FL5 Transmission Fluid recommendation

[zumbooruk]

Are the FL5 synchros made of brass or carbon?

I had no idea that synchros could be made out of carbon...

I did a quick search for the FL5, but did not find a definitive answer...

though they might be "carbon lined" (which still implies brass under the carbon?)

asked my favorite AI tool Grok about using Amsoil Sever Gear.

No, you should not use GL5 gear oil, such as Amsoil Severe Gear, in the FL5 transmission. The 11th generation Honda Civic Type R (FL5) manual transmission is designed to use GL4 or specific manual transmission fluid (MTF), like Honda MTF, to ensure proper operation and protect components. Using GL5 gear oil, which is typically intended for differentials, could potentially harm the transmission, especially if it has parts sensitive to the additives in GL5, such as synchronizers or other internal components.

Amsoil Severe Gear, as detailed on their product page , is a synthetic gear lube rated for API GL5, designed for severe-duty applications like differentials in cars, trucks, and racing vehicles. It is explicitly stated for use in "API GL-5, hypoid gear applications," with no mention of manual transmissions. This is further supported by discussions on BobIsTheOilGuy, where Severe Gear is recommended for non-commercial vehicle differentials, not manual transmissions.

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[V3N0M_VZL4]

I'm running Redline MTL so far so good, the grinding noise is gone.

 

[johnloov]

Running AC Delco and adjusted my clutch.. smoother and haven't had a grind since.

How did you adjust your clutch?

Anyone experience Redline 75W80 MTL Gear Oil ?

 

[ThunderPigeon]

I have done some research and Motul 75w90 and Redline 75w90 are both safe for yellow metals (synchros). Both are readily available from Amazon. I couldn't find either at the local box auto stores (AutoZone and Advanced). Amsoil also makes a 75w90 MTF that isn't severe gear oil and that also says it is safe for yellow metals. The severe gear oil has a sulfur based EP additive, so it is probably best to steer clear of that one.

I plan on doing the clutch adjustment, but haven't gotten there yet. I am going to do the damper delete and braided clutch line at the same time

 

[johnloov]

I have done some research and Motul 75w90 and Redline 75w90 are both safe for yellow metals (synchros). Both are readily available from Amazon. I couldn't find either at the local box auto stores (AutoZone and Advanced). Amsoil also makes a 75w90 MTF that isn't severe gear oil and that also says it is safe for yellow metals. The severe gear oil has a sulfur based EP additive, so it is probably best to steer clear of that one.

I plan on doing the clutch adjustment, but haven't gotten there yet. I am going to do the damper delete and braided clutch line at the same time

This was the one I was looking at

Yes — your Honda Civic Type R FL5 uses carbon-lined synchronizers in its 6-speed manual transmission, at least for 1st and 2nd gear. This is consistent with the previous FK8 generation, which also utilized carbon synchros for improved durability and smoother shifting.

Carbon synchros are known for their high heat resistance and reduced wear compared to traditional brass synchros, making them ideal for performance applications.

Given the presence of carbon synchros, it's crucial to use GL-4 rated transmission fluids that are compatible with carbon materials. Fluids with excessive slipperiness, such as certain GL-5 oils, can impair synchronizer function and lead to shifting issues.Dream Automotive

For optimal performance and longevity of your transmission, consider using high-quality GL-4 fluids like:

• Red Line MT-85 75W85 GL-4 Gear Oil: Offers smooth shifting and is specifically designed for synchronized manual transmissions.
• Amsoil 75W-90 Manual Transmission & Transaxle Gear Lube: Provides excellent wear protection and performance in both high and low temperatures.
• Motul Gear 300 75W-90: Known for its high thermal stability and performance in extreme conditions.

 

[ThunderPigeon]

Redline has a GL4 75w90 which is what I believe the Honda fluid is.

 

[ctechauto]

This was the one I was looking at

Yes — your Honda Civic Type R FL5 uses carbon-lined synchronizers in its 6-speed manual transmission, at least for 1st and 2nd gear. This is consistent with the previous FK8 generation, which also utilized carbon synchros for improved durability and smoother shifting.

Carbon synchros are known for their high heat resistance and reduced wear compared to traditional brass synchros, making them ideal for performance applications.

Given the presence of carbon synchros, it's crucial to use GL-4 rated transmission fluids that are compatible with carbon materials. Fluids with excessive slipperiness, such as certain GL-5 oils, can impair synchronizer function and lead to shifting issues.Dream Automotive

For optimal performance and longevity of your transmission, consider using high-quality GL-4 fluids like:

• Red Line MT-85 75W85 GL-4 Gear Oil: Offers smooth shifting and is specifically designed for synchronized manual transmissions.
• Amsoil 75W-90 Manual Transmission & Transaxle Gear Lube: Provides excellent wear protection and performance in both high and low temperatures.
• Motul Gear 300 75W-90: Known for its high thermal stability and performance in extreme conditions.

We've never had an issue with any Motul Gear 300 75W90 fluid (LS version or not).

And that article doesnt make sense. It lists Motul Gear 300 75W90 as a GL4 at the very end, but then says its GL5 above it (re: LS version). I feel this is AI generated (reads like one) and not accurate. Motul Gear 300 75W90 (what you see in my pic) is GL5. Again, havent had any issues through the years regarding GL5 and syncros, brass or not.

 

[johnloov]

Ok thanks for the feedback, AI doesn't get it right all the time, but gives me a good starting point - appreciate it

 

[Integra23]

How did you adjust your clutch?

Anyone experience Redline 75W80 MTL Gear Oil ?

Nut and rod on the clutch pedal. I adjusted most of the "slack" out so as soon as you'd express the pedal it makes contact with the plunger. I still have instances where it drags or semi catches but not an actual grind. Clutch delay valve removal would be my next mod based on others feedback.

 

[ThunderPigeon]

Motul is GL4 and GL5 certified. So it does have EP additives.
https://www.motul.com/en-US/products/34200?product=MOTUL+GEAR+300+75W-90

Here is the Redline I was looking at which is GL4 only certified.
https://a.co/d/4pfL2Vl

 

[johnloov]

I have on my LOG R the Clutch depressed % percentage displayed on upper left and wondering, how do I decide how to decide how to adjust up or down tightness. I want the best performing engagement on this stock car

In the latest Zygrene review of my car, he did grind my gears, honest mistake at ~27% depressed clutch, but we noticed he was probably used to his short shifter, and he was shifting from 3rd to second, without the clutch fully at the bottom.

Is that the only time you should shift right? When the clutch is to the floor, or can you at less than 100%?

Or is there something I'm missing. Does tightening or loosening cable remove the likelihood gear grind happens?

Honest mistake, but it it seems like he shifted only at 20% clutch engagement, but I've shifted sometimes at least 80% engagement and still grinned, and wondering is this and adjustment issue?

Here is the grind clip:



Here is the full review of the car for those interested:

 

[Spart]

75w-90 is what it is supposed to use for gear oil on these cars. The Amsoil MTF is not that weight but the gear oils do have options.

I don't mean to single you out because I've seen plenty of people repeat this, however your post was first and shortest.

The owner's manual recommends "Honda MTF" which (see below) is equivalent to a 70W or 75W.

From page 805:

Our cars would be the ones "without auto idle stop" that require 2.32 quarts or 2.2 liters.

And from page 716:

Note on the left how it says that motor oil of 0W-20 or 5W-20 can be temporarily substituted? Well, 70 to 75W gear oil is equivalent-ish to 5W-20 motor oil.

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. If those are called out as anything, it's 75W-75 and 70W/75W. Definitely not 75W-90 though.

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.)

 

[AspecR]

How did you adjust your clutch?

Anyone experience Redline 75W80 MTL Gear Oil ?

Redline MT-90 was swapped into my FL5 at 18k miles, the difference was immediately noticable. Shifted alot smoother and just felt more slick going through the gears

 

[V3N0M_VZL4]

The redline MTL is a game changer, at least in my experience holding strong.

 

[Spart]

Redline MT-90 was swapped into my FL5 at 18k miles, the difference was immediately noticable. Shifted alot smoother and just felt more slick going through the gears

I would echo your experience on my Tacoma that calls for 75W-90 (Redline MT-90 is great, very slick shifting compared to the OEM fluid) however I'd note your location and put an asterisk on using MT-90 (instead of an oil with a viscosity closer to Honda MTL) in other parts of the country that get winter. @johnloov I don't know where you're at, but the Redline MT-90 75W-90 could cause issues in the winter that the Redline MTL 75W-80 you're looking at shouldn't cause.

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