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| Center links for different cars https://slantsix.org/forum/viewtopic.php?t=57896 |
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| Author: | sandy in BC [ Mon Jun 15, 2015 1:49 pm ] |
| Post subject: | Center links for different cars |
Were there different center links for cars with different wheelbases? I know A bodys had different widths but did they also vary by wheelbase to keep the Akerman (Toe Out In Turns) correct? What about B and C bodies? and can they interchange? I have a late B ( 117"? wb) that now steers a 126" wb car. Do I just need a 75 Imperial Limo centre link? |
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| Author: | SlantSixDan [ Mon Jun 15, 2015 2:42 pm ] |
| Post subject: | Re: Center links for different cars |
Quote: Were there different center links for cars with different wheelbases?
Looks like not. I see one part number for Valiant (108" wb) and Dart (111" wb) in '72. In '66 there's one p/n for Valiant (106" wb) and Dart (108" wb) with 6-cylinder engine, and another for Valiant and Dart with 8-cylinder engine — the 8-cylinder link has deeper drop to clear the V8 oil pan, and the 6-cylinder shallow-drop link must have been a fraction of a penny cheaper to make, otherwise they'd've used the deeper-drop link on all cars.Quote: did they also vary by wheelbase to keep the Akerman (Toe Out In Turns) correct?
I'm trying and failing to reckon out how the Ackerman effect would be influenced by the wheelbase of the car. It could be because I had my usual wild par-tay weekend (not!). I don't think the steering and front suspension components have any way of knowing or caring how far away the rear wheels are.Quote: What about B and C bodies? and can they interchange?
No, you have to use the centre link of appropriate width (or length, depending on what angle you're looking at it from) to match the front track width of the car, which is why '67-up A-body drag links are wider (longer) than '66-down. You can use beefier C-body tie rod ends to stiffen up the steering linkage of an A-body, but you can't use the C-body centre link.
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| Author: | Joshie225 [ Mon Jun 15, 2015 2:52 pm ] |
| Post subject: | |
If you want to change the Ackerman the center link needs to move fore/aft. If memory serves How to Make Your Car Handle by Fred Puhn covers this. |
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| Author: | sandy in BC [ Mon Jun 15, 2015 5:20 pm ] |
| Post subject: | |
By fore and aft you mean pitman/idler arm length. The distance between the idler/pitman holes in the centerlink should increase with wheelbase.... |
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| Author: | SlantSixDan [ Mon Jun 15, 2015 6:15 pm ] |
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Quote: The distance between the idler/pitman holes in the centerlink should increase with wheelbase....
With track width, yes, that's clear. Still can't imagine why the distance between the idler and pitman arm holes in the centre link (i.e., the length of the centre link) should increase with wheelbase.
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| Author: | sandy in BC [ Mon Jun 15, 2015 6:35 pm ] |
| Post subject: | |
https://en.wikipedia.org/wiki/Ackermann ... g_geometry |
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| Author: | SlantSixDan [ Mon Jun 15, 2015 7:57 pm ] |
| Post subject: | |
OK, now I understand in theory why the wheelbase matters, but that article uses the word "approximates", and given the lack of different centre links for different-wheelbase cars, it seems that's a key word -- not just 108" vs. 111" and 106" vs. 111" A-bodies use the same centre link year by year, but looking again at '72, 108" E-bodies and 115" and 117½" B-bodies all use the same centre link. |
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| Author: | sandy in BC [ Tue Jun 16, 2015 6:27 am ] |
| Post subject: | |
..........meaning Im using a centre link on a 126" wb vehicle....that is also used on a 108"wb vehicle. Perhaps the accomodation was in pitman / idler arm lengths. |
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| Author: | Dart270 [ Tue Jun 16, 2015 7:23 am ] |
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My sense is that differences of 6" or less in wheelbase probably do not affect geometry enough to warrant different parts usage. 18" sounds like it might be enough to make a difference. I believe all 62-66 A bodies used the same centerline, pitman/idler arm, tie rod parts, so Chrysler did see this as a problem for 106" vs. 111" wb cars. Lou |
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| Author: | Joshie225 [ Tue Jun 16, 2015 9:02 am ] |
| Post subject: | |
I'm too lazy to do the geometry for the change in Ackermann for the change in wheelbase, but it appears MOA small. To get it correct will require changes to the steering arm angle. As all the '73+ A (except 9" drum) and B bodies use the same lower ball joints with built-in steering arms it doesn't appear that Chrysler placed high importance on correct Ackermann. Ackermann is way down the list of things I'm concerned about in my suspension and steering. Ahead of Ackermann I am concerned with camber control, toe control/bump steer, steering axis inclination, and caster. "Modern cars do not use pure Ackermann steering, partly because it ignores important dynamic and compliant effects, but the principle is sound for low-speed manoeuvres. Some race cars use reverse Ackermann geometry to compensate for the large difference in slip angle between the inner and outer front tyres while cornering at high speed. The use of such geometry helps reduce tyre temperatures during high-speed cornering but compromises performance in low-speed maneuvers." Milliken, William F, and Milliken, Douglas L: "Race Car Vehicle Dynamics", Page 715. SAE 1995 ISBN 1-56091-526-9 |
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| Author: | SlantSixDan [ Tue Jun 16, 2015 9:38 am ] |
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Quote: My sense is that differences of 6" or less in wheelbase probably do not affect geometry enough to warrant different parts usage.
…looking again at '72, 108" E-bodies and (…) 117½" B-bodies all use the same centre link.117½" - 108" = 9½". |
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| Author: | SlantSixDan [ Tue Jun 16, 2015 9:50 am ] |
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Wait a minute…I take it back. I don't see why length of the centre link would affect Ackerman. Length of left vs. right steering arm on the lower ball joints, yes, I can see how that would affect Ackerman. I haven't measured whether the left and right lower ball joints' built-in steering arms are symmetrical, but the same lower ball joints are used, brake system by brake system, for 106", 106½", 108", and 111"-wheelbase A-bodies. Quote: Perhaps the accomodation was in pitman / idler arm lengths.
I'm looking at '72 again. Same pitman and idler arms for 108" E-body and 115" and 117½" B-body. Same tie rod tubes and ends, and same lower ball joints w/built-in steering arm (brake system by brake system), too.
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| Author: | Matt Cramer [ Wed Jun 17, 2015 7:31 am ] |
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Quote: Wait a minute…I take it back. I don't see why length of the centre link would affect Ackerman.
It would make sense if it were part of a package that also included different lower ball joints. If you changed the lower ball joint significantly, but wanted to keep the tie rod length the same to avoid bump steer, then you'd have to change the center link length to keep the alignment the same.
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| Author: | SlantSixDan [ Wed Jun 17, 2015 8:47 am ] |
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Yeah, but that world (w/different lower ball joints) isn't ours. |
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