Hello, I'm in the process of building a '38 Dodge Coupe. The previous owner put in IFS from a Cordoba before he passed away. The project was unfinished when I bought it. I have done some research on Ackermann steering but I haven't found an answer to my question. The rack and pinion steering that he installed has very temporary-looking brackets holding it in place. If I stand on the frame rails and take a picture down from a birds eye view it appears that the steering rack is too far forward, causing the tie rods coming out of the rack to be at a pretty extreme angle. Do you think I should move the rack further toward the rear of the vehicle so the tie rods come out at a straighter angle? There doesn't seem to be bump steer as I bounce the chassis, but I haven't studied all my angles. Mostly wondering if there was engineering that went into the placement of this rack, or if some quick brackets were thrown in place so they could steer it around the shop until they made it correctly... Thanks for any input you may have.
I would remove it and put a regular steering box in. That will not work good no mater where you put it. Gary
Has the Cordoba cross-member been narrowed to approximately the same tread width as the stock Dodge ? If so, it appears that the tie rod lengths (& toe-in) haven't been compensated for; maybe he was going to address the issue. Related to that, and as for the R&P placement... yes, it looks to be too far forward relative to the steering arms. You could visit a Pull-A-Part place and scope out how a Cordoba is set up. Or......
I am thinking Cordoba was box, not rack?... The only accurate way to check Ackerman on that, is to measure the toe-out at turns. If you can get alignment specs from a Motors/Chiltons, look up that toe out spec for that year 1938 Ply, or a car that has the same wheelbase But you will need a way to measure the turned angles of the wheels to do this. Borrow some degreed tables from a race guy, or figure out another way Basically the spec will give a degree range like 21 or 22.5 whatever. You set one wheel turned in exactly 20 degrees, then go measure the other wheel to see how turned out it is. It should be the spec, and always is more than 20
Ok thanks for the input, a little more on what I know: Guy died a few weeks from retirement when a tree he was cutting down in the yard fell on him and killed him. True sad story - be careful out there! His widow asked the friend that would help him with his projects to help her sell the cars. Apparently they had done a Cordoba IFS swap on a earlier project and didn't pay attention to caster angle so had to cut it apart and do it over. By the time they did this one, supposedly they knew what to check for. The Cordoba frame sections have been narrowed to close to stock width. Ive already changed the rear axle, but I still have the original rear so I will measure the stock rear end track tomorrow to see how close they are. But I think any future Akermann measurements will have to be taken from its now altered wheelbase. He told me that the rack is out of a k-car, so I would imagine F&J is correct that Cordoba is box. I didn't think a box would work on this car since the torsion bars now run along the inside of the frame rails, but I will do some more research. I planned on sitting down and wrapping my head around Akermann, but last time I tried it was late at night and I didn't have the frame in front of me so I failed miserably! haha I was hoping they had miraculously set up the front suspension ready to run! But that was just my optimism shinning through haha Thanks for the ideas, I will get creative with marker lines or build some quick plywood turntables or something and keep you updated on what I find.
Ok Yall, found a great tech article on finding Ackermann here: http://www.longacreracing.com/technical-articles.aspx?item=45829&article=Ackermann, The Other Alignment Phenomenon - Back to Basics Look further down at "How to Check for Ackermann Effect" Used their method to find my measurements. In another Ackermann article they suggest turning the right front wheel 10 degrees and then measuring the difference both wheels turned at 10ft ahead of the spindle. I turned the left wheel 10 degrees, oops. oh well, should be able to find the numbers still. At the left wheel turned 10 degrees from straight ahead, the outside left wheel moves 16.75", the right moves 17.25" or a 1/2" difference. Because the right tire moves a greater distance than the left I have a Reverse Ackermann effect going on. If I use their chart and use my approx. wheel circumference of 85" that shows I have a toe loss of 0.113 Interestingly, further towards the end of the article they talk about rack and pinion systems specifically and say moving the rack forward will reduce Ackermann, which I dont want to do since I already have toe in, so looks like rearward is the only option! I had a few inches clearance before the oil pan, so I will try mocking up moving it to the rear and see if I can't get my angles better. Wish me luck! Sheet metal guys like myself shouldnt be engineering steering systems! haha But then thats my own fault I guess...
The tie rods should not be in a straight line with the rack front to back. When viewed from the top. Usually the rack is rearward, as yours is front ward. This little detail helps the Inside wheel turn tighter. Which is what Ackerman is about. The tierods should be relatively straight across when viewed from the front and the car is at curb weight and ride height. The inner tierod knuckles should be in line with the control arm pivots. It's real easy to get all of that correct until the engine gets involved with occupying the same space as the rack. Ackerman will be the least of your worries if you get the tie rod angles off. Ackerman is based off of wheelbase and forward triangulation thru the tierod end and steering knuckles. 90% of cars produced don't have perfect Ackerman. Ackerman grows increasingly important as the turning radius is increased. Where having greatAckerman shines brightest is when the steering wheel is rotated to the stop. Camber change is important here as well.
Ok I was also just going through a bumpsteer article to make sure I had that info correct too. I put the engine and trans back in to bring it closer to curb weight and can add some weight to the chassis to compensate for the body being off. Before when I had all the weight on there for setting the correct pinion angle I made a point of bouncing up and down on the front of the chassis and didnt see any glaring signs of bumpsteer. The only reason I mention that is because bouncing a few of my other stock classics will move the wheel all over. So are you saying that if the rack is at the correct height for good tie rod angles horizontally that I shouldnt be too concerned about moving it rearward? If the car isnt going to bounce all over going down the road and the tie rods dont look unsafely angled front to rear than I am more inclined to gusset the brackets that are on there and leave it where it is. As Ive stated, chassis engineering isnt my strong point...
From a looking down view, when you move the rack closer to the "king pin centreline" from parallel you are actually increasing the Ackermann effect. You can correct this by bending the steering arms straighter. Before you get carried away , please look at that steering set up in a stock situation. Chrysler might have already mounted the drag link approx. the same position. Ackermann isn't always engineered into the steering arms , VW did this at the pitman/steering arm on their beetles by staggering the tie-rods
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