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Thread: how to setup swing arm dragster suspesion help me

  1. #1
    Junior Member SHOW GUEST
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    Mar 2007
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    how to setup swing arm dragster suspesion help me

    I had my dragster back halfed last year and when I went to pickup the car after it was done I got their and the car was siting in my trailer in peices the guy that did it was to busy to meet us so we took it home and tryed to figure it out our self I think I have it close now but Ihave went throu 3 transmission yokes and 4 rear tranny support covers this is getting a litte rediculas we can't get a hold of the guy that did it he just over charged us and left us high and dry if any body can help please let me know what does what and why does changing the bares seem to take out the yokes or rear support.[/quote]

  2. #2
    Senior Member EXPERT BUILDER
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    I had a Don Davis Swingarm 4-link for 4 years,best car i ever owned. I never had to change anything but the adjustment on the shock. Need info on what kind of car and what the set-up is. My first guess without knowing anything is you might have too much pinon angle. Tell me what you can!

  3. #3
    Junior Member SHOW GUEST
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    thanks for the info the tranny is 1 degree down the rear end is 2 degree up the drive shaft is at +2 degree not sure if this is what you were asking me for thanks again.

  4. #4
    Senior Member EXPERT BUILDER
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    Can you post some pics...???
    Ed

  5. #5
    Senior Member EXPERT BUILDER
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    In my opinion you should never have a positive pinon angle on a 4-link dragster. Before you can set the pinon angle the ride height and the upper and lower 4-link bars must be set. Do you know what holes the bars are in and what the ride height is. this will be a slow process without being able to see the car. Does the person who did the work build dragsters for a living. Nothing says he backhalfed it correctly. Don

  6. #6
    Senior Member DYNO OPERATOR
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    VA Hospital, Dallas, Tx (214 302 1924) cell-972-464-7400
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    I got their and the car was siting in my trailer in peices the guy that did it was to busy to meet us so we took it home and tryed to figure it out our self
    That sucks. Feelo free to post the name of the guy or the shop. By all means let everyone know. Might be even better for you to post a copy of your paid recept too. No one should have to be going through what you are after paying to have it all done right.

    --------------------------------------------------------------------------------

    That said, I agree completely with Davis.

    In my opinion you should never have a positive pinon angle on a 4-link dragster.
    Never should any car or vehicle have the pinion to be in a postive angle or and up angle. A negative or downward angle is preferred or is necessary.

    Normal forces of torque rotation will cause a pinion to try to rise in the front. Even with no slack in the system it will still try to rise on acceleration becuase of the tirque forces acting from the tire backward to the engine. At the same time the front of the housing is trying to climb up the actual driveline acting on the U-Joint or the Coupling is trying to straighten out. If the front of the pinion is slightly downward when static at reast there is no conflict or problems. The drive shaft is trying to mkae the connection through the joint to be straighter and the front of the pinion is also trying to go up to be straighter.

    The ideal or perfect pinion angle will allow the drive coupling through the U-Joint or Coupler to be a straight line when under full torque. If it is still slightly down it is no big issue.

    If the front of the pinion is already up above what would be a straight driveline throught the driveshaft to pinion you will have problems with driveline whip and tearing parts up and possibly even feeling the whip as like a vibration you can't get out of it. If a pinion angle is not low or negative enough and the pinion angle rises above the straight line into a positive pinion angle it will also create a driveline whipping action.

    If the pinion angle is already up above the neutral straight line that the driveline is most comfortable with, the U-Joints or Coupler will try to get straight with the driveshaft so there is a straight line through the pinion. If you are already starting with the pinion at the positive angle your problems are multiplied.

    If your rear end is higher than your tranny there are still ways to give you the preferred negative pinion angle downward.;l If you have 4-link or ladder type bar (Swing Arm) and have threaded adjustments you can adjust your pinon angle to a more downward position.

    I would say that a pinion angle of not less than a 1 1/2 degree down will work or myabe even a 2 degree down angle. You do not want a neutral or a positive pinion angle.

    Check pinion angle in relation to driveline angle, not in relation to the level Earth or Ground Level.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.


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