BT7 rear axle seal

[Keith_M]

As I was looking over my BT7 today I noticed liquid dripping from the inside of my left rear wheel. At first I thought it was brake fluid, but after pulling the wheel and drum I could see that oil is dripping along the inside of the back plate. Fortunately the brake shoes and drums are dry.

My diagnosis is that the rear axle seal is leaking, which is really surprising because I rebuilt the entire rear axle with new bearings and seals during the restoration. They can't be more than 2 years old with only a few thousand miles on them.

I removed the brake shoes, withdrew and axle and pulled the hub. The seal looks fine, but it's obviously leaking, so I will order a new seal and gasket.

My question is: WHY? is this something that happens often with these cars? The part of the axle where the seal should ride looks fine. Have I done something wrong? and is there anything I need to do to keep it from happening again?

Keith

 

[CanberraBJ8]

Hi Keith

My axle has just gone back into the car after having it rebuilt - new seals, and new diff.

I had leaking seals too - they were 10 years old, and with very few miles on them. It had been suggested that they were in back the front - but that didn't turn out to be the case.

What the specialist who refitted the axle with new parts said was;

There are seals, and there are seals. He is a champion of NOK seals and claims all the others - NAK, NUK etc are not made to the exact tolerance that the originals are. In the end I believe he sourced some others that fit the exact requirement.
The seat that the seal fits onto must be in perfect condition - cleaned up with no rough spots. Perhaps this was the reason for the different seals - measurements adjusted after emery/polishing of the seat.

The bottom line he said was that the seal is only as good as the surface it is applied to.

I'm yet to drive the car to test his theory/quality of work ;-)

 

[Keith_M]

Hi Keith


It had been suggested that they were in back the front - but that didn't turn out to be the case.

What the specialist who refitted the axle with new parts said was;

There are seals, and there are seals. He is a champion of NOK seals and claims all the others - NAK, NUK etc are not made to the exact tolerance that the originals are. In the end I believe he sourced some others that fit the exact requirement.
The seat that the seal fits onto must be in perfect condition - cleaned up with no rough spots. Perhaps this was the reason for the different seals - measurements adjusted after emery/polishing of the seat.

The bottom line he said was that the seal is only as good as the surface it is applied to.

Thanks for the reply. I have double-checked and the seal is in correctly (although that's the kind of thing I'm totally capable of messing up!).

The surface on the axle housing that the seal rides on feels perfect. I make take a little 0000 steel wool to it before I re-assemble everything. Parts should be here Tuesday, so my down time should be short.

Keith

 

[Randy Forbes]

Were the rubber seal "lips" lubricated when they were installed, and how long before the axle was "used" meaning: could the lubrication have dried up by the first time the car was driven?

A rubber lip-type seal HAS TO BE lubricated, or it's practically guaranteed to leak.

As a rule of thumb, NEVER EVER install rubber seal, or O-ring dry.

 

[Keith_M]

Were the rubber seal "lips" lubricated when they were installed, and how long before the axle was "used" meaning: could the lubrication have dried up by the first time the car was driven?

A rubber lip-type seal HAS TO BE lubricated, or it's practically guaranteed to leak.

As a rule of thumb, NEVER EVER install rubber seal, or O-ring dry.

Hi Randy,
That could be it. Although I know I smeared a light coat of oil on those seals when I assembled the hub originally, it would have been close to 1.5 years before I actually put oil in the differential and drove the car.

This time will be different!

Thanks,
Keith

 

[57_BN4]

One thing that will kill a new seal is a shiny spot on the shaft from the old one. I found out last year that the correct finish for the shaft is 240 grit wet n dry rubbed to give a slight crosshatch pattern not unlike cylinder bores.

It looks quite rough when done right and the roughness provides tiny channels to retain oil for lubrication so it shouldn't matter how long between assembly and running. Andy.

 

[Keith_M]

One thing that will kill a new seal is a shiny spot on the shaft from the old one. I found out last year that the correct finish for the shaft is 240 grit wet n dry rubbed to give a slight crosshatch pattern not unlike cylinder bores.

It looks quite rough when done right and the roughness provides tiny channels to retain oil for lubrication so it shouldn't matter how long between assembly and running. Andy.

Wow. That's a new one for me. My axle housing is definitely shiny and smooth where the seal sits. I googled this and came up with a few highly technical articles that (based on my limited understanding) seemed to support the idea. Shouldn't be much of a problem to rough it up a little, but it sure seems counter intuitive to have that area rough when the seal will be spinning on it.

 

[steveg]

Two commnets: Speedi/Redi-Seals are pretty shiny.
The rear axle, if filled to the filler plug will have the bottom 1/3 to 1/2 of the seal submerged in gear oil so wouldn't run dry unless insufficient oil in the axle.

 

[Keith_M]

Two commnets: Speedi/Redi-Seals are pretty shiny.
The rear axle, if filled to the filler plug will have the bottom 1/3 to 1/2 of the seal submerged in gear oil so wouldn't run dry unless insufficient oil in the axle.

Steve,

Thanks for the input.

I had never heard of Speedi Seals, but after looking at them on the web, they do indeed appear to be very shiny. Hmmm....

Agreed that a portion of the seal will be submerged in oil, but that's assuming there's oil in the differential. The problem is that I didn't put oil in the differential for at least a year and probably 1.5 years after I assembled and installed the hubs. It was incredibly stupid of me. :stupid:

 

[57_BN4]

Yes, it was quite a surprise to me as well to find how 'rough' the desired surface is.

The table here calls for Ra 8-20 μin
https://www.skf.com/group/products/...aft-requirements/surface-roughness/index.html

And this table correlates roughness to sandpaper grit
https://www.ljstar.com/design/surface_charts.aspx

There is a lot more to seal surface condition than just sandpaper roughness but for the use our cars will get it is more than adequate to just give 'er a rub and put it back together.

The speedisleeves are finished to the above spec "The contact surface is wear resistant and machined to minimize directionality (0° ±0,05) with a finish of R[SUB]a[/SUB] 0,25 to 0,5 µm (10 to 20 µin.)." They appear more shiny than you'd expect from 240 grit because they are more accurately finished and may be fine polished afterwards.
https://www.skf.com/group/products/...als/wear-sleeves/skf-speedi-sleeve/index.html

Andy.

 

[Keith_M]

Andy,
This is really useful information. Far more readable than the stuff I found, and it does clearly indicate that 240 sandpaper is the appropriate finish. 240 is pretty fine of course, but it's still a rougher finish than is currently there and a much rougher finish than I would have expected.

The parts should be here tomorrow, so unless someone pipes up with a "whatever you do, don't sand that surface" comment, I guess I'll clench my teeth and give it try.

 

[steveg]

Andy,
This is good information - thanks!

This might also be relevant to some of the rear crankshaft seal kits not working as well as expected.

As an aside - sounds like it would make more sense to lube these seals on install with, say, white lithium grease - it might stay in place better than oil over a period of time before first use.

 

[Brinkerhoff]

I hate to just pile on 'cause your getting good advice but I'm adding this since nobody else has: are you sure the oil is leaking from the seal and not the o ring or the gasket? Sometimes the bearing will have spun on the stub of the housing causing it to wear slightly , you can tell if the bearing slides off the housing easily. You need to fix that if it does.

 

[Keith_M]

I hate to just pile on 'cause your getting good advice but I'm adding this since nobody else has: are you sure the oil is leaking from the seal and not the o ring or the gasket? Sometimes the bearing will have spun on the stub of the housing causing it to wear slightly , you can tell if the bearing slides off the housing easily. You need to fix that if it does.

Good thoughts. Thanks.

I'm pretty sure it's leaking from the seal because the leak goes down the front and back of the backplate. There was no oil where the hub meets the axle (where the O-ring and gasket are), and on disassembly the gasket had no oil on it. If oil were leaking there, it would have probably ruined my brake shoes (whew!).

I haven't pressed the bearing out yet, but I made a few exploratory taps with with an appropriate socket and a hammer, and the bearing is nice and tight in the hub.

 

[Brinkerhoff]

Not in the hub Keith, on the stub of the axle housing. The inside diameter of the bearing. It shouldn't slide easily on and off the housing stub.

 

[Keith_M]

Ah, OK. I'll check it.

Thanks!

 

[Keith_M]

Not in the hub Keith, on the stub of the axle housing. The inside diameter of the bearing. It shouldn't slide easily on and off the housing stub.

Sorry Brinkerhoff, I get what you're asking now. I guess the old brain is working a little slowly today.

The hub was plenty hard to get off the housing stub. Hard enough that I had to use my electric impact wrench on the hub puller to get it started (mostly because it's hard to get much torque with a ratchet 'cause the hub spins). After getting it started, it required using the ratchet on the hub puller to remove it completely. It definitely didn't just fall off.

I'll go back to sleep now...

 

[Keith_M]

Just finished putting it all back together. I would have been done hours ago, but I had to go watch my daughter play soccer. Some of you may remember how much I like watching soccer. I took a quick drive around the neighborhood and no oil came squirting out and the wheel didn't fall off, so I didn't do anything majorly wrong. I'll drive the heck out of it over the holiday weekend and see how it holds up.

Many thanks for all the advice.

 

[Keith_M]

Well...I've been driving my Healey quite a bit over the past few days, and I just checked that rear wheel: there's oil leaking down the back plate again:blue:

I'll pull it apart again this weekend, but I'm kinda at a loss here. The bearing fits tightly into the hub and it fits tightly over the axle housing stub, so it's not leaking around the bearing. The axle stub is smooth (I sanded it lightly with 240 grit sandpaper, but it still feels really nice and smooth), and the seal seems to fit nicely over the axle stub. The seal is nice and tight in the hub.

The leak is pretty small -- I'm wondering if there could be slight imperfection in the hub where the seal sits.

Any suggestions would be welcome.

Keith

 

[57_BN4]

How clear is your axle breather? If there is any more than a few psi pressure inside the axle then it'll come out of the seals. Driveshaft seal'd be leaking too if that were the case. Maybe you can make an adapter for the breather to apply a few psi from the air compressor to the axle housing and see if a leak forms. No more than 10 psi though.

If you have a camera with Macro mode, wash the seal in brake clean or similar solvent and take a very close-up, clear, well lit pic of the lip and blow it up on the pc screen. A strong magnifying glass would do as well. You should be able to see a sharp lip, if it is replaced with a flat then the seal is not bedding in properly. If the lip is present all the way around then it is unlikely to be leaking. It takes a little time to get used to looking at the lip, compare to a new seal for reference.

Any chance it is oil from earlier on still dribbling down?

Andy.