Vague steering, need help!

JC71,

I would look at some threads about Johnny Woods mods to the front a-arms. Seems that this may address some of the issues that you have. I'm not 100% sure but it seems to ring a bell with some of your issues.

Maybe someone that has done it can let you know. Here is a "sticky" thread on the modification - Johnny Woods Front A-arm mods

First thing I would say is that your spring rate is way too stiff.
I do know its personal preference & some may disagree.
But a stiff sprung car will be a very harsh ride & will tend to skip/dart around on bumps.
With stiff springs you have no choice but to run really stiff dampening settings to control the spring’s energy.
A softer spring set up will give a much better ride & better compliance to the road surfaces.

As far as darting from one side to the other on brakes.
This is likely a toe issue & your car may have” toe out”.
So whichever wheel happens to be steering outward at the time the car will dart in that direction.
Slight “toe in” will give much better tracking on hard brakes.

Wide front tyres do tend to want to trammel in ruts.
(Different tread patterns affect this also, some are better than others).
A lot of outward offset of the front rims can make the front too sensitive to road irregularities.
With a lot of outward offset, (rims widened outward) when the wheel hits a slight bump at the outside of the tyre the bump tries to steer the car in that direction.
Stiff springs just make this situation worse as with a stiffly sprung car the wheel hardly moves & the car then follows the bump.
Where as a softer spring allows the wheel to move upward & ride over the bump & be less affected by road surface conditions.

“Toe out” can produce under-steer as the outside front wheel is steering less in the corner.
So it feels like you need to wind on more steering to get yourself around that corner.
With “toe out” both wheels are slightly steering outward when the car is pointing straight ahead.
If you steer right for example, because the right wheel is already slightly steering right its turn to the right is more exaggerated.
Where as the left wheel will not steer to the right as much.
So what you end up with is an exaggerated Ackerman.
Because the cars weight is thrown to the outside of the car in a corner the left front wheel will have more traction than the right front wheel.
So in effect it’s the left front which is the wheel doing most of the steering work to steer you when steering aggressively right.
But if a “toe out” situation exists then the left front wheel is actually not steering as much as it should be as its steering angle is reduced.
Which can give you that under-steer feel.

I’m not familiar with the term “bobbling”

In reality what the Pantera needs to correct its steering faults is more Caster, more kingpin inclination. (Which would require the axle to be at a different angle to the upright).
And longer suspension arms so the front wheels don’t need to be widened so far outward to match GT4/GT5 front flared fenders.
The rack & pinion is also too long with the rack ends being too far apart.
If a line is drawn between the top arm pivot point & the lower arm pivot point the centre of the rack end ball joint should intersect this line.
With the Pantera the rack ends are way outboard of this line, which causes bump steer.

Lowering the nose of your car is canceling out some of the Caster angle, in which the Pantera has very little to begin with, maybe 2 degrees at most.
(Johnny Woods front top arm modifications to increase Caster would be greatly recommended).
So a nose down situation, combined with a lack of Caster will make the car tend to feel flighty at speed.
That is, you find yourself constantly correcting the steering & bringing the car back to a straight ahead direction.
Modern cars have more Caster, if you let go of the steering wheel the wheels tend to centre themselves, (self centering steering).
Also, another effect Caster has is to increase cornering traction.
With Caster the wheel arcs downward as the wheel steers outward.
Effectively the wheel is jacking up that corner of the car.
This is why Caster makes the steering heavier & requires more exerted force from the driver to steer.
The increase in cornering traction is due to the jacking effect.
So again let’s assume we are still steering right.
The right front wheel arcs downward which lifts the front right of the car, which in turn transfers weight to the left rear wheel.
This transfer of weight to the outside rear wheel increases its traction & helps you turn into the corner.
This technique is used a great effect on off-road vehicles & Sprint cars to help steering in loose terrain & it does the same thing on street vehicles.

Sorry for the long winded reply, suspension is my thing as I design off-road race buggies for a living & get a little passionate about the subject.
These are also just my opinions & should not be taken as Gospel.

Regards,
Tony.

Jack,

Lowering the front of your car will change the toe setting in an outward direction. You will have less toe in, and will probably have toe out. You need to have the toe reset.

The stock '71 front upper a-arms do not have shims for adjusting caster. They also do not have the larger "s" bend in the rear channel like the later cars have. This does not allow for the typical modification to be done to increase caster. Offset bushing are available.

Front wheels wider than the stock 7" will also cause the car to pull under heavy braking.

Get the toe set and then road test again. Have the caster checked and let us know what it is. Since the caster is non adjustable on the '71 cars (with stock a-arms), most likely the caster will be 3* at best, and will probably be less. You will probably find that the right side has less caster than the left side.

John

Hey Folks:

Thanks for advice. I assumed that dropping the nose would create more toe in. But I guess the rack sits fairly high. My bad. I will check and adjust.
I heard the lowering the rack helps, add some spacers or something. Can anyone provide input on that... my car is a 71.
Plus, does anyone offer an off the shelf upper A-arm that addresses the caster issue?
Best Jc71

Yes. adding 10mm spacers under the two rack mount areas does help, but does not really solve the in-built problems.
Caster is one of the main issues in which there are a few solutions shown on this Forum from different members.

regards,
Tony.

Sounds good.. is there a cheap pre-made kit for this? Spacers, new bolts, etc.

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,

quote:

Sorry for the long winded reply

I completely enjoyed reading your reply... Good stuff...

Jack, You can get the plates from most vendors. I got SS socket head cap screws from McMaster-Carr.

Adjusted front toe in to 1/8" and seems to be much better. Did not get around to shimming the steering rack. Does it really need it, when the nose is pretty low?

Yes, shimming the rack 10mm will go some way to reducing Bump steer.

regards,
Tony.

quote:

Originally posted by jackcarter1971:
Adjusted front toe in to 1/8" and seems to be much better. Did not get around to shimming the steering rack. Does it really need it, when the nose is pretty low?

Especially needs bump steer correction after you lower the car. The shim doesn't eliminate it, just helps some.

Thanks for info... will def add the shim.

other things i would check is the steering column,with the top u-joint disconected is there any loosness you should be able spin the wheel with one finger and no tight and loose spots.next is the u-joints,should be smooth no binding.next is alignment of u-joints and shafts to the rack. they should evenly spaced on the splines if your steering wheel is centered and turn signals cancel correctly should be ok.next with front wheels straight ahead,steering wheel level [centered] check the amount threads showing on the inner tie rods,should be the same .this would be a good indecation that it turns the same amount side to side. as far as bump steer goes,try this,with the cat on level ground,and where front wheels can move around,maybe in the grass,push down on the nose evenly watching the steering wheel,does it move? if no then bump steer is not an issue. if does ,how side to side ,right or left? also standing outside turn the steering wheel all the way to one side watching to see if it lifts the front end if it does check spindles could be bent or other parts.Caster , if you modify the upper arm to increase it i think you should also do the lower arm so you can keep the tire centered in the wheel opening, my opinnon.i have done this to 6915 and it feels like it has power steering.

CRXMAN,
If you push down on the nose & the steering wheel does not move, this does not mean you do not have bump steer.
Bump steer occurs with wheel travel & the steering wheel fixed in one location.
That is, the steering wheel may not move at all but the wheels still toe in or out.

So........with your test you should have someone holding the steering wheel firm to stop it moving & when pushing down on the nose watch to see if the front wheels steer.........and they certainly will because all standard Panteras have bump steer.

When you steer left or right, one side of the nose should rise, this is caused by Caster. This is normal & correct.
So if you steer left, the left nose should rise.

Increasing Caster will not make your steering appear like you have "Power Steering".
It will do exactly the opposite & make the steering heavier.
More Caster causes the jacking effect on one front corner as explained above, steer left & the left nose will rise.
This is actually caused by the left wheel sweeping on a downward arc when steering left.
The wheel pushing down raises that corner.
This in turn requires extra effort by the driver as he is exerting more force to actually lift one corner of the nose.

This does two things which are positive.
It transfers weight & thus traction to the opposite side rear wheel which increases its traction & helps the car "turn in" through the corner.
It also creates self centering steering so the driver does not have to keep correcting, it keeps the car tracking straight.

The negative side, (and there is always a compromise with engineering) is it makes the steering heavier.

regards,
Tony

JC, assuming the rack bushing has been changed to bronze and you have proper 90-wt lube in the rack housing, if your Pantera still has stock rubber a-arm bushings, you may get vague steering just from rubber bushing compliance. By changing to polyurethane, the vagueness goes away. And conveniently, urethane bushings can be had in offset versions which will increase your caster (tilts the spindle back towards the cabin). Offset bushings in only the upper a-arms will increase caster from -2.6 to -4 degrees and permanently stop tramlining with wide tires, at rather low cost. Even more negative caster (up to -6 degrees) can be had by using offset bushings in the lower a-arms as well. But steering effort will then be increased to the unpleasant level at around-town speeds.
Bump-steer can be lessened by adding shims under the rack mounts; the Factory did this as-stock in mid-'73, so check to see if shims are already in there. If not, be aware that shimming not only moves the rack down, it also moves forward due to the mount being at a 45 degree angle to the ground. Fwd. rack motion changes Ackermann toe-gain, which then contributes to understeer. In addition, new shims require 4 longer bolts to hold the rack in place as securely as stock, and the frame will need new holes drilled to replace Bill Stropp's rack-brace bracket going from rack to frame.
A less invasive and more elegant way to correct bump-steer is to remove the tierod ends and substitute 1/2"-20 SAE female heim joints- which screw directly onto the metric thread steering rods. Simple washer-shims between the heims and steering arms changes rod angle & thus bunp-steer, with none of the rack-shim's drawbacks. With close-to-zero bump-steer, the tie rods will be horizontal. The angle of the lower a-arms at either end tells one nothing about steering geometry, by the way. There are kits to correct Pantera bump-steer this way, but they invariably have you drill the tapered holes out of the steering arms. Again, a better way is Speedway Motors' tapered stud ($4.95/pr) that uses a Ford taper on one end and a straight 1/2" thread for the heim on the other; no drilling. Finally, all heim joints should also run neoprene heim-seals for weather protection, available from Speedway for $10/pk of 6. They also stock the heims. All this is common, tested dirt-track racing stuff available since the '70s.
Lastly, your understeer can also be corrected by adding a 1" rear swaybar in place of your 7/8" rear (or by going to a 3/4" front bar); a larger rear bar than front lessens understeer. Adding sphere-balls on the outboard ends of both bars allow any swaybars to work much more smoothly without binding. I've written many articles on front end mods that can profitably be done to Panteras in the POCA newsletters over the years. ...and I test all such mods on our '72 L for many miles before recommending them. Note that ALL the front end work described here will need a toe-in correction as the last step.

quote:

Offset bushings in only the upper a-arms will increase caster from -2.6 to -4 degrees and permanently stop tramlining with wide tires, at rather low cost. Even more negative caster (up to -6 degrees) can be had by using offset bushings in the lower a-arms as well. But steering effort will then be increased to the unpleasant level at around-town speeds.

Bosswrench, do you know where these offset bushes can be purchased?

regards,
Tony.

have not read all details here... but just wondering... how the hell can make "De Tomaso" such mistakes on a road car, making F1 cars ???? or did WE change things after years ???

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?

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.