The great gearbox oil debate MT90 vs TAF-X!

[fmxa]

Not to open a can of worms, but I thought I'd report on results when switching from MT90 to TAF-X (which is ~3 times the cost of MT90 and only available if you have it shipped over from the UK).

My V8 has been run on MT90 for ~7 years with the fluid changed every year other year with no issues (foam, metals etc) noticed. So last Friday the old MT90 was drained, inspected, showed no signs of contamination and was as clear as the day it went in 2 years prior - I've since spent the weekend driving around and here are my (unscientific) conclusions -

There is a noticeable difference between how the gearbox feels with MT90 vs TAF-X (hard to quantify but it's there!)

Overall the TAF-X makes the gearbox feel more "notchy" and" clunky" compared to MT90

In summary, I prefer MT90 and will be replacing the TAF-X at the next change (or even sooner) with MT90 and definitely won't be putting TAF-X in the S4s. TAF-X is also impossible to find in the US, costs a fortune, and even though it's the factory recommended choice I'll be staying with MT90.

As always your mileage may vary .....

[bigsi]

i put mt90 im my fairladys gearbox every 3000 miles, my gearbox felt great through the changer, best oil i used, tempted to have it in the esprit box too.

[CarlC]

Thanks for the info Paul. It good here your thoughts on the fluid change in the gearbox, Especially as its backed by years consistently using the MT90 product. Im not sure if I've got the balls to switch, which is a shame as the only complaint I have about my gearbox is that it is a bit notchy. Otherwise my shift is pretty good.

Ill keep an eye on your avatar member group being changed to 'Heritic' for this blasphemy.

[Kato]

Keep us up-to-date on the running of your gearbox!

We would still advise sticking to what lotus recommend, but they don't recommend increasing performance and we've done that!

You make your choices and take your chances.

[Esprit Aviation]

I've run MT90 in my '85 Turbo since 1999 w/o any problems. I also use it it my two porsche 924s, and multitudes of customer's cars. So far it's all good!

Cheers, Lee

[coreuser]

The job of oil in a gearbox is to keep the metal bits apart.

This is most difficult in the case of the crown wheel and pinion (ring gear ) as it is spiral bevel, which generates high contact pressures

How good a job the oil does in this respect has little effect on the gearbox feel, just how quickly it wears.

BUT, if it resists the synchro ring from clearing excess oil off the synchro cone, then this makes the synchro mechanism less able to drag the relevant gear and shaft to the same speed, and so the box feels clunky as it takes longer for the synchromesh to work, and the change is baulked until it does.

One other aspect is gearbox temperature, all oils to some extent lose viscosity as temperature increases.

Under sustained high speed or high power use, the gearbox can get hotter than the engine ( put temperature dabs on it and see), which has major effect on the oils ability to keep the

Edited April 24, 2007 by Derek Bell

[mike_sekinger]

This is precisely why I have a transmission oil cooler fitted. The only unfortunate downside to the installation is that the pump is very noisy when it is running.

Of course, this discussion becomes further complicated by the addition of a Quaife ATB Differential, which has different lubrication requirements to that of the gearbox.

It is a world of compromise....

Cheers,

..... Off course the best thing to do to resolve this conundrum, is to do what you do with a hard working engine, which is control the temperature of the oil, then you can have the best of both worlds. It would not be difficult to add an oil cooler to the UN1

Derek Bell

[lotus4s]

Of course, this discussion becomes further complicated by the addition of a Quaife ATB Differential, which has different lubrication requirements to that of the gearbox.

It is a world of compromise....

Cheers,

Yes and the last time I checked, Redline was the only fluid that Quaife specifically recommended against using with their diffs. I have a Quaiffe ATB also and will continue with the TAF-X. It may cost more than others but that should not be an issue when you look at how often you actually change it. I've never had a problem getting it from JAE.

Edited April 24, 2007 by lotus4s

[jfitz981]

When I bought my Esprit 3 years ago, the first thing I did was change all the fluids (after 1 week of driving it) As I was told the fluids were all new but I still wanted to make 100% positive all was new. I chose to use MT90 in the gearbox and the difference was felt on the first drive. (The car came from a dealership so my assumption is that they used TAFX but who knows...)The car shifted smoother and to an extent the notchiness was gone. Impressive stuff! Once mobil 1 changed to that gold cap 15/50 motor oil I also changed motor oils to redline. Their product in my opinion has been excellent.

Jason

Edited April 24, 2007 by jfitz981

[Esprit Aviation]

Yes and the last time I checked, Redline was the only fluid that Quaife specifically recommended against using with their diffs. I have a Quaiffe ATB also and will continue with the TAF-X. It may cost more than others but that should not be an issue when you look at how often you actually change it. I've never had a problem getting it from JAE.

Jim,

Any reason given why Quaife rec. against Redline? I cannot remember how the Quaife works.

Lee

[lotus4s]

Jim,

Any reason given why Quaife rec. against Redline? I cannot remember how the Quaife works.

Lee

Lee,

I don't remember exactly at the moment but I'll do some checking and let you know.

Jim

[yeller77]

Jim,

Any reason given why Quaife rec. against Redline? I cannot remember how the Quaife works.

Lee

It is curious, since the ATB is similar to Torsen and I don't know of any concerns there. I (and many others) use Redline 75W90 in the RX7 Torsen diff. and never heard of issues. They obviously depend on a certain amount of gear lash friction for their function which may be compromised by some of the synthetics. There are so many variations on viscosity ranges and friction modifiers that it may be a difficult compromise in transaxles. Some of Redline's choices may cause more detrimental performance than good and may need to be carefully selected. Also, no lubricants are either specified or excluded in the Quaife warranty documentation that I've seen.

FWIW, I know a fellow who performs REM finishing and someone sent him a Torsen to REM the internals. He did it and it looked pretty, but it was anybody's guess what the functional result was going to be.

YMMV

E.

[Esprit Aviation]

Thanks for the replies. I just figured that w/o clutch packs, the fluid choice would be wide open. Can you better describe what the term "gear lash friction means"?

Lee

[Artie]

Thanks for the replies. I just figured that w/o clutch packs, the fluid choice would be wide open. Can you better describe what the term "gear lash friction means"?

Lee

I am pretty sure gear lash friction is the small gap between contacting surfaces of the crownwheel and pinion actually slowly come into contact with one another. This is usually much higher in racing apps as some people set their gear lash a little differently, such as many RX7 racers put a little more toe contact in the gear pattern to take advantage of the thicker part of the gear. From my knowledge of setting gear lash(backlash) this is my assumption of what gear lash friction is.

Artie

[yeller77]

Thanks for the replies. I just figured that w/o clutch packs, the fluid choice would be wide open. Can you better describe what the term "gear lash friction means"?

Lee

May not be engineeringly accurate, but basically they work due to forces acting on a set of helical gears within the diff.

Try this which explains the Torsen a bit. I don't pretend to understand where all the vectors go! I think Quaife's ATB is conceptually similar.

Eric

[lotus4s]

Jim,

Any reason given why Quaife rec. against Redline? I cannot remember how the Quaife works.

Lee

This discussion has come up many times in the past and each side of the discussion has their own anecdotal evidence.

Following is a direct email quote from a representative of Quaife to a friend of mine who purchased a Quaife ATB for his Esprit:

"Kevin,

Not a problem. let us know if there is anything else we can do for

you. just

as a reminder, the Quaife differential requires no break in and the only

gear lube we do not recommend is Red Line. for some reason Red Line

does not

work well with our unit.

Jason Alvarez

Quaife Aftermarket Manager"

Personally I tried MT90 right after I bought my Esprit and the transaxle immediately began leaking like a sieve when there were no leaks prior. I personally think it's too thin and will continue to use the TAF-X. There are also others who have worked on and rebuilt a lot more transmissions than I have and swear by the MT90. Choose your poison...

Edited April 29, 2007 by lotus4s

[Artie]

This discussion has come up many times in the past and each side of the discussion has their own anecdotal evidence.

A couple of things to consider, Lotus specifies a GL-5 gear oil and MT 90 is GL-4.

Following is a direct email quote from a representative of Quaife to a friend of mine who purchased a Quaife ATB for his Esprit:

"Kevin,

Not a problem. let us know if there is anything else we can do for

you. just

as a reminder, the Quaife differential requires no break in and the only

gear lube we do not recommend is Red Line. for some reason Red Line

does not

work well with our unit.

Jason Alvarez

Quaife Aftermarket Manager"

Personally I tried MT90 right after I bought my Esprit and the transaxle immediately began leaking like a sieve when there were no leaks prior and I felt no improvement in the shifting. I personally think it's too thin and will continue to use the TAF-X. There are also others who have worked on and rebuilt a lot more transmissions than I have and swear by the MT90. Choose your poison...

I'm running Royal Purple GL-4/GL-5 75/140 gear oil in my transaxle for about a year and seems to work just fine. Whatever was in it when I bought it looked like black molasses! My suspicion is that the fluid was rarely changed prior to my owning the car!

Artie

[yeller77]

A couple of things to consider, Lotus specifies a GL-5 gear oil and MT 90 is GL-4.

umm....actually, FWIW, TAF-X is a GL-4 lubricant, too

E.

Edited April 28, 2007 by yeller77

[lotus4s]

umm....actually, FWIW, TAF-X is a GL-4 lubricant, too

E.

yep, you're right, I stand corrected and edited my original post

Edited April 29, 2007 by lotus4s