Rack and Pinion with Damper?
- Thread starter PotvinGuy
- Start date
Bill Pedersen
Member
Wild Mango
Member
What the youngster said!!
Thanks for the patent, Bill. Here's the deal, guys: I'm running a tube axle with a frame-mounted R&P. Any bumps in the road come right back to the steering wheel, which is a big pain. In talking to others who have tried the Speedway damper, they say it really helps. But I don't have a good place to mount it. Hence the question. I was hoping maybe there was an OEM unit with the damper built in.
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putz
Member
audi already has an internally damped rack here is a link to one.dampened rack
I took a quick look at that link and I about fell over at the price. Considering Audi puts their resale value in chrome right on the grill. I'd think you could buy a complete car for the price of that rack.
Some one has to open this can of worms so it may as well be me. I took a look at your steering set up and I think what you're feeling is a symptom of bump steer. It's a geometry problem; specifically differing arcs between the tie rod ends and axle pivot point which causes the tie rod ends to push back against the rack. A damper may buffer it somewhat, but it's not the answer to your problem. OK, all you guys who are running frame mounted racks with no problems, the floor is yours.;-)
Bob
First off, I'm a year away from being on the road.
I have a rack and pinion on my chassis however the difference is that I have a CTO or Center Take Off rack hanging over my front crossmsmber.
Potvin, I was dismayed to find out you are encountering bump steer. If if weren't for the fact I have way too much time into my CTO, I kept thinking Potvin's approach would have been better. I've had to narrow my CTO rack to clear my quarter eliptic springs. It's a power rack and I'd gladly go to a manual rack to make things simplier. However this is what I have and we'll see what happens.
I plan to drive the car unfinished because of potential changes/correctons needed and then take it apart for paint and finish.
I wish I were further along, however this thread is inspiring and I'll need to work a bit harder to complete the project. Me work harder? Here I am sitting in bed with my laptop drinking coffee. Oh well, I'll hit'er harder tomorrow.
I have a rack and pinion on my chassis however the difference is that I have a CTO or Center Take Off rack hanging over my front crossmsmber.
Potvin, I was dismayed to find out you are encountering bump steer. If if weren't for the fact I have way too much time into my CTO, I kept thinking Potvin's approach would have been better. I've had to narrow my CTO rack to clear my quarter eliptic springs. It's a power rack and I'd gladly go to a manual rack to make things simplier. However this is what I have and we'll see what happens.
I plan to drive the car unfinished because of potential changes/correctons needed and then take it apart for paint and finish.
I wish I were further along, however this thread is inspiring and I'll need to work a bit harder to complete the project. Me work harder? Here I am sitting in bed with my laptop drinking coffee. Oh well, I'll hit'er harder tomorrow.
one finger john
Active Member
I believe Ma & Pa T has a r&p set up on their car and drive it all over the place. What is their secret? Without making these little cars formulaic, there should be a set of parameters that can be applied that will give dependable accurate steering. Independent front ends have way more travel than T tube axles and they do not have bump steer. Why would a front end that has less than three inches of travel have bump steer? (Not talking about shimmy, shake, or brake shudder & shimmy). Is it because of the front ends are "spindly" ? Not really secure?
I believe Ma & Pa T has a r&p set up on their car and drive it all over the place. What is their secret?
Without addressing that specific car or builder, I would add this: Every car has bump steer to some degree. It's the nature of the geometry that prevents a perfect design. I've met many rodders at cruise in's, shows, and rod runs that don't have a clear understanding of bump steer, and that includes some that built their own car. Point is, it's entirely possible that a car may be suffering from bump steer and the owner hasn't identified it as such, but may attribute it to some other steering anomaly. Sometimes the owner has resolved to live with it, or feels it's not bad enough to warrant correction.
Without making these little cars formulaic, there should be a set of parameters that can be applied that will give dependable accurate steering.
There's been volumes written on bump steer, wherein the parameters are well defined. It's all just geometry.
Independent front ends have way more travel than T tube axles and they do not have bump steer. Why would a front end that has less than three inches of travel have bump steer?
The simple answer is proper design. The reason that independent front suspensions have minimal bump steer is that the tie rod end movement coincides with the arc of steering arm travel. In an IFS with Saginaw sector gear steering, the Pittman arm connects to a centerlink, and the inner and outer tie rods connect from the ends of the centerlink to the steering arms. This locates the tie rod pivot point in close proximity to the control arm pivots which are on the outboard frame rails. In a rack and pinion, the tie rods pivot on the ends of the rack which coincides with the control arm pivot points. With a solid axle/transverse spring, when you move the pivot point of the axle to the centerline of the chassis, the tie rod pivot points no longer coincide, and the differing radii causes movement at the steering arms as the suspension goes through it's range of travel.
Bob
From what I've heard, they work. That said, they're really just a substitute for a Vega steering box, so if you have a Vega steering system (cross steer) and it behaves properly, so will the Unisteer.
Bob
one finger john
Active Member
Bob, thank you for your thoughtful reply. Am I right in saying the T front axle, in a sense, has two 26 in "control" arms, whereas on an IFS the control arms are considerably shorter and attached to a much more stable frame? So If a CTO rack is utilised, then the rack tie rods (from rack to control arms) would need to be 26 in. also. But you can't have that because the rack width will take some of that away. Right? Would moving the shock placement outwards towards the end of the axel improve things? Perhaps having the shock mount point match the pivot point of the tie rod? Does the shock nount point really matter?
John
John
John, I don't think the shock mounting position really factors into the bump steer equation. I think it would be safe to make this generalization about minimizing bump steer with a chassis mounted rack: Keep the rack as short as possible, thus allowing the longest possible tie rods at each end of the rack. That would minimize the difference in arc between steering arm travel at the wheel and arc at the tie rod ends.
Bob
Ma_n_Pa T
Member
Good evening guys, I do have a rack and pinion frame mounted in my bucket, it works fine, I do not have any bump steer at all! We did however have wheel hop that was a sob to solve but got it done. The wheel hop was mainly caused but piss poor tires and getting a good balance job done right. I have 6000 miles on a set of motorcycle tires when we took them off and replaced with Hoosiers and tires looked good when we took them off
The most important thing on R&P system is getting it level with (Full loaded weight) all the way across from steering arm to steering arm, you can not attach the rack tube higher or lower then the steering arms. I also have the Chevy metro rack which has a shorter tube on it, which gives it longer steering rods, as mentioned, longer the rods the better. You also must run a panhard bar and it too must be level or as close as you can get it. These are just a few things we had to work with when installing the rack.
I have talked with PotvinGuy about his rack and his problem, his rack is a different manufacture then mine and also he has the Rack Tube mounted inside the front tube of the frame (if I remember right) that said it is very hard for me to see if the tube is level with the steering rods. I might add it is a Beautiful Car, in fact seeing a picture of his car encouraged me to put a rack in my car when we were building it!
If it were me I would make sure it has a level plane all the way across and also level out the panhard bar, I think it would work better, since the rack tube is mounted in the frame tube and there is not much for adjustment on the tube it self, I would have Ron (RPM) make some new steering arms and bend them to the proper height to level the arms to the rack tube. That is if it is in fact bump steer, it makes me wonder if it isn’t wheel hop, that is the way mine acted 30 mph you could feel it, 60 mph it would shake the whole dam car but you could walk though it, I did not see if it came back a 90 mph. That was all fixed with good tires and balancing.
The reason that you don’t see much of it on IFS is because it is just what it says, independent front suspension not a solid axle!
I am building a new bucket and we will be putting a R&P in it as well, I like them, a little quick on the steering but that can be changed by ordering a different ratio rack and longer steering arms which we will do on the new one!
Hope that helps,
Jerry
The most important thing on R&P system is getting it level with (Full loaded weight) all the way across from steering arm to steering arm, you can not attach the rack tube higher or lower then the steering arms. I also have the Chevy metro rack which has a shorter tube on it, which gives it longer steering rods, as mentioned, longer the rods the better. You also must run a panhard bar and it too must be level or as close as you can get it. These are just a few things we had to work with when installing the rack.
I have talked with PotvinGuy about his rack and his problem, his rack is a different manufacture then mine and also he has the Rack Tube mounted inside the front tube of the frame (if I remember right) that said it is very hard for me to see if the tube is level with the steering rods. I might add it is a Beautiful Car, in fact seeing a picture of his car encouraged me to put a rack in my car when we were building it!
If it were me I would make sure it has a level plane all the way across and also level out the panhard bar, I think it would work better, since the rack tube is mounted in the frame tube and there is not much for adjustment on the tube it self, I would have Ron (RPM) make some new steering arms and bend them to the proper height to level the arms to the rack tube. That is if it is in fact bump steer, it makes me wonder if it isn’t wheel hop, that is the way mine acted 30 mph you could feel it, 60 mph it would shake the whole dam car but you could walk though it, I did not see if it came back a 90 mph. That was all fixed with good tires and balancing.
The reason that you don’t see much of it on IFS is because it is just what it says, independent front suspension not a solid axle!
I am building a new bucket and we will be putting a R&P in it as well, I like them, a little quick on the steering but that can be changed by ordering a different ratio rack and longer steering arms which we will do on the new one!
Hope that helps,
Jerry
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