Should I Subframe Or Stretch Donor Frame???

[nite53]

I am in the beginning stages of doing my 53 Panel Van. I have a donor 1985 Pontiac Grand Prix, complete car. (with Chevy engine and trans ). My first plan was to subframe the panel, and mount the rear axle, using the Grand Prix rear, and grafting the mounts for the diff. swing arms.

This morning I started looking things over, and now I'm wondering if I would be happier with using the entire Grand Prix frame. Your opinions, please?
Grafting the front frame: I still would have to "c" notch the rear for the lowering I want. And, taking the time to check geometry of the swaps.

The GP is about 30" shorter wheelbase than the Panel, since mine is a one ton body, so I'd have to stretch the GP frame, which in my thinking is easier than to graft onto the old Chevy Frame. My Chevy frame is good. But, I would like to have the weight as lite as possible, too.

From my quick, overview of the frames, the GP frame looks relatively straight from the firewall to the rear axle, much like the Panel. Of course, I'd have to take care of the radiator support, either way, and graft on something at the rear for the bumper.


Grafting on new body mount tabs and running board mounts seems easy enough.

So, please, give me your thoughts on the best way to lower it, easy way to keep all the angles, and all. What measurements do I need to look for most of all?
My goal is to not necessarily slam it, but way lower than the one ton profile!
Thanks,

[Ipaintgrt]

Why would you want too use an 85 Gran Prix for a donor car? Not trying to be a dick, but I would find a different donor. Like a rear wheel drive vehicle. You can find a 95 or 96 caprice that would give you a FI engine, and an overdrive trans, modern radiator, electric windows, Heater assy, and many other things you can use on your project. Again not trying to shoot down your idea, just doesn't seem like adapting that frame and trying to engineer the Gran Prix to work is like reinventing the wheel. I your using it because you just have it, sometimes its better to sell your extra stuff and do it the way you would have rather done it and be happy that you did.
Scott

[blackdiesel]

Well, if you ask what I would do. I would spend the 1500 on a mustang 11 type front end. Keeping all the oem body mounts and rad suport. There is a place for a clip graft, and a place for the m 11 IFS. BUT this is just what I would do. If the sub frame graft or frame swap are the only choices. Only the one that can eyeball both frame, could tell for sure. Price rebiulding the old frontend and compare the cost. I know which one would have the higher resale.

[Steve@OldSub.com]

Is an '85 Grand Prix a g-body car? About 108 inch wheel base?

If that's what it is, it has a perimeter frame and the rails will end up under the running boards unless you narrow the frame while you stretch it.

And the rear axle is quite narrow compared to the truck you're talking about putting it under. You may need spacers or deeper tubs to get tires under it with out rubbing.

So what do you do? You could buy enough rectangular tube to remove the wide perimeter part of the frame and use that to also stretch the frame. You'd get the advantage of IFS with disks and power steering at the front and a triangulated 4-link at the rear. Get a wider rear axle.

But you have a suspension and brakes designed for a 3500 pound vehicle under one that weighs about 4400 pounds before you put gas or a driver in it. Plus it has cargo space to carry much more, so the danger of seriously overloading your brakes becomes scary.

I didn't want to come off as another nay-sayer but I'm afraid I don't think this is a great idea. First its not as simple as you indicated, and second the finished vehicle is not as safe as I want the other cars on the road to be.