Question about caster measurement

I also need to ask if anyone is checking the caster setting of their car in the garage.  If so, how are you doing it?

Steve I used a bubble tool from Longacre.  I don't remember if this is the same tool but this is what I used.

https://www.longacreracing.com...%2f-Magnetic-Adapter

You are welcome to borrow mine if you wish.  You know how to contact me.

Thanks Tony. I already have a magnetic bubble level. In Longacre’s instructions they are sayings to use a total of 40 degrees rotation (20 to the right and then 20 to the left). Thus, it looks like the chart above is assuming 40 degrees rotation.

From Longacre:

To read CASTER first turn the wheels 20º to the right when setting the RF and to the left when setting LF. If you don't have a set of turn plates you can use the angles machined on the corners of the gauge as a reference. Turn the wheels until the angle is parallel to the side of the car. Rotate the gauge until it is level. Turn the knurled nob in the center until the center caster vial reads 0º. Now turn the wheels back past center to 20º the opposite way - for a total of 40º.

Steve, That's what I did and it seems to work.  If I recall correctly I installed as many shims as possible to obtain as much caster as possible.  The Pantera is very limited in its adjustment as you probably already know.

Thank you both.

I am getting setup to modify the front upper a-arms in order to get more positive caster and have read the threads on this forum about the process of doing so.  I am currently trying to get precise measurements of caster on the car before I cut, bend, and weld my a-arms.  I am looking forward to getting better straight line handling and centering of the car on the freeway.  I will probably follow this effort with spacers for the steering rack to reduce bump steer.  That way I am only making one change at a time.

I just now checked under the car and it already has bump steer shims.  I think they are from the factory (the car is #6973).  I did not know what they were when I replaced the rack a while back but remember thinking something was different.

I was able to measure caster and it came in just under 2 3/4 degrees on both sides.  This car is a 1974 and that's the value for it per the chart above.  I attached a bubble level to an old wheel center and utilized floor tiles as turn tables.  The next step is to modify the upper arms to get more caster.

Steve, Ford/DeTomaso began installing bump-steer shims in 1973-up (there's even a part number for them) so those are likely stock parts, given your serial number. I had to make my own for my Sept '72 Pantera.

Different caster gauges use different steering wheel angles for the readings

I completed the modification to the upper front a-arms to get more caster.  This modification allows for the addition of a 1/2" shim.  The next steps are to reassemble the a-arms, measure the new amount of caster, and test drive the car.  I can move shims around to get a little less caster if needed.  Electric power steering from SACC should arrive in April.

In the photo below you can see that the top bar was removed by cutting the welds, flattened in a press, and then welded back in place.

I think that you are going to want power steering...and you may have this little issue with the tires hitting the fenders, but just when you turn?

Power steering is already on order.  I am hoping to not have tires rubbing the fender but realize that it could be an issue.  If it happens then I can reduce the positive caster a little and/or roll the fenders.  We will find out shortly.

I had 245-50 x 15s on 8" Campys touch the left front cowl drain pipe (full lock turns & hard braking when autocrossing ). Partially flattened an area about 3" long with a hammer/5 minutes.

Also had the right front tire touch the wiper motor shield in full lock/hard  braking turns. Had to modify the shield at one bend to clear. This is with 4-1/2 degrees of caster and no shock spacers. No further physical contact in 15 yrs.

Wiper shield-to-tire contact is so common, Larry Stock at PPC now offers cleaned & painted pre-flattened wiper shields on an exchange basis.

All you need in the front are 225-50-15's. They add to the Italian go-cart concept and you won't have any interferences anywhere.

Probably all that you need for high speed stability is 4-1/2 degrees like Boss has but with the power steering, you can run stock since it will add the stability without the increased caster.

If your feet are too big you may find a little interference to the PS unit. It's really close under there on the clutch side. Driving shoes are a must.

Anything over 11-1/2's, forget about it.

Steve,

As positive caster is increased, the steering arm (spindle arm) moves upward, which effects bump steer.  If you have bump steer shims installed, they may have to be removed or thinner shims installed.

John

John,

Good point.  The car has not had an issue with bump steer up to this point.  Thanks for bringing this to my attention.

Steve

@panteradoug posted:

If your feet are too big you may find a little interference to the PS unit. It's really close under there on the clutch side. Driving shoes are a must.

Anything over 11-1/2's, forget about it.

I wear a 12-1/2 running shoe and have zero interference issues with my EZ Electric system.

@panteradoug posted:

I think that you are going to want power steering...and you may have this little issue with the tires hitting the fenders, but just when you turn?

The modified upper a-arms are now installed and the ball joints are shimmed all the way to the back.  I test drove the car and there is not any tire rub on either side while fully locking the rack and doing a sharp u-turn.  You can see the additional 1/2" shim below.  I measured 6.25 degrees positive caster.

Steve, Above you say you test drove the car.  Did you drive it without PS?  Can you describe what differences you noticed?  How much more difficult is it to steer without the PS?