Limited Slip Differential for 8 1/4?

[jeremy]

I'm beginning my journey into the world of rear ends and gearing.  I found this Spicer LSD - Link

It's only good for 350 hp, which is more than I'm likely to get out of the 318 for some time, but ultimately I'd like to be in the 4-500 hp range.

My diff is leaking, and I've got easy access with the tank out, so I reckon now is the time to deal with it.

What other options are available?

[Nacho-RT74]

Cass at DrDiff is usually the best resource for this kind of stuff. If you go to Randy's ring & pinion you could compare prices too. That's another option. Sure there are more.

I never had read about an Hp limitation with carriers... maybe is just pointing out to the full axle assembly itself? This would mean you would end to upgrade to 8.75" if you think on more Hp.

[DynoDave]

Jeremy,

First, you need to know what the differences are in the types of rear differentials, their advantages and pitfalls. Then you can choose the proper design for the type of driving you will do / type of car you will build. There are many articles on the subject. The piece you linked to is a good, somewhat universal piece. a good answer for a street car wanting to balance noise of operation, good cornering habits, and of course straight line traction. Here the "Trac-Lok" name is a little misleading, as it appears to be a clutch-type limited slip, and not a locking differential as the name seems to imply.

DuckDuckGo search

Then as you've observed, you need to decide based on strength. Only you can decide if it makes more sense to add some sort of improved differential now, to the 8.25" axle, or if you should live with what you have until you make the jump to a more powerful engine, at which point you will likely be changing the whole axle assembly, perhaps to an 8.75 as Nacho mentions. It's a tough decision to make.

But that $365 diff will need fluid, a friction modifier (additive, if not in the base fluid), perhaps bearings (or at least labor to transfer your old ones), axle seals, differential cover seal, and some shims / labor to properly set up the gear backlash. You'll need gear paint and some tools to do it your self, or a good shop willing to play along. It all adds up pretty quick. At this point, the only thing you haven't done is change the pinion and wheel bearings. Should you just go ahead and do those "while you're in there"? And this assumes you are keeping the same gear ratio (318 / 8.25 axle is not typically packed with a performance ratio). A gear change will set you back another couple of hundred dollars. And you'll have to pay shipping on all these items.

As Nacho also mentioned, a conversation with Dr. Diff (Cass) will help fill in some of those blanks on pricing.

[Nacho-RT74]

actually lot of ppl in Vzla races with 8.25" axles on 400 Hp or so... most of them 318 or 360 and A bodies, of course. I think we are underestimate the 8.25" potential

[jeremy]

This Hemmings article makes it sound like the 8 1/4 isn't so bad - Link

I asked Uncle Tony about it, before his YouTube channel blew up, and he said to stay with the 8 1/4 unless planning to go over 500hp. But he blew up the 8 1/4 in Bottle Rocket and is upgrading to the 8 3/4 (Bottle Rocket segment starts at 1:13) -



Here's the 318 build in Bottle Rocket -



I love the way that motor sounds. I'd be happy with an angry little 318 - this doesn't have to be my fastest car.

I reckon some degree of work on the diff has to be done at any rate. It's clearly leaking. I don't know how much fluid is in it, if any, or how to fill it back up.

I drove the car for years with the stock differential, and never raced it once. I can leave the diff upgrade alone for now and work on another part of the car, if that's what makes sense. The tank is out of the way ATM but it's easy to drop the tanks in these cars.

[DynoDave]

I'm not being disrespectful of the 8.25. It's a good axle. There's one behind the 400/4 in my Cordoba (for now).

But Chrysler had to stand behind what they built. So I look at what THEY did. And they did NOT put the 8.25 behind ANY performance engine. That's enough for me. But yes, the 8.25 is a good piece. And if you are going to do cam, headers, intake with the 318 and be at 300 horsepower or less, I would not hesitate to keep the 8.25 for the street. Racing, I'd replace it. More power or torque than that, I'd replace it. But as I said, a personal call.

If you're in there and want to fix the diff cover leak and change the fluid, that's a totally sane thing to do. That 40+ year old whale blubber is passed it's prime for sure.

Is the pinion seal leaking? How about the axle seals?

[Nacho-RT74]

sure... 8.25" will be safe enough with some engine upgrades for street fun... not race of course, even less on a B body. Maybe on an A body will hold a bit better

[Nacho-RT74]

I don't get what he said about reversing pistons and swaping the bank side of the block will change the offset and angularity ??

[jeremy]

[jeremy]

Oct 7, 2020 6:56:18 GMT -5 DynoDave said:

I'm not being disrespectful of the 8.25. It's a good axle. There's one behind the 400/4 in my Cordoba (for now).

But Chrysler had to stand behind what they built. So I look at what THEY did. And they did NOT put the 8.25 behind ANY performance engine. That's enough for me. But yes, the 8.25 is a good piece. And if you are going to do cam, headers, intake with the 318 and be at 300 horsepower or less, I would not hesitate to keep the 8.25 for the street. Racing, I'd replace it. More power or torque than that, I'd replace it. But as I said, a personal call.

If you're in there and want to fix the diff cover leak and change the fluid, that's a totally sane thing to do. That 40+ year old whale blubber is passed it's prime for sure.

Is the pinion seal leaking? How about the axle seals?

The circled area is the only leak I see.  The dark spot on the other side is overspray from painting the tank strap.