I was surprised. These were weighed using digital Longacre corner weight scales. All were full of diff fluid.

1974 BBP 7.25" Mopar A-body axle, 10" drums and PB cables, 2.93 open diff
--> 160 lbs

1971 SBP 8.75" Mopar A-body axle, 10" drums and PB cables, 3.23 clutch SG in 741 case
--> 194 lbs

1980 BBP 8" Ford Granada axle with homebuilt 11.7" discs, 3.55 Trakloc diff
--> 166 lbs

So much for the 7.25" axle being so light. I would guess the 9" drums might save you 5-10 lbs. Adding a SG to the 7.25" will probably add 5 lbs or more. In any case, the Ford 8" is almost the same weight (maybe 170-175 with stock drums).

A BBP 8.75" w/10" drums will be 5-15 lbs more or about 205 lbs. My guess is the 64 Dart axle with BBP Moser axles, discs, and 3.91 clutch SG in 489 case is 210 or a bit more.

Lou

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Home of Slant6-powered fun machines since 1988

weight of 7 1/4 axle w/ 10" drums removed from car 160 lbs

weight of similarly equipped narrowed Explorer 8.8 w/discs 185 lbs

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Thanks for the data points, Sandy. That's pretty good for the 8.8.

Lou

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Home of Slant6-powered fun machines since 1988

no data points for me Lou....I have electronic ignition!

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Yeah....Im the one who destroyed this rare, vintage automobile.....

WOW! Thanks for the info, Lou. Goes against everything I was figuring (but I was gonna swap in an 8 3/4 anyway). 34 lbs. more? No biggie!

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vm

I was surprised too. I think I weighed a SBP 9" drum 7.25" at about 150 lbs a few years ago. The big thing for me is that it's not worth working up a 7.25" over a Ford 8". 7.25" SG diffs are too rare. Plus the 8" has an aluminum center section available for another 12-14lbs off.

I would be interested in any other axles (foreign or domestic, preferably new and plentiful) with 5X4.5 bolt circle that are lighter than the 8". The problem is nobody bothers to ever weigh these things. I might try calling DTS or Randy's sometime to see if they have any thoughts.

Of course, a light IRS would be nice sometime too, but it's hard to get IRS lighter than a stick axle of the same strength.

Lou

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Home of Slant6-powered fun machines since 1988

How about a Mustang IRS. These came in the mid 90's Cobras, but the racers did not like them, and swapped them out for live axles. All of the 90's T Birds had IRS, but I have reason to think the axles are not 5X4.5" studs. Something tells me they are a metric dimension.

I am quite surprised at the weights you measured. I think the reason I thought the 7 1/4" guys were so much lighter is because i was alot stronger when I was throwing those things around. By the time I had graduated to the bigger rears, I was getting older and weaker. I also think I read info years ago saying the smaller rears were much lighter than that, and the bigger ones were heavier. But, you have the real dope now. Thanks.

I just picked up the latest issue of Mopar Muscle, and was surprised at the number of exotic suspensions offered now for our Mopars. I wonder what the benefit is?

Sam

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The Mustang/T-bird IRS is indeed 5X4.5 bolt circle. They are too wide for an A-body even with deep offset wheels - maybe front drive wheels? I have looked at these. There's a guy on Mopax with a Slant Dart who adapted this type to his Dart. Haven't seen pics yet. Other options would be Toyota Supra, BMW, RX7... At least the Supra has 4.5" bolt circle.

I think the new rear suspension types are better, but driver skill and tires are usually bigger factors in cornering. Mostly, people just need to spend money on something to feel like they have a cool car, especially when they don't do the work themselves.

I will be very interested to see who/what I can out corner on a road course with Project V version 2.0. The 64 Dart does pretty darn well with almost stock suspension and a few tweaks. The V will be 300+lbs lighter, finally have a set of slicks, and will have 30 more HP.

I'm not sure any new suspension is much better than the Mopar t-bar suspension. I haven't heard any convincing arguments, anyway. OK, maybe for ride quality.

Lou

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Home of Slant6-powered fun machines since 1988

Actually the IRS T-Bird is 5 on 4 1/4" like Volvo. The Mustang Cobra IRS is 5 on 4.5". Most Japanese RWD IRS is 5 on 4.5". Toyota Supra and Lexus SCs, RX-7, Conquest/Starion, and 5-lug 300ZX, Infinity Q45 all 5 on 4.5".

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Joshua

The Ford Explorer IRS is 5x4.5 and just a tad wide.

The control arms are clunky . The centre section and axles and outers would be a good start for a tubular A arm build.

You get 8.8 .....discs....and a shock mount system similar to an A body.

The things are worth nothing at the wrecker.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Josh,

Thanks for correcting the t-bird spec and posting others with 5X4.5".

Sandy,

I would love to know what the disc-disc width is on an exploder IRS. You can easily get 35-40mm offset rims for front drive cars. I bet it's heavy.

Lou

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Home of Slant6-powered fun machines since 1988

The Explorer IRS lower control arm is a forged aluminum monster,,,,the centre is an 8.8 . The outers are just a spindle with a hole in the middle like a truck 4x4 front knuckle.

Its going to weigh more than an 8.8 beam axle......

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Total weight might be more with an IRS but the unsprung weight is going to be considerably less. And I am not so sure an aluminum IRS would be heavier than a steel/cast iron live axle. Coil sprinngs are much lighter thn leafs. The four link rear installed in a Satelite in the Mopar Muscle mag weighed 50 pounds less than stock. All was the difference of the spring weights.

The TBird I drove when my daughter was shopping cars 6 years ago handled really well for a car with such a smooth ride. My Daughter drove it way faster than I was comfortaqble with because it didn't feel like you were going as fast as you were. She was driving 45 through residential neighborhoods. As soon as she got in a Ford Escort, she drove ten MPH slower on the same roads. I attributed this, in part, to the power, but in part, to the ride quality. And, it handled very well. I wanted to buy it for me.

Anyway, from that point on, I have fantasized about an IRS in a Dart. It seems like alot of work, and right now there are other priorities. But maybe some day. It's not just something to spend money on, but also the challenge of doing something different.
Sam

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I was thinking more about this and it seems that one inherent problem with the leaf spring design is that a great deal of mass has to be put out behind the rear wheels. This creates yaw in the handling, which is the phenomenon of part of the mass moving in the opposite direction from the direction of the turn.

When you turn your front wheels to the right, the weight behind the back wheels moves to the left. The further behind the rears wheels, and the more of this weight , the greater the yaw effect. Yaw in the turning moment of thecar is inertia that has to be overcome, and stopped to prevent a spin, and results in a very ungainly, and awkward feeling.

This is something that changing the rear would have no effect upon, unless you changed the wheel base as well. And I am not keen on changing the basic style of the car that much. I have heightened the yaw in my car by putting the battery in the back, and put it behind the axle. It would be better if the battery were on top of the axle. Yaw could be reduced by changing the steel bumber for a glass one, but I am not sure I trust other drivers enough to leave myself that velnerable.

If you look at the T Bird design which I fell in love with, the rear wheels are very close to the corners of the car. This likely has more to do with it's appealing road manners than the style of rear, although that certainly did not hurt.

The idea of IRS in a Dart does intrigue me though. Maybe I will bite the bullet and put a plastic rear bumper on first. As battery technology gets better, a smaller battery would help as well. I don;t race, but it still is great to drive a nice handling car.

I know weight ahead of the front wheels affects yaw as well, but I am not as clear on the physics of that. The bottom line is, Lou, you were smart to leave the front bumper off your '64.

Sam

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The 7.5" axle out of a Ford Ranger pick-up weighs 155 pounds with 9" drum brakes and 130 pounds without brakes. Actual scale weight with oil. 5 bolts on 4-1/2" bolt circle. 92 and earlier model years are 56-1/2" wide drum face to drum face, 93 and later are 58" or so wide. A fair number of 302 inch / 5.0L V8 Mustangs came with a 4 lug version of this axle in the 1980s, OK for V8 power if you don't go crazy.

Piper106