8 1/4 axles

Backrd.Junkyard

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The guy on YouTube with the 600 HP 318 in the "I think" "68 barracuda fastback has a four inch crank 393 inch motor. My experience with a stroker 318 is limited to a friend's 4500 plus pound W150 club cab with a .030 over 4 inch stroke 1973 based 318/391 stroker. It had Edelbrock heads, comp XE 274H, and an air gap intake. They're stout! In this video it has 33X12.5-15s and 3.90 gears. NV 4500 five speed through second and third. It was surprisingly streetable to be in such a tank. Incidently, the stock 9-1/4 lives on without problems in that truck, even though it has 360 industrial power now.
 

JR_Charger

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Glad to hear it's streetable. I understand the appeal of 500+ cubic inches, but that's going to be a different build for me.
 

Backrd.Junkyard

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Well, you probably caught that is actually a 4 inch crank 391 inch small block. I'm a proponent of small block strokers in B bodies, especially cars that originally came with small block, poly, or slant power. The lighter piston mass makes for great acceleration, and a small block with aluminum heads, intake, and headers happens to weigh the same as a slant six. From a performance standpoint, weight reduction not only makes a car quicker, it makes for better handling and stopping performance.
 

JR_Charger

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I agree, I'm into "simplicate and add lightness" which is one of the reasons I'm glad to be working with a base car (also less stuff to restore!). I like the idea of keeping the light 8 1/4 in back if it will hold up. If a base 318 3rd gen Charger with aluminum heads/intake/headers comes in around 3300-3400 lbs (don't know how reasonable that is with steel fenders) than that is in line with a Viper. 4-500 hp is all early Vipers made stock, which appears to be well within range of a built 318. I plan on doing the Viper brakes in front and Caddy/Mark VII brakes in back, so braking should be similar. Handling, probably not with the torsion bar suspension, but Uncle Tony says Chrysler's suspension is perfect for drag racing so I can't give that up (even if I'm not drag racing). 3rd gen Chargers did race at NASCAR and Le Mans, albeit in heavily modified form, so they must have some fundamental level of goodness to them. Chrysler made them shorter and wider than the 2nd gen for a reason. And it's almost a front/mid engine layout. Half of the engine is behind the front axle. So, a lightweight 72 Charger may not be the all time best car but I think it has an interesting combination of features, especially if you like room and a bench seat. I've never seen a Viper you could pack six people into. :lol:
 

1STMP

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I'm running a narrowed 8-1/4 from a 1985
Diplomat police cruiser. (the axle tubes are
a single Dia and don't taper towards the carrier). A LPW 301-10C girdle drilled for a
watts link. I removed the foot from the torque
bolts so they make direct contact with the
bearing caps. The axles have been narrowed
3" per side. The housing is set up for a 4-link
rear. Drive train is close to stock 440 with a
2800 stall conv/727. There are disc brakes
installed which will capture the axle should a
C clip fail so a C clip eliminator kit wasn't
required.
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JR_Charger

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Are tapering axle tubes weaker? The 85 is an improved/stronger design?

I'm using mine because I don't want to throw it away. It took me all over the place when I was young,

What's going on in pics 3 and 4?

Are you planning to leave the 440 stock?
 

1STMP

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Police/taxi applications got the non-tapered
tubes. I don't think the tapered tubes are any
weaker other than the amount of weld at the
carrier. Common practice in the 4x4 world
to clean and weld the tubes with a bead all
around.
Pic 3 shows the swivel foot on the torque
bolts for the LPW girdle. I didn't care for the
way they landed on the cap bolt and bearing
cap. I cut the foot off, added some weld to
the tips, and ground them smooth. They now
hit dead center of the bearing cap.
I plan to leave the 440 the way it is. The truck
weighs less than 3K lbs.
 

Backrd.Junkyard

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I only knew of the 7-1/4 having tapered tubes that swaged down into the 2-1/2 inch diameter center section tube registers in the housing. The 9-1/4 has tubes that taper down from 4 inches from the center down to over 3 inches at the outside.
https://www.mopar1.us/875.html
 

1STMP

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Backrd.Junkyard

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From the article:
Differential: Police cars have the 8-1/4″ differential with Sure-Grip, and should also have the 2.94 gears unless otherwise ordered or changed. Civilian models have the 7-1/4″ rear ends without Sure-grip and much lower gear ratios.

Rear Axles: Police cars have single-diameter axle tubes. Civilian models have the lighter-duty axle tubes that narrow in diameter as they get close to the differential.

This denotes the change to an often confused later 7-1/4 axle with 10 cover bolts and the change across the board to the five bolt brake backing plate pattern (starting around 1977, IIRC) which required swaging 8-1/4 axle tubes to fit the 7-1/4 center section. Any axle that has tubes that swage down to 2-1/2 inches in the center to fit the housing is a 7-1/4 center section. It's often mistaken as an 8-1/4 because the cover looks very similar. All 8-1/4 center sections have 3 inch tubes, but there were major differences in those housings (and the carriers!) as to where the pinion was located according due to a carrier break at 2.72 gears. 2.45s were common in M bodies, and the highest gearset I know of in an 8-1/4 was a 2.18:1
On a side note, I'm not so sure that 7-1/4s were not available with sure grips in those years. 7-1/4 production didn't end until in the 90s or 2000's in the front of Dakota's, and as a rear axle in four cylinder Dakotas. They were an AMD produced axle, and could also be found in a lot of Ford Grenadas and Mercury Zephyrs (maybe even Pintos and Mustang II?). Being an AMD axle, there were some parts that would interchange between 7-1/4s and Dana 30 and 35 axles. But you can find sure grips in 7-1/4 in Dakotas, sometimes in the front and rear.
 

1STMP

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From the article:
Differential: Police cars have the 8-1/4″ differential with Sure-Grip, and should also have the 2.94 gears unless otherwise ordered or changed. Civilian models have the 7-1/4″ rear ends without Sure-grip and much lower gear ratios.

Rear Axles: Police cars have single-diameter axle tubes. Civilian models have the lighter-duty axle tubes that narrow in diameter as they get close to the differential.

This denotes the change to an often confused later 7-1/4 axle with 10 cover bolts and the change across the board to the five bolt brake backing plate pattern (starting around 1977, IIRC) which required swaging 8-1/4 axle tubes to fit the 7-1/4 center section. Any axle that has tubes that swage down to 2-1/2 inches in the center to fit the housing is a 7-1/4 center section. It's often mistaken as an 8-1/4 because the cover looks very similar. All 8-1/4 center sections have 3 inch tubes, but there were major differences in those housings (and the carriers!) as to where the pinion was located according due to a carrier break at 2.72 gears. 2.45s were common in M bodies, and the highest gearset I know of in an 8-1/4 was a 2.18:1
On a side note, I'm not so sure that 7-1/4s were not available with sure grips in those years. 7-1/4 production didn't end until in the 90s or 2000's in the front of Dakota's, and as a rear axle in four cylinder Dakotas. They were an AMD produced axle, and could also be found in a lot of Ford Grenadas and Mercury Zephyrs (maybe even Pintos and Mustang II?). Being an AMD axle, there were some parts that would interchange between 7-1/4s and Dana 30 and 35 axles. But you can find sure grips in 7-1/4 in Dakotas, sometimes in the front and rear.
Thanks for the clarifications. Guess I should
have read further into it.
 

Backrd.Junkyard

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Well, it's easy to get crossed up on these oddball 7-1/4s, and the way they have it worded doesn't help you out if you don't already know the oddities of F, J, & M body cars. While the later 7-1/4s are a lot better than the earlier models, it's still best to avoid buying one by accident for your muscle / hot rod project. I've got a lot of confidence in an 8-1/4 with aftermarket axles, especially if you were to use a 29 spline from an early model all time AWD Dodge Durango (for example) and set it up at later B body length. It or some of the Dakotas made around the same time would be a good place to find one of those with a sure grip and 3.92 gears. I have one from a durango with 42 inches between the spring perches. That would work well for my A body with the dr. diff inboard spring locators. But I've got two sure grip units from 27 spline axles. I'm intending to see if the open 29 spline carrier and internal parts interchange with earlier axles.
 

JR_Charger

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I've got the LPW diff cover and brace ordered - what about these ARP studs down at the bottom of this page - Link I've been looking for them from another source where I can do some 1-click shopping, but all that comes up are engine studs.
 

33 IMP

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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.
Absolutely no offense meant, and I respect your obvious knowledge about the 8 1/4 ! But if I needed that much strength upgrade, I would go to an 8.8 Ford as a cheaper alternative to an 8 3/4. Of course then there is always a 9"/dana 60 alternative.
 

Mr. Cranky

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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.

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?
Not having a brake line clip on the diff cover isn't a big deal. A clip can be fashioned to bolt to one of the diff cover bolts....or if in a bind, zip tie it.

One-wheel drive? More like one wheel peel? Even an 'open' diff distributes the power evenly to both wheels on a level surface with steady power. The rear end torques counter clockwise and will actually make the right wheel lighter (tries to lift it) while planting the left wheel and that's why you see the right wheel lose traction and the one wheel peel deal. There are ways to counter act that but using a limited slip unit is usually the better way to go.
 

Backrd.Junkyard

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I have to agree that it is a pile of money to upgrade and use an 8-1/4. I like the Ford 8.8 for strength, but the axle tubes in them are sketchy thin in a high power or heavy application. Not that I’ll have to worry about it, but thicker tubes become a priority at some point.
 

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I have to agree that it is a pile of money to upgrade and use an 8-1/4. I like the Ford 8.8 for strength, but the axle tubes in them are sketchy thin in a high power application.
Would probably be cheaper to strengthen the axle tubes on the 8.8 than mess with the 8.25? And if one is going to stay with an integral rear end, it's hard to beat a Dana 60. Those things are pretty dang tough in stock form.
 

Backrd.Junkyard

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Probably cheaper to re-tube an 8.8 than to buy the hardware that strengthens an 8-1/4. I know for definite that the axles shafts are going to be cheaper. Add on Ford positive retention housing ends and run any number of available ford 9 inch axles. They kept the 28 or 31 spline arrangement just like the 9 inch. And if you’re into the hype and decide to “upgrade”, disc brake brackets and parts may as well be raining out of the sky. And then there’s gear ratio availability. It makes a lot more sense to build an 8.8. I know the a body modified 8.8 narrowed for 3 inch spring relocation even weighed less than the 8-1/4 I got for it. But that axle was out of a ‘75 duster with stroked 5.7 Gen 3 power with a boat load (500+hp in two stages!) of nitrous. After a half season, it had bent the stock tubes to the point that I had to drive the axles out with a two pound hammer and a drift after removing the carrier bearing caps. The tubes may have been 5/32 when we cut the wheelie bar and four link brackets off it. The Dutchman c clip axles got brinelled to the point that you could sleeve them or possibly have them converted to positive bearing retention, but Dutchman makes the C clip and positive retention axles out of two different materials. I’ve not been able to bring myself to throw them away yet, though!
 
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JR_Charger

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Well, a different set of opinions from the last time I posted. Is this the same board? :D

I've got half of my 8 1/4 parts now. Not going to change horses mid-stream. I'll file all the ideas away for the next build though.

Still need another source for the ARP cap studs.
 
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