engine and drivetrain Oil for Manual Transmission, Differential and Stearing Box

[SpetzNaz]

Hi,

Looking at my choices for oils to use in my 4 speed.

From posts on this site and a shop manual I was able to find the following:

Transmission Manual: SAE 90 (book), SAE 75/80 GL-4 (site)

Differential : SAE 90 Hypoid(book and site)

Stearing Gearbox: SAE 90 Hypoid (book and site)

Ideally this all sounds great but in practice I cannot find these oils in my local shop. What i was able to find was Royal Purple Max-Gear Synthetic, SAE 75W-90 First glance at this oil it seems this should work for all three applications.

The Royal Purple states the following:

*Meets performance requirements of API GL-4 and GL-5

*Contains limited slip additive

*Great for manual transmission requiring GL-4 or GL-5 Fluids

*Meets performance requirments of MIL-L-2105E

Couple questions:

First, does anyone have any experience with this oil in any or all of the three applications? Why is GL-5 oil not recommended for the manual transmission, and can this oil be used? What i have read about the GL-5 is some additives that are present in GL-5 but are not in GL-4 will corrode some of the softer metals in the tranny. Is this the only reason GL-5 cant be used? If so the bottle of Royal Purple specifically states that it is not corrosive and their site also mentions something to that effect in the FAQ section.

http://www.royalpurple.com/rp-faqs.html

Lastly, the bottle also states that, "Max-Gear excels in hypoid, positrac and limited slip gears..." So does this mean that it can also be used in the stearing box and the differential???

Any opinions/suggestions/comments are appreciated.

[1972fritz]

i use royal purple in my rear diff and my trans in my 1993 325 and i plan on using it in my my girl friends 02. the transmission shifts soooo much better and the differential seems better as well. as far as the steering box goes if you can use it in the differential why not use it in the box must work well in that too..

[jgerock]

We use Royal Purple Synfilm GT at work in all our Roots-style blowers (yes, they are like the ones used in drag racing) and have had good luck.

My car came filled with Mobil 1 synthetic lube, but it tends to leak. I have some Redline MTL (manual trans lube) waiting for the next change.

The BMW owner's manual has great information on lubricants. If you don't have one, just search the archives for steering box fluid - C.D.'s posts contain all the valuable information.

[c.d.iesel]

Spetz - you apparently have read the BMW

specified lubricants and have it right already,

but here again for newbies in the wings.

You make your own decision about using

GL 5 gear lubs in the trans - but too many sources state

the ill effects of GL 5 spec gear oil on 'old'

design gearbox internal metals and alloys.

Do you feel lucky?, and does it matter to you?

Everyone wants to find a NEW oil that's 'better'

than the original spec. Happy Hunting

[Mike Self]

uses B-W synchros (earlier ones use Porsche style synchros) Redline MTL will work wonders with the boxe's natural notchiness. It certainly cured mine, both 4 and 5 speed; they shift as smoothly as the Porsche synchros in my '69. I have Redline hypoid oil in my differential, primarily because synthetic oil has better lubricating qualities--and both my diffs have 220k miles and are all original. Those hypoid gears in a diff generate extreme pressure when they mesh, so need all the lubrication they can get.

Trannies don't seem to leak any more with Redline than they did with conventional oil...

mike

[jimk]

Why is GL-5 oil not recommended for the manual transmission, and can this oil be used? What i have read about the GL-5 is some additives that are present in GL-5 but are not in GL-4 will corrode some of the softer metals in the tranny. Is this the only reason GL-5 cant be used? If so the bottle of Royal Purple specifically states that it is not corrosive and their site also mentions something to that effect in the FAQ section.

Any opinions/suggestions/comments are appreciated.

The gearing in the hypoid gearset in the diffential undergoes a wiping action (as opposed to a rolling action in the transmission gears). Many years ago, there was premature wear when horsepower began to climb and gearsets became smaller (heavier loading on the gears). Gearlubes for hypoid gearsets has a metalic soap additive (thats why they all seem to smell the same) which plates onto the gear faces. The plated additive wears away and is replaced by more of the same from the gearlube.

So that plating action in certain transmissions gummed up the works when it comes to the gears sliding back and forth on the shafts when changing gears and the synchros took the beating. Others had brass materials in the synchros which seemed to get an overdose of plating, more troubles.

Some posts on this board have said the 5 spd ODs are ok with the GL-5, but I use Amsoil's MTF in mine. Since I had it, no use in asking for trouble. Solves the cold weather 1-2 shift that eats up synchros. I before used the 10W-40 in the 4 speed (not to worry, it didn't have shearback troubles like mineral multigrades have). Shearback or thinning is a mechanical breakdown of the VI improvers in mineral oil and in some cheap synthetics.

Hope this helps explaining why non-hypoid oils are not the thing in certain transmissions.

My belief is that hypoid oil is ok in the steering box, I have had a synthetic hypoid oil in it since 1978.

[SpetzNaz]

Thanks for the info,

Its not so much that I am looking for something better its that I am looking for something that will work well and i can get my hands on, on a regular basis at the corner store... As advertised the Royal Purple seems very tempting...

Here is an email i got back from Royal Purple regarding this same question:

"Attached is the description of API GL ratings - direct from the API website.

There are many manual transmissions that have and still use bronze synchro's with GL 5 rated oils without a problem unless: the oil is run past it's useful life (too long a drain interval, over heated, contamination due to water, etc). Synthetics are formulated to work with bronze all the time - how do you think that we lubricate worm gears in industrial applications?

RP MaxGear 75W90 is rated for both GL4 and GL5 and MT-1 applications due to it being non-corrosive to both ferrous and non-ferrous (yellow metals) and excellent oxidation resistance. We could not advertise these rating if we damaged synchros.

You will not have a problem using RP Max Gear 75w90 with Brass Synchronizers.

Have a great day."