Fireball

iTrader: (21)

since pinion location on the 9" is different than most GM rears, what is the proper method of measuring Pinion angle???

is it angle of the pinion with respect to the driveshaft

-OR-

is it angle of the pinion with respect to the driveline (output shaft of tranny)???

I had it set to -3 WRT the driveshaft and its vibrating like a SOB (actually picked up 2.2 degrees of KR). I'm in the process of making up my own torque arm and want to establish a good pinion angle baseline. I have to make my own since I BENT the heim joint on my chassis engineering bar. The BMR looks nice but I don't really want to spend 500+ dollars on one since I can replicate it for ALOT less money <img src="images/icons/rolleyes.gif" border="0">

Looking at chromemoly tubing with plenty of x-bracing (all TIG'ed of course) and chromemoly endlinks. Any opinions?

FYI, my stocker was almost broke, the holes where it mounts to the rear were starting to egg out due to the stresses <img src="images/icons/shocked.gif" border="0">

Dom

iTrader: (2)

BMR one is not recommended for 10s so I don't think you'd want that one anyway.

I believe that 9" has lower relative pinion compared to GM axles. This causes a slightly larger drive shaft angle.

The center line of the crankshaft and transmission output shaft must be parallel to the center line of the pinion shaft. Set the components up so their center lines are parallel and so that the angle made THROUGH the U-joints is 3deg or less. While it is possible to run at zero degrees through the U-joints, something more than actual zero and less than three degrees seems to run smoothest.

Your body weight can change the pinion angle so recheck when done.

An angle induced vibration will be high frequency, twice engine RPM in direct drive. It may show up only on acceleration or deceleration. Adjust the pinion down to correct acceleration and up to correct deceleration vibrations, plus or minus one degree is usually enough. Before adjusting anything, make sure the U-bolts holding the driveshaft to the pinion yoke are not overtightened. I overtightened my driveshaft one time after a gear swap and what a loud and scary noise that was. I think I woke up the whole block with that little trick.

Here is a pic that might help.
http://www.geocities.com/d_payton1/fig2.gif

Fireball

iTrader: (21)

I've read that before but it doesn't take in account axle rotation under hard acceleration IMO

I believe you put in -2 to -3 degrees of angle so that when you launch, the rear rotates to a 0 degree angle (parallel) under power.

but is it parallel with the driveline or driveshaft??? <img src="images/icons/smile.gif" border="0">

WILWAXU

iTrader: (6)

Hey Colonel, didn't you use a Random Tech "stock style" torque till you got the TH-350?

Toph

I'm pretty sure you want it relative to the driveshaft. That way when it's under load, you have a straight input into the pinion.

Darren

You want your working angles at no more that 2 degrees difference. Do you have an angle meter? If you don't you may want to get one. You must check your front drive angle (that is the angle of the output shaft to the drive shaft) then you check the pinion to drive shaft angle. Your goal is to make these 2 angle equal. Example if you front angle is 5deg the you want your rear angle to be 5deg. You don't want more than 2 degree difference. Also you don't want anything less th .5 deg on any one of these angles. If the drive shaft was perfectly straight the little rollers in the universal joint caps would damage the caps after continuel loads in one spot.
The 2 working angle have to cancel each other out. The drive shaft vibration you feel is actually speeding up and slowing down as it goes through the jointed angle. I know i maybe talking greek but I don't know how else to put it unless I could phisically show you.


see ya

ChrisB

Typically when someone says pinion angle it's the different in the pinion and horizontal with
respect to the car. The easiest way to measure this is take the difference between the driveshaft angle (from horizontal) and the pinion angle (from horizontal). Arrange your signs so that pointing down is negative, and pointing up (the pinion) is positive.

[quote]Your goal is to make these 2 angle equal. Example if you front angle is 5deg the you want your rear angle to be 5deg. <hr></blockquote>

If I read this right you are suggesting 0 angle relative to the driveshaft and pinion? The problem is when you load (launch) your suspension/car this changes. The actual goal is to achieve a -1 to 0 pinion angle at max deflection from norm. The second you hit positive pinion angle this is going to cause a bit of unloading on the rear end and hurt your weight transfer/launch. Unfortunately I don't know any way to check this easily, so in generaly you dial in more negative pinion angle untill your sixty foots stop reducing.

Pinion angle is *Very* hard on the u-joints though (as was pointed out above) and if you run any significant amount on the street you will want to replace your u-joints as wear items.


Chris Bennight

Dom

iTrader: (2)

[quote]Originally posted by Fireball:
<strong>I've read that before but it doesn't take in account axle rotation under hard acceleration IMO

I believe you put in -2 to -3 degrees of angle so that when you launch, the rear rotates to a 0 degree angle (parallel) under power.

but is it parallel with the driveline or driveshaft??? <img src="images/icons/smile.gif" border="0"> </strong><hr></blockquote>


That's basically the idea. To get 0 deg under hard launch. I don't know how you would measure the angle while under hard acceleration. It also wouldn't be exactly the same with every launch. Traction is affected in so many different ways. So you basically keep increasing the angle and look at your times.

Fireball

iTrader: (21)

Makes perfect sense to me <img src="images/icons/smile.gif" border="0">

I'll check that out <img src="images/icons/smile.gif" border="0">

Thx

BADZ

iTrader: (5)

We did mine last night. Set it @ -3.5 reason was you have to get the car level, put someone in the car as it is sitting level, it changes the angle about 1.25 to 1.50 on the angle meter. It should read -2.0 nose down so when you launch its like the guy said, 0 angle transfer to the rear.

steve

actually jeff, i took 3.5 degrees out of the pinion angle. its sitting at -2.0 degrees right now.

i will have to check that when i get the new driveshaft back and some one sitting in the car of course.

steve frank