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MG MGB Technical - Final Drive - lubrication

Quite a lot recently on synthetic oil for the gearbox. Anyone tried it in the diff ?
Roger W

I use it in my diff (and synthetic in my engine and my fitted Ford type-9 gearbox too) all together they helped to reduce the power train losses plus are better in winter use

just doing thorough oil changes will help with the diff (g/box and engine)

on all three for changes get the existing oil as warm as possible and leave to drain for as long as possible to get as much existing oil and muck out as possible, you can also check the oil that comes out for colour, condition and metal bits

note using these synthetic oil just in themselves will not quieten a noisy diff but more regular oil changes does according to one poster so I'm increasing my frequency as it's so easy and cheap to do compared to having to fit rubbish made new parts

for longer lasting diff oil with reduced cold weather drag you could use a modern fully synthetic alternative like Castrol Syntrax Longlife 80w-90 (GL-5 spec*) or Mobilube 1 SHC 75W-90 (GL-5 spec*)

(*GL-4 spec oil is recommend for the gearboxes but the more modern GL-5 is considered fine for the diffs and if you get mineral 75w/90 it'll be GL-5 too)

http://www.opieoils.co.uk/p-737-castrol-syntrax-longlife-75w-90-formerly-saf-xo-75w-90.aspx

http://www.opieoils.co.uk/p-806-mobil-mobilube-1-shc-75w-90-fully-synthetic-supreme-performance-commercial-gear-oil.aspx
Nigel Atkins

Nigel,
Thank you. I have the GL4 spec in the LT77 gearbox which is an improvement on the automatic oil (recommended by the makers) which led to this enquiry. I will go with the GL5 - anything which improves drivetrain efficiency.
Roger W

Roger,
what oil is recommended for a LT77 can depend on it's age a 75w-90 might be a bit thick until it warms up but a 'fully synthetic' 75w-90 like Castrol might be thin enough

you do need to use GL-4 in the g/box

I use the Castrol (GL-4) in my my Ford Type-9 after using the recommended Comma 'semi-synthetic' SW 75w-90 (GL-4) for the first two years and the Castrol instantly gave better gear changes even in the temperate April weather

this is the one I recommend - Castrol Syntrans Multivehicle 75W-90 Fully Synthetic MTF - http://www.opieoils.co.uk/p-739-castrol-syntrans-multivehicle-75w-90-fully-synthetic-mtf-replaces-smx-s-75w-85.aspx

it's been a very long time since I've had a car with a LT77 box but unless my memory is totally smashed I think engine oil went in some

whatever oil you use in a LT77 I'd recommend regular changing of the oil, more so with engine oil because it beaks down more (every two years or 24k-miles in the MGB Workshop Manual for engine oil use in the g/box), how often with a 'full synthetic' gear oil is up to you but I'd think of every 2 or 3 years

for thorough oil changes of g/box, r/axle and engine have the existing oil as warm as possible at draining and leave to drain for as long as possible to get as much existing oil and muck out as possible at each change

below is a chart to show the various engine and gear oils with ATF included


Nigel Atkins

Roger,
if you use a 'fully synthetic' GL-5 75w-90 oil in your diff please let us know how you find it

don't expect major changes and do bear in mind a thorough oil change and the use of any appropriate fresh oil would give improvements anyway

it might be that the only notable difference would be on a good rolling road readout

depending on what you use now, if you were to swap to the Castrol Syntrans Multivehicle 75W-90 Fully Synthetic MTF you may like me notice a more immediate and noticeable difference in the gear changes, especially if you use the car in all seasons
Nigel Atkins

Nigel
Back after a lacuna with our internet service (BT). I will try a synthetic GL5 in the diff. I am still unclear about the viscosity to use but will let you know how I get on.
Roger W

Roger,
I had to check what that word meant!

75w-90 is what you want as it's a multi-grade with a lower figure (75w) for cold weather that helps with drag a bit in the cold and it's what's been going in many diffs for years
Nigel Atkins

This thread was discussed between 13/05/2014 and 19/05/2014

MG MGB Technical index

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