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#1
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adjusting caster
So I need my memory refreshed......on an "A" body....
If I want to add positive caster without messing up anything else, removing a shim from the front bolt and adding it to the rear bolt does the trick, right? Also, any idea what the relationship of the shim thickness and the change in caster is, if the above is true? George
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"...out to my ol'55, I pulled away slowly, feeling so holy, god knows i was feeling alive"....written by Tom Wait from the Eagles' Live From The Forum |
#2
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Generally yes all cars trucks the further in the rear of the control arm goes the more positive caster you get. Limiting factor to get a lot of positive caster is bolt length or hitting steering shaft with the back of the control arm
My Firebird shop manual actually has a whole page chart of how many shims to add/subtract front and rear to get from one setting measured to where you want it. I'll tak a look and see what it is.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
#3
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Your method will add possitve caster, yes. Whether it effects other angles, that's hard to say.
Depending on how the car is currently aligned, that may or not may not be possible. There's just not much adjustment with stock components. It becomes easier however as you dial in static negative camber. This, due to extra stacking of shims, that then allow you to remove shims or add them. I wouldn't know where to start on the relationship of shim thickness to angle changes. I know that it's not a 1:1 ratio. Given the changes you are trying to make, I'd opt to have a full alignment done. Either by a shop you trust or by yourself. Speedway makes an economy camber/caster gauge that doesn't break the bank at under $50.00. https://www.speedwaymotors.com/Speed...iABEgJBP_D_BwE As I mentioned before, I'm not certain about your method not changing the camber angle. If you are looking at the upper control arm top down, based on where the alignment measurements are occurring, the ball joint is moving in an arc and is fixed to the spindle. This means that as you add positive caster, you're moving the ball joint along that arc, about the center of the upper control arm pickup points. Since the spindle doesn't stretch, moving in this arc will pull the arms closer together. Since the lower control arm is not pivoting around the arc, this will also tend to move the spindle inboard, creating additional negative camber. That's actually how caster works in the first place and why on this type of suspension setup, you want more. This action on the spindle will also have some effect on the toe setting as the spindle relationship to the steering components has now statically changed. Now is the maybe degree or so of extra caster angle you're adding going to make that big of a difference? I don't know, but I wouldn't think so. But another reason to do the whole alignment when doing this.
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-Jason 1969 Pontiac Firebird |
#4
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As Jason said one change actually tweaks all the settings. Toe in camber and caster.
I've tried some of the less expensive front end gauges ended up best was a Longacre that has dual "bubbles. The a less expensive($100) ebay adjustable wheel attachment as the Longacre has a magnetic base-an does not work on aluminum wheels.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
#5
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Quote:
I have some work to do to my truck, which does have aluminum wheels. K
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'63 LeMans Convertible '63 Grand Prix '65 GTO - original, unrestored, Dad was original owner, 5000 original mile Royal Pontiac factory racer '74 Chevelle - original owner, 9.85 @ 136 mph besthttp://www.superchevy.com/features/s...hevy-chevelle/ My Pontiac Story: http://forums.maxperformanceinc.com/...d.php?t=560524 "Intro from an old Assembly Plant Guy":http://67-72chevytrucks.com/vboard/s...d.php?t=342926 |
#6
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George,
You are correct. But it also changes toe in & camber. I played around with my 66 with the shim trick [ one shim ] & didn't notice any difference driving the car. Not until I bought aftermarket upper arms that were adjustable & I was able to set caster at 4* did I notice two things: better straight line stability & some steering return on corners [ power steering; probably more noticeable with man steering ]. I used SPC adjustable upper arms, as they were the only adj arms I could find that had rubber bushes, something that I think GM got right... |
#7
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Latech,
No one 'çaught' it because there was nothing to be caught... George's assumption was correct. |
#8
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I just realized why.The cross shaft being inboard of the mount, not outboard. It sucks not remembering details like that Like I havent done an alignment in 100 years Sometimes I just miss the obvious. Guess I shoulda raised the hood. Geez |
#9
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Here is the shop manual chart.
__________________
Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
#10
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Thanks all for the responses.
First, I'm not against getting a proper alignment done, this is more of an experiment to see if more caster would be beneficial. If so, that would be my target when I take it to an alignment shop. The existing alignment was done REALLY long ago so I don't even know what it is, therefore it needs to be done anyway. Assuming it is at OEM specs, (that's what a shop would normally do, right), just shotgunning it towards a target number was my thought, hence the idea of knowing what shim sizes would need to move. I'll use the chart to try some adjustments, but a question: for better handling on an otherwise stock setup, what would be some good target numbers for caster, camber, toe? Thanks again. george
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"...out to my ol'55, I pulled away slowly, feeling so holy, god knows i was feeling alive"....written by Tom Wait from the Eagles' Live From The Forum |
#11
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HOW MUCH negative camber is up for discussion. So far as I'm concerned, the most-negative camber according to OEM spec is the most-positive I'd want. In other words, if the OEM spec for camber is +2 to -1/4, I would want to be at -1/4 to -1/2, maybe as much as -1 depending on the suspension geometry and intended use. I don't get too worried about tire wear at 1/2 degree, I have some concern at 1 degree or more. If you're driving a grocery-getter, you look for maximum tire life. If you're looking for cornering power, some tire life gets sacrificed. Remember, the engineers and lawyers DELIBERATELY sabotaged the handling of these cars when they were designed. They would build-in boatloads of understeer in order to absolutely prevent oversteer. Part of that was spring rates, sway-bar and tire sizing, but some of that was adding too damn much positive camber. There's also the issue of dynamic camber change--tall and soft springs coupled to too-short steering knuckles leads to lots of body roll. Lots of body roll leads to positive-going camber change on the outside, load-bearing wheel, only some of which is removed as the outside suspension compresses on the turn. Camber is a tire-wearing angle. It will also cause "pull". Caster is not a tire wearing angle, but also causes "pull"--but it takes twice the caster to pull as much as camber. Used to be, cars were intentionally aligned to pull slightly left. Roads were "crowned", so the roadway itself made the car drift to the right. Highway engineers are taking the crown out of the roadway in favor of humps and dips. I don't approve, but no-one asked my permission. Given a choice, I like to have a vehicle that will drift VERY SLIGHTLY to the right on typical roadways. Driver falls asleep, he hits the ditch instead of oncoming traffic. IN GENERAL, a 1/4 degree difference in camber L/R, or a 1/2 degree difference in caster l/R was used for road-crown compensation. I'm not sure that much difference is needed any more as roads have less crown. The trick is to get the camber where you want it, while maximizing positive caster. Positive caster makes for strong self-centering of the steering, and also increased steering effort--but these cars had way too much steering assist to begin with, so extra effort is a non-issue. Then a minimal amount of toe especially with wide tires. Too much toe wears tires really fast, and makes for wildly unpredictable handling--twitchy, darty, won't-go-straight. With rear-wheel drive, toe-in partially compensates for worn steering joints and loose wheel bearings. If the suspension/steering is still "tight",--and it better be--you don't need a lot of toe. Last edited by Schurkey; 08-17-2019 at 02:39 PM. |
#12
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#13
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So far as I know, I've never read the Hunter book. But maybe that's what the Vo-Tech used for a textbook... |
#14
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Keith the wheel attachment works great and is adjustable and get tight on the wheel. Really makes it easy and repeatable. I had bought one of those Quick Trick Aligment kits that has a bracket to attach to the wheel but does not really grip it well. Also uses a level on the bracket to measure for camber and cater sweep. Since the bracket just hangs there is way too much freeplay to be repeatable. It is good for measuring toe in/out. You can put the tires on double plastic bags for a cheap turntable but you can get cheap ones on E bay also.
Did the aligment on the Camaro IA and at 120 straight as an arrow.
__________________
Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
#15
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Thanks Shurkey.
George
__________________
"...out to my ol'55, I pulled away slowly, feeling so holy, god knows i was feeling alive"....written by Tom Wait from the Eagles' Live From The Forum |
#16
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They make offset cross shafts for the upper control arms that some refer to as "camber savers". These will help get some positive camber back for sagging frame issues but will also allow more adjustment for positive caster. Helps when you're trying to get some positive caster with stock control arms.
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'71 GTO, 406 CID, 60916, 1.65 HS, '69 #46 Heads 230CFM, 800CFM Q-jet, TH400, 12 Bolt 3.55 '72 Lemans, Lucerne Blue, WU2, T41, L78, M22, G80 |
#17
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I installed upper conrol arms that have the offset caster built in.Worth every penny.
Also I opted to run the howe upper ball joints with the .5 inch longer stud to curb the camber jumping so far postive when suspension is compressed. ( Raises the pivot point for the upper control arm / upper ball joint ) The car drives completly different.Thank God, cause it sure drove like crap before. 4 degrees caster, .5 degree negative camber, 1/8 inch toe in. |
#18
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The suspension geometry has imaginary angles through the joints and tire contact patch, which intersect at the so-called "roll center". When drawn in a "front view", you find that the roll center of the vehicle can be UNDERGROUND due to poor choices for locating the various pivot points. The roll center interacts with the height of the center of gravity. The greater the distance between them, the longer the imaginary "lever arm" that makes the vehicle lean in corners. Leaning in corners does nothing good for those suspension angles you tell the alignment guy you want. Leaning in corners is EXCELLENT for telling Doofus Drivers that they're about to lose control of the vehicle, and "slow the hell down, you idiot." GM, Ford, Chrysler, and all the others DELIBERATELY trade away cornering power in order to provide "excessive" warning to the driver regarding his "aggressive driving.". Shortening that lever arm is CRUCIAL for good handling. You can shorten the arm by lowering the center of gravity--remove weight above the CG: scrap the iron intake manifold and exhaust manifolds for an aftermarket aluminum intake and headers; or installing "tall ball joints" on the LOWERS or shorter springs to lower the whole car. Conversely, you can RAISE THE ROLL CENTER by dicking with the angles the control arms operate at--"Tall spindle" disc brake conversion, "Tall upper ball joints" or doing the "Guldstand Modification" to the upper control arm mounting bracket, as popular on the old F-body. Anything you do to shorten the distance between C.G. and roll center is like adding a stiffer sway bar--without any of the drawbacks to a stiff sway bar such as added weight, bulk, and the partial loss of independent action between left and right suspension. When the C.G. is lowered, and the roll center raised appropriately, you don't need super-stiff springs for handling. A reasonably-soft spring makes for good "ride", while the suspension geometry--not too-stiff springs and sway bars--keeps weight split among all four tires instead of under-loading the inside and over-loading the outside tires. SOME lean in corners provides necessary feedback for the driver. https://www.pro-touring.com/threads/...-Mod-Templates Last edited by Schurkey; 08-18-2019 at 02:57 PM. |
#19
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George, call Mark at SC&C.
You can get maybe 2 degrees positive caster max. What ever the factory recommends in negative you can take it to positive but that's the max. Do not pile shims under that back bolt like an idiot!! You will screw up the suspension plot. Think of a door with two hinges with two inches of shims under one of the hinges. Hows it going to swing? Its the same with your upper control arm except your caster will be changing as the suspension cycles.. Those things have enough bumpsteer! I would take it to a shop with a Hunter Hawk eye rack. Tell them. Caster positive driver side +1.5 passenger side +2 Camber negative .75 to 1 degree. Toe in 1/32 both sides.. Call Mark.. Polona Semper Fi Brother!! |
#20
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Gilstrand Mod YUCK!!!!!
I got to get the F out of here !!!! |
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