Correct pinion angle and how to read it

[Strawdawg]

pointed at the ground in relation to the drive shaft...pinion rises under acceleration as opposite reaction to the tire rotation.

Again, note that those desired angles are for strip use with sticky tires...the more bite you have, the more the housing will rotate.  See the link I posted for Brad above.

[shadango]

I have been searching the forum and the web for the correct answer as far as how much angle I should have.

One article said that most cars come from the factory with  o to -1 degrees.....and that most street cars should run  -2 to -3 degrees.

But anytime I introduce "Mopar" into the subject, the answer seems to be -5 to -7 degrees everywhere.

WHy are Mopars needing -5 to -7 but other leaf spring cars seem to need less?

I am set right now at -5.75, after using add-a-leafs to bring my back end up.

Should I leave it alone or tweak it down some? 

318, j heads, cam, car, headers, manifold, etc....2.76 gears right now, swapping to 3.55 soon.

The reason I am even concerned is that I had a dead u joint in the fall, and I am not sure but the  front one may be failing.  COuld have been cheap u joints, or an out of balance shaft I guess too....

Part of my plan is to have the driveshaft checked/balanced as well.

[shadango]

assuming that you paid attention and know that is a minus 5.75 degs, you should be fine..personally, I like a bit less on a street car with an automatic as they tend to "hit" more softly than a stick and therefore need a bit less pinion angle...  No sense in wearing out u joints in the name of something that might be unimportant unless way off or in very high hp cars.

How much do you like to run?

[Strawdawg]

I like 2-3 on a street car...

people say 5-7, or whatever, because they read it somewhere and did not put it in context as being for a strip car with sticky tires where the tires are going to grip and force the axle to rotate more than happens on a street car where the tires often spin a bit.  If you are running drag radials and the car is set up to transfer weight to them, then you need more than the 2-3...but once again, understand that it does not add to traction, it simply creates a condition where power is not lost in u joint bind.

[shadango]

So seeing as I have 5.75 now.....what do you think shim wise?
I am thinking a 2 degree shim....since it will take a little more than 2 out, right?

Are shims all the same width? Will I need to lengthen the alignment pin or will it be long enough as-is for the shim?

I see the mopar performance shims are 2.5 " wide.   

In their description on summit they say "An incorrect pinion angle can rob precious horsepower, as well as cause launch problems and parts breakage. These Mopar Performance rear axle shim packages allow you to correct the driveshaft-to-pinion angle on most any rear wheel drive vehicle to the recommended 5-7 degrees. These packages include two each of 1, 2, and 3 degree tapered steel shims."  So I guess they are figuring "strip" as well?

[Strawdawg]

the idea is to have the straightest line possible to the rear end when the car is under acceleration.  In normal driving, the rear housing is not rotated very much and therefore the pinion angle will be close to what it is when stationary...this is what causes faster wear.

I believe that all mentions of 5-7 are for performance applications as I have mentioned before.

The easiest thing to do is to leave it alone and change the u joint more often if it is truly 5.75 degs...unless you torch the u bolts to make it an easy exercise when it comes to installing the shims.  ....  I just got thru installing the hotchkis springs and on the first side, I was happy when the bolts broke off instead of making me crank the nuts all the way off.  If the u bolts are long enuf and the nuts back off relatively easily, then you can insert the shims without a complete removal....  oh, yeah, I broke the torch out on the second side

Anyway, if you decide to mess with it, I would install the 2 deg shims and call it good.  First, I would recheck it.  Rather than zeroing the device on the pinion, I would zero it against a true vertical, then read the angles on each and subtract to see if you still have 5.75

I believe in measuring more than twice before I cut anything...

[shadango]

Thanks Steve

My ubolts are pretty new and in good shape so shouldnt be a problem loosening them up to add the shims.   I was wondering about the centering pins

[shadango]

  Rather than zeroing the device on the pinion, I would zero it against a true vertical, then read the angles on each and subtract to see if you still have 5.75

The way this gizmo works is it will do a "relative" measurement...zero on one surface and then measure on the other to see the difference....

I did do it the other way too...measured the angle of the pinion , then the shaft, then did the math....it seemed to work out the same.

Not sure how zeroing out on a true vertical would help, since the vehicle isnt on a 100% level surface to start with....wouldnt that throw the measurement off??   

[Jesus H Chrysler]

I love the technical discussion, but I think you're going the long way around a simple problem.  Your U-joints failed, so you checked the pinion angle which is good.  Angle is OK.  My response is: Buy better U-joints.  The cheap Chinese joints often don't have grease points and fail within a few years.  I know from personal experience.  Pony up a few extra bucks for the top notch greaseable joints and be sure to hit them along with your front end at each oil change.  They will last for many years even behind a high horsepower setup.

As far as pinion angle goes, factory settings are good even when you "lift" the car with add a leafs.  My other projects have been lifted Jeeps and I don't start worrying about pinion angles until they are lifted over 3".  And the driveshafts on Jeeps are MUCH shorter than RWD Mopars.  The angles are much more severe.  The pinion on a Mopar is designed to rise a certain amount under acceleration (hence the pinion snubber)  Like all race cars, people tweak them for the last ounce of performance which is why pinion shims exist for them.  For street driver purposes, I wouldn't worry about it.  If you have a bad pinion angle, it usually manifests itself as driveline vibrations.  If you replace both U-joints with quality pieces and don't have vibrations, I'd call it good.

[shadango]

Thanks Jesus......(lol...thats wild).....

I have been doing a lot of internet snooping and it really does seem like opinions on this are all over the place.

I bought the first u joints from Napa when I installed the shaft initially, in spring of 09........heavy duty truck units, greasable....and I greased them.    The car hit the road at stock rear height (probably sagging a little) and then in the following winter (last winter) I added the add-a-leafs...left the ujoints alone.

That one was toast end of last season....to the point where it was flopping a bit in the yoke.....   

Mind you, that is ONLY 8-10k miles or so, tops.

So, I know something went awry.....

Was it a bad ujoint?  Note nough grease? Pinion angle? Damage due to vibration? Out of balance shaft?

I have a little vibration up around 42 mph, but I am pretty sure its engine and not driveshaft.

The replacement joint I got for the rear one (in it right now) is a sealed unit from AZone......I forget what brand they said it was but I remember thinking it was a good brand.....now I see the (original NAPA) front may be going.....

Because I lifted my rear end with add-a-leafs, the rear sits even higher than a superstock spring car equipped does.....so I am definately pushing the limit on the "stock" travel.......although because the rear springs are now pretty stiff, I cant imagine I have much in the way of axle wrap.  So the u joint is operating most of the time at 6* or so.

I would rather not have to worry as much about u joints if all I have to do is shim the pinion.

Of course that brings the question of "what is the right setting".....Seems like generically people say 2-3* negative (downward) angle is what you want.  Except when I search for "mopar" settings, then it jumps to 5-7*. But then some folks say that is for STRIP mopars and people use that setting in err for street cars.

My car isnt a strip car, a cruiser and the occasional get-on-it.....

Also, define 'top notch greasable u joint"....I have to dig up my old receipt and see what brand the napa unit was.....I paid extra to get the "heavy duty" greaseable one though.

When I do my rear diff swap I plan on going to the larger ujoint for the pinion side.....and have the shaft professionally gone over.  I am also looking to have them check my front yoke and make sure it is tight enough....wondering if that is something they can do off the car....

[Strawdawg]

The way this gizmo works is it will do a "relative" measurement...zero on one surface and then measure on the other to see the difference....

I did do it the other way too...measured the angle of the pinion , then the shaft, then did the math....it seemed to work out the same.

Not sure how zeroing out on a true vertical would help, since the vehicle isnt on a 100% level surface to start with....wouldnt that throw the measurement off??   

Just wanted to make sure you ended up with the same number...another form of of q.c.    I could have said horizontal as well as vertical.  The difference in angles would have been the same.   The relationship between the shaft and the pinion should stay the same whether perfectly level or not as I picture it.

The locating pin on the springs I removed are a half inch long.  That should give you enuf meat to install the shim if you do and still locate the spring.

[shadango]

Just wanted to make sure you ended up with the same number...another form of of q.c.    I could have said horizontal as well as vertical.  The difference in angles would have been the same.   The relationship between the shaft and the pinion should stay the same whether perfectly level or not as I picture it.

The locating pin on the springs I removed are a half inch long.  That should give you enuf meat to install the shim if you do and still locate the spring.

I see out there that they make two versions of shims.....ones that have holes, and ones that have slots......it doesnt matter, right?  In other words, the spring packs dont come apart for shims.....?  I looked at my locating bolts this morning.....I have the nut and then just a little bolt hanging below.....I replaced the stock locating bolt when I added the add-a-leaf...and cut it to length. Not sure there is enough or not......I seem to remember the nut of the locating bolt/pin having a sloppy fit in the hole of the bottom spring plate....does that seem right?

[Strawdawg]

.  The pinion on a Mopar is designed to rise a certain amount under acceleration (hence the pinion snubber)

The pinion on a Mopar, or any other brand for that matter, is not designed to rise a certain amount.  That is simply Newton's law being applied (for ever force, there is an equal and opposite force).

That means the the rear axle housing will rotate clockwise when the tires are rotating counter clockwise when viewed from the drivers side-car moving forward.

On cars with leaf springs such as our old Mopars, the rear springs have a tendency to wrap up and let the pinion move a lot more than it can with a four link suspension. Mopar put a lot of effort into spring design to resist this wrap up-particularly with the springs aimed at drag racing.  Given the problem, the snubber can reduce the rotation that remains..it is not so much for weight transfer to the tires as it is to limit housing rotation when the tires initially  receive the "hit"

[Strawdawg]

I see out there that they make two versions of shims.....ones that have holes, and ones that have slots......it doesnt matter, right?  In other words, the spring packs dont come apart for shims.....?  I looked at my locating bolts this morning.....I have the nut and then just a little bolt hanging below.....I replaced the stock locating bolt when I added the add-a-leaf...and cut it to length. Not sure there is enough or not......I seem to remember the nut of the locating bolt/pin having a sloppy fit in the hole of the bottom spring plate....does that seem right?

Now, that, I do not know.  There may not be a lot left after the add-a-leaf.....I have not used them and am not sure about the fit afterwrd.

[Jesus H Chrysler]

Strawdawg I stand corrected.  I should not have said they were DESIGNED to rise, that is just the end result of torque being applied as you said.  Engineers knew that would happen both through acceleration (axle wrap) and normal jounce/rebound of simply driving the car.  Either way, Engineers planned for this and many other parameters when selecting the u-joint to be used.  Pinion angle simply changes while driving.  My point was that under normal conditions it shouldn't change so drastically as to require shims.  I have Hemi springs at the rear of my Challenger and it still sits too low for my liking.    Maybe shadango and I can swap springs?

As far as shims go, they normally fit between the spring perch on the axle and the top leaf.  You only want to rotate the axle x degrees, not any of the springs.  The spring pack (including add a leafs) should remain together.  The tension and spacing of the U-bolts will keep them in place.   Depending on the thickness of the add a leaf and shim you may need longer U-bolts, so take some measurements before cutting stuff up.