That tie rod looks pretty small in diameter and has several bends to clear the frame. Could be flexing quit a bit when you hit a bump and causing the wobble to get started.
If you look at those oval track cars the obvious thing is that the split bones attached to the car much higher than on a typical cowl-steered hot rod. They generally didn't have the drag link a foot higher than the wishbone pivot.
HA!!!!! The controversy never subsides!!!! For what it's worth,...I've cleared 65K miles with my cowl steering and I love it,....still! It looks so cooI and there is no downside in my experience. My car originally had a Vega box and there were no issues. Did the cowl setup in 2015 and initially experienced a death wobble. I suffered the nay sayers and talking heads. I went on to replace tires, king pins, spring and axle, and fuss with caster, to no avail. Finally relented for the Band-Aid,...the dreaded dampener. That did it! One of the "experts", a name builder, who gave me shit about cowl steering also, in a separate conversation, said he installs a dampener on every solid axle car they build. Here's some of my thread. https://www.jalopyjournal.com/forum/threads/cowl-steering-first-time.996254/page-2 I am currently building a Model A and it will have cowl steering.
You are entitled to your own opinion. You are not, however, entitled to your own Laws of Geometry. There is a reason why they are not called The Friendly Suggestions of Geometry. I borrowed Gimpyshotrods tag line and modified it a little bit. It seemed appropriate to this thread.
you, me, the Rolling Bones guys and many others. My Tudor came with a F1 box but I might just build another cowl steering setup for it to get these Karens all in a tizzy.
This is just a general statement and probably no help to the OP. I have seen some very well executed cowl steering installations: steering box very well supported connected to something of substance and the correct steering / suspension relationships. I have seen even more setups that in my opinion, to quote Ralph Nader, would be unsafe at any speed. Just a bunch of 1" square tubing up under the dash with the steering box stuck on it. You could sit in the car and flex the whole cowl just by turning the steering wheel. So if you are going to do cowl steering, do it in a structurally sound manner. If you can't, stick with side steer.
“If your only going left” there is far more to oval track racing to just turning left you have to have a car that handles, and turns at speed even on rough and rutted tracks, you can’t have a car that handles poorly or that bump steers at 100 M.P.H. when it hits a 3’ long 3” to 4” deep hole in the track particularly when there are 20 or more other cars out there. We know how to make these things work and have figured out and make modifications to improve steering and handling. However none of this back and forth is helping the O.P. fix their problem, so with that I have spoken my piece, and will bow out.
I'd do something about the tie rod assembly also. Too small and the bends are making it worse. A dampner might cure it but the bends in that small of tube are flexing too. I'd go after the small tube and bent tie rod then go after the death wobble if it's still persistent. Fix the apparent problem then go after the drivability. ...
Your lower shock mounts don't have enough thread engagement. The nylock isn't doing anything. Oof. I feel the pain the fixed bushing and shaft of that damper experience every time the tie rod and axle move. Bind and bend city.
All this talk about Schroeder steering. A few years ago there was a hot rod shop in the south selling F100 boxes modified for cowl steering. If I remember I looked inside a couple Hilton Hot Rods coupes and they were using this setup. Wonder what happened to the manufacturer?
It was Mike Bartlett (mikesspeedshop) but I’m not sure if he is still producing them. I bought one from him for my A sedan. A bit spendy but an excellent piece of engineering and made the car far more pleasurable to drive with the 16-1 ratio. I found my shroeder too heavy. Lots of compromises with cowl steering with regard to geometry etc but they can work well. Personally though I wouldn’t run another.
With a little bit of trickerydickery I made my own cowl steering from a Gemmer F1 box. The only bad thing about my design vs the Barlett is mine is not serviceable because I welded on the extended shaft. I also added Zerk grease fittings for periodic lube and a shim at the outboard bearing so I can take up any wear as time goes by.
A large cause of death wobble is perch bolts not being tight or firm in the axle and allowing the axle to rock, this usually only happens when the left tire hits a bump. This is amplified on dropped axles. When building my T RPU i found that the perch bolt's shoulder didn't engage in the axle fully, this is due to the 35 to 48 bones having a much thicker top piece than the spring over bones for obvious reasons. I don't know if there are perch bolts made to correct this or not but i extended the axle purchase area of my perch bolts by adding a nut that was machined to the same size. JW
Dynamic ballance all 4 wheel and tire assys, use rod ends not original adjustable tie rod and drag link ends, adjust the play out of steering box, and add a steering damperner and you'll be set.
Remove the cowel steering,an fix it right*................Those that don't understand engineering, love too to make up BS storys about how there poorly done cowel steering works so,good*< It dose not ,they just defend to the death there mistake out of ignorants*{ I'm not saying stupid,just that they don't know,and don't want to know * ]. Stop the bump steer,by learning about engineering design.. Not learning, all excuse cover up BS why the cowel set up shown in your pic is OK to them< it is not !! Also the front tires are [too wide=too heavy an hard to control when they start death wobble.=Contributing factor to oscillation strength{ death wobble ]. You can put a band-aid on { VW steering damper on tie rod,or any of the same design dampers,it will help,but it is really just a cover up that makes if feel OK kind of. } Except it will still dart to the side on a bump, from the bumpsteer feed ,by that cowel set up. . Try to over come trendy,lazy fix ideas,that some pick as EZ way around. A small extra note,for those who want to use badly done race cars ,as a example of it works=No it dose not,but on very hi HP lite car at race speed=it is really steered with the gas pedal,with only one of the front wheels getting any bite.* If two race cars an drivers are equal*other then one car has bump steer vs other car dose not> the car with out bump steer will win . Spritcars offten use cowel steer,only do to space n pounds,an that the car is steered more with the gas then the steeingwheel at speed.
Two more points are that the front wheels are wide and have outer offset putting the scrub point way outside the king pin center line, this gives the tire/wheel leverage to try and turn out coupled with that ''funky'' tie rod that will be flexing like crazy under the load applied by the above mentioned and the extra force applied from bumps you get what you have. If you have any of the issues i mentioned in my previous post (#44) then many issues that are contributing to the problem. JW
Compare the height of the drag link above the hairpin pivot here to what is the case on the OP's setup. The greater the vertical distance, the greater the tendency to bump steer. The angle of the drag link is immaterial, and tweaking that would achieve exactly nothing. The death wobble has nothing to do with this issue. That there should be death wobble with that extremely slender tie rod would tend to support my suspicion that death wobble can be due to elastic oscillation of either the drag link or the tie rod, i.e. twanging like a bowstring, set off by momentary compressive strain. A substantially less slender tie rod should fix that, if my suspicion is true. That is, a large-diameter, thin-wall tube rather than a small-diameter solid bar.
I recently assessed that condition on my replica champ car build and decided to change the long drag link to a two-piece drag link that will mitigate that problem. The tube diameters are rather stout too.
Every time the topic of death wobble comes up it's always the same suggestions, most of them wrong. Death wobble in the jeep world is extremely common. It's caused by three things. Wide off set wheels and tires with poor king pin axis of inclination. Loose, worn or flexing steering linkage And lack of correct toe in! Ya think is scary with skinny tires, low center of gravity and 2-1/2" of suspension travel? Try it with a short wheelbase, 35" in tires in something that weighs 5500 lbs minimum and has 20" of travel. Ya better pack an extra pair of undershorts. In the OP's case I would also have the axle checked for flex. Some of home dropped axles were slow cooled in sand instead of air cooled for proper quench. It makes them super soft and bendy.
At the end of the day it is simple geometry and physics, just like ALL triangles, no matter how they are arranged all the angles always come to 180*.Point is there is a formula to steering that has basic geometry that must be obeyed for it to work in harmony. JW
My last race car would get a caster shimmy on low speed pace laps. It would start as you turned left into a corner at maybe 30 mph. I could make it stop by playing with pressure on the steering wheel. I never felt it shimmy at race speeds, but then we turned mostly right to go left. Also the power steering pump had more pressure/volume at race speeds. We ran 10 - 12 degrees positive caster, not what you want on a street car.
I’m curious about all the controversy as both a mech Eng and because I feel that I have no choice but to use cowl steering need to use for my single seat speedster build. I won’t have wishbones so that aspect will not come into play, but I will be using quarter elliptical springs attached at the end of the frame rails.
As an engineer, you had a course in kinematics. Go back to the basics, and sketch up the side view of the front suspension including the steering linkage, to scale, as accurately as possible. Now move the suspension thru it's range of travel, and look at the arcs. In particular look at the paths of the steering arm where the drag link attaches relative to the arc of the drag link itself. Unless the pivot point of the rear of the drag link is exactly over the rear pivot point of the suspension, say the tie rod end if you were to use hairpins or split wishbones, the arcs will be different. This is what causes bump steer. With quarter eliptic springs you have a different situation, and the virtual pivot moves around. Cross steering can minimize bump steer in those cases, but in reality there will still be some effect. There is a way to get most if not all of the bump steer out, but at the expense of increased complexity and unsprung weight. That is to mount a rack and pinion steering gear on the axle. Obviously you then have to articulate the steering shaft, which if done wrong will also induce steering inputs. Articulated steering shaft that can move up and down and also in plunge without inducing steering inputs. Just my 2 cents worth
So you say a pair of Friction Shocks are going to control the front axe and keep it in position, rely! JW
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