I am new to hot rodding in general and Model A's specifically. I have a 29 roadster with a V8 that I bought from a fellow who started building it but ill health and age forced a sale. When I received the car the chassis and frame were already complete and the engine in place. I have been working on it this winter completing the body, putting seats in, that sort of thing. I recently took it out for a test drive and when I got up to about 35MPH the car really wandered all over the road. A friend suggested I check the caster and I found that it was at 0 degrees. I made a pie cut on the split wishbones trying to get it to 6 or 7 degrees but I overdid it and ended up with 9 degrees. Now when I drive it, I get a violent wobble at about 15 to 20 MPH. it has a Vega steering box with cross steer and no panhard. I did try a dead spring perch but that did nothing at all and I have removed it. All suggestions are welcome. Thanks Greg
Photo's will help others be more helpful. "Dead Perch'But I removed it" WTH?,,,,= Yup,ya have no idea,so start reading up,and put up some pics,,,Most Death is just screw ups by builders,too much play n wrong setting,,but canbe bad tire , an, or balance> PIC PIC PIC's
Are the King Pins and all other steering component's tight? Check wheel balance. Are the tire's in good condition? 9 Degree's of caster isn't really a deal breaker.
Yes, I installed a dead spring perch but it caused more problems than it solved so I took it back off. That’s WTH
Panhard bar, 1/8 inch toe in and 9 degrees caster (at ride height) all suspension and wheel bearings tight and you should be good.
I wouldn't even consider it, that's a bandaid for issues. Personally if the kingpins are tight, check wheel bearings, check tie rod ends, ANY play in anything can cause this. Bad alignment can cause it also. Loose steering box can cause it also... If its a cheap speedway steering box its likely a failure there also.
Pictures, pictures pictures. It's the how it's put together that is important. Of course nothing can beat actually being there, but pictures can reveal a lot.
With my 40 Plymouth I'm also at about 8-9 degrees, works fine, till I tried raising the rear about 1"-1 1/2", intant wobble at 35 mph soon as i hit a bump, evidently does'nt take much to throw it off.
If that is a Speedway Vega box, open it up and check the bearings. They had a bad run. I was talking to a buddy last night who has one and in the past few days he opened his and the bearings were turning to dust. Warren
I'm going to go out on a limb here and guess that the scrub radius is way off. Usually is in these type of threads. We shall see............. when we get pics.
What side was the "dead perch" on ???? [with cross steer it needs to be on the passenger side or you get mechanical bump steer] Split bones and cross steer is a recipe for death wobble. [you're getting "shackle wobble" and the Axle and Bones are shifting sideways in a parallelogram fashion] Install a panhard bar so it Arcs the same as the drag link. [even a temporary clamp on to test it] There are many things to trigger wobble but you need to control it. Reverse Eyeing the front spring can also contribute to this by altering shackle angles[the Panhard is a remedy]
I'm with 2old2fast on this one. The panhard bar is to stop the axle from being pushed sideways when you turn the wheel. Standard equipment on most every modern solid axle cross steer rig on the road for the past 40 years or more. True it isn't going to fix his current issue.
Steering Dampers are a Bandaid!! Not Panhard Bars With side steer any slight lateral movement does not cause steering angle change [bump steer] because the draglink and Bones move in a similar arc. As soon as a hotrodder reinvents the wheel with cross steer, any lateral movement will cause steering angle change. This is made worse with split bones AND /OR reverse eye springs which alters the shackle angle [more vertical] The best method is to allow the shackles and split bones to "float" so there is no binding and use a panhard bar [that mimics the drag link] There are always other issues like too much scrub radius, and/or too much caster [which "triggers" wobble when on an uneven surface] Usually caused by smaller diameter wider wheels. As usual , this will turn into a H.A.M.B psychic thread where we take multiple "stabs" in different directions adding to the confusion [without photos or clues]
Also check the perch bolts are tight and there is no movement with them in the axle, commonly overlooked and is a common cause of death wobble. JW
The " this worked for me so it's the only way to fix it " syndrome. Coupled with the " throw things at the wall till it sticks " diagnostics ! Always good for some eye rolling & cheap laughs , then deteriorating into a mechanic vs engineer conflict , but sometimes finds its way to a " who's is bigger " show down , sometimes popcorn worthy ! Oh , the drama ! Culminating in to a classic "playground" skirmish ! LOL
Not trying to hijack this thread, just to illustrate how tricky it can be diagnose death wobble causes. After reversing my spring eyes the shackle angle was more vertical than the preferred 45*, but on first test run it drove fine, although carefully driven as it had no shocks and only two fingers between spring and frame. Then I fitted lever arm shocks which meant much more spirited progress on the next run with no spring/frame contact, but then I got bad death wobble 3 times when slowing from around 15mph which went on till stationary. My steering box is due for overhaul as it's not in the best condition, but it wasn't an issue before I changed other things. Stock wheels and tyres are at 35psi. 8* king pin lay back. Who would've thought it could be better without shocks? But it was, I'll get it sorted no doubt, just got to eliminate one thing at a time.
With a cross steer set up, you HAVE to have a Panhard bar. With a side steer, you're not pushing the axle side to side turning the wheels, and the harmonics are less likely to generate death-wobble. 9 degrees of castor shouldn't affect much but steering effort, and would, if the rest of the front end is in good order, make it track straighter. Worn or damaged tie rod ends, kingpins and bushings, will certainly exaggerate the problem, an will cause death wobble or shimmy. Checking the toe in (or out, which it may be if you haven't) is neccessary. Just use a tape measure. Should be 1/4" for bias-ply, 1/8" for radials. That's the first thing you need to check, then the condition of the tie rod ends, kingpins, and whether everything is tightened up properly.
Toe in is likely the issue. And easy to check. Get a couple small pieces of tubing or even wood sticks, and hold them at 3 and 9 o'clock on the inside of the front wheel outer rim, or tire sidewalls. Try front inside and compare to rear inside to see which is narrower. Adjust until the front inside measurement is 1/8"-3/16" less than the rear measurement. You can slide the tubing or sticks where they overlap each other to adjust until they fit against the tires. And loosen and double check until the rear measurement is that 1/8"-3/16" wider than the front side. Be sure the tires are sitting on the ground, fully loaded car weight when doing this! If the car is off the ground you'll get erroneous measurements!
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