Hot Rods bias ply open fender last resort (drivers please)

Hey! I like that "applied research & development approach" [ lets try it and see ]
What a simple way to find the travel , I've always used maths .
I'm gonna use this technique to measure suspension travel during an actual race

Thanks for the idea!!!

 

Im having the same problem now. Not a death wobble but a tire bounce or see saw type oscillation. The steering wheel does NOT shake but the axle rocks violently. Mine is set off by road conditions and comes on very early as in 40MPH.

First I moved the rear wheels to the front / no change

Next I had the fronts spin balanced (not shaved round) /no change

Messing w/ air pressure did not resolve the issue for me.

I am in the process of adding shocks as there are none installed presently. I've also noticed a worn king pin bushing that I will take care of first but was informed that it most probably has nothing to do with the "bounce"

The interesting thing is the shake WAS NOT THERE until I swapped from radials to bias ply's.

 

First thing I would do is borrow some wheels and tires and try them on the front.

 

Why does everyone drop air pressure to try and stop a tire bounce. I would run at least 35 psi in the front, find a shop with a Hunter road force balancer and get them properly balanced. I had the same problem with my car. Road force balancing its the only way i got it fixed. You may have other issues but it's a good place to start.

 

While everyone is focused on the tires and shocks, I looked at the pictures again and wonder what degree is that front axle at the king pin?
Looks like well past 12 degrees, I think no more that 10 degrees is acceptable. But then again you say it's bouncing? I'd have another look at the degrees of the axle.

I also agree that the shocks are doing nothing at that angle.

 

To add to the confusion a bit more

If you have too much camber [ or caster induced camber ] the front wheels try to "Bicycle" on the shoulders [ where the tread meets the sidewall ]

Camber causes "camber thrust" where the wheel tries to travel in a "cone" path, this is usually corrected with toe adjustments [ out for neg, in for pos ]

A radial tire it is very forgiving, but a cross ply will try to tramline.

Beam axles make the situation worse because the wheels are tied together.

The famous sprintcar "death wobble" is caused be not enough toe-out [ with negative camber ] or hugh balance problems caused by clumps of clay in the wheels.

Now the effects too much caster

If you "wedge" or jack up the R/R corner the L/Fr wheel tries to turn left [ because of positive caster ]
An out-of-round rear tire will cause the front wheels to try and steer left-then-right-then-left-then-right etc etc as it rotates, plus the whole car will shake violently.

Borrow some different front wheels as suggested previously [ it costs nothing to do this ]

sometimes you can spend a shitload of time and money chasing rainbows when the real problem is at the other end of the car.
Setting things up after they are built can be very frustrating [and rewarding] sometimes you can get lucky.
.

be patient and be very thorough [ I hope it is a simple fix ]

 

Search tire shaving. Coker tires are notorious for being out of round. Call around your area to old tire shops to see if anyone has kept their old tire shaving machine.

 

I had the exact problem. I have friction shocks and they lost torque when I hit a pothole 70mph, after hitting the pothole I could not get past 65 without tire bounce. Got where I was going, checked the torque on the shocks, they were only 50 foot pounds, retorque to 75 foot pounds, no more bounce. Change the shock angle, should be OK after that.

 

Bingo.

Guys, stop harping on the shock position. Yes, it's not ideal but he needs to address the root of the problem here first. If you don't find out what's causing the bounce, you're just going to end up with a pair of worn out shocks that are correctly mounted.

 

First off before you decide you have a tire problem make sure that your wheels are tru,. no flat spots or runout.

If your wheels are rounf then your next thing is to make sure your tires are round. If not get them shaved there are still places that do that. Or get ahold of diamond back and get yourself some radials that look like bia ply tires. They will be new brand name tires that have the letters shaved off and whitwalls installed if you want white walls.

But I'll just about bet that your wheels are bunged up or at least you have one bunged up wheel.

 

I think it's the 2" carb spacer. Definately needs at least 4".

 

I do get your point on "root causes" but the shocks need to be remounted IMO.

"Root cause" comes up a lot in unrelated threads like death wobble. Some will say a few thousands play in tie rod ends or king pins caused their wobble, or a flimsy tie rod flexing caused it, or not having a damper.... But the root problem is still there even if the wobble is now gone.

In one wobble thread Dick mentioned the difference in mass between a heavy duty dump truck and the much lighter Ford I beam suspension. He said the large amount of mass in the truck front pieces almost eliminates any wobble even if there is something out a bit. I have to agree. The large trucks I used to work on, the fleet owner tossed the front shocks when they were leaking or had bad bushings....the trucks acted no different with or without...with bias or radials.

Getting back to the front end in the pics. There is very little mass in that ultralight front end to absorb any minor out of round or slight imbalance.

So, just saying...if a new thread started about some front end problem, and the owner said it has a little play in the joints, everyone would agree to at least fix that first??

I just think it's wrong at this point to purchase new pricey tires without fixing the shocks first?...but if he could borrow known good tires/rims, then sure, try them out.

 

I agree wholeheartedly, Frank. Having chased this same "bounce" problem as well as slow-moving death wobble on some of my early fords, I know how hard it can be to diagnose exactly what is causing the problem. I think the difference here is, loose front end components, bent wheels, out of round tires, unbalanced brake drums, etc... WILL most definitley cause oscillations, whereas improperly mounted or non-existant shocks will not.

In theory, he should be able to drive this thing down the highway with no shocks at all and not have it bounce like a basketball. Not always the case in reality, I know...

I always like to make a thorough attempt at curing the problem rather than the symptom. If all else fails, then we can start applying the band aids the broken leg.

 

^ I agree,......... with reservations

I can't recall seeing many perfectly round mass-produced street tires in my life.

My point about the lightweight front end in those pics; As a slight out of round tire or slight imbalance "starts" to bounce, the lack of mass in the axle ass'y now tries to use the weight of the car/engine to absorb the bounce. But it has to go through the spring, which as designed, absorbs movement and then releases it in the opposite direction. That's a bad thing to try to stop a bounce from perpetuating.

So, you would be better off using the car/engine weight to absorb that initial bounce by using a correct sized shock to prevent the bounce from repeating rather than the spring alone. I guess that's why they are called shock "absorbers"

That's my spin



Good stuff to read in these threads IMO. I'd like to hear more from KerryNZ on future wobble threads...sounds like he is into front ends pretty deep

 

It's hard to tell by a picture but if your radiator is at 1 degree back then your caster is at about 10-11 degrees.

I have read that about 6 degrees is about right, but I have also read that dragsters and salt cars use even more to help the car steer straight.

It might be a combination of the caster working against the unusual shock angle.

My experience with caster is extensively restricted to super market shoping carts.

I have to admit that I do not know if a combination of caster and shock angle will cause this problem but someone else might.

It seems that the most unusual feature of your front suspension is the Shock Angle so if the tires are not out of round I would suspect that the problem is shock angle.

You might try disconecting the shocks altogether to see what happens.

Just a thought.

Dick

 

All very good points!

 

Have done this, and I get more than an inch of travel at that angle. I know it is not superb geometry for a shock, but its only a shock people. I search the beloved HAMB for topics and advice on this note and went out to see personally and I'm not the only one doin that on a narrow T style front end. If there was a way to fit a tube between the radius rods and chassis that would be where I would have put them! Any shock is better than none. I'll try to borrow someone elses tires to check as I dont have others.


I will however look into the caster, and "bicycling" effect as well. this actually makes a little sense compared to to everyones shock and carb spacer theory! I looked at this myself this morning and its about 13 degrees laid back. Goes nice and straight and the wheel snaps back well, no push, no scrub, and toe is set dead zero. Driver side of the axle has a bit of positive camber though...... I thought it would come into shape with the weight on it but it didnt so I was going to bend it to correct geometry, but I really dont think thats my problem. Oh and the car shacks so bad that I have to let go of the wheel at 80 plus. So I'm positive or at least almost positive my issue lies in the front end.
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take a wrench and try more toe after you take out some caster there is no magic number it could be .250 in or out just go for a ride and move it in or out and see if it gets better or worse all my years of stock car racing zero toe never worked

 

Street Rodder's Chassis & Suspension Handbook suggests 1/32" to 1/8" toe-in.

If you have ever tried to back up fast in an older car you might have experienced it trying to swerve back and forth, however the opposite happens going forward helping the car to travel straight ahead.

I don't know if the tow-in is having an effect on some of the other features of your front end that would cause the wheels to hop.

The only other thing that I saw in the pictures is the cantilevered panhard bar mount.

There again I don't know if that is having a wild card effect on the situation.

I have had problems with electronics projects and found that when I have intriduced a Wild Card into the equation That is the first place that I look for problems.

You seem to have several Wild Cards that hight act in combination to cause your problem.

Dick

 

Why is that??? It seems that having the front tires steer towards each other would be less stable than having them steer away from each other (toe out). Wondering if anyone can explain the preference?

 

To compensate for minute ammounts of play in the kingpins/steering linkage and/or tire tread movement due to friction against the road surface, present moreso with bias plies than radials. If you set it at 1/8th toe in, as you go down the road the wheels slightly toe out a bit and roll straight.

 

These are 16' Coker radials. They weigh a ton but run great. I'm done try to make bias plys run good.

 

Sounds like the same shake/wobble/bounce we had in our coupe. happened right at 62-63 MPH. We tried everything to work out the issues. It ended up being bad tires on the front axle. They were way too oval & would not balance properly. If they had been on an independent front end it would not likely have been a big deal but on a beam axle everything that happens on one end transfers over to the other end and you can feel it in the steering.

Check it out, had lots of suggestions, maybe some of them will help you.

http://www.jalopyjournal.com/forum/showthread.php?t=375262

I would borrow a set of known (proven) good wheels/tires from a car set up similar to yours to try and see if the bounce changes or disappears. Don't assume that brand new means good, that was a mistake we made.

And in the end, props to Coker for replacing the front tires no charge. Car rolls along smooth as butter now.

Good luck.

 

thanks for the pic fuel pump, that looks suitable to me as I dont exactly have a true traditional car. next question would be is anyone running radials up front with cheaters on the back? Im sure there is a hundred text book reasons not to mix but lets here from the people who actually have driven the scenerios. thanks for all the input so far guys, I didnt know that steep of lay back on the axle would cause any problems.
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Hi guys this post just caught my attention, this car is kinda neat so lets get it driving peacefully. First all of you that noted the shock absorber angle identified a major potential problem point.

A high speed bounce is usually a balance issue. So the first point of attention is to simply jack the front end off the ground air the tires up to about 30 lbs and place a chalk mark on the side wall, hand spin them 4-5 times to see if they stop in the same position or random positions after they coast to a stop each time. Same position reflects a tire balance or defect issue, and maybe a drum balance issue. Random position would indicate that the assembly is relatively equally balanced. At this time you can also check for lumps in the tire casing or tread and bent or out of true rims.

The next issue is the shock absorber position, slight out of balance and spring actions are damped by the shock absorber. In this case both the shock absorbers severe angle and its operational angle coincide with the rotation of the axle which produces little to no damping effect. Even though there may be a movement there is virtually no shock dampening effect. A much more efficient mounting would be parallel to the spring because you use the shock to damp the spring motion and also get a little anti roll dampening. If you had quarter elliptical springs you could run the shocks in this position but it would require a stiffer reaction unit.

Since you want to isolate the problem try these first to see if it still perpetuates or it disappears.

The next issue is mentioned that you have an excessive amount of caster angle. With the size and the style of your tires you need no more than about 5* rearward tilt of the spindle. Excessive angle produces a caster trail on an I beam angle that makes the car very sensitive to alignment of the front wheels due to the tie rod couple. Roll out the caster by adjusting the clevis ends. Do not attempt to cure an issue with excessive toe in or out over 1/8" deviation from straight. If you have to go over that then there is something else wrong.

If this does not begin to cure the issue you will have to take your car for a ride and determine if the bounce is actually a wheel fight issue because the wheels are not tracking parallel and the square of the front axle is off. The bounce is created by the conflicting tire slip angle at each tire. You can easily check this using a cheap plastic draftsman's triangle. By centering the steering and having the driver side wheel pointed straight ahead use the right triangle side to determine if the backing plate is at 90* to the axle and then check the passengers side with out moving anything, it should also be at a 90* setting, if not you will have to square and readjust your tie rod. If you have to do this take it for a test drive to see if the situation still exists.

Before it gets more complicted try this and get back to us with your results.

 

I tried radials in rear and bias front once a long time ago, very scarry!! Otherway, I have heard works but I'm not trying it. Had the same shake at 60 on my coupe a couple of years ago, everyone called it cowl shake. It went away at 80 but came back coming down till under 60. Tried 3 different sets of front tires and wheels and it didn't change a thing. Had all kinds of suggestions, one was front axle angle. Finally sold the car and told the new owner about the problem. Didn't try radials, but wouldn't have run them even if it fixed it. Good luck.

 

Had a car when I was young and not too bright that had radials on the front and bias on the back.Driving in the rain one day I went to pass a car and when I turned to get back in my lane the rear end proceeded to keep going forward.Did some awesome 360's on the highway before sliding into the ditch and hitting a pole.Radials grab...bias dont.

 

Put the radials on it and love life.

 

Yep; I would borrow a set of wheels/tires for an hour from a car that has no issues. Also agree that even with no shocks, a properly setup rig won't have wobble or bounce on fairly smoothe roadway.

Also, bias tires isn't the problem. I have two rides with Bias/tube type and they run up to 70 mph with absolutely no issues.

 

BTW, where are your kingpin grease zerks? I see empty holes....