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– Hello this Davin with
Hagerty and our DIY series. I’m in the middle of putting up gear, install an old 12-bolt on our SS396 car, and I ran into a small snag with the seal. Now if you wanna see that full install, that video will be right up here. But, we wanted to highlight
a little issue here we ran into directly with the seal. In ’69 there’s actually two seals, and they carried it on
for X amount of years. But there was two seals. One for the truck and one for the car. And the snout on the
housing’s slightly different, and that’s why there
was two different seals in the inset where the
sealing surface is at. Now what’s happened is, the car seal, for whatever reason,
has been discontinued, and the only one available
now is the truck seal. Typically speaking,
your pinion bearing here should be free-floating by about, at least a quarter inch or eighth inch, somewhere in that ballpark. And what I caught was,
this doesn’t have any when this seal is installed
fully like it’s supposed to be, where this surface hits
the surface of the housing. So come over here to the workbench, I’ve done a little homework. I’ve come up with these
three different seals that are of three different manufacturers. This one happened to
be in out initial kit, and these are two other
aftermarket, a Timken and a SKF. But the point is, all three of
these are slightly different, but none of them will actually function the way their supposed
to if fully installed. And you can see a good witness of that. So here’s your sealing
surface on the yolk, and it has this chamfer that’s
roughly an eighth of an inch. If I put this on here, I’ll flip this over so you can see it. That sealing surface, the
ridge, I’ll pull back. The ridge that actually seals, is not on the large diameter of the yolk. It’s still riding on the chamfered edge. So, yes it’ll go on there. It has a marginal seal relative
to the dust side of things, but not on the grease seal side. So this will install,
everything will go together like I showed you over on the axle, but this is still gonna leak. Now, what I found is, you can
do three different things. You can install this and
not install it fully, so you would leave a gap. Now it my opinion, that leaves
for a lot of margin of error because it’s easy to have it rocked inside the housing slightly. Second area is you can take
a piece or welding rod. This happens to be a little small, but the point is the same. Use a, say a eight-inch welding rod, bend it up and slip it
over the top of this. Now you have a firm stop, and you’ll have a gap when you’re done. And then the third option, which I think is probably the best option, is actually a solid ring. I happened to machine this out of a piece of steel I had laying around. Luckily I have access to a lathe. And this will go in here then, and act as a physical stop. That’ll give me an eighth inch of a gap, and if you can see
here, now my eighth inch forces that sealing ring up
onto the sealing surface. I’m sure somebody’s out there thinking boy, that sure is a hack
way to install that, and you know, that’s probably right, but at the same token, it
is the only way to do it because there are no seals available that brings this sealing
surface toward the yolk further. They’re all inset like this,
so the only way to do it is to short install it. If you an aftermarket
housing, for instance, like a Moser or Strange,
they’ve actually increased the length on that casting
and that gets away with that so it’s only on the stock
12-bolt housings from GM that are short, that needed that longer, we’ll call it longer seal this way to install these correctly
and make a good seal. So if you have a stock housing, you’re subject to only
having access to these because this is what’s available, then you’ll have to short
install it by an eight inch. And you can use space or you can use a couple different ways to use a spacer, and that’ll create a good seal. And you won’t have any leak problems. All right, hopefully that
was a good explanation, and it helps somebody out there because quite frankly, there’s a
lot of 12-bolts out there, and I betcha a lot of them are leaking if they’re not installed correctly. Again, hopefully this was helpful. Click the link, share it,
and you can be the hero at the next car show when
you see that drippy 12-bolt. (funky music) Oh, look at that. Now it actually has a
float like it should.

53 thoughts on “The ONLY WAY to fix a leaking 12-bolt GM rear diff pinion seal | Hagerty DIY

  1. Kinda weird it’s completely discontinued, and no after market parts.. I’ve ran across seals that is still available by the OEM, and if it’s discontinued, an aftermarket is available.

  2. I dunno, man. Looks good to me, but I just got told off when I dared ask about if it were possible/a big deal to reduce some costs by doing some of the work myself (simple body work to replace a damaged door and repaint) and bring things in when my car was at the point of needing a professional shop. Evidently, everyone's a "youtube mechanic" these days and his 40 years to my 20 years working on cars meant he was right to get pissy at having to do less work and still get paid for his time, and it'd be like "bringing your own floss to a dentist appointment." Never heard someone talk themselves out of a $1000+ (quoted) job so quick.

  3. I'm very curious…. I watched your last video when you did this modification. What I am wondering is if you push the seal as far as it will go up on the yoke (bottoming it out against the yoke) and it is not going far enough to seal on the sealing surface of the yoke, how is the spacer ring making the seal go past where it bottomed out on the surface of the yoke when it wouldn't go past the bottoming out without the spacer. Looks to me like you are not gaining anything with the spacer. When you tighten the nut on the yoke, it is going to crush the seal and ruin all chances of any kind of sealing. Also the yoke will be rubbing on the seal and cause almost instant failure. Only way this ring spacer will do any good is if when you demonstrated the oil sealing part of the seal not going far enough on the sealing surface of the yoke, there was still some space between the front of the seal and the back of the yoke. The way it appears in the video is you bottomed the front of the seal out against the back of the yoke. If this is the case, then the spacer ring will make more problems than it will fix.

    But all this analyzing I'm doing may be all wrong if there is plenty of room for the seal to go 1/8 inch closer to the back of the yoke without hitting. If that is the case, then I just wasted 10 minutes of time….. But in my defense….. it didn't appear that way.

  4. Correct me if I'm wrong, but the yoke still on goes in so far, on the seal, because of the construction of the of the seal. You will have the correct spacing to the bearing however.

  5. But if the yoke is bottomed out in the seal spacing it from the diff housing wont make a difference no?

  6. Doesn't that push the seal into the pinion yoke and cause the cap on the yoke to ride on the seal seat ring?

  7. Thank you that explains why no matter what manufacturer seal I use it still leaks I learned something tonight

  8. Well that explains everything! I was wondering why the new seal didn’t fit like the original when i rebuilt my 12 bolt last year.. great… now i need to be on the lookout for leaks… thanks for the tip!!!!

  9. I recently had a shop install a Posi unit in my 10 bolt rear end and the shop called me to tell me they weren't happy in the way it was sealing so hopefully they watched your video in case a 10 bolt rear end has the same issue. It hasn't leaked any yet.

  10. What heck man? I find it hard to believe that no one is making car 12 bolt seals considering how popular the axle is within the muscle car community. I have yet to find someone who was enthused about building a truck 12 bolt….

  11. Good find! Looks like you could turn the flange off of the seal so the outer edge is at the same height as the lip on the dust side. Effectively narrowing the seal the distance needed to get the inner lip on the yoke journal. Then install the seal until it's flush with the housing. The flush outer edge will insure the seal lips are perpendicular to the yoke. No extra metal or fabrication needed.

  12. I'm confused if the yoke is bottomed out in the seal how is a shim going to help when the sealing surface is not touching the end of the yoke it seems that the sealing surface is too short!

  13. I love Hagerty's videos so much I think I need to buy a classic car just so I can get their insurance

  14. I see exactly whats goin on! Thank u very much for this info i needed to know this i have a 69 c-10 and a 67 impala!

  15. You can put a sleeve over a harmonic balancer and seal it, maybe the same can be done for the diff, a bit longer

  16. Your thinking inside the box. The 12 bolt was introduced in 65 lots of options out there mine don't leak and it's not shimmed out.

  17. I am glad you posted this! I have a lot of 12 bolt diffs,lots of c10's to put together,I will definitely be watching out for this when I tackle the diff seals soon! Thanks!!!

  18. I'm a little lost if the seal won't go far enough on the yoke to clear the chamfered edge. What are you doing cramming the seal in? Won't that possibly cause a rubbing noise from the face of the seal and the yoke flange/dust shield?

  19. Thanks for the video and great advice. I replaced the seal on my old 12 bolt. The silly thing kept leaking. So I figured and an expensive repair. I stumbled on your video, and decided to check it out. I found a spring in my shop with a long enough tail on it, and was the right width. Cut off the tail, bent in in a circle real careful like, slightly smaller than needed so it would hold itself in there nicely. Backed out my new seal just enough to get the ring in there, tapped it back in tight to the ring, and lo and behold, works great! Not a drop. Thanks again!

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