[tubbedz]

Hey guys, I'm helping a friend with a "stock", "granny" owned, 1967 Chevelle with a 6-cylinder. The first mod he wants is an "air bagged" suspension. He wants the slammed looked, but wants to hit the drag strip when he replaces the 6-cylinder.

Looking at the rear, coil sprung, suspension we came up with a couple of questions. 1)If we install "air bags" and raise or lower the suspension wouldn't that drastically change the pinion angle?? not good for drag racing 2)Would the driveshaft have to be shortened or lengthened as when the car is lowered the driveshaft would be pushed closer to the trans, then raised, it would be pulled out of the trans???3)Obviously the car would have to be at ride height to have the optimal pinion angle, so that means broken joints/vibrations if drag raced with it lowered or raised???

Thanks for any constructive help, as I would think it would be easier to just lower the car, set the driveshaft/pinion/transmission angle once and go drag racing. Then forget about the "elevator" ride suspension.

[Scotto]

If you set the length of the upper and lower rear arms properly, there should be almost zero pinion change. My truck is set up with 14" of adjustability, and after a bit of trial and error it runs smoothly with half a degree difference. As far as the driveshaft, it wouldn't pull out of the trans or jam into it with that little travel. Your friend could also look into some of the bolt on kits already made for his car.

http://www.airassisted.com/Bolt-in-A...duct_info.html

This is a great shop to deal with as well. Its Canadian, but they do also have an American warehouse.

You should also look into the rules at the dragstrip as far as suspension requirements, around here, they aren't too fond of air equipped vehicles racing.

[tubbedz]

Originally Posted by Scotto

If you set the length of the upper and lower rear arms properly, there should be almost zero pinion change. My truck is set up with 14" of adjustability, and after a bit of trial and error it runs smoothly with half a degree difference. As far as the driveshaft, it wouldn't pull out of the trans or jam into it with that little travel. Your friend could also look into some of the bolt on kits already made for his car.

http://www.airassisted.com/Bolt-in-A...duct_info.html

This is a great shop to deal with as well. Its Canadian, but they do also have an American warehouse.

You should also look into the rules at the dragstrip as far as suspension requirements, around here, they aren't too fond of air equipped vehicles racing.

Thanks Scotto!!
The reasoning to all these questions was that another friend has an S10 Blazer with 4" lowering blocks in the rear and a 200r4 trans that had to get his driveshaft shortened due to it "kissing" the trans. Also, on our race car with a 4-link suspension, any change in ride height affects our pinion angle and our driveshaft angle. Which affects our instant center and throws the "launch" off.

I hope we're not over thinkin' this.....the pre-made kits should already be engineered correctly

[hinklejd]

Bags and the strip generally don't work too well together. If he wants a low stance and good grip on the strip...look at coilover suspension. It'll allow the low ride height along with the adjustability that air bags give. But coil springs can be wound to be progressive -- i.e., the first inch of spring compression takes 100 pounds of weight, the second takes 200 additional pounds of weight. These progressive spring rates generally give the best of both worlds...a comfortable ride along with limiting how much the suspension will squat on the line.

The suspension was designed from the factory to limit the pinion angle change to a minimum under normal suspension cycling. When you move away from 'normal' design specs, you just may adversely effect the pinion angle. If it were mine, I'd pull the coil springs then see how much pinion change there is during the entire range of axle movement. If you're talking about more than a couple degrees, then I'd look at some adjustable control arms. If you're serious about the strip, then you're probably going to want to upgrade to some tubular control arms anyway, since the stock stamped pieces aren't known to take the abuse of high horse motors of today.

[tubbedz]

Thank You hinklejd!! We did remove the coil springs and moved the suspension up and down. With air bags the suspension would probably be raised/lowered several inches more than a stock suspension. So we went past the OEM height and well below the OEM spec. Guess what, the pinion angle changed drastically.

Scotto in your gallery, you have a pic of a truck titled, "rear_frame_clip" and it is slammed on the ground. In that pic the differential is drastrically pointed towards the ground. That is severe negative pinion angle and that would definitely not work at the track. How did you get 1/2 a dgree of pinion angle change when the differential is severly pointed into the ground?? See attached pic

[powerrodsmike]

Originally Posted by tubbedz

Scotto in your gallery, you have a pic of a truck titled, "rear_frame_clip" and it is slammed on the ground. In that pic the differential is drastrically pointed towards the ground. That is severe negative pinion angle and that would definitely not work at the track. How did you get 1/2 a dgree of pinion angle change when the differential is severly pointed into the ground?? See attached pic

hahahah...I don't think ScottO drives that truck in that condition..
If you look closely at that picture you will see no driveshaft, no brackets or suspension bars...(look at the shadow under the truck, and the ratchet strap in the vicinity of the rear axle...I;ll bet there is a 2x4 in there somewhere too.), and it looks like a first mockup with wheels..The pic of the front shows no motor or trans either..

later, mikey

[Scotto]

exactly Mike, that was just to roll the frame out of the garage for working. Now its set up and the rear is at 2 deg down, and I just have to pick up a 2 piece driveshaft. I have since put a wishbone on the top to limit front to back and side movement.