Drive Shaft Tunnel Clearance Minimum

I am used to BMW 2-piece drive shafts with a center-support bearing. They don't hop around much, and the shafts are bolted the transmission output.

Right now I am motor-swapping a car, putting in a Ford 1-piece drive shaft with a slip yoke on the T5's transmission output.

It's self-apparent how the yoke would move in the front-to-rear linear dimension to absorb that kind of drive line movement.

Do drive shafts using these things move in the vertical or horizontal plane? What's the minimum safe clearance from the shaft to the tunnel wall?

There is plenty of clearance at the U-joints and ends, both on the transmission side and the differential side. The middle third of the shaft is the issue. I have expanded my tunnel as much as I can, and it clears, but not by a lot.

TIA

What's at the end of the driveshaft NOT occupied by a T5? Live axle, independent rear with the diff mounted to a subframe, some other confusing arrangement?

I shoot for at least a finger width to anything, at full suspension travel. Up, down, AND sideways.

It's independent rear multi-link suspension. The subframe bolts to the chassis with a 4-point network. Poly bushings, so limited flex. Diff is bolted to the center of the subframe.

Then assuming you've got decently stiff mounts on the engine/trans as well, SkinnyG's finger width rule is probably fine.

JBasham wrote: It's independent rear multi-link suspension. The subframe bolts to the chassis with a 4-point network. Poly bushings, so limited flex. Diff is bolted to the center of the subframe.

So basically your driveshaft will only move with chassis flex and bushing flex. A finger width should be enough regardless of what the suspension's doing.

The driveshaft itself shouldn't deflect much at all if its properly balanced. As far as the driveshaft is concerned, 1/16" would probably be fine. Given that its all mounted on rubber things and the body might flex, I'd shoot for 1/4" or better.

Thanks guys. At this point, with the 2.75 inch shaft, I am not confident I have a 0.25 inch clearance all around. More like 0.125.

I will check my pinion angles again and see if it would be okay to lower the transmission a skosh. That might get me there.

Otherwise, a man on Bimmerforums referred me to a shop that sells 2.5 inch balanced steel shafts in half-inch length increments, rated for 400/400 at track-level RPMs. For $157! Since my ultimate power target for this motor is 380 HP, I may just try to talk myself into buying one and calling it done.

I would honestly try the 1/8" clearance first. If you get rubbing, then consider swapping.

Its unlikely you'll damage it with a little rubbing, so I would say if it isn't a problem, save your $157 for a future upgrade.

You're right, what do I have to lose? We'll bolt it up and see if it squawks.

On my original challenge spitfire, the rear pinion went up so far it hit the body and ground out some metal at the drags..... we used a pinon snubber the 2nd year. New suspension for the rear is independent (RX7 Turbo LSD) and the rear can't move now (Delrin and a very substantial front mount for the FC based RX7 rear, so it won't move now (dropped the clutch in the driveway just to test it), so agree with the 1/4 inch spacing if you are pretty solidly mounted. My engine and trans are also on delrin, so no real movement to speak of and no rubbing of the body or trans tunnel now.