rear pinion angle questions...

hey guys, gota few questions bouncing around in my head about this so i thought id throw this up for the board to discuse.

when it comes to your rear pinion angle ive always been told you need your upward pinion angle to match the downward angle from the motor. in most cases its right around 3 deg.

figuring -3 and +3 cancle out and you dont have vibration troubles.

with out the correct angle its said youll have vibration troubles and go threw u joints fairly quick.

here is my question. if your angle is set correct and you throw a set of 4 inch blocks on your leafs to get it down further. why does every one always say to get some shims to correct the pinion angle? if the blocks are square shouldnt the angle still be whatever it was before you put the blocks on?

or is it because the blocks sit the rear end a little differnt and might push the angle out of a wack a bit?

ive never seen it discussed from this angle realy, all i ever here is they need to be correct and match, then what play does the vertical placement of the rear end have?

on this note do cars with air ride eat up ujoints as they often ride around at variable heights quite often? im fairly sure ive never seen this addresss and im almost certain that most link sets ups for air ride done have a magic pinion angle controller.

whats the deal?

tim

 

blocks & wedges to fix angle or cut blocks at a little wedge,the hole idea is to keep all "U"s as strait as you can. if you can set so under load(drag start)it is straitist,best if your a racer,if cruising then straitist just running down the road.

 

so throw the whole angle matching thing out the window and just try to get it as flat/ straight at possible?

 

as long as the two (tail shaft-pinion) are in the same plane, you will be okay. The ujoints don't care about anything else.

 

Ain't figured out to add a link, but you may want this, or PM me and I'll send it to ya

www.drivetrain.com/drivetrain-angle-problem

 

I agree with you on this one Tim. In theory, if the top and bottom surfaces of the block are parallel, then the angle of the rear end itself does not change.

 

Long blocks like that change the driveshaft/pinopn angle to a steeper one. u-joints don't much like steeper angles, so the shim lessens the angle by putting the pinion more inline with the driveshaft

That said, I have 4" blocks with no wedges in my '55 and didnt pick up any extra vibrations. But, I have a Mopar Ball and Trunion style u-joints, which(i think) will handle more angle without trouble.

 

This is an interesting subject. I believe we are talking about 2 different angles.

One is the angle of the rear end pinion relative to the ground. As in if the trans angle to the ground and the pinion angle to the ground are the same, then they are correct.

The other is the angle created by the 2 parts of a u joint.

So it may be preferable to have a misalignment between the trans and pinion if this eliminates angling a u joint too far?

This might be why lifted 4 x 4's purposely rotate the rear end pinions beyond the matching angle of the ******?

 

On a rear with leaf springs, the angle changes around alot anyway...due to spring wrapp up etc......Thats why some guys dial in a bit more/less? than whats needed to allow for the diff centre snout wanting to shoot upwards...if that makes sense....also the front spring mount acts as a pivot and the diff arcs from that front point...thats why running large lowering blocks makes it more prone to spring wrapp up.....thats where the spring looks like an S shape, side on on acceleration...and the reverse also.....cheers, Bert

 

Pinion angle should be set so that under load the pinion and the crankshaft centerline are parallel. Depending on suspension type you may need more or less angle to get it right. The nice thing is this is actually a very forgiving science. The shims are not always needed, but can easily be added later.

 

If the joints are too straight, they can wear from the needles not rotating. Called frettage, it's caused when the ujoint angle is less than 1 degree. Too much angle is bad, but straight is also bad.

 

It's not an exact science. As the rear moves up and down in it's normal suspension travel, the pinion angle DOES change. With leafs, or with coils. In fact, when you lower a car, it does usually change the angle, as msot times, the rear does not sit exacly parallel with the ground on the spring, so a lowering block can exaggerate the problem.
It's OK for the angle to change, as someone mentioned, that's what U joints are for, and it helps keep the needle bearing rotating, so they don't wear.
But for maximum life of the moving parts, you should try to keep the prescribed angles of the crank and pinion parallel at ride height. So MOST of the time, it is in the correct alignment.
And yes, cars with air ride, and extremely lowered cars WILL have a shorter than expected life of the U joints and such. But almost all of the time, these cars arent'd riven enough to worry about it. Or you just chalk up the extra maintenace and breakage to the "price of being cool".
We recently brought back a custom that was built a bunch of years ago, a 48 Merc that sat on a Gran Prix ch***is.
The car was lowered a bit from stock, and just fooling around underneath the car, I saw that the pinion angle was WAY off from what it should be. Since the car had coil springs, with a triangulated 4 bar set-up (factory suspension), I had to fabricate new upper trailing arms that we could adjust to bring the pinion angle back to normal at the ride height. I used square tubing, and rubber bushed rod ends from suicidedoors.com to make them, and it worked out very well.
It goes to show that lowering these types of suspensions DOES change the pinion angle radically (5-6*), and you need to do something to correct that!

 

that being said how hard is it to just make some of those shimes? i see them at stores and online and it seems a little silly to spend 20 bux on two little slivers of metal?

 

how much does a pair of new u-joints cost?

 

not saying its silly to use them just seems like alot of money for what you get

 

When you put a set of lowering blocks in between your rear end tube and your leaves, you've lowered the rear of the ch***is. Since the body, ch***is, leaves, motor are all bolted together, you have changed the angle of the trans...even though the rear end itself hasn't moved. The shims are changing the rear-end angle to compensate for the change in trans angle.

 

hmm never thought of the relation to earth not relation to the ground side of things.

i understood the reasoning of them the whole time just not how it all played into the -3 +3 discussions.

on a related note if your droping the whole car equaly front and back, the in theory the motor/trans should be just as "level" as it was un dropped in realtion to the ground

 

How do you figure out what the angle will be when you don't have anything to weigh down the springs to know what the actual ride height will be?

 

Not trying to hijack the thread, but how do you set up pinion angle on a closed drive rear/******? Or is it even an issue since the torque tube actually bolts to both?