I have a suspension mystery -- or at least a situation that's a mystery to me. Hopefully, it won't be to other members. I have a '27 Model T coupe with four-bar rear suspension and coil-overs. I recently changed the shocks and have things set up according to Hoyle: shock length on both sides at the manufacturer's recommended extension, distance between axle housing and frame on both sides within 1/16" or so of each other. But to do this I had to adjust the left shock about a half-inch higher than the right -- by that I mean that there are about a half-inch of threads showing below the adjustment collar on the left shock, but none showing on the right shock. For reasons that aren't relevant here I've thought for a while that I have a problem with the adjustment of the rear panhard bar. But before I go messing with that, I thought I'd seek the advice of more experienced rodders. Have at it, boys and girls.
A couple of pic's might help us also. Is the frame twisted, is it boxed??? Is there more weight on one side of the car light a gas tank? Just some thoughts for starters.
You may need to look at your pan hard bar. If it's not set up right it will move your rear to one side as it goes thru it's swing ,it can also hold up one side of the car. Watts bar 's work well if you can fit it. Disconnect the pan hard bar and see if you see a difference.
Thanks, Guys. I don't think there's a serious structural issue with the frame. It's a custom job made by a guy I respect out of 3"x 2" steel tube. Way sturdy and straight. Nor do I think weight discrepancy side to side is the problem. My guess is the panhard bar. ... And, of course, this isn't really a big deal. It's just a mystery to me why I'd have to adjust the shocks differently to get the same piston extension and ride height, side to side. More of an intellectual curiosity than a serious problem. Still, the anal retentive side of me would really like to resolve it. Would appreciate any other thoughts anyone has.
If you issue is with the car in your avitar check distance from face of tires to fender lip. That should tell ya if the panhard bar is pushing the body to one side.
First! check the air pressure in all four tires before you proceed and make sure it is correct and the front two match and the rear two match. I learned to do that as the first step of any front end alignment I did. Stand back and look doesn't count you have to know that the air pressure is spot on. Second although you are working on the rear the issue may be in the front. Make sure that things are up to snuff height wise and distance between wise in front. What happens if you take the panhard bar loose and check it? In a perfect world the panhard bar will be real close to level at static height but all too often we install them at an angle because we don't like the looks of the frame mounted end sticking down below the frame. Truthfully as long as the car sets level and square when you walk around and measure it with a yard stick or tape measure life is good. If it sets right and drives right a few threads difference between shocks is just adjustment.
Maybe I am missing something here but with coil over shocks it is not at all odd for the coilover shock on one side or one end of the car to be adjusted differently from the coilover shock on the other side or other end of the car. Very few, if any, cars have the same amount of weight on each wheel. Things like batteries which are not normally centered on the car and drivers weight etc, means that your corner weight will vary. To get the ride height consistent/level requires adjusting each coilover to achieve the correct ride height. People who road race spend a lot of time and money trying to get the corner weights to all be the same so the car will corner better.
Maybe the 2 shocks are not the same. Try switching them side to side and see if the problem changes sides with the shocks.
Just a thought, but you seem to be preloading the left rear corner of the car which when under acceleration is opposite of how the torque of the motor will react to that set-up.
The two coil springs may not be completely identical as to their spring rate. Close, but not identical. It is hard to match heat treatment of spring steel unless they came from the same bar of material and were heat treated at the same time. If they were just two that were pulled randomly from a bin, who knows?
Yes, I agree with your conclusion, Mr48chev. Thanks for the comment, and I will check the tire pressure.
Thanks for that comment, Marcosmadness. Frankly, confusion about whether it's unusual to have two shocks adjusted differently to achieve the same result is what drove me to make the original post. Being inexperienced with suspension matters, I wasn't sure whether my situation was normal or a sign of some impending disaster. Thanks for filling in that knowledge gap for me.
This is wrong. Standing at the rear of the car the torque reaction roatates the axle clockwise. All the wives tales about the "traction side" and such are wrong. TQ is multiplied many times over by the time the rubber meets the road. Even if you had 600 lb/ft of TQ it's impossibe for that force to lift the average drag car like it does, referencing the shots we've all seen where a badass car launces all out of whack on itself. "One wheel peel" is the force of TQ rotating the axle.
I've tubbed a lot of cars and installed many a coil-over and strut front, back when that shit was real popular. treb is in the same church pew I'm in. The other factor is that springs "go away" quite swiftly in the grand scheme of things, especially these small coils used in the C/Os out there. The best idea I've seen in this is to swap em side to side, and this assumes you have no way to scientifically test the coil springs. No worries, not may places do and the majority of such are good ol seat-of-the-pants and logic. I've had to adjust the fronts on an off topic rod build twice already and it only has 900 miles on it so far. FWIW they're not 100% even either but the car sits and handles well.
Lets see, you get on it, the left front of the car rises and the weight transfer goes to the right rear ( all standing in the back of the car ). I've corrected numerous cars that were set-up incorrectly and extremely dangerous at the shift points. Mainly the cars were trying to steer themselves at shift points. All were higher HP cars.
I built a model A coupe that was like that...frame was dead true, panhard was level, front transverse spring mount was loosened, then tightened evenly etc. still required one coilover spring to be preloaded more than the other (don't recall which...it was 20 years ago). I just went with it for a while, and then bought a few different rated springs and experimented until it was about right.
I'm wrong, it roatates counterclockwise from the rear, clockwise looking at the front. My bad. Still, the rear axle twist working in concert with the multiplied TQ is what rolls the car. 700lbs on a 1 foot lever could never raise the front of a car like we see on drag strips all over the country. Multiplied it can twist the car all kinds of outta whack. What is the TQ where the rubber meets the surface? I say somewhere around 4000+ lb/ft from a 500lb/ft flywheel value. What say you? Also, weight doesn't really transfer, load does. May seem like semantics but I'm a big fan of the basics.
Okay, when load transfers on a short wheel base, light weight car ( 2500ish ) things can get out of whack in the blink of an eye. I'm sure there's a formula for the question you ask, which I have not seen. I like basic's a bunch too, big believer in KISS theory.
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