Making The Weak 7-1/4 Rear Axle Live... Kinda

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While I don't recommend welding the spider gears together, or really locking the carrier at all in any way, I will say this. If you run a tall enough tire, you may never know the axles are locked, because the tires will take up some of the shock. I had some L-60/15s on the back of an old Chevelle with a welded up carrier...was like that when I bought it and it never made the tires chirp. When I romped it, it was a different story.
 
RustyRatRod said:
While I don't recommend welding the spider gears together, or really locking the carrier at all in any way, I will say this. If you run a tall enough tire, you may never know the axles are locked, because the tires will take up some of the shock. I had some L-60/15s on the back of an old Chevelle with a welded up carrier...was like that when I bought it and it never made the tires chirp. When I romped it, it was a different story.
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I might try this thing once I get some measurements to see if I can make it fit. The good about these experiments is that I can still get spider gears, so some things I grind and modify.

images.jpeg
 
Ant said:
Howdy!
I have a challenge for my self and would like some constructive input.
I'm building a 318 for my 73 Dart, it should make somewhere in the ballpark of 300HP. It will be bolted to the A904 auto transmission with a stock-ish stall converter. The car's weight is somewhere around 3450 pounds with driver.

So, I don't have a stronger rear yet, so the challenge becomes making the 7.25 rear hold up in the meantime. So far I know the spider gears in the diff are pretty weak, so let's start there. I have some ideas, like:
Welding the spiders together.(May not be good for street use)

Somewhow converting the open diff to a LSD.(Will be lots of research to be done for cheap)

Tuning the car to accelerate softer from a stop.

Not driving like an idiot.

Now before anyone replies with "Go buy a Dana 60 or Ferd 8.8" please understand that this is for fun and I'm not running a torque monster of an engine.
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The welded spyder gears are not for street. Making turns, especialy right, it will tend to hop and chirp the inside tire. The car will want to go straight instead of turn.
An earlier Dakota rear with 8.25 may be an easy conversion. I know they are not overly strong either, but better. Just that road apples 6 bolt pattern they used. Get the axles redrilled for the 5 on 4.5 pattern. Some came with Sure Grip. Later ones even have disc brakes.
 
Ant said:
Howdy!
I have a challenge for my self and would like some constructive input.
I'm building a 318 for my 73 Dart, it should make somewhere in the ballpark of 300HP. It will be bolted to the A904 auto transmission with a stock-ish stall converter. The car's weight is somewhere around 3450 pounds with driver.

So, I don't have a stronger rear yet, so the challenge becomes making the 7.25 rear hold up in the meantime. So far I know the spider gears in the diff are pretty weak, so let's start there. I have some ideas, like:
Welding the spiders together.(May not be good for street use)

Somewhow converting the open diff to a LSD.(Will be lots of research to be done for cheap)

Tuning the car to accelerate softer from a stop.

Not driving like an idiot.

Now before anyone replies with "Go buy a Dana 60 or Ferd 8.8" please understand that this is for fun and I'm not running a torque monster of an engine.
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Drive gently until you find and 8 3/4 but you will have to pony up some bucks I have broken several 7 1/4s with a slant six
 
Just for the sake of conversation.

The offroad VW powered Dune Buggies, we built the transaxle differential with a Super Diff. 4 spider gears instead of 2.

Doubled the strength of them, yet with these we did not need the locking diff as we use Steering Brakes to assist steering in the soft sand terrain.

Also did a nice 280-Z drive shaft conversion that eliminated the weak factory VW CV Joints.

Unbreakable . . .

large-AC301132__32491.jpg


ac301132_2.jpg


Took 4 stock spiders to make it work.

Screenshot_20230520-194152_Firefox.jpg


Brings back a lot of fond memories looking at this again.

Screenshot_20220109-201330_Gallery.jpg


Twin Steering Brake levers at the center console.

Only limited by your imagination.

☆☆☆☆☆
 
George Jets said:
Just for the sake of conversation.

The offroad VW powered Dune Buggies, we built the transaxle differential with a Super Diff. 4 spider gears instead of 2.

Doubled the strength of them, yet with these we did not need the locking diff as we use Steering Brakes to assist steering in the soft sand terrain.

Also did a nice 280-Z drive shaft conversion that eliminated the weak factory VW CV Joints.

Unbreakable . . .

View attachment 1716092388

View attachment 1716092389

Took 4 stock spiders to make it work.

View attachment 1716092390

Brings back a lot of fond memories looking at this again.

View attachment 1716092391

Twin Steering Brake levers at the center console.

Only limited by your imagination.

☆☆☆☆☆
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If I could, I would. That would make it much stronger, but what is available for the Chrysler 7-1/4? I and many others just can't find upgrade parts for them, which seems kinda weird since the 7-1/4 is a very popular rear axle.

I have a few ideas, maybe I'll get another carrier just for doing some experiments.
 
Firing up this thread again.

We know a sure grip unit for 7.25 rear is harder to find than old pirate treasure. So doing an lsd conversion may be the way to go if we can figure it out for a reasonable cost. I kind of have a plan, it will require some feedback though.

We know when a bevel gear is driving another bevel gear that they want to push away from each other and the greater the force against the gear the more force there is pushing away. So rather than having the shim on each side on the gears splined to the axles, we use friction/clutch disks instead? I know other lsd diffs use 4 or more clutches and having two is a compromise but maybe this with a mechanism that provides preload on the two gears and can apply extra force when the pin kind of rotates in the mechanism's slot we get not a true lock, but still a limited slip differential.

Now of course this means the splined bevel gears are now wear parts because it's rubbing against the friction disks, but most of the time when I service a higher mileage differential, I end up changing the spider gears anyway.

Any thoughts or ideas, let me know.
 
Ant said:
Firing up this thread again.

We know a sure grip unit for 7.25 rear is harder to find than old pirate treasure. So doing an lsd conversion may be the way to go if we can figure it out for a reasonable cost. I kind of have a plan, it will require some feedback though.

We know when a bevel gear is driving another bevel gear that they want to push away from each other and the greater the force against the gear the more force there is pushing away. So rather than having the shim on each side on the gears splined to the axles, we use friction/clutch disks instead? I know other lsd diffs use 4 or more clutches and having two is a compromise but maybe this with a mechanism that provides preload on the two gears and can apply extra force when the pin kind of rotates in the mechanism's slot we get not a true lock, but still a limited slip differential.

Now of course this means the splined bevel gears are now wear parts because it's rubbing against the friction disks, but most of the time when I service a higher mileage differential, I end up changing the spider gears anyway.

Any thoughts or ideas, let me know.
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How will you do an LSD conversion when there are none?
 
Ant said:
Uh... we make it, kind of like how I wrote it or somethin.
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Are you talkin about like in post #27? That's not limited slip, man. That's locking the axles together. Same as welding the spider gears. There will be no differential action whatsoever. The axles will be locked. But hey, if that's what you want, go for it!
 
RustyRatRod said:
Are you talkin about like in post #27? That's not limited slip, man. That's locking the axles together. Same as welding the spider gears. There will be no differential action whatsoever. The axles will be locked. But hey, if that's what you want, go for it!
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Post #33. Also post #27 is not a spool of any kind, it is a device that uses pressure via the pin wedging it to the gears. It kind of cheap and crappy and would need modification to hold up for long. My idea in post #33 is different.
 
Ant said:
Post #33. Also post #27 is not a spool of any kind, it is a device that uses pressure via the pin wedging it to the gears. It kind of cheap and crappy and would need modification to hold up for long. My idea in post #33 is different.
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Ok, I see it now. But, as you said, the gears now become the "clutches" so to speak. Very high wear. Also, unless you somehow convert the unit to four spider gears, good luck with any type of performance driving.
 
RustyRatRod said:
Ok, I see it now. But, as you said, the gears now become the "clutches" so to speak. Very high wear. Also, unless you somehow convert the unit to four spider gears, good luck with any type of performance driving.
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Hmmm... then maybe that other device thing from post 27 help a bit. That puts most of the load on the side gears and the pin.
 
I have found out this much from researching something very recently. There is a Volvo application that uses the same clutch pack as the 7.25. I don't know which application it is. But remember, the 7.25 is a Dana axle. Some people don't realize that, but it is. If any of that helps at all.
 
Ant said:
Hmmm... then maybe that other device thing from post 27 help a bit. That puts most of the load on the side gears and the pin.
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I don't know. I see it scoring the side gears and case all to hell. But keep on keepin on, brother. That's how progress is made.
 
RustyRatRod said:
I have found out this much from researching something very recently. There is a Volvo application that uses the same clutch pack as the 7.25. I don't know which application it is. But remember, the 7.25 is a Dana axle. Some people don't realize that, but it is. If any of that helps at all.
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I've been thinking about that in the past, but I don't know if there are small or big differences.
 
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Several years ago, I contacted Dana about the 7 1/4 clutch parts. I don't know if the person I talked too had any real knowledge of these parts. However I was told they have nothing that will fit. I even inquired about clutches that would have the correct spline count, but not the correct OD, that could possibly be turned down. Or maybe a clutch "kit" that did not have the correct number of discs/plates. With todays technology, I wouldn't be surprised if it would be possible to have the clutched and plates custom made. But then the question becomes, WHY? There are better options for rears at a lower cost.
 
Charrlie_S said:
But then the question becomes, WHY? There are better options for rears at a lower cost.
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If I could get my hands on a 8.25 rear axle with a sure grip for a reasonable price I would not be trying to experiment with the 7 1/4.
 
Ant said:
Is it a direct swap or is modification needled?
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My small bolt pattern 7.25" rear is 57.125" wide. a dakota will be way too wide for an A body, they're over 60" wide, and the spring perches would need to be cut off and rewelded.

the closest easy to find latish model rear end that is close to the right width are 93-09(?) ford rangers. they're 58.5" wide. 90's to early '00 ford explorers are 59.625" wide. both need spring perches cut/rewelded.

the closest mopar product is an XJ cherokee, they're 60.5" wide, and 3.55 geared 8.25's are common in them. to get any real width as far as tires with that much width, you'll probably need high offset wheels, somewhere in the +30-+38mm offset that mid 90's-mid teens mustangs had.
 
Ant said:
Is it a direct swap or is modification needled?
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I do not know. Axle width and perch width could be different. There are thousands in breakers, many with disc brakes. You would have to check with a tape measure. Check flange to flange using a couple of pieces of angle iron a foot long and c-clamp or vicegrip on the flange.
The centering pin on the spring would need to be checked for proper fit and the width. The advantage is the number available with 3.55 and 3.91 gears, sure grip and newer with discs, makes them fairly inexpensive.
Dakota's had a couple of widths depending on the year.
 
michiganpat said:
My small bolt pattern 7.25" rear is 57.125" wide. a dakota will be way too wide for an A body, they're over 60" wide, and the spring perches would need to be cut off and rewelded.

the closest easy to find latish model rear end that is close to the right width are 93-09(?) ford rangers. they're 58.5" wide. 90's to early '00 ford explorers are 59.625" wide. both need spring perches cut/rewelded.

the closest mopar product is an XJ cherokee, they're 60.5" wide, and 3.55 geared 8.25's are common in them. to get any real width as far as tires with that much width, you'll probably need high offset wheels, somewhere in the +30-+38mm offset that mid 90's-mid teens mustangs had.
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For the hard core Mopar people, either cut the long tube and shorten to the short side length. Then get a NEW short side axle. The reason for new is the axles can "get used" to torque applied in one direction. If you switch sides and apply higher torque, you could end up with a failed axle.
Another way is to hole saw the welds out that hold the tube in and press the tube out. Cut the axle length difference off the inner end before pressing it back in. Verify tube is straight and weld it back in. Go around the outside off the tube starting 90° apart, and verify straight. Weld one 90° and then directly across. Verify straight and weld the rest. Weld where you cut the original welds out. Weld the short side tube to the housing the same way.
 
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