I've got a 4" dropped axle with split wishbone front end, just installed a front panhard bar and it improved the bumpsteer issues considerably. I took the car for alignment to try and get everything set up as correct as possible. 1 degree positive camber and 1/8th toe in all seemed ok, but they weren't able to get more than 3 degrees caster, and after reading HAMB and some suggested books, it appears 6-8 degrees is more desireable. The shop said the only way to get there is to lower the frame mounting point of the wishbones, so that the axle "twists" in more caster. He disconnected the bone and as he pulled it down, we could see the axle twist, so it seems to make sense. Before I fab a new bracket and remove and replace the exisiting one, I thought I'd check for a second opinion. Any thoughts on this plan?
Try driving it with 3 degreesWhen I have read this6-8 degrees ,i didn't see anything tire size or power steering
The other option is to cut the bottom or top of the wishbone close to where the forged end is attached, and pull the top back or push the bottom forward based on where you cut, then reinforce while welding. Your alignment guy showed you one way of how the math works and is correct in how it was shown to you.
I agree with sdluck Are you driving it? If yes, what does it do that you don't like? More caster will make it harder to steer when parked or parking. The 7 degrees is an average of the specs I just found yesterday in an old Motors Manual. It says: 4.5 TO 9. Halfway is 6.75 and some ancient guy way back then decided halfway is the right way, and it gets repeated without any questions as to why (IMO) No other cars had such settings that I could find. My 32 has a very heavy motor and a very fast ratio steering box....I just de-castered mine to below 2 degrees. I will see how it is on the road. I drove it all around a big lot today and it steers nice so far. Did they check "toe out at turns" ? That should be 23.5 degrees, plus/minus .5 degree. Turn one wheel into a turn 20*, then look at the other alignment table to read the total on that wheel, and it should be near 23/24. Mine was perfect but only after I went lower caster, but I'm not sure why.
Pie cut the bones to adjust caster, Dick Spadaro may chime in here but I think I recall him stating that no more than 4 is needed. That said I run mine at 7
I drove it almost 50 miles back from the shop after the 3 degrees was put in. It certainly improved the wander and twitchiness, but on uneven seams, etc. it was still pretty jumpy, and a bit challenging to keep centered in a lane. However, this is my first dropped axle hot rod, with bias tires, and I'm not sure if I am expecting too much, as I don't have a comparison. Parking steering is fine, not hard at all. This is an A frame with no kick, and sits high on the rear springs, so perhaps the high center of gravity accentuates the lack of "preciseness"? Maybe I should just drive it a while before doing anything more? I was just hoping to get it driving as well as possible before driving down to LSRU.
Well, on your solid axle the only real adjustment is the toe. Caster is built in the axle and can be adjusted by bending the axle. The caster is adjusted by tweaking the radius rods or the rods frame mount point. More caster will make it more self-centering.
Russco, I noticed in photos of your (beautiful) coupe, the frame mounting point for your bones is about twice as low as mine. Perhaps that is the difference between my 3 degrees and your 7?
Isn't caster determined by the angle of your front crossmember? Changing the mounting point of your bones could put your front spring and shackles in a bind.
The front crossmember is the upper mounting point and holds the spring. If the crossmember is mounted an angle that's not comlimentary to how the wishbone or (same subject) four bar rear bracket height is built, the crossmember will induce wear into the spring and shackle bushings. The rear mounting point of the split bones determines caster. The height of the spring also determines. It's an arc based on...................
Right there you answered your own question. I'd say the car wants a bit more caster. If it was intended primarily as an around town cruiser that seldom would see see long freeway miles it would probably be good as is but I would want to be able to feel comfortable at freeway speed limit speeds for hours on end without having to manhandle the car on a constant basis. Before you make modifications though you might want to play with air pressure a bit. I'd see what somewhere between 26/28 lbs of air would do especially if you are running something like 32 now.
I had the same issue with mine . First the caster was about 3-4 degrees and the car was just like it was floating over the road , no feeling at all.I changed the caster to 9 degrees , now I got hairpins with adjusteble clevises in front so that was pretty easy but there were to mutch bending on the spring so I´ve had to cut loose the front crossmember and angle it aswell. After that was done the car runs like anyother on the road even in freeway speeds. In your case I would have cut the wishbones and angled them just behind the axle and try, but I belive you have to angle the crossmember too to avoid bending and twisting spring and schakles.
I have an AV8 with 4" dropped axle. I set mine at almost exactly 7 degrees, and it steers and rides great. I have no need for a panhard rod. I have toe-in set at 1/8". Pie cutting the bones or fabbing a new mount for the bones are your only options.
Forgot to tell you in the last post. SoCal speedshop have some adjustable perches you can use as well, that means you dont have to cut loose the crossmember them perches allows the spring maintain it s location while the axle have another angle.
From a 1947 Motors Manual. A good truck alignment shop should have the equipment to bend the axle like they used to do. Caster in the axle can be adjusted by adding a small twist in the axle between the spring perch and the king pin. This equipment may be difficult to find now a days. Not much demand for it. We used to do it on the Ford truck twin I beam front ends before they changed the design.
My bones are pie cut as well. I dont think it would matter how you get there either by lower mounting point or pie cutting the bones. but leaning the axle beck a few more degrees should increase stability.
The bones on my A Pickup were cut up front at the clevis just to tuck them up closer to the frame rail, I'm at right around 6+.
Thanks guys, I'll work on adding caster, sounds like the best place to start. I'd like to freeway cruise without all the drama.
Everyone has called it right on the money.........you are too light on caster at 3 degrees. Take it to 7 and it will be a different car. So, your two choices are to either make up a new mounting bracket for the rear of the bones that puts the rear down lower, or you can pie cut the bones a little to achieve the same results. My vote is to make a longer bracket unless it ends up too long and looks goofy. Also, add a SoCal steering stabilizer to the front by welding a tab or two onto the passenger side bone. It will give you a car that you can drive on the interstate at high speeds with no wander. (but it won't fix too little caster, like you have) Don
If you do this major change in caster, be sure to repost here on what happens. You say "but on uneven seams, etc. it was still pretty jumpy, and a bit challenging to keep centered in a lane"... This is more likely with bias tires. I am looking at your tiny avatar pic; I believe your scrub radius is way off, your tire centerline "appears" to be much further away from the center of the car as was designed when new. When you move the tires out like that, the car will be much more sensitive to bumps or holes in the road as well as pavement seams. If you try to use caster to correct that error, you may end up with other issues. EDIT>>>> Kerrynzl just did an excellent post (#46) on this thread about front ends, and he does mention scrub radius. If your car really does have the wrong scrub, you might want to read it.http://www.jalopyjournal.com/forum/showthread.php?t=640643&page=3
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