Renee- posted March 20, 2018 10:58 AM
'And we know where this instability comes from? Aerodynamics? Hence the big front and rear spoilers on GT3 and GT4?'

Off topic for this forum category, but there is some evidence hi-speed nervousness come from front end aero lift, just like GT-40s w/no front spoiler. The only known wind tunnel test published on a Pantera showed 136 lbs of frt lift @160mph while the GT-40 showed 120 lbs of front lift @ same speed. A 2 degree nose-down position seems to raise but not eliminate the speed at which the nervousness starts to get scary. Lack of enough front caster may contribute as well. SS runners say a rear spoiler/wing is needed for balance on Panteras above about 175 mph, maybe due to rear lift (only 20 lbs @160mph)
Tx René
checked my situation and no option to mod unless we would somehow add/modify the front arms for ASYMETRIC bolds, which I think off but not fully through my brain..
(well besides that I have a simliar issue on the rear, as need to to mod custer)

MG
Renee, to increase caster, we use offset a-arm bushings rather than altering the a-arms. Offset upper polyurethane bushings plus stacking all the shims on one side will give about 3-1/2 degrees of caster. Adding a second pair of offset bushings to the lower a-arms will give in total about 4.5+ degrees. Shaving one side of the steel upper ball joint carrier by 0.100" with give in total about 6+ degrees, all without touching the a-arms. Remember, as caster goes up, steering effort also goes up although its only evident to most drivers at parking-lot speeds..
quote:
Originally posted by Bosswrench:
Renee, to increase caster, we use offset a-arm bushings rather than altering the a-arms. Offset upper polyurethane bushings plus stacking all the shims on one side will give about 3-1/2 degrees of caster. Adding a second pair of offset bushings to the lower a-arms will give in total about 4.5+ degrees. Shaving one side of the steel upper ball joint carrier by 0.100" with give in total about 6+ degrees, all without touching the a-arms. Remember, as caster goes up, steering effort also goes up although its only evident to most drivers at parking-lot speeds..


Where can I find these offset a-arm bushing, do you have a reference?
Yhank you
Rene, offset a-arm bushings are sold by most or all U.S Pantera vendors. Try (larrys@panteraparts.com) in Nevada. They are constructed with one of the pair of bushings having a 1/4" thick flange while the other has an 1/8" thick flange (measurements are approximate).

Obviously, if these are fully installed in an upper a-arm with the thick flange closest to the front bumper, the a-arm will be displaced back towards the driver seat and thus caster will increase. Offsetting only the upper a-arm will gain about 1-1/2 degrees of caster; added to the max possible with all the shims on one side of the upper ball joint, you'll get around 4 degrees.

The same thing occurs if you add another pair of offset bushings in the lower a-arms but with the thick flange closest to the driver, to offset the lower a-arms forward. For us, that gave too much camber, which increases slow-speed steering effort- unless you plan on installing some type of power steering.
I don't have all the measurements in front of me but expecting 6 degrees of caster from just the offset bushings and shims is ambitious IMO, maybe 4.5 degrees from both upper and lower which is good target for a narrow body car.

I modified my a-arms and have a 3/4" spacer (i.e. moved the ball joint rearward) by that amount and I have 6.5 degrees of caster on a wide body GT5.
Every 3/16 inch (4.7mm) the upper ball joints are moved rearward should increase positive caster by 1°.

The tires were shoved forward in the wheel wells when Ford modified the upper control arms. To the point some cars experience rubbing in the forward portion of the wheel opening. Moving the lower control arms forward shall serve to make things worse. Moving the upper control arms or ball joints rearward shall serve to properly center the tires in the fender openings and improve clearance issues.

There are several folks available to modify the upper control arms, that's the best way to accomplish this. I like "best ways".

Check out the topic at this link:

Sticky #2: Increasing Front Suspension Caster

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So, to improve the stability at high speed it is necessary to tilt the car forward of 2 ° and to obtain a caster angle of at least 5 °.

Do we know the original attitude of the car because if it is zero, two degrees with a wheelbase of 2.50m makes a height difference of 87 mm between the front and the back, it's almost impossible to get even playing with tire dimensions

5 ° + 2 ° = 7 ° with respect to the 2.5 ° of origin, it is + 4.5 °, it is necessary to move back the upper a-arm of 22 mm and it is unfortunately impossible with just asymmetric bushings, too bad.

I have Flash Player on my computer but I can not see the gallery of Sticky #2, a computer scientist could he tell me how to do? TX
quote:

Originally posted by René #4406:

I have Flash Player on my computer but I can not see the gallery of Sticky #2, a computer scientist could he tell me how to do?


I could see the album with internet explorer and firefox, with google chrome I got a message informing me I needed Flash Player 9.0.124, but it also provided a link to upload the latest version. Do you think uploading the latest version of flash player would help you?

quote:

Originally posted by René #4406:

Do we know the original attitude of the car


Flat, same height above the ground along the length of the frame rails. The door sills should be level when measured with a 24 inch (60 cm)bubble level.

Tilting the chassis "nose down" has drawbacks, the angle of the windshield worsens, and the angle of the seat cushion tilts forward. Instead of tilting the chassis, just install a front spoiler as far forward as possible. It only needs to be effective enough to zero-out lift. I have one of Kirk Evans spoilers on my Pantera.

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Attachments

Photos (1)
The car's laden ride height is difficult to measure by the factory method since they check to ground at the lower a-arm mount bolt centers, way under the car. This is because there are no perfectly horizontal surfaces for easy reference on the curvy DeTomaso Pantera body. The rather confusing stock ride height figures are in the Ford TSBs at the end of BULLETIN 4, ARTICLE 27: 7.28" frt & 6.39" rear and likely include the U.S. DOT headlight/bumper height spring-spacers which we all discarded decades past.

Note also that ride heights will depend quite a bit on the ODs of your current front and rear tires. And after 45 years of driving on public roads with a spot-welded monococque chassis, the two sides of the car will likely be at slightly different heights. The rear suspension in particular is well known to collapse a little over time and needs a far better upper rear bay brace with adjustment device.

The desirable nose-down rake of about 2 degrees is an estimate and is not a hard-and-fast measurement, for the same reason that the car has no easy horizontal reference surfaces. I use adjustable spring-perch Koni shocks to adjust ride height or small individually sized spacers on all 4 non-adjustable shocks. Sometimes it's just easier to go and do it than it is to laboriously calculate things like this, what with all the various modifiers.
quote:
Originally posted by George P:
I could see the album with internet explorer and firefox, with google chrome I got a message informing me I needed Flash Player 9.0.124, but it also provided a link to upload the latest version. Do you think uploading the latest version of flash player would help you?

I believe there is an inherent error, I have updated Flash Player numerous times and can never get it to work on this site with Google Chrome, not a new thing.
quote:
Originally posted by Bosswrench:
The car's laden ride height is difficult to measure by the factory method since they check to ground at the lower a-arm mount bolt centers, way under the car. This is because there are no perfectly horizontal surfaces for easy reference on the curvy DeTomaso Pantera body. The rather confusing stock ride height figures are in the Ford TSBs at the end of BULLETIN 4, ARTICLE 27: 7.28" frt & 6.39" rear and likely include the U.S. DOT headlight/bumper height spring-spacers which we all discarded decades past.

Note also that ride heights will depend quite a bit on the ODs of your current front and rear tires. And after 45 years of driving on public roads with a spot-welded monococque chassis, the two sides of the car will likely be at slightly different heights. The rear suspension in particular is well known to collapse a little over time and needs a far better upper rear bay brace with adjustment device.

The desirable nose-down rake of about 2 degrees is an estimate and is not a hard-and-fast measurement, for the same reason that the car has no easy horizontal reference surfaces. I use adjustable spring-perch Koni shocks to adjust ride height or small individually sized spacers on all 4 non-adjustable shocks. Sometimes it's just easier to go and do it than it is to laboriously calculate things like this, what with all the various modifiers.


Here is the reinforcement I made:



I also made a dismountable rear crossing



And I'm going to modify the upper a-arms to increase the caster
Good mod, Rene! I've not seen an adjustable clevis built into the lower crossmember but it's a good idea. FWIW, once the stock welded crossmember under the oil pan is cut away for service access, the space between the lower subframe rails always varies a little and 'adjusting' the fit by cranking on the a-arm mount studs to pull the rails together changes the rear wheel alignment. I usually use custom shims between rails and crossmember to adjust the fit but Rene's clevis simplifies this.

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