Pinion angle help

[paint2361]

Giving that my trans tunnel is level with the ground, what's a good starting pinion angle for a 4link set up? I'm kinda doin this all ass backwards, I don't have a motor/trans in my car yet and I need to get my rear lower arms mocked up. If I can remember it needs to be 2* to 4* down right?

[wmhjr]

You need your driveline angle first. Or are you planning to fabricate motor/tranny mounts to adjust driveline angle after having a static pinion angle?

[paint2361]

I guess I can if I have to. Is there no way I can get a round about pinion angle?

[wmhjr]

My understanding (and there are others here way smarter about this stuff) is that the pinion angle as it relates to the angle of the output shaft of the tranny and the driveshaft u-joints is what is really important. So, knowing the driveline angle would seem to be a critical variable in setting the pinion angle. If you set the pinion angle first, then for correct setup you'd need to adjust driveline angle to insure you have the correct geometry.

The chassis builders on this site ought to know the real story, though. Mine is just theory - I set my pinion angle based on advice of others.

[paint2361]

Once I get my motor and trans installed I can fine tune the pinion angle with the adjustments on the 4 link bars. I'm just looking for a ball park angle of the rear end to the trans tunnel. I am worried that when it comes time to set up my pinion angle it will be soo far off that I'm goin to have to adjust my 4 link bars so much that it might really through off my wheel base. Would it be safe to say that if my rear end it straight with the trans tunnel, it's too high?

[monteboy84]

I'm goin to have to adjust my 4 link bars so much that it might really through off my wheel base.

Can't you do your pinion adjustment with both your upper and lower links? This should keep your wheelbase change negligible.

Also, I'd worry more about the pinion angle more than the wheelbase, since the pinion angle determines how what effect torque will have on the rear suspension.

-matt

[paint2361]

My lower links are not adjustable....

[cobraguy65]

What kind of car is it? maybe someone with the same model could check there driveline angle. This would give you a reference. Otherwise, I would start with the pinion 1-2 degrees upward toward the front of the car. Also, what kind of bushings in your 4 link?

[68400BIRD]

I know most GM cars have 3 degrees angling down at the back of the transmission. Like mentioned above 1-2 degrees angling up should put you in the ball park. I would just tack weld everything in place. Then send it home when the drive train is in the car.

[discipletwo]

Pinion angle is relivent to ride hight so you relly need to set it last with wheel tire combo and full weight of car I would drop engine tranny in and tack it up close to mock up and weld it out when your done. The degree of tilt back of the engine is also not relitive to the frame its relivent to the ground so if say it was 3 down as compared to the frame then with tall tires in rear it might only be 1 down. All and all what u want is your rear 1 degree down as compared to the front angle so u need the combo in car don't over think it if your angles are parallel with the rear down alittle one other thing your mounting locations for your bars are for adjusting ic which affects your anti squat line that's what will make a car hook or blow the tires off pinion shims ar made for your purpos. My advise is worry about ic and weight transfer first and weld your rear pads last. To set your angle