PDA

View Full Version : Where to measure on a unibody



fordsbyjay
04-19-2010, 11:11 AM
I have a couple questions about suspension. I am installing some rear frame rails in my Falcon for Autoweld. I build stands a couple years ago to get my car up in the air. Using 4 string levels I shim the stands up so they are all level with each other. This gives me my level surface to measure from.

https://static1.pt-content.com/images/pt/2010/04/DSC03652-1.jpg

My first question is where to measure on the uni-body to tell if my car is level? I use a 24" level across the front frame rails and is off about 1/8" on the drivers side. Of course if I shim the tire up that extra 1/8" then my block level is off but the front frame is level. I also measured from the block string to the frame rail to confirm the slight difference in distance. To me the the block level needs to stay consistent as that is my reference line.

On the rear I used several different points with the level and get different readings so that is question #2, where is the best point in the rear?
I used a couple spacers (the same height) on the rocker panels with a 6' level to check the rear of the car. It is level in this position. There is a flat spot right above the rear shock mount and I put a shorter level there and it is off about 1/8-3/16" on the drivers side. This is consistent with measuring level at the rear gas tank mount.

So, I bought a 4' level and measured the bottom of the factory rear frame rails. The rear frame rail is a little banged up on my field car so I couldn't get a quality level reading there but once again it was within 1/8".

I tried to get a good picture with both levels (the string level and the regular level) but I can't get a quality shot you can tell the difference on.
This is the front string level on my boxes. As you can see it is just barely off center. The regular level across the frame is on the left edge instead of the right edge. The amount you can see in this picture is less than 1/8" under the tire (eg if I shim the passenger tire 1/8" it goes to the left edge on the string level.
https://static1.pt-content.com/images/pt/2010/04/level-1.jpg

As you can see it is very small amounts that I am talking about but obviously I want to make sure it is as close as possible.

MrQuick
04-19-2010, 11:55 AM
I like to use the rocker panels to find level.
As you stated the frame rails can be banged up and twisted so it can be questionable. Try not to set with suspension as a minor tweek can change everything. Take the wheels off and use jack stands and sturdy shims. An assortment of 1/8" thick metal sheets are very handy.

On suspension stuff, the lower control arm mount holes are a great place to measure from after checking square. GM has a central located hole in the subframe cross member.

Bubble levels are ok but get your self a smart tool. Bubble levels can be off as far as .4 degrees. I have a table to set the calibration. Orchard harware had a sale on them a few weeeks ago. Keep your eye out.

Try to find a spot in the garage where it will not move till it gets buttoned up. Level it out and keep it there.



vince

fordsbyjay
04-19-2010, 12:04 PM
I have the short Smart level as well as a craftsman 24" digital level.


Try not to set with suspension as a minor tweek can change everything.

I assume by this you mean to put the jack stand under the frame vs under the tire to take out any differences in suspension (like different spring heights).