Thread: Driveshaft Clearance

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Can anyone tell me what the minimum floor to driveshaft clearance should be? - Thanks

1" more than the highest position your driveshaft will ever get to---when the rear axle is against the bump stops on the frame.

Thanks for the quick reply, I maybe should have worded it differently - How much travel should I allow the driveshaft to have up toward the floor. The car is a 55 Bel Air with a four link suspension. I.E Should it have 3-4-5 etc inches of travel?

How do you plan on limiting driveshaft movement??? The end which is attached to the transmission tailstock will not move at all, vertically. The end which is attached to the rear axle will move up and down as much as the rear axle is allowed to travel. You limit how much the rear axle can travel vertically by the bump-stops on your frame. what am I not understanding here?

Also the travel is limited by shock length. So what Brian said IS the answer you need. You need to find where the suspension bottoms out. Make sure you have clearance at that point....then ride height clearance will take care of itself.

Never have your upward suspension travel limited by the shock absorbers. That will very quickly destroy the shocks internal seals, even bend the internal main rod. Ideally, you want the rear axle to hit the frame "bump stops" while you still have about 1" of travel left in the shock absorber.

Sorry, I didn't word that right. Just letting him know, how much drive shaft clearance he has at ride height really makes no difference. If it clears though out the travel of the suspension, that's all that he need worry about.

pro70Z28---well, at least we know what we mean---

There are some shocks that have travel stops built into them. Heidts uses them on their superride IRS. Also an IRS leaves the driveshaft stationary except for chassis flex which should hopefully be small.

Kitz

Hello again,

I guess I'm still not being clear. We took over a build that someone else had started and where he had the ride height set, there was no clearance for the drive shaft to travel up when the suspension moves without hitting the floor. We will have to recut the floor and lift the "tunnel" to allow the shaft to travel up. I will fab the bump stops as needed to limit the travel once I know what the "normal" amount of travel that the rearend should be allowed to travel for normal pavement driving and speed bumps, etc.

Thanks for your help

I suppose that in a perfect world, you could find another 55 and measure it. ---But----The world is not a perfect place. I have always worked on the premise that a rearend will travel a maximum of 4" up and 4" down from the "normal" ride height. that has always served me well when building early hotrods of the twenties through thirties.

The best way is still to drop the suspension down as far as it will go (on the frame bumpers) and make sure you have clearance at that height. If it's a four link I assume it has coil over shocks? If so, take them loose and drop the frame down as far as it will go. If you still have clearance, you good to go. If the drive shaft hits the tunnel before the suspension bottoms out, you can modify the tunnel or raise the static ride height of the vehicle. How much drive shaft clearance you end up with at ride height will vary depending on your particular vehicle. My 4 link suspension has about 5" of travel(2.5" up - 2.5" down). You may have 8" (4" up - 4" down). All depends how it was designed.

Hi guys,

Thanks for the replies. I was thinking that 3-4" of travel of upward should be enough. "Pro" you replied that your car had about 2.5" up and down, do you find that to be enough or does the car bottom out on the bumps a lot. When you wrote about un-bolting the shocks and allowing the frame to travel down to the bumps is good advice, but that's the problem we have. There aren't any bumps yet, we have to fabricate them once we settle on how much suspension travel we will allow. Thanks again for the replies, I will probably be asking quite a few questions over the next few months. We have built quite a few different projects over the years (mainly trucks and ralley cars), but this is the first street rod. It makes it a lot more difficult because we didn't start the project. When it got to my shop, it was a body shell, a partially completed frame and hundreds of bits and pieces in 2 truck loads of boxes and parts. There is a reason my hair has turned completely grey at 40

55. Hope you get it all set up o.k. It just takes time, patience and a little head scratchin'.
Mine is a race application. 5" front & back and the front will be restricted to travel even less. It's still in the shop, but yea' it will be a bumpy ride. I won't be drivin' it more than 7 or so seconds at a time tho.

remove the springs, let the axle sit on the bump stops, and measure.

Sure it is a pain in the ass, but that way it is a no-brainer