6 speed gearbox oil

[Nevyn72]

Bottom line, the 6-speed will always have a difficult 1-2 shift, especially when cold.
They still make and use the same box, now in the Toyota 86/Subaru BRZ, and it has exactly the same problem.....

Replacing the shifter bush with a new factory / Derlin / complete SSK often helps somewhat.

Also using the right fluid (USE ONLY GL-4 KIDS!!), normally Redline MT-90 is recommended, In the USA they love their 'unicorn juice' Ford fluid but the only way to get the real thing in Australia is to import it yourself.
I've heard of people using Nulon before but never with good results......
(Note there are mixed reviews in comparisons between the Redline & Ford products on the forums in the US)

So, replace the bush and/or shifter, use the correct fluid, and just be gentle until the box has warmed up fully for the best shift you can get!

[bruce]

Just don't expect miracles from an oil change.
My Nissan box is clunky from 1st to 2nd when cold. Put in Redline, no change. I just shift a bit slower until warm.

[Mr Morlock]

The perfect manual change probably does not exist. Just change 1st to 2nd with a bit of care when its cold. A number of guys here are saying you can put magic brew # X in it and it works like vanishing cream and others dont think it makes any difference - technique helps and crash bang ultimately takes its toll.

[Red_Bullet]

Search for this.

Genuine Ford Fluid XT-M5-QS Full Synthetic Manual Transmission Fluid - 1 Quart

[Okibi]

MT90

[Magpie]

One thing to consider that if the wrong oil has been used in the past it will take a fair amount of time for the old oil to be flushed from the system.

This also applies if you change to a different GL4 oil. Pick a oil and stick with it, it make take a few changes before you will notice a difference.

[93_Clubman]

The perfect manual change probably does not exist.

NA6

[Roadrunner]

I experience worse/crunchy cold shifting when I went from Redline Lightweight Shockproof to MT90 in the SE 6 speed.
Fine when warmed up.

Personally I'd use the Redline Lightweight Shockproof if you are having crunching now.

I never had crunching gear shifts when cold previously on the LW Shockproof and am considering dropping brand new MT90 out of the box

[RS2000]

See point 3 about MT90 on https://www.redlineoil.com/mt-90-75w90-gl-4-gear-oil that says:
"safe for brass synchros, as it lacks the reactive sulphurs found in most GL5 oils that cause damage"

Go to https://www.redlineoil.com/lightweight-shockproof & use the Compatibility Check:
If you select a 6 speed Miata LS or SE, it will say LW/SP is NOT recommended. Maybe it's GL5, as it is used for diffs?

This came up years ago in the NSCC. Some S15 owners (same 6 speed as MX5) reckoned LW Shock proof ate synchros. Others said they had no problem.

[CrazyRacer]

Another vote here for Redline MT90. It transformed the 6 speed in my SE.

I don't know what had been in it previously (when I bought the car), but the gear change issues that it had disappeared with the MT90.

[Roadrunner]

See point 3 about MT90 on https://www.redlineoil.com/mt-90-75w90-gl-4-gear-oil that says:
"safe for brass synchros, as it lacks the reactive sulphurs found in most GL5 oils that cause damage"

Go to https://www.redlineoil.com/lightweight-shockproof & use the Compatibility Check:
If you select a 6 speed Miata LS or SE, it will say LW/SP is NOT recommended. Maybe it's GL5, as it is used for diffs?

This came up years ago in the NSCC. Some S15 owners (same 6 speed as MX5) reckoned LW Shock proof ate synchros. Others said they had no problem.

That's very interesting. I've always been under the impression LW was GL4.
Also to note with that compatibility checker that for a 2003 NB it only has the option of a 5 speed manual or 4 speed auto, so may not be quite accurate.

[RS2000]

6 speed shows up for me when I select 2003 Miata or Miata SE or Miata LS.

[Red_Bullet]

I run MT90 in my 2002 6 speed, haven't noticed any real problem once warmed up. 1st to 2nd resists a bit when cold. I bought it coz it's GL4 and others reckon it works.

I only bought the Motorcraft stuff to have it on the shelf for when (and if) I stick the 6 speed in the NA8. I broke second gear in the NA 5 speed box (user error most likely) and had it replaced at Automotive Plus with another 5 speed as there was no 6 speed box available at the time. Here is what Plus put in it. Seems to work just fine, the 5 speed is a much nicer box to use than my much newer low km 6 speed in the NB. Hence my deliberations on putting the 6 speed in the NA. I'm kinda lazy too.

martini extreme pressure 75/80
------------------------------------------------------

edit more info:

Sint 75/80 Road & Track Gear Oil

An extreme pressure, low viscosity, lubricant designed for the modern high performance vehicle. Sint 75w80 R/T is suitable for the most sophisticated types of manual gearboxes or trans axles operating at maximum capacity. The advanced Synthetic* technology of this product will help to increase component life and greatly extend drain intervals. Sint 75/80 R/T meets all the requirements of the specification API GL-4.



Sint R/T Gear Oils meet or exceed the following specifications.

API GL4
MILITARY SPECIFICATIONS MIL-L-2105D, MIL-PRF-2105E
GENERAL MOTORS HN-1561, HN-2040
FORD MC20119 A, MC2-104
MACK GO-J * BORG WARNER 5M - 48


Sint R/T Gear Oils Should be used in manual transmissions that specify this type of high performance full synthetic gear oil.



CHARACTERISTICS 75W80

Viscosity Index : 152

Viscosity @ 100 C (cSt) : 8.8

Viscosity @ 40 C (cSt) : 55

[wasp47]

I have also found them to be very sensitive to slave cylinder condition and pedal adjustment.

[Nevyn72]

I have also found them to be very sensitive to slave cylinder condition and pedal adjustment.

Don't forget engine mounts!
Worn or torn engine mount rubbers cause selection issues too.