home alignment - points of reference

[jpnovak]

I am building the jigs for a home alignment. These will be laser based.

Where do you guys reference the center line of the car? Center of engine bay? In between the pinch seams under the car? Just looking for a point of reference for initial setup.

thanks

[Daves911L]

When stringlining, I always based my centerline on the center-to-center distance of the front crossmember, and the rear trailing arm mounts.

[Daves911L]

Sorry, I meant the front crossmember mounting holes ( the big bolts going vertically up into the body)

[donagain1]

Does this help? Someone posted this pic to illustrate jacking points. I really wish that I had the key to all the point-to-point measurements, but I don't.

[David E. Clark]

Originally Posted by donagain1

... I really wish that I had the key to all the point-to-point measurements, but I don't.

Here ya go.

This is for the short wheel base cars:










This is for 72-73:









This is for a 74-78:





and the is for the SC:

[jpnovak]

Thanks David,

I think I can pick-up these points easily.

[Arnage]

David;

Is there an inverted plan view (bottom of car) for the SWB model that shows the "A - O" dimensions like those shown above for the 74-78 model?

Thanks, Art

[Elombard]

I am not sure you need it unless the chassis is tweaked? I always just measure out from the hubs - I think the Ray Scruggs alignment book showed the differnce in track at the hubs? I cant remember it has been a while.

[T77911S]

this is how i was going to make one based on what was used on my car.

2, 1 inch square tubing jigs, one that attaches to the front, one to the rear. run the strings between the two. make the strings parallel to each other at the jig and level with the center of the wheels. then at the front, move the jig left or right to get the strings the same distance from the hubs of the front wheels. then do the same for the rear. (the front and rear would be different on my car, the rears have a wider track) no need to find the center of the car. although it could be a check of what you are doing.

[DRACO A5OG]

Originally Posted by elombard

i am not sure you need it unless the chassis is tweaked? I always just measure out from the hubs - i think the ray scruggs alignment book showed the differnce in track at the hubs? I cant remember it has been a while.

+1

[Arnage]

I need the reference point dimensions because I have a tub that requires me to replace the front pan (rust) and the cross/support member mounts (a/k/a bearing brackets) because they are both bent, that's right, bent! Accordingly, the front suspension is pushed to the left by 11/16th of an inch. Tweaked? I found it to be the first car I needed to calculate set and drift to go from point A to point B.

[Elombard]

wow, will a pan fix that or will you need to pull the frame straight?

[Arnage]

No, I established a centerline and measured numerous points on both sides of the bottom of the tub and all seems good. Somehow the bearing brackets were bent (pushed) to the left. Those are the "B" dimension reference points shown in donagain1's illustration above. Very obvious once the cross member was removed. There does not appear to be any accident damage to the tub because there is no evidence that the tub was repaired; although it may be it was hit in the right front wheel and that pushed the cross member to the left, bending the bearing brackets. Those SWB cross members are very stout. This caused the a-arms to be misaligned longitudinally. I am working off centerline line with a square to realign but would also like to have the reference point dimensions from Porsche to double check my work.