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Now, about this steering rack issue?
Okay,
I believe it was Morris who stated that the Flaming River Cobra steering rack is too long? I would prefer to use this rack and the original mounting points if possible. So, what are the alternatives, if you are using the original style mounting brackets? Can the Inner tie rods be shortened to make this unit work? If not, which rack are you guys using and what are you doing about modifications to mount your rack? Since I've decided to take the easy way out and use the MII spindles, will another rack work easier? I've looked at the ATSCO 6804 and 6812 but haven't decided which way to go yet- but I need to decide soon as I hope to have suspension pieces in my greasy,grubby little hands very soon. BTW, anyone have the web addy of Morris's build site? I couldn't find it on the Gashole site for some reason? Thanks, Bob |
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Bob
What I said is that the steering rack is to long if you are building a CSX or Kirkham...... The original steering of a MGB steering rack and originals uprights with steering arms has way to much bump steer and you have to use so much toe-in or out which ever you like to try to over come the characteristic's of the car..... Not a good thing..... each car and mfg is different so checking bump steer is very important on these cars..... So we are going to install a different rack and one made to our spec's..... Morris |
Here's a question: How the heck do you bumpsteer a leaf spring chassis? You can't (obviously) take the spring off for freedom of movement to measure.....
I guess one could make a test spring out of mild steel and bolt it in place of the real spring but would the arc of the test spring follow the same path as the real spring? --Mark |
Hi Mark
When I drove 2276 you could quite distinctly feel the upper mounts moving sideways on bumps. It felt like it was spring movement but I got out of that car and said "those guys that drove them fast had big balls".
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I've been fiddling with a drawing of an original suspension's profiles. It has way too much ackerman - maybe to compensate for the too-long rack causing toe-in. The rack should be moved forward about 1.5" to make the ackerman correct. I estimate that the rack length is 19"- 20" between inner pivots, but that's subject to a real bump-steer check. Obviously... |
Mark,
You can remove all the leafs except the bottom one (the one that actually connects to the uprights) and it is pretty easy to cycle the suspension. |
If you are going to use a Rack and pinion ...then the steering arms on the upright need to be in front of the rack so that the tie rod comes back to the rack and pinion....
In the straight ahead position....the tie rod link and the rack should have a 10*degree angle So that when the steering is turned to the lock position in either direction the steering arms are lined up with the rack when looking from the top...... Hope I communicated ..... Morris |
Thanks Morris,
Now I understand what you were saying. I'm not real savvy on steering geometry and suspension design, so I'm trying to understand what I can through the forum. I think I'm starting to get a little bit of a start on it, but not enough to feel confident to design or decide on components for myself yet. Bob |
Morris,
You did, and I was shocked and surprised to find that was exactly what I was looking at with the MG rack on my car just now......steering arms 10 deg. forward of the rack when straight ahead, and parallel on the particular wheel turned to lock. I've been obsessing about this, and never could exactly understand it. |
With the rack set up this way, how does it affect Ackerman? How exact is the 10 degree measurement when the rack is in place?
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--Mark |
Clay
The idea is that as you turn your steering wheel ... the inside wheel..... will turn a little tighter radius then the outside wheel there by helping the car get around the corner.... Morris |
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--Mark |
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Some trivia: The MII spindles have the steering arm tie rod point nearly inline with the balljoints thus necessitating the movement of the steering rack backwards to have an Ackerman effect. Some spindles have the steering arm angling outward at the spindle which allows the steering rack to be inline with the steering arms and have an Ackerman effect, (if the steering arms were rear mounted they would angle inward)
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Wrong, the Mustang 11 spindles do have some akerman built in. As for plotting the leaf spring suspension. The spring acts as the upper control arm. It's inner pivot falls somewhere between the u-bolt mount on the frame and the trunion at the uprite, depending on where the spring is flexing at any given time. Might get close at static, but what about when on the road. Ever see rear wheel hop on a leaf spring suspended rear drive car? (example: Bullit's Mustang)
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Here is a photo of the rack layout on a Shelby chassis. The only way this would be different from an original chassis is the steering arms. The Shelby arms may be longer than the originals.
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Morris is that what you did with the rack on your coil sprung car? I thought we were talking leaf sprung:confused:
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how can we get a compromise for road & track?
road calls for some ackermann, getting the inside wheel to turn in more than the outside, but on the track, due to slip angles of the tires, we don't need or want that. plus steering angles on the track are quite small anyway. to get the best of both worlds one would have to have two (forward) mounting positions for the tie rod ends. or three, or...? I have seen that on a T70 once, and it was heigt adjustable also. where are we going? who would feel the difference? why do road racers compensate for wrong ackermann by dialling in lots of "static" toe-out? must re-read C.Smith's book... dominik |
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