Pinion Angle...




















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Thread: Pinion Angle...

  1. #1

    Default Pinion Angle...

    The new UMP rule states upper control arm may be altered to get correct pinion angle, just want to know what length upper control arm most are running since they can be altered to any lenght as long as they are not adjustible... And is anywhere making them or is it a do it yourself... I considered buying adjustible uppers, getting it to the correct pinion angle and then welding the nut in place, not sure if that meets the requirement by UMP.. Specs I am looking for are for:

    78 Cutlass
    Metric G Body
    Ford 9 inch floter rear end

    Any help would be great

    Thanks Troy

  2. #2

    Default

    The upper control arms are not that hard to modify. What we did on my floater was cut the upper control arms in half, then installed the ends on the frame and the floater. We took an angle finder and rotated the housing down to about -5 or -6 degrees pinion angle then set the two peices of the control arm on top of one another, clamped them then tacked them together. Once they were tacked we made sure that everything was good and the control arm bushings werent in any kind of bind (as you shorten you will change the side to side angle and it can but the bushing in a bind on the frame or floater) we took them out and fully welded inside and outside. With good welds around they are just as strong as before, but now you have the proper pinion angle. We try to run the pinion angle at about -5.5 degrees, but we have a local guy that sets all of his up at -8 degrees. The more negative you go, the more forward bite it will have, but the higher chance you will have of destroying the driveshaft or transmission case. I am running an early 80's Cutlass metric frame, so it should be the same as what you are dealing with. Hope this helps.
    Last edited by hot_rod; 03-17-2011 at 11:45 AM.

  3. #3

    Default Adjustable Uppers

    The only adjustable upper control arms that I have found are made by edelbrock and are ridiculosy expensive. Expensive enough that I wouldnt want to weld the nut. If you wanted to be able to change pinion angle, you can use what I wrote above and just make a couple of different sets of upper control arms. You can probably find enough of them at a junk yard and try them out. Would be a lot cheaper than the adjustable ones. JMO

  4. #4

    Default

    If you are using stock uppers just re drill the rear holes forward of the originals.......I've done it many times.

  5. #5
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    pinion angle doesnt add traction

    It should be set by whoever jigs your rear end and where they place the upper and lower mounts

    If you re drill the upper arms to make them shorter you need to cut the mounts off the top of the housing and place them in their new position so they will fit without a bind. Which would be closer to the front of the housing and further towards the wheels. If it was a 3 link and had only one straight top link you could shorten it to change the pinion angle but not with a 4 link.....
    IMCA Modified #66

  6. #6

    Default Question...

    I was watching the Bob Harris Videos and he was talking about pinion angle, according to him since the rear end cant really rotate like a 4 babr / 4 bar modified the pinoin angle is important for two reasons. 1) By the pinion being down, when you are on the gas it acts as a lifting mechanism and as power increases it lifts the car and it applys force down on the rear wheels which actully gains forward bite... 2) Second it allows play for the drive shaft to line up straight under power causing less bind, it is important to have enough pinion angle to keep the car trying to pick itself up all the way down the straightway creating forword bite, but not so much that it binds ththe car when off of the power acting like a brake, it is important though not to let everything bottom out for obvious reasons... Maybe I am incorrect could someone line me out on this theory... Also I really like the thought of multiple lenghts of uppers to be able to adjust pinoin angle quickly... Thank for the help so far...

  7. #7
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    There is no reason to EVER have to adjust it.
    IMCA Modified #66

  8. #8
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    jeff i have to disagree with you about never having to change it because i run a three link and i run my pinon at 5 deg down and i can move my rubber biscuit bar down a whole and it makes the car have better forward bite in the slick.
    You have to got to be FREAKIN kidding me!!!!!!!!!

  9. #9
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    i also believe that you can run a ford upper link on a chevy and they are a lil shorter and give you more pinon angle
    You have to got to be FREAKIN kidding me!!!!!!!!!

  10. #10
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    Quote Originally Posted by taslowroller View Post
    jeff i have to disagree with you about never having to change it because i run a three link and i run my pinon at 5 deg down and i can move my rubber biscuit bar down a whole and it makes the car have better forward bite in the slick.

    Nobody is talking about a 3 link here, lol... This is a discussion about a 4 link oem rear suspension.
    IMCA Modified #66

  11. #11
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    it would still be the same principle as moving the biscuit bar down now wouldnt it?
    You have to got to be FREAKIN kidding me!!!!!!!!!

  12. #12
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    Quote Originally Posted by taslowroller View Post
    it would still be the same principle as moving the biscuit bar down now wouldnt it?
    No not in the least.

    A 3 link has a link that is 90 to the rearend THUS you can move it up and down as you choose and shorten and lengthen it.

    A 4 link oem style has uppers like this / at a angle if you shorten it the mounts wont bolt up. without a bind.
    IMCA Modified #66

  13. #13
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    Jeff is correct. With the OEM 4 link, it has zero effect. No need to change it once you have it to where it is at minimal resistance to the drive shaft.

  14. #14
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  15. #15
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    some of that made some sense... but most of it was nonsense, i think that article was based on the trailing arms being at 0 degrees at ride height, i also think most of it was referring to asphalt
    Last edited by bushracing67; 03-25-2011 at 05:48 PM.

  16. #16
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    Quote Originally Posted by bushracing67 View Post
    some of that made some sense... but most of it was nonsense, i think that article was based on the trailing arms being at 0 degrees at ride height, i also think most of it was referring to asphalt
    It all made sense BUT I dont know that it was all factual.

    I copy pasted this and I did the same thing this guy did when I built my first coil car and did not find the same results as he claims.

    "I found that simulating chassis roll by using 3 inches of right-rear down and 1 inch left-rear up, the metric chassis pulled the right-rear tire forward almost 3/8 inch more than the left."
    IMCA Modified #66

  17. #17
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    thats why i was figuring he was simulating ride height wit 0 rr bar angle, 3" of compression would drag the rr forward, however i think the idea is to run enough angle in the rr lower to get the bar to come to about 0 or full rr trail in a dynamic situation, he did mention that on dirt getting more lr "roll steer" might be best... which we all know is the general idea, he measured 1" lr extension, i think im getting closer to 7" i was getting more before i added an adjustable strap to limit lr down travel because the inside edge of the lr tire was rubbing on the frame... that article did not even begin to touch on what that will do for a metric, as far as the original post on the mystery of pinion angle, i do not believe in the whole pinion angle adding traction theory, it really doesn't totally add up, i believe that the idea is to keep the pinion at 0 or negative angle at all times, i ran one car with a truck bar suspension, the rear was solid mounted to the truck bars with u-bolts, it had -2 degrees of pinion angle and it had all the traction you could ever want... and it didn't really matter if you had 1 or 1000hp that thing was gonna stay at -2, i set my metrics at -4 - -6, i have set leaf cars with as much as -11 depending upon the car/weight/engine/and how old the springs are, the true "mystery" of pinion angle applies more to leaf cars and any car with bird cages that offers more of a variable on how much axle wrap you are going to see

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