Any easy way to run a line pararel to the center line of the car?? - PeachParts Mercedes-Benz Forum

ah-kay · #1 09-02-2011, 02:11 PM

Change the tie rods and lower ball joints and like to play around with the toe and camber of the car. Any quick way to run a line parallel to the center line of the car? Simply put, how to find the center line of the car?

Thanks.

Air&Road · #2 09-02-2011, 02:21 PM

There are a number of poor boy alignment methods involving minimal tools or maybe even no more than a piece of string, but when doing alignment I've never thought in terms of vehicle centerline.

There are some pretty ingenious, low dollar alignment tools out there. If you want to adjust toe, say so and I can run through an easy, but accurate method for doing this that works well on a flat floor. A low dollar gauge can be had for measuring camber.

Hope this helps,
Larry

ah-kay · #3 09-02-2011, 02:46 PM

Welcome back Larry.

I want to measure toe to make sure it is not too out of wrack. I want to setup a 'true' line parallel to the car to measure toe from front tire to the line. Any suggestions?

Stretch · #4 09-02-2011, 03:02 PM

Here's what I did

http://www.peachparts.com/shopforum/showthread.php?t=284337

It is probably a bit involved but you might be able to pick out something that helps.

I don't quite see (just yet) why you want the centre line of the car but in direct answer to your question try this.

Assuming that the jacking points are all OK - meaning you've got no rust or accident damage there...

Get a stick that will slide in nicely to the jacking point hole.

Wrap a bit of string around the stick and push it up against the sill (= rocker = longeron!)

Hang a weight on the string - plum bob style (http://en.wikipedia.org/wiki/Plumb-bob)

Mark on the floor with chalk where the plumb bob meets the floor.

Repeat for the other three jacking points.

If you have a tape measure you can simply measure the distance between each mark and divide by two...

...lots of crawling under the car.

To make things easier to reach - get a length of string longer than half of the width of the car. Tie a bit of chalk to one end.

Get someone to hold the chalk free end of the string at one of the four transposed jacking point marks and draw an arc - with the string taut - with the chalk end.

Go to the transposed jacking point on the opposite side (not end) of the car and dissect the first arc using the same method above.

Do this for the other end of the car.

Draw a straight line between arcs you've made - and what have you got?

Air&Road · #5 09-02-2011, 03:41 PM

I don't have but about five minutes to write this, so I hesitate to go into anything, because I would probably not think it through and end up sending you on a wild goose chase.

I will be away from email or internet until Tuesday. If you're still exploring this then, I will spend some time to lay out some ideas.

Have a nice holiday,
Larry

ah-kay · #6 09-02-2011, 05:19 PM

There are quite a few write ups on the web about running a string parallel to the car but most are very time consuming. I can then use the string to measure the distance from the string to front of rim/back of rim to measure toe. I am just wondering anyone has done it here with ease.

The center line is the term they use. Once I have 'it' then I can use it to lay the string. I just want a line to be parallel to the car. The mid point of the bumper is not quite right, need some reference point which is more accurate.

Duner · #7 09-04-2011, 01:53 PM

I don't know if this is easy or not. I doubt it. I use a laser level and and set a tape measure 8 feet ahead and behind axle center line .If you wheels are straight and tires not lumpy you should get a fairly accurate measurement of toe in. I figure 1/8 inch of toe will show up as 1 inch being tape is 8 feet away. I also use a smart level to set the camber . Castor is another story with smart level as you will need to make a jig for axle centerline .
I would say nothing easy about it and time consuming for me but I do it anyway . Good luck and have fun.

ah-kay · #8 09-15-2011, 05:09 PM

This is how I did it. It is quite simple on the 190D, other cars may be different but the concept is the same.

1) I use a laser level like this and set the beam to a line, not a 'dot'

http://www.harborfreight.com/24-inch-digital-laser-level-with-angle-finder-93884.html

2) Locate the center of the rear diff, mark it. On the 190D it is very obvious as it is the lowest point of the diff.
3) Locate a 'cross member' support at the front with a center point. I found one just under the engine with a hole right at the middle. I mark the hole with a pencil and plumb it.
4) Put the laser on the ground and line up the 2 points and that is the center line. I marked both ends on the ground using the laser line.
5) I got the inspiration from this

http://advantagewheelalignment.com/Lazer_Align.html

6) I measured a fixed distance from the center line on either sides and I can now do my alignment. It is quite fun.

Now steering is straight, the alignment is not quite to spec yet.

I need a toe in spec in Degree for 190D. A toe-in spec in inches or mm is ambiguous as it depends on how you measure it, at the rim or at the outside of the tires. The spec I found here is not in degree. One can always use arc-tangent to obtain the degree with the measurements. I find a spec stating the toe-in is 0.33 degree but NO tolerance. Can some one confirm it or have a correct spec?

Thanks