Engine and rear end at 3 degree down

tramminc · Veteran Member

Engine and rear end at 3 degree down

jim_ss409 · Guru

Driveline angles are pretty simple. For most cars you want the engine and pinion to be parallel to each other while you are accelerating. In your case if the back of the engine is pointing down three degrees you'll want the pinion to be pointing up at the front about three degrees when you accelerating. Many will say that you'll want to set the pinion about three degrees lower to allow for the way the pinion will tip up under acceleration but I think that's too much. Maybe on a powerful leaf spring car. Three degrees is quite a bit if you're dealing with a 65-70 full sized car one or two degrees should be enough.

So, in your case I would set the pinion so that it's pointing up one or two degrees. Be sure to have weight on the wheels when you check it. You may find that it's close to that already and close is good enough. The angles have to be off by a fair bit before you'll experience a vibration.

tramminc · Veteran Member

C5R 427, 748 hp motor, 12.25 inch wilwood rotors, 4 piston calibers with e-brake and 3.55 gears. Also going with 13 rotor and corvette calibers in the front.

-- Edited by tramminc on Tuesday 29th of March 2011 09:14:36 PM

jim_ss409 · Guru

WOW! That's a nice setup!

With that kind of power the pinion might come up more than normal. I'm guessing you'll also have polyurethane bushings so that will lessen the amount the rear axle will wind up.

I still think setting the pinion a degree or two lower than parallel to the output shaft on the transmission will be enough.

Here's the thing I learned about driveline angles that really enlightened me.

Take a normal car where the engine is lower on the back, the driveshaft level with the floor and the pinion pointed up so that it's parallel to the engine crankshaft. Now if you put a degree wheel like you'd use for installing a cam on the crankshaft, another one on the driveshaft and a third one on the pinion. You'd find that the angle of the front U joint would cause the driveshaft to speed up and slow down a little on each rotation. The readings on the crankshaft and driveshaft degree wheels would only match up twice on each rotation. But, because the pinion is at the same angle as the engine that U joint has an opposite effect and the reading on that degree wheel would match the one on the engine.

If the pinion was on the same angle as the driveshaft the surging caused by the front U joint would not be corrected and it would cause a vibration. As long as the angles are within a few degrees of being correct any vibration would be so slight that it wouldn't be noticed so you don't have to be dead on. It's just nice to know what the ideal setup is.