Sticky #2: Increasing Front Suspension Caster (Upper Front Control Arm Mod)

Johnny,
Question....
More caster gives the car more stability at high straight line speeds and also makes the steering harder, correct ?

What would be the point of more caster having for a street car or a car that is occasionally raced on a shorter track ?

quote:
Originally posted by Johnny Woods:
This is a follow up the "Wheel alignment question" post. Here are some pictures of how I modify the front top A arm to gain more caster.

Johnny
Coz, I am no expert on chassis engineering, but I have found more caster makes the car a lot more stable at high speed, and stops it darting around. It also dials in some self centring. The steering may have become a bit heavier at parking speeds, I have not noticed. Your GT5 would benefit from this mod, because you have excessive scrub radius. When De Tomaso came out with the GT5 they just added 2" to the outside of the wheel. What they should have done is put an inch either side, and made longer A arms. They corrected this on the SI in 1990.
But of coarse, those gorgeous GT5 wheels wouldn't look so cool without there positive offset.

Djezc, I charge 200 pounds for this mod in England. I don't do an exchange because some are in bad shape. People normally just send me there arms. I would be happy to do them for you, but as you are in the US, it would probably be cheaper for you to send them to Pat Mical in Boston.

George, Thanks!

Johnny
Johnny,
Excellent follow up to the alignment question. Very nice work. I do have a couple of questions on your process. First, when you staighten out the rear arm, does this move the slots for the upper ball joint forward? On my car, I have to move the upper ball joint all the way in to get the camber adjusted into spec. Do you find that you have to open up the slots rearward? What type of welding process are you using (MIG, TIG, or ARC)? I really like your fix for the caster issue with the Pantera and I feel that my car would benefit greatly from this modification. I have a complete extra set of a-arms so I think that I will use this winter to perform this modification on my extra set so that I can install them in the spring. Living in Michigan, there isn't a whole lot more that you can do over the winter but improve your car for the next season. Thanks for your insight and knowledge.
Panteraufo,

I use the MIG for this job. None of the welds in this process are critical to the structural integrity of the arm. All the Pantera's suspension arms were originally welded with a MIG in the De tomaso factory. Plus a few spot welds on the front arms. If I was fabricating this arm from scratch I would use the TIG because it gives me more control, penetration and it looks pretty.

Straightening out the arm makes it 2mm longer so I file the slots 2mm.

Living in England we the same weather constraints that you do, maybe not as cold as Michigan, but salt on the roads for 5-6 months of the year. I like to spend half of my time improving the car, and the other half driving it, so it suits me.

Johnny
Mark,

As you have a narrow car I think you should try 5 degrees. I used to run 7 degrees but found 5 degrees puts a bit of life back into the steering. The maximum you can get on a stock car is approx 2.5 degrees.
I have found the wide bodied cars respond best to 6-7 degrees due to the increased scrub radius of those wide front wheels.
If you move the top ball joints forward from it's current position by 9mm it will get you close to 5 degrees. You can make the spacers yourself out of aluminium plate if you have a pillar drill. Or you can use the factory steel spacers.

Make sure your ball joint is touching the camberlock bolt while you tighten it off. I find putting a scissor jack under the hub the easiest way.

Johnny
Serge,

You are getting castor mixed up with camber. There is no castor effect on the rear.

On the rear there is adjustment for camber but unfortunately it's only adjustable in the wrong direction. The top arm is fixed and the bottom arm is adjustable with shims.
A typical Pantera with all it's lower arm adjustment used up (all possible shims removed while still maintaining the correct toe in) will have approx 1.0 -1.5 degrees negative camber.

Negative camber means the wheel is leaning in at the top. My car (with non adjustable arms) has 1.5 degrees. This is not excessive but it does mean the inside of my rear tyre wears down a bit quicker than the outside.

The wider the rear tyre the more critical camber becomes. I think the De Tomaso factory specs for a GT5 where 0 degrees on the back. This is only possible with an adjustable or extended top arm. I have installed some very nice adjustable top arms on my friends GT5, we bought them from Roland Jaeckel in Germany roland@jaeckel-partner.de This gives us all the adjustment we could ever need. For example if we wanted to do a track day with the car we could dial in some more negative camber for aggressive driving and then wind it back for driving on the road. I personally like to have 1 degree negative camber on the rear for a road car.

Johnny
I made a jig to make control arms. The jig I made is marked by 1/4" increments to move the ball joint forward, aft, left or right. The jig is set up to do upper or lower ball joints.

I am considering selling the jigs so people can do virtually anything they want with their suspension; and if they don't like it they can change it.

The jig is laser cut. Our laser machine is coming on line today but Pantera parts are not a priority. We have a month or two of customer back orders to get to before I can play at all.

My first a-arm I did with tubes. It was a learning experience but wrong. I got my adjustments backwards. Caster is adjustable by shim but I adjusted the wrong way and I have just enough adjustment to get back where I was.

Second, the arms a little over done. While unsprung weight has about 1/2 the effect on a-arms as compared to uprights (due to the location) they were about a pound more then the originals. The originals are quite light for what they are.

The direction I am going now is to build the a-arm from flat sheets more like the original. I will keep the adjustable ends which means I do not need adjustment for caster or camber on the a-arm itself.

The a-arms will be laser cut and welded up to look similar to originals.

Gary














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