Driveline/pinion angles

[BBC71Nova]

From another installment of the "This doesn't fit either" video series...

The other day I took some measurements and it seemed like my driveline angles were pretty extreme. Here is a rundown of the setup:

'71 Nova leveled using the door sill/rocker area as reference point
OEM subframe w/stock height bushings
BBC using empty block for mockup purposes
T56 Magnum w/Quicktime bellhousing
ATS/Speedtech trans crossmember w/poly trans mount
G-link rear suspension w/Fab9, set at lowest possible ride height

Initial measurements:
Engine/Trans pointed down almost 4 degrees
Driveshaft pointed up 3 degrees
Pinion was down 1 degree

Working angle up front looks to be almost 7 degrees which is extreme, correct? Would require pinion to be pointed up 3+ degrees. Problem is that puts the pinion even closer to the tunnel and it is already close. And why do that just to make a 7 degree working angle "work". From what I've read that isn't close to being ideal anyway.

SO... today I try and reduce the engine/trans angle by raising the tailshaft. I raise it 1 1/16" which yields a new angle of 2.1 degrees. This is an improvement. Just that it comes at the cost of putting the driveshaft into the tunnel requiring a complete replacement of the tunnel on top of the already custom front section. It would also require a custom trans crossmember. In short, this sucks :(

OK so what's wrong with this picture? There are tons of builds using these same parts and I don't often hear about this level of fab work being required. It is true that being a Nova and having BBC is a little unique around here but does the LS sit that much lower to reduce the engine/trans angles? Are these angles just being ignored? Are they just not that important after all?

Thanks!

[chicane]

The actual shaft angle is irrelevant. All that is required is equal and opposite angles of the output shaft and the pinion itself.

The one thing that stands out here is your measured pinion angle. The factory pinion angle for standard Hotchkis style rear suspensions (read: leaf springs) from General Motors is 4* up, with a output shaft angle being 4* down... which would nearly match your measured output shaft angle of 4* down.

It looks like you will need to adjust the G-Link to obtain the necessary pinion angle. And yes... it is very much important if you want this thing to live. Furthermore, the more power/torque... the less angle necessary. For high power applications, I try to stay under 2*... and more towards 1* if you get near the critical shaft speed of the drive shaft itself.

This is the most simple example: MW Operating Angles (http://www.markwilliams.com/Catalog/pg68.pdf)

[Vegas69]

John, working angles are that important. 7 degree working angles will net you a very good vibrator for a car. They would work pretty well on a post hole digger. :unibrow:

You also need to consider your headers when raising the driveline to far along with other things like hood clearance. You really need to find the sweet spot and it may not be by the book.

In these circumstances which everybody runs into on a muscle car that has been lowered this far from factory, you need to concentrate on getting your working angles as small as possible. Preferrably under 3 degrees at ride height. Find the sweet spot for your driveline and start playing with your pinion angle and keep an eye on your driveshaft. You must get it flat(Close) or sloping down towards the rear of the car so it decreases your angles, not increases them.

I'd try 2.5-3 degrees of driveline angle with 0 pinion angle to start. Once you find your sweet spot, remove your springs from your shocks and run it through compression to make sure you have the clearance needed around your pumpkin and driveshaft tunnel.

Keep in mind that your U joints need a minimum of .5 degrees of working angle to prevent premature failure. I'd also like to see your front and rear working angles as close to .5 difference as possible. (Front working angle is 2.5 while back is 2 for example)

When you lower your pinion angle, your wheel will move towards the front of your wheel well. You may as well make the fore and aft adjustment once you find that sweet spot as well.

[GregWeld]

This may help you.....


http://www.carcraft.com/howto/91758/index.html