Bumpsteer .... The topic that won't die
Racer
Joined: Sep 2002
Posts: 462
Likes: 1
From: York PA
Re: Bumpsteer .... The topic that won't die (427V8)
Hmmm...these threads have been interesting reading. About all I really understand is that Bumpsteer is something which maneuvers a suspension topic to the top of the thread postings every few weeks... :jester
Seriously, though, fascinating subject. Thanks to all.
Seriously, though, fascinating subject. Thanks to all.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Re: Bumpsteer .... The topic that won't die (norvalwilhelm)
UHH, Norval, if you look closely at your front and rear rotors, you will find a subtle differance, they can be looked at all day while on the car and you will not see it, take them off, and you find the REAR rotors are 1/4 inch thick at the mounting face/flange where the lug studs stick through....and the fronts are about 3/8 thick allmost.....that gives a 1/8 inch offset to the rotor when switching them around, hense your idea with the boss/offset thing on the spindles....
I dunno why the general did that, except someone was in a hurry in the initial design way back in 63 or so for the 65 model, and so they created two part numbers, and that is the differance....
don't ask me how I know, I scratched my azz for about two hours trying to find out why those rotors would not fit the pads on my car....
talk about sneakey, that's it.....
GENE
I dunno why the general did that, except someone was in a hurry in the initial design way back in 63 or so for the 65 model, and so they created two part numbers, and that is the differance....
don't ask me how I know, I scratched my azz for about two hours trying to find out why those rotors would not fit the pads on my car....
talk about sneakey, that's it.....
GENE
Race Director
Joined: Dec 1999
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Re: Bumpsteer .... The topic that won't die (mrvette)
:withstupid:
I noticed the same thing after gene told me this some time ago, I hadn't noticed it before, so I went and measured and lo and behold they''re different
I noticed the same thing after gene told me this some time ago, I hadn't noticed it before, so I went and measured and lo and behold they''re different
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
Re: Bumpsteer .... The topic that won't die (Twin_Turbo)
Thanks Gene. It could be that over the years I mixed the back and front rotors up. I did remachine all 4 rotors at one time to remove 3 pounds per rotor to cut the weight down.
Once the rotors are installed I check the clearance front and back of the caliper to make sure the rotor is in the middle and not pushing to one side.
I found both my fronts needed the caliper moved towards the centerline about 1/16-1/8th of an inch.
Once the rotors are installed I check the clearance front and back of the caliper to make sure the rotor is in the middle and not pushing to one side.
I found both my fronts needed the caliper moved towards the centerline about 1/16-1/8th of an inch.
Thread Starter
C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
Likes: 2
From: Twin Cities Minnesota
Re: Bumpsteer .... The topic that won't die (norvalwilhelm)
Norv,
those spindles look pretty nice. I can't wait to hear what they do to the roll center and the camber curve.
one of the things I plan on doing, maybe this weekend, is to baseline the Camber curve, so when you put in your new spindles we can see how much of a change they made.
Gene,
thats scary! I wonder how many Vettes have them mixed up?
those spindles look pretty nice. I can't wait to hear what they do to the roll center and the camber curve.
one of the things I plan on doing, maybe this weekend, is to baseline the Camber curve, so when you put in your new spindles we can see how much of a change they made.
Gene,
thats scary! I wonder how many Vettes have them mixed up?
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Re: Bumpsteer .... The topic that won't die (427V8)
427, I would imagine not many as when the pads are new, and the pistons pushed back into the calipers, the rotor better damn well be in the center os the assy or the pads will not allow it to work....I would say damn near no one had them mixed up.....certainly can't get a rear rotor on the front, anyway....like I said, don't ask how exactly I know this.....
I don't mind broad learning curves, but it's better spend on learning the curves of a broad if you get my drift......
but on a highly wrung out modified car like Norvals with that machine work in the rear spindle area that he did, all bets on anything are off.....hell, he got a custom everything there, damn near....
GENE
I don't mind broad learning curves, but it's better spend on learning the curves of a broad if you get my drift......
but on a highly wrung out modified car like Norvals with that machine work in the rear spindle area that he did, all bets on anything are off.....hell, he got a custom everything there, damn near....
GENE
Race Director
Joined: Nov 2000
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From: Waterloo ontario Canada
Re: Bumpsteer .... The topic that won't die (mrvette)
Having the caliper riding 1/16-1/8th of an inch off center of the rotor won't hurt anything. All the happens is one set of pisons ride further in/out then the other set. But if it is easy to change, take me 5 minutes to machine 1/8th off this boss why not do it.
One thing that I don't think anyone but redvetracr and myself have done is plate over the hole on the frame on the outside of the steering box. This area is extremely weak/flexable. Just have a steering control valve not balance and the wheel going back and forth and this area flexes like it is make of paper,'
I plated over the outside and underside to strengthen this area. Makes for quicker response to steering input.
Look at this site guys and look under chassie for tips on helping our frames http://www.corvettefaq.com/susp.asp
I intend to remove my entire front suspension, add a spreader bar. reweld the area around the towers and lower mounting points of the trailing arms, box the frame where the sway bar bolts, beef up the lower mount for the sway bar on the A arm and gusset everything. Alot of paint to remove, cracks to clean out then mig weld everything.
One thing that I don't think anyone but redvetracr and myself have done is plate over the hole on the frame on the outside of the steering box. This area is extremely weak/flexable. Just have a steering control valve not balance and the wheel going back and forth and this area flexes like it is make of paper,'
I plated over the outside and underside to strengthen this area. Makes for quicker response to steering input.
Look at this site guys and look under chassie for tips on helping our frames http://www.corvettefaq.com/susp.asp
I intend to remove my entire front suspension, add a spreader bar. reweld the area around the towers and lower mounting points of the trailing arms, box the frame where the sway bar bolts, beef up the lower mount for the sway bar on the A arm and gusset everything. Alot of paint to remove, cracks to clean out then mig weld everything.
Instructor
Joined: May 2003
Posts: 249
Likes: 0
From: atlanta GA
Re: Bumpsteer .... The topic that won't die (norvalwilhelm)
I've been thinking alot about this bumpsteer thing lately. I think my first idea will work with steeroids. My second idea involves the recirculating ball system.
This is a pic of mustang II suspension, but the idea is the same...
Let's call the ball joint side of the lower a-arm point 1, and the right side point 2 :skep:
Now let's place a tie rod directly in front or behind the lower a-arm with one end of the rod in line with point 1 and the other in line with point 2.
(The tricky part) Modify the spindle so that it has a steering arm that reaches down and connects with the tie rod in line with point 1.
At point 2 move the steeroids mounting plate (the one on the hydrolic pump) until it can connect with the tie rod.
Because the tie rod is on the same plane as the lower a-arm and pivots at the same points, there should be no bumpsteer when the car is pointed straight forward. It moves exactly like the a-arm.
There's more, but I want to see if I am making any sense so far.
Comments?
[Modified by applevette, 10:53 PM 11/19/2003]
This is a pic of mustang II suspension, but the idea is the same...
Let's call the ball joint side of the lower a-arm point 1, and the right side point 2 :skep:
Now let's place a tie rod directly in front or behind the lower a-arm with one end of the rod in line with point 1 and the other in line with point 2.
(The tricky part) Modify the spindle so that it has a steering arm that reaches down and connects with the tie rod in line with point 1.
At point 2 move the steeroids mounting plate (the one on the hydrolic pump) until it can connect with the tie rod.
Because the tie rod is on the same plane as the lower a-arm and pivots at the same points, there should be no bumpsteer when the car is pointed straight forward. It moves exactly like the a-arm.
There's more, but I want to see if I am making any sense so far.
Comments?
[Modified by applevette, 10:53 PM 11/19/2003]
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Race Director
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Re: Bumpsteer .... The topic that won't die (applevette)
no need to place the tie rod in line with the lower arm, as long as it's parrallel and the correct length you'll be fine. Correct length is determined by a line from upper to lower cross shaft and a line through upper and lower balljoint. Where the line parrallel with the lwoer arm intersects is where you want your pivot points in the steerin setup (the outer one is alredy correct with the stock steering knuckle) Read through the older topics, there''s lots of pics in there with the drawings.
Thread Starter
C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
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From: Twin Cities Minnesota
Re: Bumpsteer .... The topic that won't die (Twin_Turbo)
In fact you can't say for sure that you want the tie rod parallel with the lower A-arm, cause what really matters is that the tie rod moves in the same arc as described by the combination of the upper A-am and the lower A-arm :crazy:
And I'm talking about within .050" or so I think!
I'll know more precisely when I do more testing...
And I'm talking about within .050" or so I think!
I'll know more precisely when I do more testing...
Race Director
Joined: Dec 1999
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Re: Bumpsteer .... The topic that won't die (427V8)
yeah, okay it''s a generalisation. If you want to do it absolutely right you have to find the instantaneous center, then draw the lines from upper to lwoer balljoint and upper to lower cross shaft, determint the rack height and set the pivot point on the rack to intersect with the line from upper to lower cross shaft. Then extend the IC to this point and on to the line from balljoint to balljoint. The intersectionn point there is where the balljoint center on the steering arm side must be.
The parrallel assumption is a rule of thumb used because most tie rods are either very close or just above the lower arm, most modern (..ooops corvette falls out of this category LOL) have lower arms that are almost vertical so the tie rods are too.
Doing it with the IC will ensire the proper arch on the tie rod. However, it takes VERY carefull measurement and you can''t transfer it from one car to another. Measure everything as good as you can, a little error can already upset the design.
The parrallel assumption is a rule of thumb used because most tie rods are either very close or just above the lower arm, most modern (..ooops corvette falls out of this category LOL) have lower arms that are almost vertical so the tie rods are too.
Doing it with the IC will ensire the proper arch on the tie rod. However, it takes VERY carefull measurement and you can''t transfer it from one car to another. Measure everything as good as you can, a little error can already upset the design.
Race Director
Joined: Nov 2000
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From: Waterloo ontario Canada
Re: Bumpsteer .... The topic that won't die (applevette)
The tie rod MUST point to the instantanous center and be of the correct length for zero pump steer. Any one of these being off and you do not have zero bump. The tie rod is often make parallel to the lower A arm because the lower A arm always points to the instantanous center. If you are above or below the A arm you must raise or lower one of the tie rods to point to this center. Charts show which direction to raise/lower by looking at the bump curve.
Twin Turbo it is too late to really put thought into your idea but tomorrow I will certainly try to understand what you are saying.
For a kid of only 28 you seem to really know you stuff. :lol: :lol: :lol:
That's a joke Twin turbo.
Have a nice evening.
Twin Turbo it is too late to really put thought into your idea but tomorrow I will certainly try to understand what you are saying.
For a kid of only 28 you seem to really know you stuff. :lol: :lol: :lol:
That's a joke Twin turbo.
Have a nice evening.
Instructor
Joined: May 2003
Posts: 249
Likes: 0
From: atlanta GA
Re: Bumpsteer .... The topic that won't die (norvalwilhelm)
Norval-
"The tie rod MUST point to the instantanous center and be of the correct length for zero pump steer..." "...the lower A arm always points to the instantanous center."
So does this mean that my idea, provided the length of the tie rod is correct, will work also? Or am I just being dense?
"The tie rod MUST point to the instantanous center and be of the correct length for zero pump steer..." "...the lower A arm always points to the instantanous center."
So does this mean that my idea, provided the length of the tie rod is correct, will work also? Or am I just being dense?
Drifting
Joined: Oct 2002
Posts: 1,818
Likes: 13
From: ar
Re: Bumpsteer .... The topic that won't die (427V8)
I have been following the bump steer discussion for some time now and it seems to have really come up since everyone is trying to put a rack on our rear steer vettes. My question is , is the bumpsteer on our stock chassis that makes the c2-3 drive funny or is it the old design of a slave power assisted steering system?
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Re: Bumpsteer .... The topic that won't die (silverslashstreak)
Well SilverSS, I see you from Mena Ark.....home of Street/Performance...
you work there??? they used to do a lot with pulleys and engines, and TPI a few years ago....been a while since I got a catalogue....
Yeh, the front ends and also the IRS are open topics to us more advanced hotrodders here, all sorts of good information from a bunch of smart guys....
Pete79L82 is one, Norval is another, 427 is a good source too....just to name a few....
IMO, the original steering was fine in it's day, well before even radial tires were common, but with modern tires, well some of the inadequacies show up, just one of them is the tendency even with new steering/suspension work/parts to follow the truck ditches in the roads at speed....huge problem here in Florida with all this sand underneath....I was constantly fighting the issue, and cured it with a rack....I think it's due to the valve in the hydraulic assist of the old original design, that and the olde tyme suspensions....
GENE
you work there??? they used to do a lot with pulleys and engines, and TPI a few years ago....been a while since I got a catalogue....
Yeh, the front ends and also the IRS are open topics to us more advanced hotrodders here, all sorts of good information from a bunch of smart guys....
Pete79L82 is one, Norval is another, 427 is a good source too....just to name a few....
IMO, the original steering was fine in it's day, well before even radial tires were common, but with modern tires, well some of the inadequacies show up, just one of them is the tendency even with new steering/suspension work/parts to follow the truck ditches in the roads at speed....huge problem here in Florida with all this sand underneath....I was constantly fighting the issue, and cured it with a rack....I think it's due to the valve in the hydraulic assist of the old original design, that and the olde tyme suspensions....
GENE
Race Director
Joined: Dec 1999
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Likes: 9
Re: Bumpsteer .... The topic that won't die (norvalwilhelm)
The tie rod MUST point to the instantanous center and be of the correct length for zero pump steer. Any one of these being off and you do not have zero bump. The tie rod is often make parallel to the lower A arm because the lower A arm always points to the instantanous center. If you are above or below the A arm you must raise or lower one of the tie rods to point to this center. Charts show which direction to raise/lower by looking at the bump curve.
Twin Turbo it is too late to really put thought into your idea but tomorrow I will certainly try to understand what you are saying.
For a kid of only 28 you seem to really know you stuff. :lol: :lol: :lol:
That's a joke Twin turbo.
Have a nice evening.
Twin Turbo it is too late to really put thought into your idea but tomorrow I will certainly try to understand what you are saying.
For a kid of only 28 you seem to really know you stuff. :lol: :lol: :lol:
That's a joke Twin turbo.
Have a nice evening.
:thumbs:
Thread Starter
C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
Likes: 2
From: Twin Cities Minnesota
Re: Bumpsteer .... The topic that won't die (norvalwilhelm)
It does? Cool I never knew that. It does explain some things tho...
Norval said
Thats two of the reasons!
Being rear steer in it's self has a lot to do with the squirrlyness due to what happens when bushings deflect on a rearsteer car vs a front steer car...
But I think Bumpsteer is a pretty good bang for the buck!
SSS Said
[Modified by 427V8, 8:02 AM 11/20/2003]
Norval said
The tie rod is often make parallel to the lower A arm because the lower A arm always points to the instantanous center.
Being rear steer in it's self has a lot to do with the squirrlyness due to what happens when bushings deflect on a rearsteer car vs a front steer car...
But I think Bumpsteer is a pretty good bang for the buck!
SSS Said
I have been following the bump steer discussion for some time now and it seems to have really come up since everyone is trying to put a rack on our rear steer vettes. My question is , is the bumpsteer on our stock chassis that makes the c2-3 drive funny or is it the old design of a slave power assisted steering system?
[Modified by 427V8, 8:02 AM 11/20/2003]