Driveshaft angle

So, I know u-joints need some angle and don't like to live straight. I also think I know that they like 3-5* best. Does it matter WHICH way that 3-5* happens to be? 

Reason I'm asking is after the axle flip instead of a downward angle to the diff, there is now an upward angle of right about 3.5*. If need be, I can remove the carrier bearing hanger and move the front section of the driveshaft about 3" but I think thats going to make the angle too shallow. 

thoughts?

The angle needs to equal and opposite, I think.  If the shaft angles down out of the trans, it needs to angle up from the diff. 

Direction doesn't matter, so long as the transmission output shaft and differential pinion are parallel but not colinear.

This is because universal joints aren't constant velocity (hence the need for CVs), so you cancel out any error that you've introduced in to the driveshaft with the second u-joint on the other end, bent at the equal and opposite angle.

Yeah as long as the angles are equal (and opposite) on both ends, it doesn't matter if the driveshaft slants upward, downward, leftward or rightward, they're not gravity-sensitive

To make matters more confusing, its a 2 piece shaft with carrier bearing. So there's 1 u-joints on the front shaft, 2 on the rear shaft. the shaft out of the trans angles downward to the carrier bearing, then the rear shaft angles upwards to the pinion.

In reply to GameboyRMH :

funny man huh? A friend of mine moved his engine to the left to make more angle so I thought I was safe here just making sure. Hate to find out on the highway at 70mph an hour from home I was wrong. 

If the rear driveshaft is TOO steep (more than 5° angularity between the yolk and the shaft), then you could raise tha carrier, but I would run it and see what it does.

Bajillions of folks have flipped these axles, you're probably going to be fine.

I went through this on my lowered 79 GMC Dually. As I learned, the pinion angle should match the angle of the front driveshaft on 2-piece driveshafts. If you have too much angle, then moving the carrier bearing up can help out. In my case the second driveshaft went uphill a bit from the carrier bearing to the rear axle. This ended up putting too much angle on the u-joint, resulting in a broken rear joint and pinion flange. I chose to raise the truck back up (I was pulling trailers with it), instead of moving the carrier bearing.

In reply to Bobcougarzillameister :

What about bolting a driveshaft flange directly onto a differential flange if the differential doesn't move( IRS) 

In reply to frenchyd :

That'll work, but only if you have solid motor, trans and diff mounts and a very stiff chassis.  Or a setup to tie the trans and diff together like a Miata PPF (but stiffer).  Otherwise, they'll still move relative to each other (even if it's only fractions of an inch) and that'll cause issues.  

The angles can be equal and in the same direction, too. The main source of vibration is the speed variation that happens twice a revolution. This gets cancelled out at the pinion yoke by equal angles in the same phase. 

In reply to rslifkin :rear engine cars tend to bolt everything together and hang suspension off the engine  the "frame" sort of exists to hold the front wheels in near proximity to the engine, etc. 

I'm thinking of doing sort of the same thing only with a front engine car.  

Or should I put a single u-joint in there to allow for some frame flexing?  

So, I don't call my Ford 302-swapped E36 "the Fubari" for nothing.  The transmission and pinion (differential) angle are ALMOST parallel but not quite.  About 0.7 degrees off parallel was the best I could get without major subframe surgery.  The one-piece driveshaft has 3.5 degrees of down-slope.

I'm replacing the u-joints once a season and hoping for the best.  It's holding up after a full summer of track days, spinning that sucker like the bartender's blender on a Chi Omega spring break cruise ship.

In reply to JBasham :

If you don't have noticeable vibration from that slight mis-match, it's probably not much of a concern.  

frenchyd said:

In reply to rslifkin :rear engine cars tend to bolt everything together and hang suspension off the engine  the "frame" sort of exists to hold the front wheels in near proximity to the engine, etc. 

I'm thinking of doing sort of the same thing only with a front engine car.  

Or should I put a single u-joint in there to allow for some frame flexing?  

 

You could use those flexible joints like BMW and Camaros (probably others as well) use on the driveshaft for IRS. That would allow for frame flex.