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Axle leak at backing plate

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SteveHall64Healey

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I have diff oil leak at the backing plate, where oil is leaking down the inner and outer faces of the backing plate. It is definitely not brake fluid.

I suspect the oil seals may be bad and began by removing the half shaft and noted immediately that oil came out through the bearing. I think the purpose of the oil seal is to keep oil in the axle and out of the bearing - is this correct? Are failed oil seals the likely culprit?

Thanks
Steve
 
SteveHall64Healey said:
I have diff oil leak at the backing plate, where oil is leaking down the inner and outer faces of the backing plate. It is definitely not brake fluid.

I suspect the oil seals may be bad and began by removing the half shaft and noted immediately that oil came out through the bearing. I think the purpose of the oil seal is to keep oil in the axle and out of the bearing - is this correct? Are failed oil seals the likely culprit?

Thanks
Steve
Click to expand...

The bearing runs with the lower half in the axle oil. It is not a sealed bearing. As discussed in the linked thread, too-thick gaskets permit bearing to spin, the heat from which causes seal failure and oil leakage.

This is a common problem.
 
Steve--

The paper gasket and O-ring in the outer face of the hub are merely designed to keep oil from leaking from between the half-shaft and the hub.


If you have only removed the half-shaft and not yet pulled the hub you have yet to access the lip seal which is pressed into the inboard face of the hub and rides on the machined end of the axle housing. This seal is what keeps oil within the hub and yet allows oil to lube the bearing if need be. (The bearing may be sealed (on both sides), semi-sealed (on its inner side only--which allows axle oil to lube it) or not sealed at all, but it plays no real role in keeping oil within the axle assembly.)

The culprit is almost certainly the lip seal, and when you replace it you should make sure that the polished surface on the axle stub is not scored or worn. If it is you should restore the surface with a speedi-sleeve to give the new lip seal a good surface on which to ride.
 
Michael,
That's correct the immediate culprit is the lip seal.

I believe this is the usual failure scenario - it was mine: the lip seal fails because the bearing spins and generates a lot of heat. The reason the bearing spins is the aftermarket gaskets are too thick. The thick gasket keeps the axle flange from properly clamping the spacer ring protruding above the outer rim of the bearing, which spins in the hub and overheats the seal.

Discussed in linked thread with documentation.
 
Last edited:
Steve--

You may be right about the cause and in any case he is probably gonna have to replace the lip seal.

Frankly I have never had an axle leak on my 100 but have experienced lots on the Courier and the G4, both of which use BMC A (Spridget) axle housings, even though fitted with double-bearing hubs. My take is that flexion under racing conditions causes slight deflection between the hub and the axle stub, resulting in wear on the axle tip and/or the lip seal, bearing damage, wet brakes, etc.

If you're lucky you can even spin in your own oil leak!
 
Really helpful everyone - thanks!

The lessons I am taking here are:
1) replace the oil seal as it is likely the culprit, and
2) use Permatex Gear Oil Gasket maker instead of the paper gasket because current paper gaskets are too thick and will cause bearing sin.

two questions:
1) which is the correct orientation for the oil seal? It is a channel shape in profile: |___| -does the channel face inboard or outboard?
2) when measuring for clearance between the outer face of the spacer ring and the hub face, in the absence of the paper gasket, what should my target clearance be?

thanks,
Steve
 
Steve--

As to yor first question, after removing the old lip seal place the hub on a flat surface with its inboard side face up. Take the new lip seal and with what you describe as the "channel" facing down (outboard) carefully press/drive the seal into the hub. Obviously you will want to do this carefully and gradually so that the shape of the seal does not get distorted. Before reinstalling the hub carefully inspect the polished surface of the axle stub and if it is scored, scratched, etc. restore it with a speedi-sleeve.

I cannot comment on your second question and will defer to Steve and others who have knowledge of the issue.
 
Steve, Michael is correct and if you look at Section J, page 208 in the Bentley manual there is a really clear exploded view that shows the relative positions.
BTW, I like to smear a little sealant on the outer side of the seal to help make sure it seals to the hub housing. ​

As to your questions #2, the top of the same page in the manual says the spacer needs to extend .001 to .004 beyond the hub and paper in order to 'pinch' the outer bearing race.

My method is to assemble the bearing & spacer without a paper gasket. Make sure the bearing is fully seated, then place a straight edge across the spacer and check with feeler gauges to find how much it is extended. You may get lucky and find the purchased gasket is the right thickness, but, if not, make a gasket of whatever thickness you need (copier paper, yellow tablet paper, whatever?) - eg, if the distance is .012, then find some .010 paper for a gasket and you will then have .002 protrusion. If it only protrudes .001 to .004 then no gasket and paint it with sealant. otherwise, paint both sides of your gasket with a thin coat of your favorite sealant (I prefer Permatex 300) and don't forget the 'O'ring.

The idea is enough protrusion to 'pinch' the outer bearing race to prevent turning but not enough to possibly distort the hub.

Dave
 
Steve, IMO 40# is not near tight enough.

Mine are bolt-on wheels, not knock off adapters, and I have always used 65# & never had one loosen. However, mine are also easy to check regularly :smile:.

As steveg noted, there are lots of charts with different ranges, e.g. Tire Rack's website says 70-80 for 7/16" stud/nut but also states that figure is for dry threads and conical nut surface so there is maximum friction included in the calculation.

Dave
 
Hey, thanks Steve...I've been using 65# for so long that I couldn't remember where I originally determined the number :smile:! I completely forgot there was a torque spec in the Bentley book for pressed wheels.

Dave
 
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