

 

[DomGSR-T]

I have been using the GM synchromech since year 2002 or so in my 1998 turbo Gsr with a Quaife LSD, same for my 2008 TL-S M6 with factory LSD and I would not change it for any other brand... Really love this transmission oil...I will use it in my DE5 for sure once I choose to change it.

 

[Spart]

Motul has one with a friction modifier meant for LSD’s. Used to run it in my sti. Pretty solid and always looked new after draining it too. As if my abuse didn’t challenge it any.

just can’t remember the model of the oil. Sorry. But search around subbie forums, hopefully you’ll find it quick.

Not all LSDs are the same. Our LSD does *not* have clutches and as such does not need LSD additives. It is a "helical" differential that works using gearing and geometry to bias torque.

In fact, LSD additive may damage your synchros and degrade their function.

Do not put LSD friction modifier in your Integra transmission!

On top of LSDs not all being the same, friction modifiers are not all the same either. I will quote MolaKule (a well-known SME) from BITOG:

Just to add to the understanding of Friction Modifiers:

Each fluid type and fluid application has a different additive package and contains different Friction Modifier and AW chemistry for the specific materials used in those transmissions or differentials.

The friction modifiers in engine oils are NOT the same friction modifiers as found in ATF's. The friction modifiers in ATF's are NOT the same friction modifiers as found in LSD gear oil.

For an LS differential with flat plate or cone clutches that friction modifier is used to prevent chatter.

In MTF's, the friction modifier is used to enhance synchro engagement/disengagement. The two chemistries are entirely different and react differently.

In engine oils the Friction Modifiers are primarily there to reduce friction.

To expand on this, LSD additive (friction modifier) typically allows for more slip of the clutches in a clutch-type LSD, which can chatter and bind without any additives despite being in a bath of gear oil. Friction modifiers in a manual transmission fluid typically allow for less slip of the synchros in a manual transmission. If your fluid is too slippery in your manual trans, your gear shifts will crash and grind instead of smoothly engage.

Friction modifier meant for an LSD can upset the function of synchros. Don't do it!

 

[UWU-mancer]

Not all LSDs are the same. Our LSD does *not* have clutches and as such does not need LSD additives. It is a "helical" differential that works using gearing and geometry to bias torque.

In fact, LSD additive may damage your synchros and degrade their function.

Do not put LSD friction modifier in your Integra transmission!

On top of LSDs not all being the same, friction modifiers are not all the same either. I will quote MolaKule (a well-known SME) from BITOG:



To expand on this, LSD additive (friction modifier) typically allows for more slip of the clutches in a clutch-type LSD, which can chatter and bind without any additives despite being in a bath of gear oil. Friction modifiers in a manual transmission fluid typically allow for less slip of the synchros in a manual transmission. If your fluid is too slippery in your manual trans, your gear shifts will crash and grind instead of smoothly engage.

Friction modifier meant for an LSD can upset the function of synchros. Don't do it!

Oh gotcha. My bad. I’ll delete my post

 

[Spart]

Oh gotcha. My bad. I’ll delete my post

Motul *does* have a trans fluid product that seems suitable for our cars:

Motul Motylgear 75W-80 <-link
10.1 cSt @ 100°C
58.8 cSt @ 40°C

Now, I said "seems" on purpose. Someone will have to try it to see how it goes.

Is it as good as or better than GM (ACDelco) Synchromesh 10-4014? Dunno.

Given your location, I can't really recommend going to any of the products in the 75W-85 or 75W-90 viscosity range. Could make the gearbox a lot more sluggish in the winter. If you store the car all winter and track it in the summer, that's a different story.

 

[MrStip14]

I decided to go with the Amsoil 5W-30 Manual Synchromesh Transmission Fluid. Seems very comparable to the AC Delco 10-4014. Pennsylvania winters aren’t terrible, but not good by any means so I think it should be a good fit.

 

[Spart]

I decided to go with the Amsoil 5W-30 Manual Synchromesh Transmission Fluid. Seems very comparable to the AC Delco 10-4014. Pennsylvania winters aren’t terrible, but not good by any means so I think it should be a good fit.

Let us know how you feel about the winter performance! I've heard a few good things here and there about it when used in the FK8/FL5.

 

[UWU-mancer]

Let us know how you feel about the winter performance! I've heard a few good things here and there about it when used in the FK8/FL5.

My fk8 handled Colorado winters well. Had dws06+ tires on them. Never drove in super deep snow tho. But after the roads were plowed I’d pull the type r out. She did fine. Decent tires, just shitty sidewall. The all season 4’s by Michelin really did offer the same performance dry wet and snow but with way way way better steering feel. IMO

Sponsored