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Author Topic:   Moving Upper A-arm Mounts on a Metric Chassis
WesternAuto17
Dirt Forum Champ
Total posts: 569
posted September 10, 2004 09:08 AM  
If you were allowed to move your front upper a-arm mounts on a metric chassis, where would you put them?

My thinking is to get the cross-shaft on the upper as low as possible and to make the angle of the cross-shaft match the angle of the lower a-arm. In other words, I want the the upper a-arm cross-shaft (when its bolted to the mount with no shims) to be directly in line with axis through the lower a-arm mounting holes.

Am I on the right track? If not, where should I relocate it to?

The car is 3000lb Metric with Impala spindles, but I thought you modified guys might have some ideas about this.

Thanks---

Ego Racing
Dirt Forum Champ
Total posts: 724
posted September 10, 2004 09:17 AM  
In line is a great idea as it helps with caster changes. As far as as low as possable that is not a good idea. You need to figure the top mounts to be at the correct height to acheive the correct front roll center location. This will depend in a few things like spindle heigth and the ball jopints you use. You will end up with them mounted at slightly different heights. Several of Steve Smith's books go in depth into the subject and I would reccomend getting one and reading up before you make any changes as you could ruin the chassis and make the car impossable to drive. If you do not want to do all of the reaserch just pay to have it done by a local chassis builder.

RaceDoctor
Dirt Full Roller

Total posts: 55
posted September 12, 2004 03:09 PM  
WA17, your thinking is correct for the most part. I have done several chassis's with that setup, the upper shafts parallel to the lower shafts. It eliminates the caster change thru the up and down travel. Also try to get 5 to 7 degrees of RF caster to promote left rear weight during backsteer. Run 2.5 to 3 degrees of caster split.. On the metrics I have been swapping the right and left uppers side for side, just stick a bar thru the ball-joint hole and twist them to straighten up the upper ball-joint. This is if you have to run stock uppers. You shouldn't have to lower the inner mounts to much because you are running the taller Impala spindles. You don't want to get your front roll center too low.. If your interested I'll post and explain my method for setting the caster first then mounting the upper shaft mounts after...Rick...

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