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pinion angle

george68hemirr

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hi guys....just wanted to ask a question....i am going up to the track saturday and i am trying to get my rear set up right.....95% of the time i drive it on the street and maybe hit the track 4-5 times a year......right now with the suspension loaded and the car level my trans is -5 degrees and my pinion is 0 degrees....i am running super stock springs on my roadrunner with a pinion snubber about 1 inch from the floor...i am cutting off and rewelding new axle saddles since the rear is out of square with the center line of the car.....should i minus the pinion ?? degrees

to find center of the car....i had some help
Actually, you need to find the suspension centerline, which is a measurement from the pivot points of the suspension at all four corners of the car.

I will try to explain how to find a centerline for the suspension system. This can also be found in the door-slammer chassis book by Dave Morgan.

Raise the car high enough you can get under it easily - since we will be working with the suspension pivot points, it doesn't matter if the supports are under frame or the suspension. Try to keep the car level.

First, find the "center" of the car. Use a string and plumb-bob to transfer these points to the floor. On the back of the car, hang the string from the leaf spring front bolt. Doesn't matter if its the inside or outside of the spring, as long as you do the same on both sides. (on 4-link or ladder bars, use the front hiem joint)

Lower the Plumb-bob to the floor and make a mark (black sharpie worked best). Repeat for the other side. Measure the distance between the two points on the floor and mark the center. Measure 2-3 times if necessary to get it accurate.

Move to the front of the car. Hang the string off the pivot bolt on the lower control arm. Again front or back, inside or outside doesn't matter as long as you use the same point on both sides. Mark the floor directly below these points. Measure between them and mark the center.

Using a chalk line, snap a line from front bumper to back bumper across the two center points. You now have the exact center of the suspension system. Using the plumb-bob you can now measure the distance of anything on the car from the center line. Hopefully the ends of the axles are even, but points on the body will probably be off some. I like to use the front of the brake register on the axle.

Now we need a line perpendicular to the centerline to be able to measure whether the suspension parts are square with the suspension centerline as well as centered.

Using a piece of string about 3 feet long, tie one end to the marker, hold the other end on the center line near the center of the car. Mark an arc or semi circle (which extends to both sides of the car. Move the string down the centerline about a foot one way or the other and make an arc in the opposite direction). These two arcs should cross near the outside of the car. Span the chalk line over the two intersection points and you should have a precise perpendicular line.

Now you can measure front to back from the perpendicular line to the rear axles and front rotors (or any other parts) to insure everything is square in the car.

i did that and ended up moving the driverside axle 3/8 of an inch back and the rear was off by 1 7/16.....split that in half its 3/4 of an inch i have to slide rear toward the passenger side
 

george68hemirr

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i am going to answer my own question.....trans slopes downward 5 degrees [towards the rear] and the pinion slopes upward 3 degrees [towards the front] the pinion angle is referred to as 2 degrees nose down.....ideal for a street car and sometimes the track
 

george68hemirr

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well i got another opinion........level car suspension loaded....check degree of driveshaft which is minus 1 degree and the pinion is 0 degrees....so i was told by a guy that fabs race cars/street cars...ladder bar/4 links.....that i should nose down[never nose up] the pinion to minus 2 degrees which would give me minus 3 degrees nose down.....so this guy knows his stuff and thats what i am doing :cool:
 

george68hemirr

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george68hemirr said:
i am going to answer my own question.....trans slopes downward 5 degrees [towards the rear] and the pinion slopes upward 3 degrees [towards the front] the pinion angle is referred to as 2 degrees nose down.....ideal for a street car and sometimes the track
this is what i did except i went 2 degrees positive to make it 3 degrees nose down
everybody has a different view on how to do this.....i called gear vendors up and when he explained this to me it was all clear then
if the trans slopes down 5 degrees then the pinion should slope up 5 degrees to be parallel but u-joints dont work so well exactly parallel so you degree it so its around that range to allow for spring wrap up and the pinion snupper also helps for too much spring wrap up

2 DEGREES SLOPING UPWARD the pinion and the trans sloping downward 5 degrees which DR. DIFF explained is 3 degrees nose down and no vibrations going down the road and no vibrations down the track
 

george68hemirr

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Roadcuda said:
So did this help you in your recent drag strip adventure?
before i put on the slicks i took it out and i jumped into her and it was great......no vibrations at all.....i did have a slight vib before cruisin......at the track it really hooked up and the driveshaft stayed in so i guess i did something right........and my welds held too :lmao: :lmao: :lmao:
 

Roadcuda

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george68hemirr said:
Roadcuda said:
So did this help you in your recent drag strip adventure?
before i put on the slicks i took it out and i jumped into her and it was great......no vibrations at all.....i did have a slight vib before cruisin......at the track it really hooked up and the driveshaft stayed in so i guess i did something right........and my welds held too :lmao: :lmao: :lmao:
If you're going to start teach welding, I would hope the welds hold together!!! :jester: :lmao:
 

george68hemirr

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Roadcuda said:
george68hemirr said:
Roadcuda said:
So did this help you in your recent drag strip adventure?
before i put on the slicks i took it out and i jumped into her and it was great......no vibrations at all.....i did have a slight vib before cruisin......at the track it really hooked up and the driveshaft stayed in so i guess i did something right........and my welds held too :lmao: :lmao: :lmao:
If you're going to start teach welding, I would hope the welds hold together!!! :jester: :lmao:
the teacher that teaches the kids during the day doesnt think he could pass all the tests ive passed....ny state dottest/aws test/innershield test......he is book smart and i am hands on smart......which is better....you already know ...right
 

moparchris

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Hey George, I know you have already set up your car, but I wanted some clarification as to how the angles worked out. When you say your pinion is "up" do you mean that the centerline of the pinion gear is sloping upward towards the floor of the car? I used to be a co owner of a chassis shop years ago and built some serious leaf spring cars. This area is typically misunderstood by most Mopar owners and I think that the boys around here could benefit from a discussion on this subject.
 

george68hemirr

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moparchris said:
Hey George, I know you have already set up your car, but I wanted some clarification as to how the angles worked out. When you say your pinion is "up" do you mean that the centerline of the pinion gear is sloping upward towards the floor of the car? I used to be a co owner of a chassis shop years ago and built some serious leaf spring cars. This area is typically misunderstood by most Mopar owners and I think that the boys around here could benefit from a discussion on this subject.
yes chris the pinion is sloping up towards the floor pan 2 degrees and the trans is sloping downward towards the ground 5 degrees.....this is within reason for a street 90 percent and a drag car 10 percent of the time
expain 5 to7 nose down for a drag car with superstock springs...chris
 

moparchris

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george68hemirr said:
moparchris said:
Hey George, I know you have already set up your car, but I wanted some clarification as to how the angles worked out. When you say your pinion is "up" do you mean that the centerline of the pinion gear is sloping upward towards the floor of the car? I used to be a co owner of a chassis shop years ago and built some serious leaf spring cars. This area is typically misunderstood by most Mopar owners and I think that the boys around here could benefit from a discussion on this subject.
yes chris the pinion is sloping up towards the floor pan 2 degrees and the trans is sloping downward towards the ground 5 degrees.....this is within reason for a street 90 percent and a drag car 10 percent of the time
expain 5 to7 nose down for a drag car with superstock springs...chris

George, Pinion angle is measured in relation to driveshaft centerline. Usually a street car, like our Roadrunners, the driveshaft runs parrallel to the ground. I dont know if yours is set at an angle, it sounded odd to me that your pinion is pointing up. Most leaf spring cars (race cars) are 6-7 degrees negative pinion angle, pinion pointing down in relation to the drive shaft. Of course if your driveshaft centerline angles down as it approaches the rear end, the pinion will angle upward. A street car will run less maybe 2-4 degrees. When a serious street car with leaf springs, such as yours, is drag raced with the pinion set at 2 degrees it puts a unbelievable strain on the universal joints and can lead to failure or loss of et in the 60 foot time, we have all seen the pogo effect from a car that is set up wrong and when it spins it does the pogo. Even with super stock springs the pinion will still climb. If you would be so kind to post some pics of your car leaving the line and then at rest you will see the body does rise as it launches. The goal is to have a straight line from the crank centerline through the trans and down the driveshaft and then straight through the pinion gear, in a straight line under load. U-joint angles should be parallel to eliminate vibration. U-joints are made to be used at an angle not straight. With a car such as yours that is driven quite extensively on the highway 6 degrees will cause vibration and premature u-joint wear, so your kinda stuck in a quanrdy. Now, I am not disputing that your car is set up wrong, I just wanted to exchange some info that the guys here could use to their advantage when setting up their car.
 

george68hemirr

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no pics ....there was no camera guy there that day.....as for 60 foot times.....1st run redlited...forgetaboutit.....5 runs....1.479,1.514,1.476,1.497and 1.496....all close
since i install the carbon fiber trans shield....i lowers trans to make room for that.....then i lowered even more for the overdrive which came up -5 degrees....when i checked my driveshaft angle it was -1 degree sloping downward and the pinion was at 0 degrees......i had a slight vibration going down the road....chris where would youve gone from here??
i think if a sloped down the pinion angle the vibration would get worse cruisin....right chris?
 

moparchris

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george68hemirr said:
no pics ....there was no camera guy there that day.....as for 60 foot times.....1st run redlited...forgetaboutit.....5 runs....1.479,1.514,1.476,1.497and 1.496....all close
since i install the carbon fiber trans shield....i lowers trans to make room for that.....then i lowered even more for the overdrive which came up -5 degrees....when i checked my driveshaft angle it was -1 degree sloping downward and the pinion was at 0 degrees......i had a slight vibration going down the road....chris where would youve gone from here??
i think if a sloped down the pinion angle the vibration would get worse cruisin....right chris?

Well, the weird thing is that you dont have a vibration. Since the trans is -5 down and the driveshaft is down -1 then the pinion should be +4 to equal out the the angles of the driveshaft. That would be ideal for vibration, but bad for traction. If you are at a point that you have no vibration and the car hooks, then leave it and keep an eye on the u-joints. Ideally the motor and trans will need to be level and then set the pinion at -4 to 6 degrees on the pinion. Then I would loosen up the gap on the pinion snubber to let the car squat when you drive it down the road and to relax the pinion angle. Then when you get to the track you tighten the pinion snubber gap and let it ride.
 
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