Rear Alignment, ... anybody have a tech article? Options

[vesnyder]

I just redid the entire rear end on my 914 - had to replace one of the rear control arm mounts so I replaced all the bushings - and now I am putting it all back together. Anybody have details on how may shims I shoudl start with and what I need to do to make sure it at least close on alignment? Fow some reason there were three shims on one side and none on the other? Just curious where the adjustments are made and how I can make sure it is close just to road test.

[East coaster]

Just did mine too......... (IMG:style_emoticons/default/popcorn[1].gif)

[brant]

probably put back what was in there and make certain you get a correct 4 wheel alignment done very soon.

brant

[TravisNeff]

Since you replaced the console (which would be the reason for the extra shims - I am assuming the shimmed side was the passenger side) I would start with no shims at first and just eyeball if each side looks even once you get it back on the ground. If you need less negative camber, add a shim and look again. You won't know for sure until you get it to an alignment shop anyhow.

[Joe Ricard]

Well I have over 1/2 inch of shims in my car. Very low 3 7/8" at the rear donuts. I am striving for -1 degree camber in the back. Slicks ya know.
I set rear toe at just a smidge toe in. difference of 1/32 or so difference front of rim to back of rim.

Don't use this alignment setting unless you absolutely know why you are doing so. better to go with 1/16" toe in each side.

Just string it.

[vesnyder]

Come on guys, racers do it with string - I should not have to take it to a shop to align it? Can't somebody provide me with an instruction sheet other than "take it to the shop"?

[r_towle]

set up two parallel strings, one on each side of the car, have them at the height of the centerline of the wheel (its easier)

I would say you should first set the camber, that is what the shims are for...
so find a book, or a spec on what you should have for camber....get a small level and plump the tire...add or subtract shims to get the desired camber...
camber is tire dependant , use dependent (race tires like lots, street tires like less...)

The toe in/ toe out is set by moving the trailing arm...loosening the three bolts that hold the shims in place.
You measure the front and rear of the tire, or wheel...
If you measure the tire, you are looking for 1/16 inch toe in on each tire...then bolt them down tight.

I would also suggest that you go out for a quick drive,,,settle the suspension a bit, come back and measure again...things shift sometimes...

Rich

[Joe Ricard]

So now you are out of excuses.
just go do it. easy as that. couple of tricks to get the toe perfect with wieght on the wheel is use a ratchet tie down strap to go from toe out and incrementally move the tire to toe in. then sinch down on the bolts and whala your done.

[r_towle]

I use a hammer and a 2*4...hit the 2*4, not the trailing arm..

R

[lapuwali]

This has been discussed here before. The line "set up two parallel strings" sounds easy, but isn't. The strings not only have to be parallel with each other, but they also have to be parallel with the centerline of the car. You can't use the wheel hubs to get this, as the track isn't the same front and rear. Moving the car much after setting things up destroys the alignment of the strings to the car, so you have to go through it all again.

The rear suspension with no shims at all gives you something like -2.5 of camber, which way more than you need. 0.5-1.0 degrees is what you'd shoot for on a street setup.

Setting camber is fairly easy. A plumb bob, a good ruler, and lots of patience will do. The plumb bob will move a great deal if you touch it even slightly, and you need some trig to convert degrees into horizontal measurements.

Setting toe on the front is also fairly trivial, as you really only have to get the steering rack roughly centered (not hard to do), then measure the distance between the tires front and back (can use a pin in the tread, measure, roll the car, measure, subtract the difference, viola).

Setting toe on the back is the hard part as, unlike the front, you have to get it centered to the centerline of the car. On the front, the steering will ensure the tires are always "centered" (even though the steering wheel may not be). Finding the centerline of the car is not an easy task.

Oh, and you'll need some way of levelling the car, assuming you don't have a surface plate at home.

[r_towle]

here is a suggestion.
Get two pieces of 1.5 inch angle aluminum, 8 feet long.
attach one to the bottom license plate screws in the rear, attach the other to the front.

this elevation is pretty damn close to the wheel centerline.
measure from the center or the rear (plumb down from the trunk latch)
measure from the center of the front..(plumb down from the hood latch)
attach the strings the same distacne from center...easy as pie.

Now you have parallel strings that are centered on your cars centerline.
and you have a tool (If you save it and no use if for something else...)

Small PCV pipe will also work...and its cheaper...1/2 pipe...drilled out for the bolt holes.

Rich

[lapuwali]

Is the rear trunk latch actually on the car's centerline? Which part? The tolerance here is pretty small (about 1mm side to side), or the error at the wheels will be pretty large.

What you really want is the centerline at the rear. The relationship to the front is immaterial (unless you suspect the car isn't straight). You could measure between the trailing arm ears to get a center, though that's not particularly easy with the car on the ground and the engine installed.

[URY914]

Is the rear trunk latch actually on the car's centerline? Which part? The tolerance here is pretty small (about 1mm side to side), or the error at the wheels will be pretty large.

What you really want is the centerline at the rear. The relationship to the front is immaterial (unless you suspect the car isn't straight). You could measure between the trailing arm ears to get a center, though that's not particularly easy with the car on the ground and the engine installed.

How about using the seam of the tranny as the rear centerline? Thats what use being that I dont have a trunk. I wouldn't trust the trunk lock as being the "true" center of the car.

[McMark]

From what I've read, you really want the centerline between the two suspension mounting points, not the centerline of the car. So to find it in the rear, you would have to drop a plumb from a point on the rear suspension console (inner nut, outer mount bolts) and then measure the distance between each side and divide by two. Then do the same at the front and connect the line. Now you have the "true" centerline of the 'car'.

[URY914]

From what I've read, you really want the centerline between the two suspension mounting points, not the centerline of the car. So to find it in the rear, you would have to drop a plumb from a point on the rear suspension console (inner nut, outer mount bolts) and then measure the distance between each side and divide by two. Then do the same at the front and connect the line. Now you have the "true" centerline of the 'car'.

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[r_towle]

I love the fast reply option....

I agree that the suspension points would be the perfect place to measure....
I do not agree with the rear tranny....I have mounted my engine/tranny crooked before...I dont think that would be consistant.

How about some part of the rear body?
Can we assume that the bolt holes for the bumper are centered on the car?
why not the key hole? just a Q,,,dont get mad...

I have used the key, and it works for me...but I have not had it checked by a machine afterwards....
Rich

[brant]

Come on guys, racers do it with string - I should not have to take it to a shop to align it? Can't somebody provide me with an instruction sheet other than "take it to the shop"?

now you see why "take it to the shop" is the usual advice
you can do it yourself, but it will take most of the day unless your practiced and have a system.

even with a string system, the repeatablility is in question.

but at the correct shop (I have the best one of all time local to me)
you'll get extremely accurate and precise settings...
and my last 4 wheel, from my local shop was 90 bucks.

I had things "close" by myself when I took it in and they only had to tweek it a little bit. plus they will give me a very accurate print out to prove that they put it exactly (not give or take a degree) to the setting I asked for.

brant

[Downunderman]

There is a simple way. First take off the sills. Find 2 straight edges about 2.5m long and attach one to each rear wheel so that it sticks our beyond the rear tyre by about 1 m and the same at the front. Use bungy cord through the spokes of the wheel. Set the toe so that straight edge is the same distance each side from the long. Then measure the toe at the back of the tyres and adjust as necessary side to side. Keep the distance from the long at the front the same each side so it doesn't have a crab. This assumes that the car is square and the longs are straight. They are on mine.

I have done it this way for years and when checked on a laser aligner is within a mick hair as they say.

[Borderline]

I'm working on an alignment system that involves shining a laser light forward to a mirror and observing the reflection back at the wheel. I have the same problem with getting the mirror square to the centerline of the car. I really want to come up with something. I like playing with suspension settings too muchto have to take it to an alignment shop everytime I change something. I like using the laser light as it makes it easy to see the angle and with a little trig calculation can be more precise as the measurement is over a much larger distance. So far all I can say is that the steering wheel is straight ahead when cruising on the fwy, (IMG:style_emoticons/default/confused24.gif)

I'll post some photos when I'm more confident in the system. Even if it takes a couple hours to set up, it would take me more time to drive to a place around here that can do 4 wheel alignments.