GofasterFirebird

iTrader: (3)

If I put springs in my car that lower it, won't my pinion angle become more negative? Has anyone noticed positive or negative effects from this?

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1991 Firebird
350 L98 (was a 305 TBI),T-5,Edelbrock TES and cat back,Accel manifold
NOS,subframes,jegster torque arm,MSD Digital 6
AFPR,Lakewood lcas
Hurst linelock,SLP cam (206 212 .480 .486),relocated battery,cold air,Hypertech chip,centerforce df,clutch
poly bushings and mounts
AFR 190s
Harland sharp 1.5 rockers
autopower rollbar

12.33 @ 114.83 juiced uncorrected

13.510 @ 102 non juiced uncorrected

ViciousZ

iTrader: (1)

Never really thought about it before, but I suppose it would change the angle a little. I have no idea about possible effects, but I'm sure it's not near as severe as on trucks with big tires and lift kits. My truck goes through u-joints like there's no tomorrow. Gotta fix that sometime...

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91 Z28
Come see The Vicious...

onebad82z

iTrader: (7)

I lowered my Z 1" and threw the whole rear suspension out of whack.Yes the rear will be offset and pinion angle will go way positive.If you do not hook up now,you will have no chance once you lower it.I had to invest in all the goodies to correct this,panhard & torque arm(both adjustable) ,LCA's and relocation brackets.Yes these parts allowed me to set everything up to spec but a $250 spring change turned into a complete suspension upgrade.On the other hand the car looks so damn good lowered and I was eventually going to do this to the rear suspension anyway for the strip,just quite a bit to spend at once.It does handle and ride better than ever now,I used Hotchkis springs.

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1982 Z28:355,4 Speed,Lots of bolt ons

GofasterFirebird

iTrader: (3)

I really think that pinion angle will go more negative; that is the front od the torque arm will point more down. Right????

ViciousZ

iTrader: (1)

But the slight change in pinion angle is not what causes the lack of traction. That's from changing the angle that the lower control arms are at.

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91 Z28
Come see The Vicious...

onebad82z

iTrader: (7)

The front of the torque arm will point up or positive along with the rear(pinion angle).I measured mine after I lowered and it was positive.The combination of the wrong pinion angle and the control arms angle being the reverse of what is ideal for traction is what causes the loss of traction.

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1982 Z28:355,4 Speed,Lots of bolt ons

89ProchargedROC

no, you are wrong here.

the TA has the bigger effect

Tory Hess had this problem. He was pulling 1.60 60's and running like low 10s, so obviously having traction problems

he shimmed the TA so that he would have negative pinion angle and his 60s went to 1.40s

IROCKZ4me

I may as well throw some more wood on this fire.


Both, pinion angle and instant center are effected by the torque arm. Lowering the car will effect both.


Negative pinion angle is when the nose of the carrier housing (the pinion area) is pointing down towards the ground instead of parallel with the tailshaft of the transmission. Positive pinion angle is when the carrier housing & pinion are pointing up from the parallel line.
Pinion angle is measured at the pinion when the vehicle is sitting at rest and is the angle of the pinion, it is not necissarily the angle of the torque arm.

If you do not change the outside diameter of the rear tires, and you lower the vehicle with springs then the rear axle is still at the same height from the ground, but the front torque arm mount is lower in relation to both the ground and the rear axle. Since the rear of the torque arm is solidly attached to the rear axle, If you lower the front of the torque arm that will twist the front of the axle down. This would cause negative pinion angle. To return the pinon angle to 0° or to just make the pinion angle adjustable you can use a torque arm with a turnbuckle or threaded rod-end at the rear axle end of the torque arm. This will allow for adjustment of the pinion angle in relation to the trannies tailshaft. You can also change pinion angle by moving the front mount of the torque arm up or down but that also changes the point known as the instant center.
Ideally you want 0° pinion angle at all times.
When using constant velocity U-joint driveshafts, both ends must be at the same angle (0° difference) to maintain constant velocity. Any angle difference, positive or negative will cause driveshaft U-joint binding with pulsing and surging. This will eat U-joints over time and the vibration, pulsing and surging will cause traction loss and the binding wll slow the car.
Drag cars are set up with negative pinion angle when at rest (usually around -4° or so) so that when the axle twists under extreme force from acceleration and the pinion moves up towards the floor board the pinion angle will be 0°. The idea is to have 0° pinion angle while accelerating so there is no surging, pulsing or binding in the driveline. If the pinion has positive angle (angled up) when at rest and then when under acceleration it moves up more, that would throw the driveshaft and U-joints way out of line and cause a very large amount of bind and surge.

Now for the fun stuff:

Where the instant center is effects traction much more than pinion angle. When the rear axle twists under acceleration it applies a rotating force on the control arms and the torque arm. This force pushes up and back on the body of car. The point at which this force is concentrated is called the instant center Moving the instant center back will push up on the car body over the rear tires, forcing the tires down into the pavement. Think about doing pushups. Your arms lift your shoulders away from the ground while pushing your hands into the ground. Moving the instant center up in relation to the cars center of gravity will help transfer more of the front weight of the car onto the back tires.

Finding the instant center is easy on a car with a four-link rear suspension. Draw a straight line through the center of the front and rear bushings of the upper rear control arms to the front of the car. Do the same thing for the lower rear control arm. The point where the lines cross is the instant center.
Move the mounting location of either the front or rear mounting location of either the upper or lower control arms and you will move the instant center. The front and rear mounting points of both the upper and lower rear control arms of a four link are static. Their bushings pivot around bolts and have no forward or backward movement.
The front and rear mounting location of the rear control arms on an F-body is also static. The rear mount of the torque arm is also static but the torque arms front mount is not. The front of the torque arm not only rotates in the bushing but it also slides forward and backward in the mount. This makes it a little more difficult to find the instant center in an F-body, but it is still the same basic relationship between the torque arm and the control arms. In simplest terms the torque arm more or less replaces the upper control arms of a four-link.

On an F body, instant center is affected by the angle of the torque arm (front mount height in relation to the axle), the length of its front mounting location from the rear axle, and the angle (front and rear mounting locations) of the rear control arms.

When Tory moved his front torque arm mount up he moved his instant center upwards, in relation to the center of gravity, helping to transfer more of the weight of the car onto the rear tires. Moving the front of the torque arm up twists the axle and would cause positive pinion angle. When you add the natural twist of the axle when under acceleration it would go even more positive causing bind and pulsing in the U-joints. The pinion angle would then need to be adjusted to compensate unless the car had too much negative pinion angle before moving the front torque arm mount up.

If you lower an F-body you lower the front mount of the torque arm in relation to the rear mount of the torque arm, moving the instant center down. You also move the front mounting location of the rear control arm down in relation to its rear mount. Due to the short length of the rear control arms their angle changes drasticly. This moves the instant center way further forward and way, way down. This will seriously hurt traction. A lowered car needs to have the mount of the axle end of the rear control arm lowered also to correct the instant center geometry.

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Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"

• 355 cid
• AFR heads
• Arizona Speed & Marine hydraulic roller cam w/ AFR hydra-rev kit
• modified SLP runners
• TRW forged pistons/ceramic coated
• fully balanced
• Edelbrock headers/ceramic coated
• SLP cat-back
• Paxton supercharger
• Nitrous Express nitrous oxide

EFI Performance Club on Yahoo




[This message has been edited by IROCKZ4me (edited November 03, 2001).]

89ProchargedROC

WOW!

remind me to consult you when i do some suspension changes

crucial

Now if he only knew the difference between "effect" and "affect" he'd be a genius! lol

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1991 Z28 5.7 TPI

ZZ4 heads, ZZ4 cam, Harland Sharp roller rockers, Accel base, SLP siamesed runners, 52MM SLP Throttle Body, Hooker Headers, Flowmaster catback, MSD6A ignition, Home made ramair system, aluminum driveshaft, WC 5-speed etc

IROCKZ4me

A english major I weren't one.
But I's give it a try.
<font size="6" color="green">
Affect = to act upon or to produce a change in.

Effect = produced by a cause, result
</font>

Is I a genuine genious now.