Driveline Angles - Splitting Hairs?

I am sure this topic will start some interesting responses. So here goes.

I am working on getting engine mounts spot welded into my chassis. It's my understanding that ideally I would have about 3 degrees of angle down on output of the transmission. To keep the unjoints on the same harmonics you would want the pinion angle at the same 3 degrees tilted up in this case. In my case the carb angle is about three degrees so this would in turn level the carb on top of the intake.

Here's my challenge. The rear is an IRS (Winters Quick Change) that is hard mounted to the chassis with about 0.5 degrees of angle tilted up. It's essentially at 90. To get an equal angle on the transmission output shaft I would have to drop motor to being level which in turn takes the angle out of the intake and tilts the carb down 3 degrees. This also means driveshaft would be running at zero degrees essentially on both ends.

The specs on a Spicer 1310 U-joint say to keep things within 0.5 degrees. My drive shaft is going to end up being about 24" long.

The car has about 450 HP with 425 ft/lb torque. Trans is rated for over 500 hp (fresh build). The car will be a cruiser for the most part. Probably want see a dragstrip in its lifetime. I will definitely put the foot into the gas from time to time. But truth is it will be a show car the first two years and then a cruiser after that. If the cars gets more than 800 miles a year on it I am going to be shocked.

It's my understanding that a zero degree pinion angle is not ideal to keep from wearing too much on the lower side of the joint.

So should I ...

1. Cut the rear end brackets and put the 3 degrees in? This is not crazy fab work but it's going to take some effort. Hate to cut up fresh chassis.

or

2. Leave rear pinion angle alone split the difference on carb angle and trans angle and call it good.

I just don't want some annoying vibrations from the drivetrain at cruising speed of 60-70.

Like I said, splitting hairs.

Kevin

 

you should post pics and more info on what you are working on. no rear suspension on a possible street car?

 

It's IRS.

Bob

 

The car is a Zipper Coupe. Essentially a fresh model A style frame. Rear is Winters Quick Change (IRS corvette style).

Here is rear of car.

 

Put the 3 deg in the rear end. Do it now and forget about it.

 

Heres what I know...you have an excellent grasp of how it should be, you're absolutely right on the math, that IS how the driveline should be set up.
The reasons for setting driveline angles are simple, if you have one end at 3 degrees and the other at .05, you'll get the dreaded hum, because...one u joint has to turn farther and faster to get thru its turn than does the other one. Set both at the same degree setting on a parralell plane, they cancel each other out by turning the same speed. If there is 0 degrees at both ends, longevity suffers because the u joint can't work the way its designed and will ultimately fail.
If it were mine, I'd fix it, you'll certainly thank yourself for doing that when you're behind the wheel. Good Luck.

 

Having the pinion angle and engine/trans at 0 degrees DOES NOT necessarily mean there is no driveshaft angle. It depends on if they are on the same plane or merely parallel.

If parallel, but not on the same plane, there WOULD BE some driveshaft angle.

Conversely, having both at 3 degrees could also result in no U-joint angularity. Again, it would depend on the centerlines being either same plane or parallel.

Ray

 

Angle prevents brinnelling of universal joints.

 

Get your engine mounted properly set it on the groud and go from there.

Someone mentioned the U joints brinelling, this is correct, you need some angle at the U joint for U joint life. I know this doesn't sound logical but it is still a fact of life.

Oh on a side not at a glance in the picture of the car it looks like the engine in mounted in front of the hood, I had to look twice.

 

Correct.

The critical angles are the angle between the engine/transmission axis and the driveshaft axis, and the angle between the driveshaft axis and the pinion shaft axis. These have to be the same. The angle of anything to the ground, frame rails, or any other constant is secondary.

Conventional wisdom dictates that if the engine/transmission and pinion axes are parallel, their angles to the driveshaft axis will be equal. Hypothetically there is another state that satisfies this requirement, i.e. where the angles are in opposite directions, for instance where the engine is at 2° up, the driveshaft is at 0°, and the pinion shaft is at 2° down. In practice, and with a live axle, this doesn't work because it will be true at only one point in the suspension's travel.

Because your IRS diff unit isn't going to move up and down relative to the engine/transmission, you can actually make this work. You want both critical angles to be 1¼°. That means, with a 24" driveshaft and your stated angles, you want the front U-joint to be ½" higher than the rear one. That'll place the driveshaft at an angle of 1¾°.

The usual provisos regarding U-joint phasing apply.

 

First you need to re define or add to this "up and down" nonsense - to the front or to the rear
That will help by not changing the reference of the mental pictures and most likely help you.


The most important thing is that the angles be equal !!!!!
Parallel or opposite doesn't matter >>>> equal.

Next you choose parallel or opposite by trying to equalize the angularity of the yokes thru the Ujoint.

However , first and foremost before any of this starts , the vehicle must be on a level surface, at ride height, and dressed weight if you'll be using the gravity based weighted angle finders as pictured.

 

Enough floor clearance to just add spacer under trans mount?

 

Put the engine in to match the pinion angle... if you're running a carb , set the float levels accordingly , engine doesn't care if it's at 3* or 0* .... just setup so you have some operating angle [1* is enough] in the u-joints... my .02

dave

 

I hope the attached will help you. I find it handy and just keep it in a file in my computer. It has helped me immensely.
Normbc9

 

Don't over think this, it's not complicated. You want the 2 angles to be the same as in parallel and as close to 3 degrees as you can get it. Inline is not good as the needles will not roll and over 5 degrees is too much is the way I understand it. I've never had any vibration or excessive wear doing it that way.

 

On closer look you don't have a trans yet. Mount it and then check.