Vague steering, need help!

quote:

Originally posted by PanteraDoug:
They aren't "mistakes' per se. They are just staus quo technology and engineering for 1970.
There wasn't a lot of point into making these cars handle like a race car simply because the weakest link in the solution is the lack of capable street tires.
Average street tires today out perform race tires of that era by a long shot.
The reality is that the modifications necessary on this vehicle to bring it up to current technology really are kind of moderate all things considered.
That alone speaks for the design considerations from 1968?

so yes, WE did change things.... good reminder on the tires !!!! thanks !

As others have stated here, they were not really mistakes, more the technology of the day.
I'm sure Dallara would have put his utmost into the design & done the best he could.
And years later his designs would have been that much better.
Everything evolves.
I have a huge collection of books on race car suspension & design from the 1960's to the latest offerings.
Suspension has changed allot.
Although most of the geometry was well known in the 1960's, some aspects were simply ignored or considered as less important.
Toe change due to bump steer is not a huge issue if the vehicle has very little suspension movement.
The less the wheel moves the less toe occurs.
In my job where I'm designing off-road suspension with 20” plus of wheel travel it has to be right.
If I allowed the Pantera’s geometry on a buggy the wheels would literally turn into a corner all by themselves after 24” of travel.

Remember though, that the tyres of the day were considered high tech, they were as good as it gets then.
And if your tyres were not up to scratch you had to make the suspension that much better to find an advantage.

It was simply evolution, designs have evolved over the years & we have much higher expectations now.

regards,
Tony.

Bosswrench... you bump steer solution is awesome. simple, fully adjustable and cheap. Nice, thank you... I will be converting over in the next few weeks.
Cheers JC71

Hi All,

I have a precistand problem in Pantera, that may have to do with caster. Or not enough caster.
My Pantera is full trackday car, it doesn't see the roads. When I brake real hard, my steering wheel starts to rumble, shimmy or how you call it. It can be stopped if grap the wheel with two hands. I alway's thought that it was in the rack, or the mounting brackets. So I checked them both, and got it working as it supposed to do. I checked the brakes, put on new rotors, no succes.

Could it be that the problem is not enough caster ? If you brake hard, the car will dive a bid, and the relative caster will become almost zero. The hub will be approx in a vertical line with the ground. Could this create this agrassive shaking in the steering under braking ??

Arno

quote:

Originally posted by Edge:
For mine I made two rectangular plates from 10mm thick, (approx 3/8") Aluminium.
Each plate has two holes that match the rack mount.
The two plates measure 10mm thick x 20mm wide x 96mm long.
Two 8.5mm holes at 76mm centres.
The four M8 bolts will need to be 10mm longer than standard.
Sorry, I can't remember how long the standard bolts are.

regards,
Tony,

...Allow Me,
The Stock Rack Mount 8mm bolts are 70mm Long, so You'll have to go to 80mm, with shims installed. The pitch is 1.25mm. ONE word of Caution!! The Torque on these Bolts is Only 20 ft/lbs!! Strip these threads and You'll have to cut a Hole in the Trunk Floor to Replace the Nuts!...

quote:

Originally posted by MARLIN JACK:

quote:

Originally posted by Edge:
For mine I made two rectangular plates from 10mm thick, (approx 3/8") Aluminium.
Each plate has two holes that match the rack mount.
The two plates measure 10mm thick x 20mm wide x 96mm long.
Two 8.5mm holes at 76mm centres.
The four M8 bolts will need to be 10mm longer than standard.
Sorry, I can't remember how long the standard bolts are.

regards,
Tony,

...Allow Me,
The Stock Rack Mount 8mm bolts are 70mm Long, so You'll have to go to 80mm, with shims installed. The pitch is 1.25mm. ONE word of Caution!! The Torque on these Bolts is Only 20 ft/lbs!! Strip these threads and You'll have to cut a Hole in the Trunk Floor to Replace the Nuts!...

Marlin is right. Be very careful with these bolts. You do not want to have to deal with anyone working on your nuts in such a tight space. I don't care if she has little tiny hands. It still is a nightmare. The drugs just make it worse!

In my case I used Halls stainless battery box which just about takes up every available millimeter of space. How I even got the bolts in to the rack with the shims is a complete blank.

I do remember having to use allen socket bolts with some type of an extension to reach them AND having to grind a flat spot on the mounting caps to clear the box. I hate when that happens. If I had help, I don't remember, and I certainly don't remember her name or face either? Maybe a lot of Bud Light though, and that COULD be the problem? Don't remember where this dam tatoo came from though either? Geese?

Dago, it may well be your caster, especially with wide tires. Stock Pantera suspension cannot adjust caster to more than about 2.6 degrees back. Corvettes of the same era use up to 6 degrees (with power steering to compensate for the extra steering load, the wimps!) The tiny amount of caster possible produces the car's equivalent of a motorcycle speed-wobble or tank-slapper.
There are a whole variety of ways to increase caster, but the simplest (and completely reversable if you desire) is by adding offset urethane bushings to the upper a-arms. Pantera caster then goes to about -4 degrees. Adding a second set of offset bushings to the lower a-arms increases caster again, to about 5-1/2 degrees total. By shaving 0.080" off one side of the upper ball joint carrier, will give an additional 1/2 degree.
I've found that on a street car, more than about 4-1/2 degrees of caster becomes hard to park or drive slow around town. But 4-1/2 degrees was tolerable and was enough to cure shimmy and hunting in our '72, even on bumpy crowned roads.

How much play should be in the steering... I seem to have 1/2-3/4" at the steering wheel? Wondering if my steering rack is shot. Tie rods seem fine.
Thoughts.
JC71

Play? Should be practically none. There are a few easy fixes possible:
1)- under the dash there is a 'D' shaped shaft that telecopes inside a hollow tube which is part of a collapsible steering shaft in the event of a collision. There is almost always considerable slop between the two parts which can be minimized by somehow squeezing the sides of the tube in. Originally, there were strips of plastic in there; some try forcing home-made replacements inside. Others less patient simply drill a hole clear thru both parts and install a big cotter pin, figuring the pin will shear in a collision and the shafts will then work as planned.
2)- there are two u-joints in the steering- one of which may be failing and can be checked by hand from under the dash & front end for tightness. New u-joints are pricy and are the same ones used in the shift shaft.
3)- the coupling between the steering rack pinion shaft and the steering shaft sometimes loosens up; servicable by pulling the left side front wheel off and tightening up the bolt. Beyond that, damage to the rack or pinion itself- often from lack of lube, a worn steering rack bushing, worn tie rod ends, a cracked bushing inside the steering column- the list of les common possibles goes on.
Every year, I like to lay under the car and grab, pull and jerk on everything I can reach. If something moves at all under my poor efforts, I start investigations right there.