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MG MGA - Oily brake backplate

Hi All .
Any idea what has failed to turn my dry brake back plate so oily.
My thoughts are oil deal on the rear hub but as is reasonably new I wondered what else it could be.
Thanks


s page

S,
I'm guessing brake fluid seepage from somewhere because axle oil leaking past the hub seal would be on the inside of the brake drum and drop off at the bottom of the drum when left long enough. Such oil would not normally 'wick' on the backplate.

Regards
Colin
Colin Manley

Brake fluid would be inside the brake drum. Gear oil leaking from the hub seal does indeed run down the inboard side of the brake backing plate. That is the intentional design. Replacing the seal will stop the leak, but the leak may return shortly due to damage of the new seal. The seal rotates with the hub, and the mating seal surface is on the fixed axle housing. If the ale housing has a groove worn in it, that will damage a new seal. The fix is to install a Speedy-Sleeve to repair the axle housing surface, and then another new seal. See here:
http://mgaguru.com/mgtech/rearaxle/ra101.htm
barneymg

Hi Barney.
I was leaning towards the oil seal. On my racing Sebring Sprite I am about to try a sealed bearing due to scoring and pitting on the hub. This is easier and cheaper than speedy sleeves.Thanks again for your help and site.
s page

I thought a sealed bearing just kept the grease in and dirt out of the brg. Does it stop the flow of lubricant past the bearing? If not you will get it in the drum.
If your new seal leaks, take Barney's advice!
Art Pearse

Brake fluid leaking from cylinder seals will run inside the backplate, yes, but fluid leaking from the banjo fitting into the brake cylinder will run down the outside of the backplate as photographed.

Regards
Colin
Colin Manley

I had brake fluid running down the outside of the rear brake plate. It came from the cylinder boot which filled with brake fluid until the level inside was high enough for the fluid to seep through the cylinder slide mechanism and run down the outside of the back plate.

I had previously replaced the cylinder seal with a modern clone which had shrunk to the same OD as the cylinder ID, hence the leak after only about 300 miles.

There was no oil leak from the hub seal.

Cheers

Dave
Bolney Coupe

Could be brake fluid as Dave says but more likely diff oil that is best fixed as Barney says. If your bearing lock nut hasn’t been tighten properly 150 ft/lbs bearing may have worn banjo housing stub and will need a bit of Loctite bearing mount.
Mike
Mike Ellsmore

If you give it a squirt with the garden hose-
If it's brake fluid it will wash away but if it's oil it will stay there
willy
William Revit

Hi,
Thanks, all good advice. I hope to look later this week. I will let you know what I find.
s page

I have fitted sealed bearing to this style axle in the past. The seal will stop the oil passing through from the back axle, but I would still put the lipseal in place anyway. Just make sure the seal is well greased as it won't (hopefully) have any diff oil to lubricate it.
Graeme Williams

In my limited experience, the oil leak from the diff along the axle can and will end up inside the brake backing plate and thus foul the shoes. Barney's site gives excellent repair guidance. I sourced the Ford socket for tightening the pesky nut. It works but a "tommy bar" is best to provide centralised torque on that damn nut!
Tom Heath

Your picture shows a very rusty backplate, I reckon you have a slave cylinder gone. Brake fluid will strip the paint and leave it rusty. Back axle oil will stop rust.
Whip out the brake shoes and check the brake cylinder.
How's the master cylinder level doing? If the brake shoes are wet it would fail an MOT and would need replacing too.
PeteT

This thread was discussed between 14/10/2017 and 02/11/2017

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