I am considering installing a rear spring relocation kit on a 70 Roadrunner. I have been doing some research and looking at cars with the kits installed. I have noticed that the cars with the kits installed have a ride height a little higher than other cars. I believe this is because the rear frame rails sit a few inches lower than the leaf spring mounts. Is there any way around this problem. Even if you drill the hole up higher in the frame rail you can not get the spring shackle to sit at the same height. If you try to do that the spring will be resting up against the frame rail. I already plan on lowering the ride height from stock height. But if it ends up sitting higher then i will have to use some big lowering blocks to get it to the ride height I want. And I would really like to avoid that. Hopefully this makes sense how I am saying it. Any advice would be appreciated.
Thanks,
Chris

On my 67 Dart, the front hole location was at the same height as stock. I know because I used the stock front hole to determine where to drill the holes in the relocation boxes. Same height, but in about 3.5" or so.

I knew however that my ride height would be higher because of the tire selection for my 15" prostars on my car. I went from 25.5" to 28", raising the car by half of the difference or 1.25". So I chose to install some 1" adjustable lowering blocks to end up with only 1/4" more height in the back. Just as easily could have added taller blocks.

But I bet the reason those cars have higher ride heights is due to the relatively few choices of tires for a minitubbed car, at least in 15".. e.g. from 295 to 325 or so, there aren't really any short tires in the mix. That plus people may be using SS springs.

you can put extra holes in the front spring boxes to lower the ride height, i just welded these in last night. the aluminum pin is in the standard hole, the other hole is 1 1/4" higher in the box.

Typcally the 3" relocation kit is done because of the need for massive amounts of rubber to absorb a drag style launch. A part of the geometric set up of leaf springs for drag racing means they typically will have a lot of arch. Combine with a large diamter tire which goes along with drag racing, and they will tend to raise the rear of the car.

You can lower them down for appearance, but it may compromise the springs action to some degree, as well as the resulting rotational weight transfer, and impact your 60' times in a negative manner.

For a pure handling application, you typically do not need that wide of a tire to need to resort to a 3" relocation.

For a street car, as long as it all looks all right, set it up with whaterver tickles your fancy.

How big of a tire and wheel do you want to run?

Cars like my 67 coronet and 70 dart need these kits because of th wheel well openings and tubs. However a roadrunner can get a huge tire in the wheel well without modification.

With the right offset you can fit a 10" wheel back there with an appropriately sized tire. But some people like the look of a deep wheel which means narrowing the rear end as opposed to moving the springs. If you want bigger than a 10" wheel then you need to move the springs AND mini tub the car.

However, most inboard kits or even do-it-yourselfers have the stock spring hole if only for the purpose of proper alignment when intalling the boxes. Go into the tech archives, there is a complete "how-to" with photos in there.

Ride height is determined by the tire and the spring arch.

Couple of Comments.

If you buy your kit from Reilly Motor Sports, he pre drills the relocation boxes with four holes.

stock ride height / stock axle location
lowered ride height 1" to 2" / stock axle location
stock ride height / axle moved back 1" to 2"
lowered ride height 1" to 2" / axle moved back 1" to 2"

For a purely drag car you'd want to run 15" X 325 drag radials.

If you want a lot more choices in tires you pretty much have to move up to 17" or larger wheels. The choices for performance tires in the 14" 15" and 16" range are simply non-existent anymore.

JAMESC,

I noticed that you did your spring relocation on a lift? Where you concerned about body flex and or tweaks. I am thinking of buying a lift but a lot of guys say to do the spring relocation and subframe connectors on jack-stands to mimic the cars weight on the ground.

Did you do anything to minimize distortion?

Regards,

Joe Dokes

Quote:

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JAMESC,

I noticed that you did your spring relocation on a lift? Where you concerned about body flex and or tweaks. I am thinking of buying a lift but a lot of guys say to do the spring relocation and subframe connectors on jack-stands to mimic the cars weight on the ground.

Did you do anything to minimize distortion?

Regards,

Joe Dokes

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Joe, the car is completely stripped/empty basically just a shell. the only additional weight that could be removed is the doors and glass. i seriously doubt any flex would occur and judging by the measurements and what i've seen i don't see any problem. the car was also leveled as best possible front to back/side to side (using aluminum shims between the lift and car) using a digital protractor that reads to .01°. i'm guessing most people end up doing this on a basically complete car. this one as it sits is probably lighter by about 2000# so there's no real weight to bend anything. even still i put a stand under the back of the car before i cut the frame rails out. also the lift/car was not moved at all once it was leveled, the rails cut until the boxes were well tacked in. once that was done the car could be raised and lowered to make welding easier. personally i don't see that doing it on stands would be any better, the only improvement would be doing it on a jig table which i don't consider necessary.

Thanks for the reply.

I like your methodology for thinking through the cutting and welding. It is quite clear from your pics that you spent a lot of time thinking through the process to weld in the relocation boxes.

I have been seriously considering buying a lift, but was hesitant if I couldn't use it to weld in the spring relocation boxes. I already have the motor and transmission out of my car. Removing the doors, fenders, hood, trunk lid, plus the rear should make the car light enough to do the welding.

Being able to weld at eye level will be worth its weight in gold.

Regards,

Joe Dokes

If I had a lift I'd obviously use it, but I am far from an expert welder and had no problem MIGging my spring boxes in with the mid/back of the car supported by the homemade frame connectors. It's a very easy area to access. Making measurements with the car on jackstands is fairly easy too.

A lift probably would have made welding the wheelwells during a minitub much easier. That was much more awkward.