Jays_SSZ28

iTrader: (2)

I've got a vibration problem with my '01 Z28.
I replaced all of the rear suspension, TA, trans mount bushings with polyurethane, the vibration didn't change.
I checked the driveline angles, the pinion is 2* up.
The trans yoke is 4* down.

The torque arm is not bent. I'd like to mount the torque arm off of the transmission.

Are the TA mounts adjustable for changing pinion angle?
I know they are adjustable, but is this a good way to adjust pinion angle when you have a non adjustable TA?

Sofls1

iTrader: (16)

The re-location cross-members allow you to adjust instant center. This is different than pinion angle. However, pinion angle will change with this adjustment. If you do not have an adjustable tq arm, then which ever way you adjust the instant center, the pinion angle will follow. It is possible your vibration could be coming from that pinion angle.

joblo1978

iTrader: (14)

Yeah, an adjustable torque arm really is the only way to get pinion angle where you want it. -2 to -4 is great for a drag car. If your car sees street use only than a 0 degree angle is preferred.

Pinion angle cannot be adjusted without an adjustable torque arm.

Jays_SSZ28

iTrader: (2)

Thanks for the replies.
I've been searching and reading since starting this thread.
Seems like typical results with the torque arm relocation is adjusting it's mounting point higher than stock for more bite off the line. And for the pinion angle a few degrees down is a typical starting point.

Seems my idea is off because I'd have to move the TA mount to the lower position to try to correct pinion angle, which might make it bite less.

I can only afford one so I guess I'll get an adjustable TA first and maybe the relocation crossmember later.

jimmyblue

iTrader: (11)

Relocation is for setting instant center, launch bite.
Do that and you will change pinion angle. Maybe, or
not, in a way beneficial to driveline angle.

Adjustable at the rear, is for getting driveline angle
right after you're all done changing links, to get rid
of vibration. That does nothing to instant center
but a lot of people buy adjustable TAs thinking it
will.

Two problems, two degrees of freedom, have to pick
the right one for the job (or just do both, but then you
have to tolerate the cabin noise/vibe).

Jays_SSZ28

iTrader: (2)

According to a video from BMR my pinion angle is -1.5.
Thats 3.5 down for the DS, 2 up on the rear, 2 - 3.5 = -1.5
I guess thats right, on my car if you put an imaginary line through the engine pulley bolt all the way to the pinion gear head everything is on the same angle. The pulley leans back at the same angle as the driveshaft so I'm assuming the front u-joint working angle is 0*

To put it another way, under hard acceleration if the rear rotated 1.5* from torque this imaginary line would be straight.

Stock is supposed to be 2* so I'm assuming the poly trans mount being 3/8" taller might have changed something. But it's close enough so I'll leave it.

BTW there are several references to the BMR video on this site but all the links take you to something about mustang upgrades. The video is here. http://www.youtube.com/watch?v=5V6gTrFHK4k

454spyder

All the research I have done recently on setting pinion angle says that the BMR video is flat wrong.

Pinion angle is in relation to the crankshaft centerline (or transmission output shaft), NOT the driveshaft.

For correct pinion angle you measure the angle of the engine/trans. Say is is -2 degrees (pointed down) toward the rear of the car. This is your baseline.

Then measure the pinion angle. Lets say +1 degrees pointed up toward the front of the car.

This nets a -1 degree pinion angle (IN RELATION TO THE CRANKSHAFT CENTERLINE).


1 The Straight Scoop on Pinion Angles
by Ron Rygelski
Performance Products-Red Line Synthetic Oil
http://www.myoilshop.com
(formerly www.redlineoilracing.com)
rlracing@sgi.net


Myth #1: The pinion angle somehow affects how much traction the car
will achieve.

Straight Scoop: No way. The pinion angle doesn't mean squat as far
as the rear suspension is concerned. Think about it: why would the
suspension care about u-joint angles? What determines the "hit" on
the rear tires and the rate and amount of weight transfer is the
intersect point of the upper and lower rear bars (control arms).
That's known as the "instant center" (IC), and combined with weight
distribution, spring rates, and shock valving is what affects
traction.

Myth #2: You increased the pinion angle and the result was increased
traction, so Myth #1 must be correct.

Straight Scoop: You haven't been listening. Pinion angle doesn't
affect traction. What happened is you shortened the length of the
upper bars and that changed the intersect point, moving the IC
farther forward. You also screwed up the pinion angle in the
process. If you want to change the length of the upper or lower
bars, or change their mounting points, that's fine. But after you're
done you've got to go back and check and properly reset the pinion
angle.

Myth #3: The garage floor is the correct reference point for
measuring the pinion angle.

Straight Scoop: You've got to be kidding, right? The garage floor
doesn't have anything to do with anything. What's important is the
drivetrain angle. It so happens that professionally built racecars
are constructed so that the crankshaft is parallel to the floor,
meaning that the transmission output shaft will also be parallel to
the floor. But this usually doesn't hold true for cars using a
factory chassis. In most of those cases the engine is tipped
rearward. Take a look under the hood of your Buick and you'll see
what I mean. The drivetrain angle is the reference point and is
considered to be zero.

How to Measure It: The best way to do this is with the car supported
on jackstands, with stands under the front control arms and rear axle
tubes, with the full weight of the car resting on the stands. Next,
it's best to remove the driveshaft. Using an angle finder (these are
available from Competition Engineering or at Sears Hardware stores--
they're a commonly used carpenters tool), measure across the surface
of the rear transmission seal vertically(see illustration 1). This
surface is perpendicular to the output shaft of the trans, so
subtract the measurement from 90 to get the drivetrain angle. Let's
say that the measurement is -2 degrees(pointed down). That is our
reference point. Look at illustration #3. The pinion angle is the
difference in the angle of the rearend to the angle of the
drivetrain. So, in order to have zero pinion angle, the rearend
would have to be tipped upward (pinion yoke pointing upward) 2
degrees. If our drivetrain angle measured -5 degrees, we'd have to
tip the rearend upward 5 degrees to have zero pinion angle. Get it?
Now turn the pinion yoke so that the u-joint cups are sideways, and
measure across one side of the pinion yoke vertically(see
illustration 1) where the u-joint strap connects. Again, this
surface is perpendicular to the pinion, so subtract the measurement
from 90 to get the rearend angle. compare this number to the
drivetrain angle to get the pinion angle. If the drivetrain angle
was -2 degrees(pointed down), and the rearend angle measured +1
degrees(pointed up), then the pinion angle would be -1 degree. If
the drivetrain angle had measured -2 degrees (pointed down) and the
rearend angle had measured -3 degrees (pointed down) then the pinion
angle would be -5 degrees. In my particular case, the drivetrain
angle measured -4 degrees, and the rearend angle measured -6 degrees,
resulting in a pinion angle of -10 degrees, a wasted tailshaft
bushing, and a slower than necessary racecar. The idea is to have
the pinion angle at zero with the racecar under power and going down
the track. To allow for suspension movement and loading, the pinion
angle should be at around -2 degrees for our cars.


How to Adjust It: Adjustable torque arm or shim the transmission.

How important is all of this: Well, excessive pinion angle can bind
the u-joints up pretty good and rob quite a bit of horsepower. It's
not at all unusual for a car to pick up 2-3 tenths and as many mph
after getting this straightened out. Also, excessive pinion angle is
often the real culprit behind broken parts. Racers love to attribute
busted driveshafts, exploded tailshafts, and cracked bellhousing to
the raw torque and horsepower produced by their motors, when in fact
it's usually a problem with driveline geometry. It's definitely
worth checking before you break something expensive. See you in the
lanes!!

BMR Tech

iTrader: (9)

I see you have been researching pinion angle and have found what all of us already know there are literally 100 different ways to do it and even more opinions on what is the right way....

The method we use is the same method used by Jerry Bickel NHRA/IHRA chassis builder. And he seems to do pretty well for himself. We also have some of the fastest stock suspension cars in the country using our method without issue.

The method Madman uses (ground reference) is completely different but he also has tuned/installed components some of the fastest stock suspension cars in the country.

So who is right?

mad_steve

iTrader: (2)

I don't think it's a matter of who's right. More of a matter of what works for your car. We set pinion angle off the yoke of the pinion on the rear end, with the car at ride height. We don't factor in driveshaft or transmission angle. This method has worked for us through the years with every car we build. Is this method better than BMRs? I doubt it. BMR builds alot of good drag cars that make tons of power and win races. All a matter of preference IMHO.

jimmyblue

iTrader: (11)

Pinion angle in itself does not determine the suspension
reaction. It's the torque arm nose point to axle center
as a ray (line), and the lower control arm angle, that
project to an intersection (the instant center).

The torque arm and the pumpkin are in this respect a
single unit. You jack the pinion angle around within
that unit, you change nothing much about where the
instant center sits. Just how much U-joint angle you
bump over twice a turn.

If you are trying to tune reaction you do it at the
nose of the TA or the back of the LCAs (relocation).

If you are trying to measure driveline angle the way
to get it right is consistency. Be sure your angler finder
is oriented the same for both measurements and not
flipped around as you crawl around. You may want to
put a reminder dot for "front of car" and one for which
direction you are going to call negative, and stick to
it. First time I tried to measure driveline angle I did it
wrong about half a dozen times (probably one or two
right, in there, just couldn't tell which). Got to keep
your numbers straight, starting with measurement
conditions. Especially if you're jacking, driving, jacking
trying to dial it in, you need to get to where it's all
dead repeatable by method.

01ssreda4

iTrader: (96)

I dunno where the pinion angle pissing match came from but its somewhat irrelevant to the OP at this point.

1. Why would you think poly bushings would reduce a vibration? They magnify vibrations.

2. Saying you have a vibration means **** to a reader. We need to know when, where, and how of the vibration to help.

3. A chassis/cross-member mounted TA will further MAGNIFY drivetrain vibrations. Why you think this will solve your problem again is beyond me.

4. Has your driveshaft ever been checked for balance? Or been serviced i.e. u joints been replaced?

454spyder

You guys are all right that whatever works is good to go, I was just trying to point out the definition of pinion angle I've found after talking to different chassis builders.

Pinion angle is truly in relation to crankshaft centerline. Race car builders use only the reading of the pinion at the rear because (my understanding) they already have their engine/trans at zero degrees and level when they build the chassis, that way all they need to do is measure the pinion off the yoke and they have the true pinion angle in relation to crankshaft centerline (without needing to add/subtract for crankshaft centerline).

The straighter the U-joints are under load, the more HP you will put to the tires.

If you use the same procedure on a street car (or factory chassis), then you don't usually start with zero degrees on the crankshaft centerline (they are usually tilted back 2-4 degrees.

Again, like some of you guys said, whatever is working for you is great.