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Rearend alignment

  
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Rearend alignment

 
mintstick mintstick
New User | Posts: 22 | Joined: 05/11
Posted: 11/24/12
07:10 PM

'68 Camaro project car (the details are extending build time) - need help with rear end alignment.  I have car on rotisserie upside down; the leaf springs are new from Hotchkis and check as close to the same rate as I can check on a flat surface (springs have fabbed alum/Delrin bushings in front and back).  Can I install springs at fixed front position and locate back on shackles and use the perch locators for alignment?  I have a 3" round DOM tube tacked to extra perches at correct spring spacing with 15" extentions both sides.  I have the centerline of the car identified on the bottom of car.  What is the best way to assure perpendicular location?  The plan is to set the right side front eye mount with a flathead bolt and use an offset bushing (max offset is 1/8") on the left side for future fine tuning at ride height and corner weight matching for 90 degree setup with car centerline.  How should that be attempted when on a flat surface?  Any help is appreciated.  

pepsi1 pepsi1
Enthusiast | Posts: 301 | Joined: 10/11
Posted: 11/25/12
12:42 AM

mintstick

The car would have to be right-side up.

  Do the springs have a bolt in the center of them holding them together? The Head of that bolt is usually the alignment pin for the Rear End Housing pads to sit on.
  They should just sit on the springs themselves. Then the U-Bolts go over the Axle housing. Then there is a bottom plate that mounts to the the lower spring. They should also have the holes for the rear shock mounts. Some also have anti squeek pads between the lower plate and the spring.

Bob  

redneckjoe69 redneckjoe69
Enthusiast | Posts: 388 | Joined: 04/10
Posted: 11/25/12
09:13 AM

i think i understand the solid bushing eccentric for adjustability.   its a great idea.     i would pick some referance points front and rear.    measure front to rear, and then pull a X measurement off your referance points to make sure everything is squared up.  

  i had problems with a leafspring car alignment once.   we would get everything squared up.   do a few practice launches and then the car would shake bad.   i sent it to an alignment shop and they couldnt figure it out.  Confused    what we discovered was the rear was walking on the rubber/perch mount.   we tightened the krap out of it and it did it again.   the solution was to lay some small tack welds right to the leaf spring. Crazy    never had a problem again, but im sure there was a better way to fix it?

  my point is,....that 1/8 eccentric wont mean much with rubber perch mounts,...IF your putting down lots of power with sticky tires, cause its gonna move more than 1/8 inch.

  food for thought.  

idrivejunk idrivejunk
Guru | Posts: 1041 | Joined: 12/09
Posted: 11/25/12
09:51 AM

I'm still trying to grasp the question but I sure know how to measure. It sounds like you need to flip it over and establish a datum plane on the shop floor to confirm your thrust angle?

With the body perfectly level on a level slab and right-side-up, strings weighted on one end can be hung from points on the body and used to mark the shop floor at those points. Once you establish the torque box (four points out by the wheels but on the frame, such as front spring eye perch bolts and maybe subframe bolts up by the transmission) and confirm that it is "square", THEN you can reference those floor marks, do the geometry on the floor and use the strings to transfer the measurements straight up to the body/chassis. Can't do this if its windy.

In any case, all bets on where it will ride are off until its been fully mocked up and weighted like it will be in use. At that point, simply centering the steering wheel and measuring wheelbase should confirm where you are. I say if it comes out within a quarter inch you're probably good because the front is adjustable and you have your offset pin for the rear. They were really sloppy from the factory but they drove straight.

I may be way off the question. I'm no racer, more of a crash-fixer. Wear out the ol tape measure!  
idrivejunk

mintstick mintstick
New User | Posts: 22 | Joined: 05/11
Posted: 11/25/12
03:25 PM

Thanks all for input; I'd like to use project in autocross events so I'm trying to reduce potential movement areas.  I didn't mention it, but I added lowering blocks with correcting angle to set pinion.  In doing so, I removed the rubber mounting pads for a solid mount, and yes the multi-leafs have pin at center for perch location.  I did measure to body points for an objective measurment, but thought there may be a more accurate measurement process.  I'll try the plumb bob method and return if I run into new issues.  Thanks again to all!  

idrivejunk idrivejunk
Guru | Posts: 1041 | Joined: 12/09
Posted: 11/25/12
05:07 PM

If you have access to a body shop with computerized measuring equipment such as a Shark, and a person who really knows how to run it, you can easily create custom measuring points and assure symmetry with 3 dimensional 1 mm accuracy. Other than that- its tram gauges, levels, tape measures, and yep the ol plumb bob. Good luck with the project!  
idrivejunk