Model A straight axle shake. WHY?

High Class Rat, your point is very well taken and could be the cause of my problem. I have access to a pair of Weld Wheel front skinnies with whatever tires to experiment with, haven't gone to pick up or buy lug nuts to be able to mount.
I appreciate your feedback very much!

 

Can you get your hands on one of those on car shock testing machines ?

You know, the type that has a variable speed electric motor and a crank or cam that vibrates one wheel up and down a fair distance, and a pen chart to show the actual wheel movement amplitude.

That will test the shocks, but if you watch what that wheel does, it may be flapping around quite a lot, and not just moving straight up and down as it is supposed to move.

You might be able to spot something happening as the machine shakes the crap out of your Rod.

 

good ole death wobble.... my truck used to do that at 65/70ish if i hit a bump...it would make you have to change pants... rotating my tires cured it

 

I had that problem on the T at 58 mph...................I drove through it and didnt run 58!

But, try dropping 2-3# per front tire. The difference between 22/3 and 25 was night and day.

 

Hi Patrick I just started to follow this thread, I dont think that this is a shock problem, to check them out simply unbolt the top mount and push/ pull the shock thru a couple cycles, if there is a drag both ways its not the shocks.

Warpspeed gave you some good info on king pin inclination and tire offset so if you think that is in acceptable area that is a lesser issue.

In later posts you mention that you have a little bump steer and even later mention that you have a Mustang side steer box with no panard rod, your statement that panard rod are for cross steer is inaccurate, with a side steer box you need the panard rod to control the side movement of the frame thru the shackles, the cross steer drag link acts as a panard rod to locate the front end. Installation of one will clear up some of the slight bump steer that you are experiencing.

Going back to the shake that you experience leads me to question the accuracy of the front axle to square with the spindle. The vehicle steers to the heavy tire. If you are going down the road and you go over a deflection one tire becomes more loaded than the other and becomes the dominant steer tire. If your spindles are not square to the axle they can still be parallel to each other but not on the same lateral coordinate.They form a parallelogram. This puts one tire slightly ahead of the other and as long as the loads are somewhat equal the tires react uniformly. When the loads unbalance the tire with the most load tries to track straight ahead which sets up this wobble, as that tire tries to find its square and the opposite reacts. This can only be stopped when you slow down and the tires rebalance the tread loading.

Since everything is relatively new my suggestion is to recheck the square of the axle to the centerline of the vehicle first. Then after squaring the axle check the square of the spindles to the axle at that point by using a small carpenter square insuring that the spindles are both 90* to the axle. If you find that one spindle is square to the axle and the other is off even a slight amount unhook the tie rod , square the spindle and adjust the tie rod to match the steering arm hole, then reset the toe in to 1/8" in and give the car a try slowly increasing the speed to determine if the issue still exists.

One of the reasons that this only occurs at intermediate speeds is that at a slow speed the weight of the car on that tire overrides the tires tread forces attempting to center and the tire just scuffs slightly. At a very high speed the high rotating mass is so great the tires center themselves and are probably bowing the tie rod slightly to compensate for the misalignment.

Anyway thats my input ,let us know what you find out.

 

Mr. Spadaro, I appreciate your knowledge and feedback very much!
FWIW, the best I can recall, after straightening the front axle from having been bent in a pull type situation and cast off as swap meet garbage, I had straightened the beam based on beam being straight to a known flat reference (deck of drivehsaft building equipment) and afterwards checking kingpin inclination with a digital angle guage to be the same on both sides after using a little 100 ton press to straighten the beam.
When checking camber like my front end alignment guys do, both sides check equal, and caster checks same on top of the axle kingpin boss before installing the spindle.
The spring perches and kingpin centers also check good for being square with a know square frame my measuring to the rear crossmember centerbolt hole, which has not been modified since Henry had it build.
The jackass mode is not speed sensitive unless it happens because of road surface changes. It can be as simple as an expansion joint in concrete. You retake control by slowing the vehicle down. You can have one palm on the steering wheel and not have to hang on to drive thru it. It has no feeling of the car wanting to jump left and right like being self-steered. I have been relaxed enough to watch the left front tire jump up to a better view thru the windshield, drop, and repeat. Can't see the right front or had anybody ride with me to scare the fire out of them to watch for the jackass. THE CAR GOES DOWN THE ROAD STRAIGHT. IT HAS no feeling of being shaken left to right to left in any way.
I won't have the driving answer tonight. I have dropped the front tire presure to 21 psi FWIW.
Many thanks again for thinking out loud, please continue! As we do this, others will learn too.

 

I had the same problem. All new parts and pieces, allignment performed by an old school front end guy geometry right on the money. A simple fix for me was to have the wheels and tires balanced at a shop that had new state of the art equipment.
I had the wheels and tires balanced by another shop 500 miles earlier and the car was scary to drive.
State of the art balancing solved this issue.
Goood luck on finding a solution.

 

The car doesn't have a straight axle either.
It does have a dropped I beam, two different things. It seems a lot of terms are being misused on this thread.

 

Great thread, I have similar issues with MoFo, (Avatar) and there is a lot of food for thought here.
Question: Can the perfect behaving I beam front end be had, or are these issues only able to be at best minimised?

I have all winter to find out, and will be using ideas from this thread, starting with the least expensive.

Good luck with your search Patrick.

 

Hi Patrick, back to your issue, since you have a known straightened axle that is a good sign but again I would suggest that you recheck the spindle relationship to the axle. As a starting point they should be initially set a 90* angle to the axle as I indicated before. This can be done with a simple plastic drawing triangle or small carpenters square, I have one made up for this and have the corner nipped off to allow spindle boss clearance. From this point the tie rod can be adjusted to set the toe in. This is a common error, people just stick the spindles on and set the toe not realizing that the spindles will find a self center position, read the correct toe but actually are tracking at an angle to the axle. This causes all kinds of issues when they are disturbed in bump and it doesnt have to be off by much.

If you are still of the idea that it is a tire issue lowering the air pressure only masks the problem. It is important to have both tires at even air pressure. The soft tire will hide the deflection or in some cases make it worse, in the case of a severe bump, due to the excessive sidewall deflection from the oversoft tire. Since you indicate the tires have been setting its a good idea to bump the pressure up to 25lbs and then swap the tires side for side to determine if it is a balance issue, flat spot or damaged casing causing some of the tramp. Swapping side to side will indicate a tire issue if the problem changes sides.

My last suggestion for now is to rollout some of the caster. With wider tires and wheels the tire requires less caster so as an experiment you can try to cut the caster to 5* and give it a test drive.

 

There is a lot of good info on this thread. Just make sure you start with the SIMPLE things first. Before you start replacing parts, buying new tires, changing your geometry start with the easy stuff like lowering tire pressure etc...

 

Front beam axles with narrow kingpins have some severe built in limitations that are inherent. If everything is set up absolutely perfectly, it can still never work anywhere near as well as a properly designed modern IFS.

Every aspect of automotive engineering has made huge strides over the last eighty years. Engines, transmissions, brakes, tires, suspensions, electrical systems.

Being traditional and using the old original stuff is fine, just don't expect modern day handling, braking, steering, or performance from it.

 

A few things to check!! Tires out of round, a bent rim, anything more than 1/8" run can be trouble. A panard rod sounds like a good idea and maybe add a steering dampener one from a VW bug works well.

Do you get a wooble at a low speed 5 miles/hr or less. bent rim.

Some ideas!!!


The Old Tinbasher

 

Hi Warpspeed. I think this was just a misunderstanding. I believe Patrick meant that the left tire would go up as the right tire went down, and vicy-vercy...not a violent left to right situation. You notice that he said that there is no feedback of this violent action at the wheel, and that the radiator is "waving" at him. The violent action is the axle tipping left and right very quickly...like a see-saw.

Hey Patrick...have you checked to see that the spring-mount is good and secure? I'm wondering about the condition of the spring itself...could it possibly be broke, yet still being held within the center mount? I doubt it...I'd expect the car wouldn't sit level if it was. Just thinkin' out loud. I still suspect that something is amiss with the shocks, or possibly the shock-mounts, but also still think that there's another issue, but that maybe the possible lack of dampening is magnifying it. If this doesn't happen on smooth pavement at 90mph, I doubt that the wheel/tire is out of balance or out of round. Thinking of the violent "see-saw" action of the axle, and the fact that it seems to be brought on by bumps in the road leads me to imagine that maybe the spring is not secure in the mount, or the mount itself is loose, or even that the front crossmember could possibly be broke. If the crossmember is broke, or came loose from the rails, that sure would help to explain the "waving" of the radiator...that is, if the radiator is mounted to the front crossmember. (I haven't seen how your rad is mounted.) Did you notice if the radiator "waves' more to the right or left side? That could indicate which side of the crossmember would be loose. One step beyond that...is your front portion of your frame boxed? In other words, could there be excess flex in the frame-rails themselves? I suggest that you take it to a shop with a hoist, and get two guys to rock that front axle to simulate the see-saw action, while you look very closely for play in any of the components. Be careful not to rock the car off the hoist though! Maybe even jacking up one side of the axle, and then the other would give an indication of where there may be excess play. Rocking the axle would probably be best to simulate those "jack-ass" conditions though. LOL. Good luck with this! - Rick

 

BULLSHIT. My late Model Ford Ranger with IFS has fuckin bumpsteer. New does not always mean better. I have ridden in and driven many early cars that handled as good or better than most late models. Where is Metalshapes wehn you need him?

 

I did say A PROPERLY DESIGNED IFS.

No, new does not always mean better.

But the very best new stuff is always going to be a lot better than the very best old stuff.
If beam axles, leaf springs, and lever action friction shocks were still the absolute best design of front suspension technology available today, Formula One cars would still be using them.

 

ok fellas i have a little to add as i am no stranger to Death Wobble.I have a 96 Dodge 1 ton Dually and it has this problem.Mine is a 4x4 and has straight axle out front! The cause of my death wobble is caused by an insufficient track bar put on by the factory and a weak frame where the steering box is bolted in causing the front end of my truck to jump around violently.The track bar or pan hard as it would be in a hotrod keeps the steering goemetry correct when you hit severe bumps or potholes,etc... I would start by adding a panhard bar.To correct the problem with my truck they suggest upgrading my track bar and addind a stabilizer to my front frame that ties both frame rails together and also to the steering box.

 

Are you comparing apples to oranges or kiwis to mangos? You say newer tech is better as in daily drivers vs. old hotrods, then bring in billion dollar F1 as a reference?

I would say modern cars are MORE DANGEROUS. THey remove the driver so far from teh road that they can overdrive ANY road condition. Is it that they are so much better or do they just mask things to the point that Soccermomsally can put on Mascara and talk on her cell while doing 50 in a 35. See it every day

 

Try 8 to 10 degrees caster salt flat cars sometimes use even more than that. Forget the book ,check for slop in tie rod ends heim joints etc. Let us know what fixes it. please.

 

No just saying a hundred years of automotive development technology has produced far more powerful and fuel efficient engines.

A hundred years of technology has produced far more efficient and reliable braking systems.

A hundred years of technology has improved the performance of tires immeasurably.

And seriously, what are you guys smokin if you seriously wish to dispute any of this?

 

This is a traditional hotrod forum, what did you expect?

 

Hi i had that problem just as he has i had to put the caster back to 4*.
more caster will make the steering wheel come back to center faster.
it would start the shake as i would get into a place in the road that was uneven.
i put a steering dampner in to only make harder to steer and no fix.
i use a mustang gear also.
the other thing that i had was not having the gear box in the high center that added to it.
i also had a tire problem with a tire ballance that was correct only without a load on it
swaped right to left that changed the problen some.
double check high center in gear box with draglink off as you count turns then feel for a little bit of a snug spot.
may need to tighten the gear slightly to feel the snug spot

 

All the people with beam axle front suspension problems seem to be turning up here in droves. There are some very good reasons why that is so.

 

DUH, becuase this is the benchmark of traditional hotrodding which means buggy sprung rods galore! Understand that many/most folks here, myself included are 40 or younger. Even if you are on older rodder you may be 60ish which means you graduated in THE 60s. If you are here and STILL in it at 70 it means you were born in 1940, didnt drive until 1956 and probably moved right into dorrslammers with Overhead valves. Lots of time for troubleshooting and tech to disappear. Thank the HAMB and Fordbarn.

 

This may or may not help, but fwiw, my wife's long gone Uncle "Mutt" Hill that lived over in Indy used a Vega steering gearbox on his hopped up hotrodded '23 Bucket T Roadster P/U that he drove on I-70 running 70 mph back to Moberly, MO to come home for a visit! "T"-engine and all...............

I mention Uncle Mutt's name because he sold Herculoy/Sili-Bronze (??) maincaps for Model T engines that he had cast locally way back then that he then machined and sold big enough for individual engine fitment by those that bought them.

And he could pour babbited bearings and then line-bore w/ shims in those old engines in a NYM. I watched him line bore one years and years ago.

pdq67

PS., I want to say a Ruckstall OHV head, Rajo 2-speed rearend w/ Buffalo wheels, but I have to admit that I don't know squat about hopping up a "T" engine so may be WAY off.

But I do remember the "bee-hive" oil filter/cooler he had on it.

 

I am almost 60 and have the truck in aviator on the road since the 70's
still build rods

 

Back to my drivability problem!!!
I tried dropping the tire pressure from 25 psi to 21 psi as suggested. That made no change to the road surface induced jackass mode.
There is a strong possibility the problem could be caused by the tires, they are a little out of date. Unlike many customer vehicles I have driven, they do not have a speed range vibration. I do not have any sort of low speed wheel wobble or tire separation induced wobble.
The front spring is a monoleaf and is held properly by the u-bolts I installed. The front crossmember is not broken or blown out like the original I cut out and replaced when I built the chassis.
I have two choices for changing caster because I'm on split wishbones. I either change the height of the front of the car by moving spacers on the front spring, or have the fresh painted wishbones bent. Kinda like a Catch 22.
I have borrowed a pair of Weld front runners with new 165R15 tires and will experiment some more this weekend. I'll have to buy a batch of lug nuts.
The steering gear is very fresh and does not have a tight spot at any position. The pitman arm is centered vertically when the vehicle is straight ahead.
More updates later. All suggestions are taken seriously.

 

Does panhard = stabilizer bar?

 

Difficult to know for sure, because you changed several things at once. Maybe put the original suspect wheels and tires back on, and see if the problem comes back.