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Transmission & Gear oil

C

Chadlebowski

Cruisin' Guzzisti
Joined
Jul 28, 2015
Messages
149
Location
West Sussex; UK
The Stevlio manual specifies 80W 90 for transmission and 85W 90 for the final drive. Is there much difference in these two ratings? Would a trace of one contaminate the other, or is it a practicably negligible difference?
 
Chadlebowski said:
The Stevlio manual specifies 80W 90 for transmission and 85W 90 for the final drive. Is there much difference in these two ratings? Would a trace of one contaminate the other, or is it a practicably negligible difference?
Click to expand...

I think you will find that either weight is fine for both. So long as the higher number is 90, you should be good. I've been using fully synthetic 75W90 in my 1100 Breva for years and so far all is good.
 
Only big difference (other than the cold viscosity) is the gearbox oil is GL5 and the Carc is GL4. Not sure why they spec'd the GL4 since there is no yellow metal that I am aware of but that is what they did. Draw your own conclusions......
 
canuck1969 said:
Only big difference (other than the cold viscosity) is the gearbox oil is GL5 and the Carc is GL4. Not sure why they spec'd the GL4 since there is no yellow metal that I am aware of but that is what they did. Draw your own conclusions......
Click to expand...
API GL-5 is normally specified for hypoid gears (sliding action) or for very heavy loading applications. From the cut-away picture of the CARC on wikipedia, it doesn't look like the pinion gear is offset, so it's probably not a hypoid gear but a spiral gear, hence the reason for GL-4 (GL-5 is not required) or because of yellow metal, as canuck1969 mentioned. Why MG specifies GL-5 for the gearbox I can only guess:
  1. The gears in the gearbox experiences high loads and they need the extra protection a GL-5 will offer (due to the extra EP additives).
  2. GL-5 has a lower coefficient of friction than GL-4, and the MG engineers decided they want to get maximum efficiency out of the gearbox.
  3. There's a hypoid gear inside the gearbox, hopefully not. It is unlikely, since the engine is longitudinal and hence the drive-train up to the drive shaft can make use of parallel shafts.
From https://www.engineersedge.com/gears/gears_lubrication_general.htm:
GL-5 is not necessarily backward-compatible in synchro-mesh transmissions which are designed for a GL-4 oil: GL-5 has a lower coefficient of friction due to the higher concentration of EP additives over GL-4, and thus synchros can not engage as effectively. Also, transmissions which explicitly call for GL-4 oil may have been designed around this lower concentration of EP additives and thus may contain yellow metal parts which GL-5 will corrode.​

In short, without knowing the details of the gearbox and rear drive design, I'd stick to MG's requirements.
 
MotoZA said:
API GL-5 is normally specified for hypoid gears (sliding action) or for very heavy loading applications. From the cut-away picture of the CARC on wikipedia, it doesn't look like the pinion gear is offset, so it's probably not a hypoid gear but a spiral gear, hence the reason for GL-4 (GL-5 is not required) or because of yellow metal, as canuck1969 mentioned. Why MG specifies GL-5 for the gearbox I can only guess:
  1. The gears in the gearbox experiences high loads and they need the extra protection a GL-5 will offer (due to the extra EP additives).
  2. GL-5 has a lower coefficient of friction than GL-4, and the MG engineers decided they want to get maximum efficiency out of the gearbox.
  3. There's a hypoid gear inside the gearbox, hopefully not. It is unlikely, since the engine is longitudinal and hence the drive-train up to the drive shaft can make use of parallel shafts.
From https://www.engineersedge.com/gears/gears_lubrication_general.htm:
GL-5 is not necessarily backward-compatible in synchro-mesh transmissions which are designed for a GL-4 oil: GL-5 has a lower coefficient of friction due to the higher concentration of EP additives over GL-4, and thus synchros can not engage as effectively. Also, transmissions which explicitly call for GL-4 oil may have been designed around this lower concentration of EP additives and thus may contain yellow metal parts which GL-5 will corrode.​

In short, without knowing the details of the gearbox and rear drive design, I'd stick to MG's requirements.
Click to expand...

Good info !!
 
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If you do some research, you will find that different brand oils of the same grade, say 80W90, have quite different actual viscosities. I take the grade designation with big grain of salt.
The same is the case with engine oils (unfortunately).
 
Is anyone running Redline Shockproof in their CARC bikes? I ran it for years in my '86 Lemans.
 
Todd, are you running the heavy or light? Both trans. and bevel box? Thanks for your input.
 
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