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Achieving high camber/caster for road race |
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tyrodtom
AMC Addicted Joined: Sep/14/2007 Location: Virginia Status: Offline Points: 6199 |
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In circle track racing we only have left turns, so you see extreme right side negative camber, as much as 9 degree's, on mine, not a AMC though.
I do it by cutting the lower arm, outside of the lower strut mounting location, and extending the length of the lower arm, welding it back together, with a sleeve inside at the weld joint. I first extended the lower right arm 1/2 inch, and it resulted in, less tire edge wear, more even tread temperatures, and lower lap times. So finally I extended it a whole inch, and have stayed there. But have always wondered if extending it even further would help. Then I did the opposite on the left side, shortened the lower arm. for positive camber. But of course, you'd never want positive camber on a road race car.
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66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
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blenny
AMC Apprentice Joined: Dec/13/2014 Location: 77541 Status: Offline Points: 82 |
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Saw this, thought it would help camber but hurt caster. Our next two changes are going to be to move the battery to the back, but behind passenger may be better, and tie the shock tower/spring perches into the firewalll/cage. |
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9081 |
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Ah, that's from my thread. I must explain a bit before one can understand why the arms were lengthened 1 inch. I lowered my suspension by changing spring seat height, which changes the swing of the lower arm. Makes the lower arm's resting posistion more horizontal to the ground than stock. Also my modified mounting of the upper arm 1" outboard and 1" back to the firewall, via modded suspension hump, makes it necessary to compensate by lengthening. All my mods work hand in hand, as I saw limitations and concerns with a straight stock setup with modernised performance requirements. Basically the longer the arm, the less effects on angle under spring compression. So once set in a sweet spot, the change under loads is less severe to camber. |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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73Gremlin401
Supporter of TheAMCForum Joined: Mar/02/2013 Location: Stmbt Sprgs CO Status: Offline Points: 941 |
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I just re-read my post about relocating the battery, and realized that it didn't make sense, so I fixed it - I relocated the battery to behind the passenger front seat - I didn't set it into the footwell, as my subframe connectors are there - but rather to the flat area where the rear-seat bottom used to be. I agree that you should look at tieing in the shock towers to the cage, but don't expect a massive change in how the car drives, if anything it may make the car understeer more due to the extra rigidity. Are you running a 6-point cage, and is the main hoop and rear down bars triangulated over the spring perches? And have you looked at connecting the sub frames? For road racing use, underslung connectors can be problematical from a ground clearance standpoint, I engineered up internal ones that fit in the rear seat footwells, and work really well. I'll upload a pic tonight.
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73 Gremlin 401/5-spd.
77 Matador Wagon 360/727. 81 Jeep J10 LWB 360/4-spd 83 Concord DL 4-dr 258/auto |
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tomj
AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7522 |
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a lot of understeer in AMCs and i assume others is in the *rear suspension*. i haven't measured a Gremlin; but in earlier cars the leaf springs are not precisely parallel to the chassis, but are angled inboard at the front. that plus the difference in front and rear pivot heights is such that it causes the unweighted (inside turn) wheel to shift aft *very slightly* which induces understeer. this is designed in, and no accident. i have my '61 American absolutely neutral now -- throttle oversteer, decell/brake understeer. the rear is now air springs and a rigid wishbone (lol, geometry similar to torque tube) and up front, due to the simpler design -- a '70 Mustang upper arm pivot with "Shelby drop" that stops the instant center from shifting around. alas, that won't work on the 70-up 01 chassis. you'd have to chop out the upper arm "socket" from the unibody and drop it, no small project. Edited by tomj - Jun/26/2018 at 11:59pm |
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1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com |
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tomj
AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7522 |
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there's a decent 2D suspension simulator at vsusp.com. the hard part is measuring and entering the data |
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1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com |
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9081 |
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Tomj, I had thought of that as well, with the rear leaf spring setup. Though my mods are covering the issue, just have not pointed out details and measurements. Mostly because I have not finished my front end work, and I am the only one that I know of to move rear spring locations outside of frame rail by grafting frame rail segments and reinforcement, and widen track as one big mod.
From years of seeing rear end collisions with AMC cars, the rears crumple and twist. The frame is rigid up to the start of the back seat or wheel arch. Once you get there, the arc of the frame allows flex and bend because there is no structure to support corner rigidity, just the body as a shell. The front section has cross members, firewall door supports and added frame support. A cross brace in the trunk area to support corners that is tied to the roll cage should stiffen twist to help with cornering. A rear sway bar helps, but the hidden weakness of the rear, has to be looked at and addressed. Sorry i cannot be any more details to help, as the rear end stage of my build is yet to start. I get Ideas time to time, but mostly when i get down and dirty with seeing what i have before me as i go. |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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73Gremlin401
Supporter of TheAMCForum Joined: Mar/02/2013 Location: Stmbt Sprgs CO Status: Offline Points: 941 |
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Excellent points - my experience with this was when I built my cage for my Gremlin, and used Team Highballs IMSA setup as my guide. the main hoop is centered and welded directly over the front leaf spring eye, and the rear down tubes are welded directly over the shackles. The main hoop is cross braced, and the main hoop is also gusseted to the B pillars. While I don't have a cross bar going from the right top of the main hoop to the lower left of the down bar, the B pillar gussets provided more than enough torsional stiffness for me to need to slow down the rear sway bar actuation to prevent terminal oversteer. I did this by replacing the end-link tubes with springs, and using rubber bushings on the end links instead of polyurethane. |
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73 Gremlin 401/5-spd.
77 Matador Wagon 360/727. 81 Jeep J10 LWB 360/4-spd 83 Concord DL 4-dr 258/auto |
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73Gremlin401
Supporter of TheAMCForum Joined: Mar/02/2013 Location: Stmbt Sprgs CO Status: Offline Points: 941 |
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Here's a pic of my internal subframe connectors - the front bolts
directly to the end of the front sub frame flanges, the back is bolted & welded
to the leaf spring eye box. the main hoop lower connector is arched
over the transmission tunnel, this allows the lower connector to provide
rigidity at the lowest part of the hoop. The tube that runs parallel to the rocker panel connects the main hoop to the A pillar down tube. |
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73 Gremlin 401/5-spd.
77 Matador Wagon 360/727. 81 Jeep J10 LWB 360/4-spd 83 Concord DL 4-dr 258/auto |
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9081 |
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Looks nice enough to copy. Thanks for the picture.
Most have no idea when they move into AMC road race and rally race from other brands. AMC is a lost art, if you call it that. Old school helps but tech has improved since the last big effort to compete, and it was with late 70s / 80s cars mostly. Many also go with copy this or that without really knowing where to set it up, unless they are continuing with past experience, in some way. Yes, there is a lot to learn about these cars, from past racing setups and the people who knew what they were doing. I had racing blood in me, but nobody to guide me, and drifted into other things in life. Hardly any real experience, just able to see weaknesses as I go. Practically if you were to give me a car and all the stuff I needed to make it the way I want to set up, it would never be completed on time. I have ping ponged about so many small things, and some of which really would not matter on a street car, yet that racer in me may come alive, and I wouldn't want to break something or feel I could have done better. So, any who... until I put my mind into the rear section, I hope to utilise the setup you have shown with a wee mod, as I do want to keep things low profile and not make a gym setup under my car. |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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