rear axle centerline question, a-body

Working on 71 dart swinger. I am putting ladder bars in it and was curious of some kind of hard measurement that could help me locate the rear in the factory location. The car has a hacked up spring relocation kit in it that was never finished and basically have nothing trusty to go off of. Or should I just put a tire under it and get myself a comfortable amount of clearance and go with that?

If someone could give me a measurement from the front of the front leaf spring perch, or in other words the back of that crossmember, to the centerline of the axle I think that would get me pretty close. looking to run a 28-10.5 tire.


thanks

I measured a 71 Duster body with a stock leaf and 8 1/4 rear and I get 21" from the mounting plate that the front leaf spring hanger bolts to to the top middle of the axle tube and I get 21 inches, with the car on jack stands and the suspension hanging down, no shocks. But I'd not go with that - put the tire/rim combo in the car where it gives you the clearance you need and work from that, and work out any changes needed to the drive shaft length, shock mounts, fender trimming, etc. Most Swinger bodies need a bit of trimming on the front edge of the lower qtr for tire clearance when the rear is in the stock location. Some guys resort to adding spacers between the front hanger and the body mount. See the tech pages on BigBlockDart.com for a step by step to show trimming one.

good deal. that will ball park me anyways. I will definitely read that article. Upper shock mounts wont be an issue due to the fact I can put them wherever they need to be and driveshaft hasn't been made yet either. I was thinking about just putting it where I felt I had comfortable tire clearance but the way the wheel wells are, if you move it back then you run into clearance issues on the back side of the tire quick. centered in the well, is tight on the front side. thanks again

71 A bodies with 8 3/4 rear had 43" from spring perch to spring perch. Measured on center, with the pinion centered.

Darts and Scamps have longer wheel base then Dusters and Demons...fwiw....

dually noted good sir. I'll bring this back to the top and see if anyone else has anything to add. I know that there are several different ways to change wheelbase on cars. I would assume that if they take the same front leaf spring segment length, then the length from the mount/crossmemeber/bulkhead, whatever u wanna call it, to the axle would be the same, but I also know what assumptions are the mother of.

When i put ladder bars under my valiant i measured from where the factory perches bolted to the frame back to where i wanted the axle centerline to be in the wheel housing. FWIW, you will probably have to move the axle back a little to fit a 28" tire into a stock wheelhouse as the axle was towards the front of the housing from the factory on Darts. I made 3/8" plates to bolt between the spring perch and the factory mounting location to fit a 28" tall tire under my dart, otherwise the tire would rub the front of the 1/4 panel.

Late to the party, but I'll offer my thoughts.
If I were replacing the stock suspension and installing a crossmember and ladder bars, the original location of the rear is irrelevant to me. If I need to open up the wheel opening for a larger tire, I would move the rear centerline forward enough so that I only need to move the front half of the opening forward.
If I wanted it in the stock appearing location, I would take everything from under the car, mock the wheel/tire combination in the wheel opening where I wanted it for clearance and apperance and let that determine where the rear goes.
Bottom line is, put the wheel where you want it. Let that determine where the rear goes. Also consider that moving the rear forward some will improve the weight distribution.
In other words,if you consider the entire rear suspension (rear, bars, crossmember) as a unit, it can be mocked up and measured to determine the distance from the axle centerline to the front of the crossmember. Put the wheels (aka. axle centerline) where you want them and measure forward that assembly dimension. That is where the crossmember will meet the stock floor.
Level the car, string line or laser everything, draw it out on the floor and make it straight and square.
All of this is assuming you are eliminating the leaf springs.

just wanted to let you know the last comment didn't fall on deaf ears. That is basically the way I went. I am lowering the car significantly and found the wheel wells on these things are far from symmetrical. I basically found a happy medium on wheel well clearance, and worked from there. I actually came up with 21 inches as of now for a starting point, but its gonna be tight on the front, and plan on trimming the quarters to gain clearance. This is my first ladder bar install, and I have learned a ton along the way. I also found the front eye mounts are off about 3/8 of an inch from square to the frame, so that already invalidates my 21. Planning to tack all my brackets on the rear, and the front crossmember this weekend and start actually fitting it up as it will be installed. came up with about 1 1/8th yoke offset towards the pass side, on a slant 6 crossmember with engine swap mounts that I picked up along the way. I really enjoy this forum due to the patience with newbies. I due have a experienced chassis guy helping me with my million questions I come up with along the way though, so that helps.

Also car is definitely leveled, and I have plotted everything out on the floor with chalk lines and plumb bobs. I have the block and trans in it to find engine centerlines to find yoke offset before I narrow rear. And going to coilovers, with the upper mount located on the down bars from the roll bar also.

A-body springs are 20 inches center bolt to spring eye,brackets are 2 inchs, hole to flat where its attached to frame.
Meant to add 7 1/4 brackets different than 8 1/4-3/4

here are some pics of my progress so far.

another

and another

last one for now

What rear is that?

That looks like a ford 8.8

Looks like a Ford 8.8".

busted...lol. I don't have any 8 3/4 stuff so I went this route. can buy a limited slip, disc brake, 31 spline explorer rear for 200 bucks locally with the gear ratio I wanted. my plan was to tell people its a dana, cuz 90 percent of people wouldn't know the difference. figured they would see the cover and say, "must be a dana".

Quote:

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Looks like a Ford 8.8".

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How strong is an 8.8?
Do they have adjusters or shims to set the carrier like the Dana S60? Matt