So what is leaking here.......

[5akman]

New to me 1980 K20 project truck. As you can see, its had a rear disc brake conversion. Both ends of the 14 bolt FF axle look like this. Having never torn into a FF to know what seals are at the outboard ends, does this look like a leaky axle seal or leaky brake caliper?

 

[77 K20]

I'd say it is from a leaky axle seal. The axle seal if it leaks will then fling itself into the inside of the disc brake- then will come out the vent holes (behind the wheel lugs) and make a big mess.

I'd also check your master cylinder and see if your brake fluid is topped off...

They are pretty easy to change. But you do need a special socket for a nut inside the hub.

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There should be a metal tab locking that nut in place. Pry up with pick/screwdriver then use castle nut socket.

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When I've replaced mine before I put the jack under the axle near the tire and lift up just the side of the truck quite a bit. Then use a jack stand. Then I eat lunch or take a break. This allows the gear oil in the axle tube to drain back to the differential a bit. Otherwise when you remove the axle shaft it will sit there and drip out and make a huge mess.

 

[5akman]

Ok, so the axle seal would be different than the inner hub seal then? I'm thinking that if I pull the "cap" off with the 8 bolts in it at the end of the axle, that I wouldn't find a seal correct? guess I need to find the manual or an online pic.

 

[77 K20]

There is gasket under the "cap"... the cap is the end of the whole axle shaft. On the other side of the "cap" there should just be a piece of plastic with some ribs on it. I clean it with carb cleaner/brake cleaner then put a very thin coating of sealant/RTV on it when reassembling. This piece usually doesn't leak.

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Now when you remove the axle shaft, the pre-load nut (think that is what it is called), the lock ring, another nut... then take the whole hub/disc brake assembly off. Slides right off the axle stub. Then if you turn it around and you look at the "inside" of the disc brake that is where the axle seal/oil seal is. Remove that then inside there is the wheel bearings.

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This picture looking at the inside of the disc brake shows the axle seal. Its blue. When that leaks it then drips all over. Oil residue will also get on the inside sidewall of your tires.

 

[77 K20]

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Here is a nice diagram with official names. What I call an axle seal is apparently a "seal, oil deflector".


Is the truck driveable? It messy enough it might be worth using a can or two of brake clean and blasting everything in the area to clean it up. Then check to make sure your differential fluid and brake fluid are full. Then drive it a bit and keep an eye on it. The oil seal can be seen by crawling partially under the truck and looking at the inside of the brake disc. Without the dust shield on the backside you can see it will.