Question about caster measurement

Tony,

It does not have power steering yet.  I need to drive it more to get a better feeling of the car with the increased caster.  My initial impression is that the steering is heavier but not sure yet if it actually needs power assist.  I will take it out on the freeway in couple of days and try to get a get a better understanding of the change.  Before the caster change, the car tracked well (I could take my hands off the wheel when driving straight) but the car did not return to center well when turning or changing lanes at speed.

Steve, That's what I was trying to figure out.  Does it really need PS?  What were the caster readings before the mod? Its interesting that it doesn't center.

Tony,

Caster was just under 2 3/4 degrees on both side before the change.  Out of five Panteras that I have owned, this one has been the poorest at returning to center.  The car seemed to be happy to continue going whatever direction it is momentarily pointed.  

Caster is now at 5.25 degrees positive and it has completely changed steering in the car.  I took the car on the freeway today and the outcome of the a-arm modification is what I was hoping for.  The car now returns to center when changing lanes or turning.  Steering is significantly heavier than before the modification.  However, the heavy steering is reassuring and the car simply handles better.

I'm not sure if power steering is necessary.  At very low speeds it could be helpful while at 35 MPH or above it might be undesirable.  I have SACC's power steering on order with delivery in mid April.  I'm not sure yet If I will put it in the car.  I suppose it can't hurt to have it there since it can always be turned off.

I was fine tuning wheel alignment with the car in the garage and the front wheels on my floor tile turn tables  and noticed you can actually feel how the steering returns to center now that it has extra positive caster.  It took some effort to turn the steering wheel to full lock and then it took almost no effort to turn the wheels back to the straight ahead position.  I sprayed WD40 on the bottom of the floor tiles to let them turn easier.  Driving the car feels similar.  It will be interesting to drive it with power steering.

Floor tile turn tables??  A DIY alignment aid?  How does that work?

Turn tables are necessary to measure caster, at least using a bubble level.  My bubble level needs the wheels to rotate a total of 40 degrees (20 degrees on each side of center).  You can buy turn tables for alignment starting at around $200.  Or for around $4 you can use a couple of linoleum floor tile as pictured below.  I used my cam degree wheel as a protractor to make the degree lines.  A little WD40 between the tiles and epoxy floor allow the tile to rotate with the tires.

The bubble level above measures caster and camber (not at the same time, they are two separate measurements).  I also use a Trackace laser to measure toe.

My front end alignment specs todays were:

Caster: Driver side 5.25 degrees positive, Passenger side 5.0 degrees positive

Camber:  .5 degrees negative both sides

Toe:  Toe in 10 minutes (about 1/16 inches)

http://www.trackace.co.uk/

Here is a photo of a commercial turntable.

Thank you for the reply.  I had been trying to think of a way to make DIY turn tables for alignment.  Maybe by using BBs between two steel plates, but your idea is much simpler and better.

I have been driving this car for a while now with the increased caster and I am wondering if it will actually benefit from the power steering that I have on order.  It has stock Campy wheels along with relatively small tires in the front that are 205/60/15.  It seems like the only time power steering would be of benefit is in parking lots but it is not that difficult to maneuver it at this time.  Once the car is moving the steering feels very nice.  

I am thinking the power steering would be more beneficial if I had larger wheels and tires.  I remember that when I put big wheels and tires on my first Pantera the steering took a lot more effort at low speeds.  And if that car had the a-arm modification with increased caster then power steering would help quite a bit.

Your input on this appreciated.

Steve,  our '72-1/2 L model uses 4-1/2 degrees of caster via offset bushings and shaved upper ball joints- a bit less than your car at 5-1/4 degrees. We use no power steering and when she was driving, my 5'3", 115 lb wife said our heavier steering was tolerable at low speeds and not noticed above 40 mph, even with 245-50 x 15" front tires. High speed handling was much improved, as you found. So it sounds like you and your Pantera really don't need P/S. 

To recap, I did a few things to make steering a little easier for her without going to the trouble and expense of power steering or re-engineering the suspension.  First, I installed 8" Campy rear wheels in front. These are built with 1" less scrub radius than 7" Campys- the pivot point of the 8" wheel/tire is exactly under the wheel/tire centerline. The 7" Campys are offset outboard by 1".

Second, I installed a MOMO Protitipo steering wheel that is a little larger in diameter than a stock Pantera steering wheel, thus giving her more turning leverage. The larger wheel does not interfere with either of our legs under the wheel, although some owners do find interference with larger OD wheels.

Third, I use minimum settings for camber and toe-in with stiffer polyurethane a-arm bushings, and have Hall sphere-ball fittings on both ends of both anti-sway bars, to take out any possible binding. I also had the stock early seats rebuilt for good support and modified them for adjustable 'rake'.

These easy tweeks seem to allow tolerable manual steering effort on our car even with max-diameter tires. We both formerly autocrossed this car in N.CA without arm-pain; she won her year's class 4 times and I won my class 3 times against 'Vettes and Camaros with P/S, back in the '80s/90s.