8 1/4 axles

JR_Charger

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Does anyone make performance axles for the 8 1/4? How much power can the stock axles take? I'm having a tough time digging this info up as Jeep stuff dominates the search results.
 

Backrd.Junkyard

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Moser Engineering. Later model axles have 29 splines as opposed to earlier 27 spline. Switching to a later carrier unit with more splines is a potential upgrade. LPW makes a girdle kit with a set of tie rods that connect up at the shock plates that add a lot of strength. The best option for a high strength 8-1/4 is to upgrade to the 29 spline carrier and install 8-3/4 Dana 60 Mopar housing ends for positive axle retention and order a set of 8-3/4 axles from Moser or Dr. Diff cut for 29 splines. Outfitted with the girdle and housing brace kit they’re supposed to be almost as strong as an 8-3/4 but a whole lot more mechanically efficient.
 

JR_Charger

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Moser Engineering. Later model axles have 29 splines as opposed to earlier 27 spline. Switching to a later carrier unit with more splines is a potential upgrade. LPW makes a girdle kit with a set of tie rods that connect up at the shock plates that add a lot of strength. The best option for a high strength 8-1/4 is to upgrade to the 29 spline carrier and install 8-3/4 Dana 60 Mopar housing ends for positive axle retention and order a set of 8-3/4 axles from Moser or Dr. Diff cut for 29 splines. Outfitted with the girdle and housing brace kit they’re supposed to be almost as strong as an 8-3/4 but a whole lot more mechanically efficient.

Well that sounds like just the thing. The brake line is supported by a clip on the differential cover though, isn't it? I don't see any accommodation for that on LPW's cover.

So, as far as LPW goes it looks like I need the 301-10C or 311-10C cover and the 341-A standard depth brace kit. The ARP bolt covers are nice. What are the AARP main cap studs for?

About the carrier unit, this carrier unit is relatively "open" and is for stock, one-wheel drive cars, right? - Link

Doctor Diff has this link limited slip unit, the outer casing is a different type of carrier, right?

I've currently got one-wheel drive so I'll need a limited slip unit. The Spicer trac-lok is only good for 350, which is not enough. What other options are there?

These are the housing ends I need? - Link

Here are Moser's 8 3/4 axles, but they all say 30 spline - Link.

DoctorDiff's axles also say 30 spline.
 

Roger63

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I got my limited slip unit from Dr. Diff and just dropped it in my 8.25 without changing anything else. Runs quite and performs flawless.
 

Backrd.Junkyard

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You have to call them to custom order a set of 29 spline axles. The ARP cap studs add quite a bit of extra clamp load to help keep the pinion pushing the ring gear away from center. A cap strap kit with studs would be of even more benefit, but require milling the tops of the caps. To my knowledge, the strongest sure grip unit available is an Auburn gear. You could run a lunchbox locker in the stock carrier but reviews are somewhat mixed on them. Those are the correct housing ends. What vehicle and engine combination is your 8-1/4 in? Eventually, mass, torque, and most importantly, SHOCK LOAD come into play in the sizing of the ring and pinion. A 4 inch stroke small blocks in a 3200 pound car with a manual transmission is considered by some to be the practical limit of a well built 8-1/4 axle.
 
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JR_Charger

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I got my limited slip unit from Dr. Diff and just dropped it in my 8.25 without changing anything else. Runs quite and performs flawless.

Is it this one - Link

How much power are you making?

You have to call them to custom order a set of 29 spline axles. The ARP cap studs add quite a bit of extra clamp load to help keep the pinion pushing the ring gear away from center. A cap strap kit with studs would be of even more benefit, but require milling the tops of the caps. To my knowledge, the strongest sure grip unit available is an Auburn gear. You could run a lunchbox locker in the stock carrier but reviews are somewhat mixed on them. Those are the correct housing ends. What vehicle and engine combination is your 8-1/4 in? Eventually, mass, torque, and most importantly, SHOCK LOAD come into play in the sizing of the ring and pinion. A 4 inch stroke small blocks in a 3200 pound car with a manual transmission is considered by some to be the practical limit of a well built 8-1/4 axle.

Have you got a link to a cap strap kit? I don't know what that is. Same with the lunchbox locker.

My Charger is currently a very base 72 318 auto. The 318 is not going to stay stock and may not stay at all, but at any rate I'm not shooting for more than 500 hp MAX at this time as that is twice as powerful as anything I've driven before. I don't want to do the Cars and Coffee fishtail of destruction. I've got to build up my skills before I'm ready for 900 hp in a car that doesn't drive itself.

I found a 29 spline Auburn diff a couple days ago, before the power went out and ate my work. The specs didn't say how much power it was good for though.
 

Roger63

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Is it this one - Link

How much power are you making?



Have you got a link to a cap strap kit? I don't know what that is. Same with the lunchbox locker.

My Charger is currently a very base 72 318 auto. The 318 is not going to stay stock and may not stay at all, but at any rate I'm not shooting for more than 500 hp MAX at this time as that is twice as powerful as anything I've driven before. I don't want to do the Cars and Coffee fishtail of destruction. I've got to build up my skills before I'm ready for 900 hp in a car that doesn't drive itself.

I found a 29 spline Auburn diff a couple days ago, before the power went out and ate my work. The specs didn't say how much power it was good for though.
I don't think that is the same one I bought, I will check. I'm making a shade over 400hp which the 8.25 will handle as long as you don't put slicks on.
 

Backrd.Junkyard

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There are no commercial strap kits for 8-1/4, or any other axle that I'm aware of. Actually, you wouldn't need to strap them with the LPW girdle. Straps are more of a band aid when a girdle isn't available. It involves long studs with spacers and then a 1/4 inch plate that goes across cap and a stud in place of the bolt that holt the adjuster lock. It's more of a Smithy home mill project unless you're on good terms with your machinist and ready to lay out the $$$. But it's just a method of preloading the caps when a girdle isn't available or strengthening the caps if it is (in which case it's really time to upgrade to stronger axle!). Given what I'm talking about with an 8-1/4 costs the same as doing it with a 9-1/4 and we're probably talking about a heavy third generation charger, I would find a 9-1/4 to retrofit. This moves you up to a stronger 31 spline axle. Sadly I've let several B body 9-1/4 70s station wagon axles get away from me through the years. But here's a video of a 9-1/4 truck axle being fitted for an A body. One thing I can say about a 9-1/4 is that the people I know who managed to break them said they knew better. Big tires, heavy trucks, and beating on them hard in the rough.

 

JR_Charger

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I don't think that is the same one I bought, I will check. I'm making a shade over 400hp which the 8.25 will handle as long as you don't put slicks on.

No slicks or racing, just looking for a fun cruiser. Car is a 72 Charger.

There are no commercial strap kits for 8-1/4, or any other axle that I'm aware of. Actually, you wouldn't need to strap them with the LPW girdle. Straps are more of a band aid when a girdle isn't available. It involves long studs with spacers and then a 1/4 inch plate that goes across cap and a stud in place of the bolt that holt the adjuster lock. It's more of a Smithy home mill project unless you're on good terms with your machinist and ready to lay out the $$$. But it's just a method of preloading the caps when a girdle isn't available or strengthening the caps if it is (in which case it's really time to upgrade to stronger axle!). Given what I'm talking about with an 8-1/4 costs the same as doing it with a 9-1/4 and we're probably talking about a heavy third generation charger, I would find a 9-1/4 to retrofit. This moves you up to a stronger 31 spline axle. Sadly I've let several B body 9-1/4 70s station wagon axles get away from me through the years. But here's a video of a 9-1/4 truck axle being fitted for an A body. One thing I can say about a 9-1/4 is that the people I know who managed to break them said they knew better. Big tires, heavy trucks, and beating on them hard in the rough.



I may go for a 9 1/4 in the future, but that will be more of a "stage II" thing. It's good to know the LPW girdle replaces the need for the cap strap.
 

hyde-park

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Hmm, I just took a complete functioning 8.25" out of my 1975 Coronet only because it has a slight gear whine from 45 mph and up. It has a track lock with 3.90 gears. I also have a semi complete 9.25" rear with a sure grip and 3.21 gears. I can't vouch for that one as I never put in it a car. It will need bearings at least though as an inspection revealed metal flakes in the gear lube.
 

Backrd.Junkyard

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With an 8-1/4 with th girdle and brace kit along with a semi floating 8-3/4 axle cut down to 29 splines, you should be good for anything an NA small block with an automatic with your probable 3300 plus pound weight with driver. If you plan on power adders, a third gen, or big block power in the future, go ahead and invest in the 9-1/4 (maybe a even a Dana or 9 inch!) to keep from having to spend the money twice.
 

JR_Charger

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FWIW.

Although the consensus among many Mopar enthusiasts is that a Sure-Grip (limited slip) equiped 8.25" rear is good for up to 500 crank horsepower, it fares much better in street applications than the strip, and in lighter cars than heavy cars.

Link
 

JR_Charger

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I've been looking at Moser's 8 3/4. I'm restoring the car now so I'll use the 8 1/4 as a stepping stone and later on when the whole car doesn't need money and I'm making real power I'll upgrade to the 8 3/4.
 

JR_Charger

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I ordered the Moser 7400 housing ends from Summit. I noticed Summit also sells these spider gear sets - Link

Is this something I will need to buy separate from the axles and limited slip, or will one or the other of those come with this stuff?
 

Backrd.Junkyard

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If you buy a limited slip, all that will be loaded into it. I myself am hoping to similarly upgrade my 8-1/4 I’ve got to put under my all steel Duster. With built 318 power and 3200 pounds or so with me in it, it should handle anything I throw at it.
 

Backrd.Junkyard

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Also, the reasons I didn't suggest an 8-3/4 is because they're usually more expensive and they are less mechanically efficient (absorb more power) than the later designed axles. For the people that are bolting slicks up to an 8-3/4, they really should be back braced. There is some evidence out there that the stock stamped steel housing toes in under heavy loading. Some people et quicker when switching from an unbraced 8-3/4 to a Dana with the same gearing, even though the Dana is around 40 - 50 pounds heavier.
 

JR_Charger

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40-50 lbs doesn't sound like a significant amount of weight except for hard core racers. Maybe I'll scratch Moser's 8 3/4 off my wish list. Sure is pretty though!

How much power do you think you can squeeze out of that 318? There's a guy on YouTube who's claiming 600 but if that is real I wonder how streetable it is. On the other hand, if it's possible to get 900 out of a little Japanese 3.0 with turbocharging, could a 318 do it too if built properly? That's more than I'm going to want for a while, but what I'm trying to say is, "Why throw out the 318?"
 
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