85/140 oil in W58/F series diffs

[mullett]

Who wants to enlighten me on the pros and cons of running heavier-than-spec oils? I'm looking mainly for improved shift quality and reduced noise. I'm hoping the improved shift will come from a step up to fully-synth oils (looking at Royal Purple) and the reduced noise from the heavier weight. The only downside I can see is a slight reduction in fuel economy (and I imagine it would be very slight indeed...unless someone knows otherwise?)

[RA35GT]

I used Redline MT90 (75/90) in the supra. Shifted awesome.

Too thick an oil may make the synchros not work as effectively, dunno how thick is too thick though.

[fixeruperer]

i was having shifting problems with my w58 so i tried lighter oil, like 50/50 atf. and tried some synthetic agip gear oil. but still doesnt change into 2nd under load. even after a rebuild.

ive always used a lighter oil for smoother changes. usually it helps, but not with my w58.

[mullett]

Have heard before about mixing auto trans fluid with normal gear oil. Seems like a scary prospect for my freshly-rebuilt box!

Something else that crossed my mind...surely you'd have to flush the gearbox (with mineral turps or similar) to clear the old oil out if you were going to do a proper oil change to a different brand/spec...

[sneaky pete]

If you have a rwd drive type seperate type diff and gearbox you can use it an 85w/140 in the axle. If you check the specs you will find it is GL5 and I would definitely not use it in a front wheel drive type setup where you are lubing both diff and gearbox. The high additive GL5 level can seriously effect synchromesch and the heavy viscosity will be a real pain when the box is cold. Do not mix ATF and gear oil. If you are developing big power then use a synthetic with an API GL4 75W/90. If std or slightly modified use a mineral GL4 SAE80W or synthetic GL4 SAE 75W/85. What a lot of people do not realize is that good quality engine oil can be used in gearboxes (fwd & rwd) calling for GL4 and gives a good shift quality. You can comfortably use a synthetic engine oil SAE 10w/40. It really works well.

[fixeruperer]

people have been mixing atf and gear oil in transmissions for years.

[mullett]

Beware of using engine oil! Motorbike oils you can, but most automotive engine oils aren't structured to take the shear which occurs constantly with meshing gears.

[sneaky pete]

Beware of using engine oil! Motorbike oils you can, but most automotive engine oils aren't structured to take the shear which occurs constantly with meshing gears.

In the old days the first Viscosity Index improvers then were prone to shear. Nowdays not. The polymers used these days are virtually indestructible. Thank goodness for technology. Multigrade oils are put through a multitude of tests, including by cycling it through a Bosch injector rig which will reveal any "weakness" (and this is a harsh test). Certain motor munufacturers have recomended engine oils in gearboxes for years (eg Honda). However to play it absolutely safe use a synthetic (as I mentioned above) which has a natural High VI and without the VI improvers typical of mineral based engine oils. Full synthetic engine oils have excellent oxidation resistance (which means they can take excessive heat and will last a very long time) and offset the higher cost. Full synthetics also have excellent film strength which is critical for the Elasto Hydro Dynamic lubrication phenomenea (oil goes virtually solid) between pressure surfaces.

With regard to mixing oils yourself (eg ATF and gear oil) you might get away with it some times (testimony to Toyota quality). DexronII type ATF is zinc based while typical gear oils are sulphur phosphorous. ie they do not work together. Rather use a formulated product made for a specific purpose and you are safe. Also if you using say an SAE80 and still need a slight improvement you can move to SAE75w or even SAE70w. At least you know what you are working with. [B]Use good s....t - don't thumb suck.

[lexsmaz]

Years ago Mazda did a recall on some of their rotary engined cars & actually changed the manual gearbox oil over to straight Auto trans oil & no blends, i have done it myself to quite a few cars over the years & never had an issue & the shift quality has improved dramatically, basically as i see it Auto trans setups have planetary gear sets in them & run auto trans with no wear issues to the boxes so i cant really see why not use it .. The only down side i have noted from running Auto trans is there is a little bit more bearing type / roll over noise noted mainly when idling in Neutral, once driving nothing sounds different .. Also the synchros i have come across have lasted a lot longer in the Auto trans filled boxes too, compared to similar cars of similar mileage running the good old gear oil set ups ...

Also some fords falcon & a few other manufacturers years ago ran Auto trans fluid in some of their Manual boxes too from the Factory ..

I must admit that Manual box oils have come along way in the last few years, so there is now many choices Now, so the pick / choice is yours but certainly as has been said Never run a heavier grade oil in the box it will just feel shit ... And dont flush it out either with mineral turps etc as what you mentioned, you are just adding more issues into the pile, just get it warm by taking it for a drive & then make sure its on level ground & take out the drain plug & leave it for as long as you can & then fill with whatever you end up using ..

[sneaky pete]

Manufacturers have now come up with their own branded transmission oil products. This is due partly to economics and partly requiring the most ideal viscosity for their transmissions. As mentioned transmission oils all used to be sulphur phosphorous based. The Japanese in particular are not happy with the sulphur phosphorous additive and have moved to their own branded products which are zinc based transmission oils. As mentioned in my previous post engine oils are zinc based.

[RyleyMA61]

i was also interested in this.

my F series diff with torsen LSD is quite noisy- there is some wear on the ring gear and pinion.

it is the most noticable once it warms up.

I was hoping a thicker diff oil, or a fully synthetic one would help alleviate any problems with the oil losing viscosity under temp and help shut up the whine and clunkiness...

so what sort of viscosity is safe?

[CELICASUPRA7M]

mine is the same, trutrac center, all new bearings and top quality oil. still gets noisy on the over run once warm.

Since its not a clutch pack stye LSD we should be able to run a simple heavy gear oil with no problems.
I'm going to try an 85/140, see what happens i spose

[RyleyMA61]

report back your findings son

i will do the same


woot

[supra2]

Ive just fitted a new 6 speed tremec magnum in the rally car and have been looking for a good race oil for the gearbox.
The recommended oil for these manual boxes is plain old DX111 auto fluid.
The older tremec can use an oil called Castrol Trans X , but the new box uses a different sincro material and can become sticky if dx111 is not used.
These boxes are behind some powerfull cars and survive well using standard auto fluid.
As mentioned before, I think the only negitive would be a little more mechanical noise.

[SHEPPO3930]

^^^ The 6spd manuals (tremec?) in the BA/BF/FG XR6T & XR8 falcons use dextron 3 auto trans fluid rather than normal transmission oil. there's actually a tag on the fill point to remind you NOT to put normal oil in it.