gear box/ OD oil

[tahoe healey]

I'm using Redline 90m gear oil in my BJ8 and I just read in the Healey Marque (by Norman Nock, Oct 2004) that it should be 30-w-50. I've had no problems and I feel it is actually an improvement. What do you all feel?

 

[Dave Russell]

I used 20-50 motor oil for a while & thought it was pretty good. Switched to Redline MT-90 which is a SAE 75w/90 GL-4 gear oil & equivalent to SAE 10w/40 motor oil, & found easier, smoother shifting & the OD shifts a bit faster & more positively. I have also tried Redline MTL which is a SAE 70w/80 GL-4 gear oil & equivalent to SAE 10w/30 motor oil. I can't tell much difference between the two Redline oils. They both work noticeably better than the previous SAE 20w/50 motor oil. I attribute the better performance to the higher coefficient of friction of the Redline oils which lets the synchronizers & OD clutches work better.
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[tahoe healey]

Thanks, I feel better with that answer. Dave, had you seen that article?

 

[bighly]

I will always use redline MT90. I tried others but RL make it shift better same as Dave's comments.

Tracy

 

[Dave Russell]

[ QUOTE ]
Dave, had you seen that article?

[/ QUOTE ]
I went back & read the article, just glanced over it the first time. I think some folks don't realize that engine oil & gear oil have two different viscosity rating systems. Thus 75w/90 wt gear oil is equivalent in viscosity to 10w/40 wt motor oil etc. I think that engine oil viscosity is rated at 210 degrees & gear gear oil viscosity is rated at 100 degrees.

Redline MT90 & MTL are GL4 rated oils which means that they doe not contain the sulfur compounds found in GL5 rated oils. They have a higher coefficient of friction than a GL5 rated oil. This helps the synchronizer rings in the transmission to work more efficiently.

The sulfur in GL5 rated oil provides necessary protection against the shearing/sliding motion that occurs with hypoid type gears in a rear axle. Hypoid gears are always in a sliding motion. There is very little shearing action & much less friction in the transmission than in the axle so this type of protection is not needed. The sulfur compounds in GL5 tend to damage brass/bronze parts such as the synchro rings in the old Healey transmissions. So the general warning to not use gear oils in Healey transmissions. Many available rear axle oils state that they are acceptable for GL3, GL4, & GL5 usage. These oils obviously contain the sulfur compounds which may damage the brass synchro rings.

Triumph suggested gear oil for a similar transmission, but this was before the advent of available GL5 rated oils which might have caused problems..
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[Brakin80]

Quote: So the general warning to not use gear oils in Healey transmissions.

Dave, so you are suggesting that using Redline MT90 in the transmission is not a good idea? I was under the impression that most were using it.

 

[Dave Russell]

I said:
"Redline MT90 & MTL are GL4 rated oils which means that they doe not contain the sulfur compounds found in GL5 rated oils."

Also:
"The sulfur compounds in GL5 tend to damage brass/bronze parts such as the synchro rings in the old Healey transmissions. So the general warning to not use gear oils in Healey transmissions."

RL MT90 is a GL4 rated oil with no sulfur, & thus an exception to the general warning, & can be used in transmissions. MT90 is not suitable for use in hypoid rear axles. Sorry I didn't make it as clear as I should have.
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