Gearbox & Rear Axle Oil

[hpeier12]

I have searched the Forum but could not find any relvant Information and new Full syntetic Gearbox Oil.
What is recommended? what other 400 owners are using?
On one hand I think that newer Gear Lube like syntetic should be better all overall , but Im not sure if this type of oil is compatible with the older Type seals we have in our Cars.
Any insight in this matter would be greatly appreciated.

Kind regards
Heinz Peier UML 333

[hpeier12]

Good morning Jeff
Thank you for explanation and your Insights which are always very much
appreciated .
I have no problems which synchro's cold or hot but the Gearbox is pretty noisy
and Maybe with an different Oil it would be less noisy.
My Car is fitted with an Overdrive and close rate 1 Gear which is free wheeling
, and this is where I think most the noise is coming from,
sitting idle with engine running I can hear the Gears spinning and as soon I
press the Clutch the Noise is gone. Then shifting true the 1 or 2 or 3 Gear the
Noise is always present but gone as soon Im shifting in 4 th Gear.
In 4 Gear with or without Overdrive the Gearbox is very good without any Noise
and an pleasure to drive.
It might be that the Gear combination for this freewheeling 1 Gear has something
to do with it.
Im thing to find another Gearbox and start over overhauling this yet to Purchase
Gearbox and swap it out when done , because this whining in the first 3 Gears
gets on my nerve and I like to improve that.
Again Thank you
Kind regards
Heinz

[Thor]

I can't see Geoff's comments on this so I may just be repeating stuff he has said.

My advice would be that modern synthetic gearbox oils should not give any trouble at all in old gearboxes as long as the actual fluid viscosities are about right. Synthetic oils can be thinner in viscosity, while still providing the excellent lubrication of an older oil which achieved the lubrication quality through being thicker.

The really dangerous thing you must be careful about is to only use EP type oils in gearboxes designed for EP oils. Syncro rings are sometimes made of bronze and as such are not compatible with EP oils. I am no expert on Bristol gearboxes so I can't tell you whether this is relevant.