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MG MGB Technical - Diff Cover Gasket - Tube Axle

I'm just in the final stages of finishing the overhaul of the rear axle on my MGB and I am about to fit the differential cover and would appreciate a bit of advice.

Is it recommended to use a sealant on the paper gasket when refitting the diff cover? Also is there a recommended torque setting for the cover bolts? I've searched the web and can't find any.

Thanks

Andy
Andy Robinson

It's a good idea to use some gasket sealant on the cover itself, but not on the differential itself. Make certain that the mating surfaces are clean and that the cover is completely flat where it comes into contact with the axle assembly for a perfect seal. The bolts should be torqued to no more than 15 lbs. RAY
rjm RAY

Only a smear, non-setting not that poxy silly-cone stuff.

How thick is the gasket? The only time I've replaced one I made one out of thin card. If it really is paper then you might be crumpling that up trying to smear it. Not sure why one wouldn't put it on the diff casing and the cover, except that you would go round the bolt holes in the casing so as not to fill the holes and therefore push it into the casing when inserting the bolts.

No special torque figure given in the books, so just the standard for that thread size, so Ray's 15 ft lb is fine.
Paul Hunt

Thanks Ray and Paul. I planned to use Hylomar Blue, which as a non setting sealant has been great when I have used it on my cars before.

On my quest for the torque settings for the diff cover bolts, I have come across a lot of debate about the correct diff oil to use. I've decided to stick with EP80/90 gear oil as originally recommended by the manufacturer.

Andy
Andy Robinson

Andy, Hylomar Blue should work just fine.I also use EP 80/90 gear oil in my differential. Try to locate oil that's rated as GL-4 and not GL-5. GL-5 has a high amount of sulfur that can damage brass components. RAY
rjm RAY

As far as the oil goes I disagree.

GL4 is primarily for gearboxes, GL5 for differentials. The last Castrol oils (the V8 gearbox takes gear oil) I bought clearly state that GL4 is gear oil and includes a picture of a gear lever, and that GL5 is differential oil and includes a picture of an axle with diff. Both are 80W/90. GL5 is designed to take the additional stresses of the hypoid gears in the diff.
Paul Hunt

Thanks Ray and Paul for the info. I have copied some text below from a couple of web sites

http://www.mgexp.com/article/mgoc-basic-2.html

All post 1950 MGs require EP 90 oil for the rear axle, with the exception of the MGB V8 which uses EPX 80/90. The oil in the gearbox and back axle operates under considerable pressure and serves a vital function protecting expensive gear components from wear, it is sensible to always ensure that the correct specification of oil is used.

GL4
Description

EP Transmission oil to API GL4 for classic transmissions. High quality solvent refined mineral base stocks with performance additives.

Application

Use in gearboxes and differentials requiring extreme pressure lubricant to API GL4.

User Benefits
◾Wide ranging applications.
◾Ideal for vehicle gearboxes and trans-axles. Recommended for gearboxes with overdrive.
◾Suitable for rear axles not requiring Hypoid oils.

http://www.millersoils.co.uk/automotive/tds-automotive.asp?prodsegmentID=197§or=Classics

GL5
Description

High quality solvent refined base stocks with performance additives for highly loaded hypoid transmissions.

Application

Use in Hypoid differentials requiring extreme pressure lubricants and GL5 specification. For highly loaded hypoid transmissions. Also suitable in transmissions with brass and bronze components.

User Benefits
◾Well proven superior performance. Provides 'trouble free' operation.
◾Imparts exceptional load carrying ability. Friction modified for mild limited-slip applications.

http://www.millersoils.co.uk/automotive/tds-automotive.asp?prodsegmentID=217§or=Classics

The way I read all this is GL4 for basic transmissions with overdrive. GL5 for V8 applications. Well at least I think so.......

Andy
Andy Robinson

That's my understanding.
Paul Hunt

GL-4 EP-90W oil has been the standard of the industry for many, many years. It's more than adequate for the needs of an MGB. GL-4 is an extreme pressure oil designed to work in differentials as well as various gearboxes.I've been using it for close to fifty years in rear axles without any problems whatsoever. GL-5 contains a higher level of sulfur than can attack brass or bronze components in your differential. RAY
rjm RAY

My reading of the GL5 debate.
I read a technical paper recently and if I remember it correctly it read as follows.
The additives in GL5 are superior in their high pressure and wear capabilities. They are "sacrificial but form a temporary bond with the gears etc.. and when scuffed away are obviously replaced. However they bond so well to the parent metal that, in the case of copper alloys, when scuffed away, they remove some of the softer alloy.
It's an on-going and often discussed topic but I'll stick with GL4 Hypoid 90B for my V8's.
Allan Reeling

This thread was discussed between 31/01/2016 and 04/02/2016

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