Adjusting pinion angle...please confirm I am on the right path...

[Pumpkinfish]

I have had a vibration in the rear and my shop keeps insisting he has my pinion angle at -2.5 degrees. So I decided to check myself. Here is what I found when I put the car on four ramps and used a non-digital angle finder and a metal carpenters square so I can read on the protractor in the same orientation.

trans flange: 2.5 trans pointing down
pinion flange: 2.5 pinion pointing up

To me (and what I have read in the pinion angle sticky), this would be a pinion angle of 0 and it still needs to be adjusted at least 2 degrees down on the pinion, correct? I can see where this shop thinks the pinion is -2.5, but and maybe he is right. That is why I am making this post.

Also, what pinion angle should I start with for a car that makes between 480-490 at the wheels with around 450 torque? I haven't had an updated dyno since the Supershaker went on, but I am guessing I am at similar power levels and I have an all poly suspension.

I am using a BMR uca, so how many turns equals a degree of pinion movement? I downloaded their directions and they don't mention anything.

 

[tmcolegr]

glad you have the vehicle supported by the tires - that's the first step in correctly measuring pinion angle.

with the measurements you have posted, both the transmission output flange and pinion flanges are parallel with each other - which is good. Now you need to measure the drive shaft angle at both ends and determine the actual working angle (difference between the drive shaft angle and flange angle) of each. Since your transmission and pinion are parallel, the working angles should be identical. Usually anything more than 1* difference between the 2 working angles can result in unwanted vibrations.

As the vehicle launches, 2 changes occur: the rear suspension compresses and the pinion tries to rotate upward. The 2 working angles (transmission output flange to drive shaft & drive shaft to pinion flange) decrease, and if the pinion angle was adjusted correctly, form a straight line between the transmission output flange and the pinion flange. Horsepower, rear springs and suspension bushing type (solid Vs poly), can all affect how much the working angle changes when the vehicle launches - therefore no 2 vehicle's setup will be identical.

Note: too much pinion angle, which does not allow the transmission output flange and pinion flange to form a straight line when the vehicle launches, can waste horsepower and negatively affect ETs.

For what it's worth, I have both the transmission and pinion angles parallel to each other and a working angle of 2.3* on each end of my Axle Exchange 4" Aluminum one piece drive shaft. I have roughly 550 RWHP, 5R55S and am running a complete BMR suspension with poly bushings. I am also using a BMR K-Member with lowered mounts which also changes the transmission output flange angle over the stock K-Member.

http://www.carcraft.com/howto/91758/index.html

http://www.wolferacecraft.com/pinionangle.aspx

 

[gil_t2]

Do you have a 1 piece DS? If you do then the quick answer is , your pinion needs to be adjusted to .5 to 1.0 pinion facing up, you want a difference of 1.5 to 2.0

My car is Trans 2.55 down and Pinion .8 up and no vib's

If you are running a 2 piece check the sticky for instructions

 

[808muscle]

I could never adjust out the vibration and I tried two different one piece DS's. I tried all the calculations and even used two differents PA finders (analog and digital) to no avail. The only thing worse than a bad rattle is a vibration. One piece DS came out of my car. Good luck man, I hope you can dial it in.

 

[DiMora]

Your pinion angle is set to zero right now. You are correct.

The shop doesn't know what they are doing. If your trans output flange is at -2.5 as you say, your rear pinion flange needs to be at + .5 (pointing up) if you want a pinion angle of -2.0, or rear pinion flange at +1.0 (pointing up) if you want a pinion angle of -1.5.

I would set it to -1.5 for street use and -2.0 if you are a drag racer who runs stickies or slicks.

That's the Cliff's notes...here is some rambling:

I want to help clarify pinion angle, as nobody seems to understand it, and even fewer can explain it. I don't even know if I can explain it without pictures, but I will try. (I will add pics / drawings if necessary)

A proper target according to BMR and Steeda is to have the rear pinion flange at minus 1 to minus 2 degrees...with -1.5 being a nice compromise for a street car and -2 being good for drag racing.

Here is the skinny. On our cars, the engine / tranny are angled such that the tranny output flange is tilted downward roughly 2.7 degrees.

Imagine if you will for a moment that we LIFT the rear of the car so that the engine crankshaft (and transmission output flange) are perfectly parallel to earth, IE zero degrees of tilt. ...THEN we adjust our upper third link so that the pinion flange also had zero degrees of tilt, it would be parallel to earth...thus our pinion angle would be zero, correct?

Some more examples of ZERO pinion angle:

If the tranny output flange was set to minus one degree, we would have to set the rear pinion flange to plus one degree...they would be perfectly parallel then...thus ZERO pinion angle.

If the tranny output flange was set to (-2) then we would have to put the rear pinion flange at (+2)...they would be parallel...again, zero pinion angle.

If the tranny output flange was at (-3) the rear pinion flange would have to be set at (+3) in order to have zero pinion angle.

We do not want a zero pinion angle, I just want you to understand the math.

What happens is when we launch the car, the car "squats" in the rear...the rear pinion flange tilts up, and if you were to put a magnetic angle finder on the front tranny output flange, since the engine and front of the car are raising upward due to weight transfer, the tranny output flange would tilt downward (in relation to earth).

If we were to run solid bushings for hard-core drag racing, we could possibly get away with a recommendation of setting zero degrees pinion angle, since squat would be minimized.

However, most of us run polyurethane bushings (BMR calls them "Poly" and Steeda calls then "Urethane"...but it is all the same thing)...and those bushings flex just a little bit. Not as much as stock, but more than solid bushings.

Because of the polyurethane bushings, Steeda and BMR say we should set the rear pinion angle at (-1) to (-2) in relation to the front tranny output flange) so that when you do launch the car from a stand-still, and the suspension squats, the AMOUNT of squat is in that 1 to 2 degree range, and therefore when the driveline is under the MOST stress, the pinion angle is zero and all is parallel.

Let's do some more examples: If the front tranny output flange is sitting at (-3) (pointed downward toward ground) you would have to point the rear pinion UP to (+3) if you wanted ZERO pinion angle (remember, zero is parallel), point the rear pinion flange up to (+2) if you wanted (-1) degree of pinion angle, and point it to (+1) if you wanted (-2) degrees of pinion angle.

If you want precisely (-1.5 degrees) of pinion angle which is a good compromise between street and drag, you would have to set the rear to (+1.5 degrees)...again that is if your front tranny output flange is at (-3) degrees.

http://www.buickperformance.com/Pinion.htm

 

[mustanger]

With your current pinion angle at zero I don't think that would be the cause of your vibration. Especially under normal driving conditions. I think you should start looking at other things. Perhaps the driveshaft itself. You may even want to check the bushings on your LCA's. I had a worn out poly bushing once and the extra slop was causing some vibration, probably because it was allowing the axle to move around and become misaligned.

 

[tmcolegr]

and the debate continues...

 

[Pumpkinfish]

Update: I could not get under there with my 1 1/2" wrench. Do I need to take off the over axle pipes? Maybe I print out these emails and discuss it with my shop...either that or pay a driveline specialty shop. I was driving the car today and it just gets tiresome with all the noise. I went with poly bushings just to avoid this!

 

[gil_t2]

I cut my wrench down so it is short enough to fit. using lock tight on the adjuster makes up for not making it real tight.

 

[tmcolegr]

No need to remove the over the axle pipes

 

[DiMora]

With your current pinion angle at zero I don't think that would be the cause of your vibration. Especially under normal driving conditions. I think you should start looking at other things. Perhaps the driveshaft itself. You may even want to check the bushings on your LCA's. I had a worn out poly bushing once and the extra slop was causing some vibration, probably because it was allowing the axle to move around and become misaligned.

Maybe, maybe not. I would still set it to minus 1.5-2.0, and if it still vibrates, unbolt one end of it and rotate it 180 degrees.

 

[908ssp]

The only reason not to run parallel is for axle wind up during acceleration. With after market upper and lower control arms you shouldn't have too.

Honestly drive shafts with two universal joints are a thing of the past if they need a sliding joint in between. The CV jointed drive shafts don't require alignments at all.

 

[gil_t2]

Sliding joint has nothing to do with the u-joint or CV joint. As long a car is using a floating rear it will move closer to , and farther away from the trans as it moves up and down. Only independent rears with fixed housing like corvette starting in 1963 have fixed length drive shafts. Also some 4link setups with limited movement can use fixed length D.S. But i don't see were this has anything to do with setting pinion angle. Even corvettes are designed with a little pinion down angle to make up for axle wind-up.

 

[908ssp]

Maybe some old Corvette but new ones run a torque tube locking the transaxle to the motor no wind up with that.

The CV joint eliminates the need for a sliding joint. A CV joint eliminates the need for alignment. A CV joint is the only way to go checkout the new driveshafts from PST and DSS.

 

[gil_t2]

Obviously a car with a torque tube doesn't need to worry about pinion angle. I was responding to you reference about the sliding, I meant that the only cars that did not need to consider the sliding was cars with fixed diff housing. If you read the description of the DSS drive shaft closely you will see that they modified the CV joint too incorporate a slide feature, so it still slides front to back. So don't get me wrong if I ever need to replace my Coast DS, it will be with a DSS unit. The CV joint is very nice.

 

[DiMora]

Obviously a car with a torque tube doesn't need to worry about pinion angle. I was responding to you reference about the sliding, I meant that the only cars that did not need to consider the sliding was cars with fixed diff housing. If you read the description of the DSS drive shaft closely you will see that they modified the CV joint too incorporate a slide feature, so it still slides front to back. So don't get me wrong if I ever need to replace my Coast DS, it will be with a DSS unit. The CV joint is very nice.

Same here; I run a 4" coast, but everyone is raving about the DSS.

 

[Pumpkinfish]

Bumping this back up for an update...I can't get enough adjustment. My BMR uca is not extending enough to get me to a -2.0 or -2.5 degree down position from the trans angle. What to do? Do I go to adjustable lca's or is there another uca that will give me more adjustment? I am able to get to a -1.0 angle at best. It is really weird.

I should add that I am running the Ford K springs and I have read during searches that this is common with lowered cars. No one seemed to say what uca they used to get the desired adjustment!

 

[gil_t2]

Why are you going to 2.5, You posted that your trans is 2.5 down, you should be adjusting your pinion .5 to 1.0 up.

 

[BMR Tech]

First, you should verify your center adjuster is "centered" within the arm. (both sides of thread are equal)

Second, if you have 2.5 down on drivetrain and 2.5 up on pinion flange....that is zero, like previously mentioned, which is good when the car is accelerating.

To achieve an angle that I recommend on most full poly combos.....you need to extend the arm until it is 1 degree up (pinion), assuming the drivetrain is still 2.5. Which will be about 1.5 difference.

I would be highly surprised if you could not get enough adjustment with our arm. It typically takes a little less than 1/8" length change to move 1 degree.

 

[tmcolegr]

From the sounds of things, based on Kelly @ BMR and others, post #2 is incorrect. Please disregard this post.

I guess I can go back and readjust mine correctly now