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MG MG Y Type - Gearbox/diff oil choice

Now I think I will bore some readers, as this subject must have beeen treated many times (I browsed through the Archive without finding any conclusive infos). The question is: What exactly happens when you put an API GL 5 spec oil into your gearbox? It is said that the additives will attack bronze parts. So will they be eaten away like iron in water? And is any GL5 oil the same in this respect? All oils you find in "normal" outlets are now GL5, even Castrol Hypoy which was always recommended. So is it imperative to use "classic" oils like Penrite or Castrol? As I have been using Wynn's HPLS additive in my newer car (a 1971 Fiat) almost since new and it works great there (without it there is distinctive whine), I e-mailed Wynn about using it for older gears. The answer they gave me proves that they are not really aware of this problem themselves. They wrote: "HPLS upgrades the oil spec, for example a GL4 becoming a GL5" (so why do they have to produce it at all now that GL5 is the highest???)"There has been an evolution from zinc based towards phosphorous/sulphurous based additives. Often there are compatibility problems between these 2 families. Recently we have changed the HPLS formula from zinc to phosphorous/sulphurous based. So we followed the market evolution and avoid compatibility problems. This means that in your case it doesn't seem advisable to use the product. Can you inform us if the bronze problem is the only reason why you cannot use these additives or GL5 oil. Or are there other reasons to avoid the use of these components in old timers? Please let us know, it could help to inform other old timer users." So it seems to boil down to us having to help the oil companies sort out such questions...
And what are your experiences with molybdene disulphite based additives, like MolySlip or Molykote?
Thanks for stopping my head spinning. Remo
Remo Peter

Remo

Dont know about all the techy stuff (Neil is the man for that) but I have just refilled my gear box and diff with Penrite Oil, Gearbox oil 40 for the gear box, and Mild EP for the diff.

Penrite is NOT the cheapest, and someone will comeback and tell us what is, but we have a stockist near me here and it's actually not as expensive as I feared it might, so my mind is resolved.

Paul
Paul Barrow

My past experience and knowledge is to NOT use any gear oil marked "EP" in a transmission, differential, or steering gearbox with bronze bushings, thrust washers or other bronze parts. EP (extreme pressure) additives attack the bronze and will disintegrate it. I haven't checked to see if GL4/GL5 is extreme pressure or not. This also applies to EP chassis grease for spindles and kingpins.
John Masters

See the MGA archives for this subject. GL 4 synthetic is my choice.Bottle states for manual trnasmissions, which are not intended for ATF [trans-axles]. I have not seen a GL 5 that states, for use in manual trans.
Ask the professional racer's, in your area, what they use. Len
Len Fanelli

I checked the MGA section and found that this gearbox originally uses engine oil, whereas in the YB manual, the same oil is specified for gearbox and rear axle, for instance Castrol Hypoy. So I think MGA and YB (TD/TF) boxes are different breeds in this aspect, too.
Remo Peter

From the MGA perspective, the gearbox uses engine oil except the close ratio 'box which recommends EP80. The diff has a hypoid oil. When refilling both on my MGA, I found that most gearbox oils, both EP80 and hypoid, are not safe for yellow metal bearings and had to get Penrite ones which are. They may be more expensive than other oils, but it's still not a lot of money.
dan

This thread was discussed between 22/01/2002 and 23/01/2002

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