pinion angle

[papastoyss]

I'm trying to set pinion angle on my 40 Ford project. I' ve got the pinion down 3.5 degrees but the trans is down 1.5 degrees. The engine/trans mounts were already welded in when I got the car. I can't raise trans up enough to get to 0 degrees w/o hitting floor. I haven't welded spring perches to axle housing so I have wiggle room there.If I understand correctly the ideal is 2 up on trans & 2  down on pinion.Do you think this will cause a vibration? I don't want to cut out & redo motor mounts , if  I lower the engine (94 LT1) the a/c compressor hits the frame, it has stock Camaro accessory brackets. But I don't want a vibrating drive shaft either. Opinions?

[chimp koose]

Ideally the driveline would run parallel in the horizontal plane, meaning the pinion should be up 1.5 degrees to match the angle of the transmission.When I set up drag cars,I tend to put the pinion 2 to 3 degrees down in relation to the transmission angle to compensate for housing rotation an acceleration.

[Fat Cat]

There is a really good explanation of this in the tech section located here http://www.roddingroundtable.com/tech/articles/driveline.html

[papastoyss]

There is a really good explanation of this in the tech section located here http://www.roddingroundtable.com/tech/articles/driveline.html

This was obviously written by someone a lot smarter than me. In the picture of two drive shafts are both correct? If so , with my trans down 1.5 degrees would I be ok with pinion down an equal amount?

[model a vette]

The first example has a description saying it is for special apps.
I think the second example is what you want to follow.
If your trans is going down 1.5 the pinion should point up 1.5.

[Fat Cat]

There is a really good explanation of this in the tech section located here http://www.roddingroundtable.com/tech/articles/driveline.html

This was obviously written by someone a lot smarter than me. In the picture of two drive shafts are both correct? If so , with my trans down 1.5 degrees would I be ok with pinion down an equal amount?

If you are talking about this image
Then yes both examples will work in any real world application.

[Charlie Chops 1940]

So, If you haven't welded the spring pads on the rear, rotate the front of the rear end up to  1.5 degrees up and weld 'er in there. That would make the centerline of the rear and the crank centerline parallel which is the most common form of alignment.

Just my $0.02 worth.

Charlie

[PeterR]

In the picture of two drive shafts are both correct? If so , with my trans down 1.5 degrees would I be ok with pinion down an equal amount?

That article was written in my more verbose days and while it may make interesting reading on a cold evening, has more detail than most readers want.

To put it in the fewest words I can manage.

Whenever a universal is not in dead straight alignment it introduces a pulsed rotation into the driveshaft.   There are two pulses per revolution.   If there is a second uni at the other end of the driveshaft and both joints operate at the same angle, then the pulses introduced by the uni at one end are cancelled out by the uni at the other.  

Because there are two pulses per revolution, either of the arrangements shown in Fat Cats post above will allow the gearbox output shaft and the pinion turn in synch.   There will still be rotational pulses in the driveshaft itself, but the flywheel effect of a skinny piece of metal is small and rarely causes a problem.

Most vehicles will use the arrangement shown in the lower diagram.   The arrangement is described in many ways using expressions of nose-up nose-down etc, but I prefer to say the crank and pinion must be parallel because this is less likely to cause confusion when lying under the car.    Take a magnetic angle finder measure the angle of the engine then roll back and stick the angle finder on the pinion and compare them.

A point sometimes overlooked is that the same requirement exists when viewed from above.   If the engine or the diff pinion is offset, they must still be parallel to each other.    

The setup shown in the top diagram has a distinct advantage in certain applications.   "Monster trucks" with huge lifts have very large driveline angles, and these can be reduced by adopting this arrangement.

[enjenjo]

The setup shown in the top diagram has a distinct advantage in certain applications. "Monster trucks" with huge lifts have very large driveline angles, and these can be reduced by adopting this arrangement.

It's also usefull on a very low car.

[38HAULR]

Also, to consider is that the small angle under normal operation allows movement of the universals. Zero angle has no needle roller operation. This can result in  a term called "brinnelling' where the needle rollers actually wear grooves into the uni yoke. Some may argue that with zero degrees ,rear suspension movement itself would be sufficient to give the rollers a working.......Frank.

[papastoyss]

THANKS to all who replied!

[chimp koose]

remember that zero angle means crank,driveshaft and pinion in a straight line. In full chassied drag cars you can aim for this and then use solid bushings instead of needle bearings in the u-joints for more load bearing.