On a significantly lowered C-3 (short springs in front, long bolts in rear) How do adjust out bump steer? I've seen the VBP kit but I don't actually know what it does. Any info would be appreciated.

 

Norval once said those kits were no good, but i can't really comment myself.

 

i belive that you want the tie rods to be parallel to the lower control arms and the strut rods to be parallel to the half shafts.

 

I think a lot of problems are caused by play in any of the suspension parts, control arms, tie rods, ball joints wheel bearings, etc. when i changed my front end suspension for a transverse spring and new U&L C/ARMS my bump steer was 99% cured. It's hard to see movement on the car with C/ARMS but i did notice the very slight movement on one when itwas removed. So i'd check other parts as well. Whats the condition of your suspension like at the moment.
Peter

 

The bump steer blocks aren't perfect, but they do yield a significant improvement over the stock geometry. Jason Staley plotted before and after on his C3.

BTW, there was some confusion over how Ackerman is effected. Looking back, it may have been incorrectly implied that it was reduced by installing the blocks, but I believe it would actually be increased as the effective steering knuckle to tie-rod link point is moved inward from stock. Since the C3 has rear steer, that means increased Ackerman, which should improve low-speed turn-in.

 

All parts are almost new. I don't know If there's going to be bump steer or not...I'm looking for how to check for it and if there is, how to correct it.

 

Makes sense to me. How do you plot it? Measure toe wit the suspension being loaded and unloaded? Do you pull the springs?
Thanks

 

Before starting, make certain to accurately measure your static Z-height so you'll know where in travel the zero bump/droop point is. Of course, you'll need to purchase or make a bump-steer fixture. I've seen several ways to go about doing this, but I really like the idea of mounting a plate directly on the hub and using a stand with dual dial indicators rather than attempting to keep some board in place against a wheel or tire and measuring gaps.

Below is an in-depth article on the proceedure. Longacre is one of the top providers of racing alignment equipment.

http://www.longacreracing.com/articles/art.asp?ARTID=13



edit - found the plot I mentioned earlier, credit to Jason...

 

Search the archives. Norval & TT had extensive conversations on this a year or 2 ago.

 

I sure do appreciate the input...My "Z" dimension is 1 inch. I've cut 1/2 coil off a VBP 550# spring which now has a free length of 11 1/2". I will be removing the springs again because I'm looking at a higher spring rate for the front. Correct me if I'm wrong. I could plot toe with the springs removed and suspension reassembled. i know it's a little bit of work but I will have it apart again anyways.

Here's a new question. If my 550+ springs have a free length of 11 1/2 inches and a compressed length (between crossmember and lower A-arm unloaded) of about 10 1/2 inches, the best I could measure. If I use a higher spring rate of let's say 800#'s It has to have a free length of atleast the 10 1/2", correct? or it could become loose on full unloading (if I'm airborne). I'm concerned that that free length will raise the front of the car under static load. could i use a slightly shorter spring or am I asking for trouble? Thoughts, comments...

 

Airborne? Do you run at Grattan Raceway? JK; there's a jump just before turn 5 there.

Yes, removing the springs for the bump-steer plot (and other homework) makes it easier.

I'm assuming you mean your compressed length in full droop is 10.5" (bump-stops in or out?). Yes, a spring with a free length less than that could rattle about, but I should think it would take more than fractions of an inch for anything to move. Never tried to find out just how much was necessary firsthand, tho.

Don't remember all the numbers, but years ago when I got tired of bottoming out and repairing/replacing oil pans and such due to the 550's being inadequate, I stepped up to Daytona's (860#+) I purchased from Guldstrand (great source). They were long enough that I had to cut off about 3/4 of a coil, if I recall correctly, to get my Z-height down to Chevy Power specs, having an iron BB block & heads. No un-seating issues. If I had my spring lengths I'd share, but it's going to be a while before my coils come back out for any post weight-loss adjustments.

 

Here's the tool I used to measure the bump steer on my 76. It's pretty good for the money. If you had to use it alot, I'd go with one of the more expensive units, but for the home hobbiest its a pretty good unit. Just drill your bolt pattern in the plate and its very easy to use. The plate is marked every 1/4". Just move the suspension up and down thru its range of travel and take the readings off the two dial indicators. I did mine like 3 times to get rid of any measurement errors.

http://www.racerpartswholesale.com/p...mp_Steer_Gauge

 

Jason,
Thanks for the link, looks pretty straight forward. I appreciate the help.

 

[QUOTE=TheSkunkWorks;1563379198]Airborne? Do you run at Grattan Raceway? JK; there's a jump just before turn 5 there.


I raced a CP Datsun there a looong time ago. I'll check out the the Daytona springs. Our track out here in Albuquerque has this nasty hump and off camber down side where the roadrace track joins the circle track. Getting airborne is a reality. We have miles and miles of desert and they crammed a 1.8 mile roadcourse and two ovals onto a postage stamp. There are several nasty spots and a lot of walls. I really miss my old Elkart Lake but not the snow.

I appreciate all the help. I've been trying to set up this old '73 for fun running and I hate to do things over because I should've known better. It's why I ask a lot of questions.

My other challenge is going to 17" wheels and tires and getting away from the 10X15's. I've been mocking up and test fitting spacers and wheels off my '99 with Z-06 wheels to see what backspacing I can get away with and be able to put wide enough tires on new rims. It looks like I can run 295-35-17's on 9.5X17's on the front with a 3.75-4.0 BS and 335-30-17's on 11X17's with a 4.5 BS on the rears. Any comments would be appreciated.

 

NMsharkracer, those sound like the same Vintage Wheel Works sizes I'm looking at, in the V48 series, tho not necessarily with the same BS's. Haven't bothered to nail down exact tire sizes yet, knowing that my selection today may not be available when I get to that point.

The rule of thumb being to have tread widths no wider than bead widths, so as not to reintroduce sidewall instability back into the picture, I believe if you check the 295's and 335's are a bit beyond that point for 9.5's and 11's, respectively.

I'm missing RA, Elkhart Lake and Siebken's myself.

 

SkunkWorks Siebkens was a blast. I started corner working at Elkhart Lake in '66. I was in SCCA and we worked all the Goup 7 "CanAm" races. Saw some really wild machinery back in those days, Chaparrals, McLarens, home-builts...there were so few rules..just a lot of fun.

Regarding the wheel/tire size and back spacing, I did a test fit of the Z-06 wheels and found that there was JUST a little over 5" of BS clearance to the spring. With the flares, I thought I'd give myself some wiggle room for movement and use 4.5" BS. With 4" BS on the front, the test tire would just polish the side of the frame and scuff the inner fender at full lock. I've notched the inner fenders for my old tire/wheel setup. a 3.75 BS would again just give a little clearance. I'm still kicking around the tire sizes. Hoosier said the 295, 335 setup would be OK for the rim sizes, but I'm not getting the same warm and fuzzy from Kumho, I may have to go with 275, 315's instead. From your picture, you aren't running flares, correct? You're going to have a more challenging fit with 11" in the rear?

Brother-in-law lives near Germantown, he's into Mustang restoratations so when we visit, I give him a lot of grief. Next time we're headed over that way to see them, I'll let you know and I'll buy the beer for all your help.
Jack

 

De nada.

Yes, I will have to add some minimal flares if/when I can swing the 11's.

Just wondering, did you ever happen to see Redman's cat or add any rocks to his monument at 10?

Charlie

 

Charlie,
Brian Redman's cat story ...I vaguely remember a story. I think they sent new corner workers looking for it...I don't remember the monument at 10, that was the "Kink", right? It's been a very long time and the memory has gotten a little fuzzy. I did help push Mario off the track, at corner 13. He was leading in a Ferrari last lap last corner and ran out of gas. He was so angry he threw his helmet in the woods. We pushed him out of the way. After we got the car hooked up, we went back to the paddock. It dawned on a couple of us that his helmet was out there so we ran back and searched for an hour. I'm sure some spectator got it. Oh well.
have a great New Year...Jack

 

Duh! It just came back to me, the monument was for the Cat! I think there was a tombstone out there with something about a blurr of fur. There used to be a lot of drinking and the stories kept changing and growing. We used to go to Schwartz's in St. Anna's for the steaks and camped out at Firemans park.

 

The "Bloodshot Blur with Fur" was buried about 50-100' or so insidde the carousel's apex. He had long since passed when I first ran there in 1985, and stories were already sketchy as to his demise. I Googled "Redman's cat" and found this rather entertaining read...

http://www.september8th.com/news_br_cat.htm

Think I'll open a thread over in Autocrossing & Roadracing to see just what kind of tall tales may emerge.