Hi All, I was looking ahead on my project and was hoping for some insight. I have always been told the rule of thumb is 3deg down on trans and 3 deg up on rear diff for pinion angle. My question is if the trans yoke is on a different height than the rear diff yoke should you angle them at each other then do the 3 deg up and down? For example. Say you trans yoke is 6" off the ground and your rear diff yoke is 13" off the ground. Do you set them up at parallel to the ground then do 3 up and 3 down (not worrying about the height difference) or do you angle them at each other ,lets say it is a 10 deg angle so you set the trans aiming up 10 degs then angle the rear diff 10 degs down and then do the 3 deg up and down after the 10 deg is setup? Did that make any sense? Thanks
Never considered the height difference. I guess could be an issue with super small front tires and huge rear tires.
But we make a two degree difference with a 4 link and 4 degree difference with leaf springs.
Typically we run engine down hill at 2 degree sand set the face of the pinion at 2 degrees up which happens to be dead level and fine tune from there on the road. Big horse power cars or cars with stout link bars can be adjusted for.
Think about lifted trucks - or heavy trucks etc - they have pinions that might be far below the engine/transmission plane. The operating angle of the driveline is all that you care about. And that's a calculation of the various angles involved. In your case engine/trans slope - driveline slope - pinion slope. You don't want a 0* operating angle. Typically you're looking for 1 to 2* of operating angle.
Here's a video that might seem boring - but it should help you get a picture in your head of what you're trying to do.
As Greg said, what's important are the operating angles. You want them to be equal, opposite, and as small as possible (less than 3 degrees), but not zero.
That said, the type of rear suspension that you have will make a difference because the pinion will rise under power and thus change the operating angles. So once the angles are set statically, the rear angle will need to be played with in order to find the sweet spot under dynamic conditions.
As for tire size, it has zero effect on operating angles. What does have a direct effect on operating angles is the rear ride height, assuming that you are using a solid rear axle.
Thanks Guys. Really appreciate your help. I think I got it. Its been a little while since my last project so I'm re-learning a lot of stuff i forgot. Thx
As Greg said, what's important are the operating angles. You want them to be equal, opposite, and as small as possible (less than 3 degrees), but not zero.
That said, the type of rear suspension that you have will make a difference because the pinion will rise under power and thus change the operating angles. So once the angles are set statically, the rear angle will need to be played with in order to find the sweet spot under dynamic conditions.
As for tire size, it has zero effect on operating angles. What does have a direct effect on operating angles is the rear ride height, assuming that you are using a solid rear axle.
Andrew is correct. Tire size does not affect the angles. If you put larger diameter tires in the rear, the rake of the car changes, so does the relative angles with respect to true level. The working angles however do not change with just a tire size change. Picture a car going down a hill (same as a larger rear tire), the driveline angles do not change.
If the axle is moved relative to the rest of the chassis (ie ride height change with coilovers for example), then the working angles do change.
Andrew is correct. Tire size does not affect the angles. If you put larger diameter tires in the rear, the rake of the car changes, so does the relative angles with respect to true level. The working angles however do not change with just a tire size change. Picture a car going down a hill (same as a larger rear tire), the driveline angles do not change.
If the axle is moved relative to the rest of the chassis (ie ride height change with coilovers for example), then the working angles do change.
True but who just bolts on taller rear tires and doesn't lower it further.
But just raising the rear of the car without a rideheight adjustment changes the engine angle. Most engines need to have downward angle for float level adjust mentioned and engine oil level. Yes the working angle does not change but other issues do. But like I said who stuffs bigger rear tires under a car and doesn't lower it further. Let alone have a 6 or 7 inch rise in the drive shaft.
I don't have the motor and trans mocked up yet but I know the rear pinion yoke should be 11.1" off ground to center and guess the trans yoke will be around 7" off ground. So that will leave approx 4" rise over 36-40" long drive shaft. That shouldn't be that much of an angle. So I will just setup the irs to go with 2 degs up. Thanks guys. Really appreciate the help! Pics will come soon. Just want more done before. Have a great day!
True but who just bolts on taller rear tires and doesn't lower it further.
But just raising the rear of the car without a rideheight adjustment changes the engine angle. Most engines need to have downward angle for float level adjust mentioned and engine oil level. Yes the working angle does not change but other issues do. But like I said who stuffs bigger rear tires under a car and doesn't lower it further. Let alone have a 6 or 7 inch rise in the drive shaft.
You're conflating two different issues. The operating angles do change when the rear suspension is lowered or raised. This is because the position of the pinion relative to the transmission changes.
Changing front ride height or installing taller or shorter tires, front or rear has zero effect on the operating angles.
Brian Hobaugh SCCA National Tour June 2014
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