Technical Caster Adjustment on Straight Axle Frontend

What's the best way to adjust caster on the dropped axle front end in these pics?

 

Third picture. And it'll help to get that spring off of the top of the axle.

 

With bones like that you need to either lower the rear mount or cut and pie-cut the bones where the tube meets the forged ends at the axle.

The thing about bones is they need to be set up right at the get go...including factoring in rake.

 

How much caster is on it now, I prefer 7-8*. Easiest and cleanest way would be to fabricate new brackets to replace those bolted to the frame. Sometimes guys pie cut the split wishbone at the front and change the caster there, but your radius rods are nicely chromed.

 

I'm at 7.5*

 

What problem are you having? The caster math is correct.

 

I'm trying to eliminate some occasional very low speed death wobble. I read all the threads and figured I 'd start with reducing caster

 

Start with Toe In and tire pressures.

 

Toe, tire condition.
I've worked in a shop that performed alignments on Kenworths and Cadillacs. In all cases, including my hotrod A, I've seen tires to be the cause of grief of vibrations and death wobble more than anything else.
Same on 4x4 trucks. New tires, look like new tires, old tires, big, small.

 

One thing you could do to test if the caster is too much, causing the problem, is to temporarily install taller rear tires. It will make the car have more rake, and hence less caster. Or maybe shorter front tires.

 

I've played with the toe-in from 1/8 to 3/16 and no difference.
I've played with tire pressure between 25 and 30 lbs - no difference.

 

Tires are relatively new. I checked for out of round and they seem OK, but I do get a lot of up & down hop over 55 mph

 

I damn near tore the grill shell and radiator off the front of my car at 75 because of MY JUNK new appearing tires, that I bought new.
At the shop I worked at, we spun balanced big truck front tires on the truck with a 240V spinner motor machine, to have the tire spinning at 80 mph truck speed. Keep in mind, that a truck tire at 60 is in the neighborhood of 400 rpm. I've seen hoods, mirrors, stacks shake,---while watching the tread of the tire convulse. Stop the spinning, set it down, advise the customer to come back with another PAIR of front tires. No different than the jack*** **** my car did to me.
Our tires, at ***uming 27" height, spin at neighborhood of 700 RPM at 60 MPH. To get a feel of something wrong, pile on a bunch of weights for the temporary on a good setup, then remove.

 

I tried every thing, still could not get rid of it. Put a SoCal steering stabilizer on it got ride of the wobble. Yea I know it did not fix what ever is wrong, but the car is drivable now.

 

I'm thinking of buying a set of radials and eliminate the 4 bias plys. Some sacrifice in looks but better handling and ride.

 

Just for the sake of it, perform an experiment. Keep in mind it's for low speed.
Put a piece of duct tape across your tire so you will have and added noise to ***ist in what you might be feeling in the steering wheel.
If the beats match.......you know where you stand with your wallet. And if you can video for thread info, it may prove to others what you are trying to overcome.
And FWIW, the jack*** shake was from a pair of BAD radial tires. Nothing is sacred from failure in car parts.

 

Wow- That's surprising about the radials. I'm trying to find a shop locally that can high speed balance while tires are on the car. Not many shop still have the floor type balancer.

 

I stopped using bias plys years ago,as I drive by, no one can read the side of tire anyway,an been much better ride an all,always being sure the're round an balanced. However I got some cheepy radials just 3 months ago*,and these things* just have near no side wall intagrity,feel like ho****er bag/no matter the air PSI=they are the only time low speed death wab has showed up in 58 years of driving my hotrod,an all though I've never needed a steering shock,between axle an tie rod,with these I do. In my case its tires} Other factors can make it happen,I've seen when new set of rims added along with tire my bubbys rod=new rim had more out set to rim moving tire away from kingpin, can make tire scrub too high=can make wabble show up ,when it did not before the change.

 

I gotta throw in one more observation I made on I-40 westbound during about 1991. This will throw in some info on how dynamics of something going awry will affect a vehicle, OT is it is, but something to learn from.
Traffic was being slowed by a semi truck in the right lane, afternoon rush. The grocery store's delivery truck has a bad problem with its tires at its drive axles, tandem drive on Hendrickson walking beam, pivot in the center at each side.
At 45-50 mph, the tires were causing a hop so hard that you could see the suspension move, and the truck cab was shaking violently. BANG, BANG, BANG, metal suspension limits getting put to their limit on a road truck! Not an oil patch bed truck! I hope the trailer didn't have milk or eggs in it!
If it had an orange placard on it, I'm sure the results wouldn't have been the same as the warnings on the containers for the freight.
Tires!

 

Seems more and more that there is a strong possibility that tires could be my problem. Sounds like I should be ruling the tire problem out first before I start modifying suspension.

 

How many thousands of pounds of force does it take to make a loaded truck have drive axle tires come of the ground? This is a parallelagram type suspension. Just for reference.
This is a suspension of typically 40K to 46K lb capacity.
The truck I spoke of had 34K suspension.
Other than that, I don't know nothing.

 

I realize that zero scrub is almost impossible on a modified hotrod front end, but what do you think would be the maximum scrub you could safely get away with without having excess wear and possible wobble?

 

Wow -- Must have had some REAL BAD RUBBER

 

Welcome to my world of enjoyment, and hotrods!

 

One more piece of advice.
On an object that is spun, that has an out of balance condition, and it's shape doesn't change with speed, ..... the out of balance condition squares when you double the RPM.
And with ***uming that, if a tire is separating or not, its shape always changes. SO, because of that, you cannot balance out a problem.
And I've seen sticker tires sent back to their source because they were junk when new. Again, nothing is sacred from being junk.

 

A friend cured his front end strangeness recently. He had been driving it for years and in some cir***stances had a concerning wobble. He chased everything. In the end, about 3 weeks ago changed the radials that were on it for new ones...magic, instant cure...after god knows how long suspecting everything else, because the old tyres 'looked' ok.

 

Well -- Looks like I may in in for NEW tires, but I'm keeping my "receipt" until I know they are round true and will balance.

 

Got rid of my new bias plys a few years ago on my avatar, radials I have on now have 12,000 on them, I'll never go back to bias plys.

 

Just because I didn't see it mentioned and it's free to check, make sure all suspension and steering bolts/components are tight without play. Eliminates another possibility.
We had a death wobble situation show up on a truck after many trouble free miles. Turns out a previous owner had removed too much of the gusset for the steering box mount, and the metal had finally fatigued enough to cause the problem. Probably wouldn't have lasted much longer, dangerous.

 

Beyond trying some different front tires, I would look for any slack in the steering gear. Could you show a head on picture of the front axle. From what I can see, as much material that has been removed from the beam, could cause it to flex.