Bump steer or... ?

Decurion · Jun 2, 2008

65 v8 manual centerlink measurement

Ive been having some trouble with my cars handling, and suspect it may be my "custom" center link. If someone has a 65 v8 manual steering center link, I would appreciate if you could measure the distance on center between the tie rods, and the distance between the pitman/idler holes. I bought a Mustang center link and cut it, but I may not have measured right or it may not have gotten cut/welded correct.

I tried to make a diagram of what I need, in case I was unclear.

View attachment 315794
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Ever since I put my car (65 Falcon) together last year, its handled terrible. After a simple oversight on my part, I fixed the problem and had it re-aligned and it drove MUCH better, but still not right. Its hard to describe how it handles, but if I accelerate hard the front end comes up and the steering gets real squirrly and stays that way until I stomp on the brakes, which brings the front end down.
The suspension is all new stock v8 stuff, except for 1" down, 1/8" back shelby drop and 1" sway bar. I dont remember alignment specs off hand, but it was at about 0.25*+ cam, 2.5*+ cas. At full droop (wheels off the ground) I measured 2 1/2" of toe in. This cant be right. WTF is going on here? The front tires have maybe 200 miles and its already eating the inside edge off and feathering like its got a ton of toe out. Ive already gone through a few times and rechecked torque on all tie rods and balljoints.

Decurion · Jun 2, 2008

Sitting at normal ride height, the wheels are straight, but if I put it on a jack, I get about 2.5" of toe in. There doesnt seem to be any difference between the sides, theyre about even, so I dont think its something like a bent spindle, and the tie rod sleeves are pretty close in length. Just for giggles I lifted up my DD (01 focus) and measured less than a 1/4" toe in at full droop.

bnickel · Jun 2, 2008

this is a common problem on early mustangs and falcons with granada brakes/spindles. is that what you have on your car? if so Degins has a granada kit specifically for the early cars that uses a different geometry spindle and if you already have all the rest of the parts i'll bet he'd sell you just the spindles.

if you don't have granada spindles it may have something to do with the control arm drop as the people who have done the granada swap and have this same problem only experience it after they've done the UCA drop, so maybe there is a problem with the drop itself or something.

Degins website is www.discbrakeswap.com BTW.

Decurion · Jun 3, 2008

Its got stock 64 drum spindles, all the linkage is for 65. I know the Falcon v8s had different steering linkage on the 63.5 and 64 versus the 65, but no change to the spindle as far as I know.

Pakrat · Jun 3, 2008

Just as a reference, a stock Mustang spec would be 1/4* positive caster, 3/4* positive camber and 3/16" toe in. With the Shelby drop the optimal setting changes to 2* positive caster, 0* to 1* negative camber and 1/8" toe in.

Opentracker · Jun 3, 2008

Pakrat said:
Just as a reference, a stock Mustang spec would be 1/4* positive caster, 3/4* positive camber and 3/16" toe in. With the Shelby drop the optimal setting changes to 2* positive caster, 0* to 1* negative camber and 1/8" toe in.

I go with that too, I bet it's an alignment problem. We run the same settings on all of our street cars.

0 - camber

2deg. pos. caster

1/8" toe-in

If the car was set to factory settings, that is for sure your proeblem.

John

rbohm · Jun 3, 2008

it sounds like you tightened the lower control arm bolts with the car up in the air rather than on the ground. loosen the bolts up, then with the car on the ground, bounce it a few times and let it settle, then tighten the lower control arm bolts.

Decurion · Jun 3, 2008

rbohm (...how you spose to say that anyway?)
Thats a good point, Im sure a lot of people dont think of that. However, I have done a lot of prototype and vehicle development, particularly vehicle dynamics work for Ford and Chrysler, and I got my @$$-hole reamed one time when I first started for not setting a 3500 on the ground when I tightened the bolts on a set of leaf springs I swapped. Those engineers were PISSED! So yes it was on the ground at ride height when I tightened the control arms.

The spindles were on another car and it handled exactly the same way my car does now, BUT it also had an upper control arm shaft that was falling out, so I cant say for sure its the spindles that are the problem. Ive examined them pretty close and cant find anything, but I guess anythings possible. Anyone have a set of bare 65 spindles for sale? Anyone in the Detroit area want to LOAN me a set? This is such a discouraging problem.

rbohm · Jun 3, 2008

did you use granada spindles? if you did that could also be part of the problem. it seems that sometimes using granada spindles in conjunction with the shelby mod causes issues like you have. it doesnt always happen, but it is one more thing to consider.

Decurion · Jun 4, 2008

First post updated.

Decurion · Jun 17, 2008

I think Ive figured out the problem. It turns out I had a few things working together. What I did was pulled the spring/shock out, disco'd the sway bar and put a long rod on in place of the wheel so I could move the suspension from stop to stop easily and watch how much toe changed. It turns out my center link being cut almost an inch too short was a small problem, but by itself probly wouldnt have done much. I think the 64 spindles have a higher steering arm placement, similar to Granadas, which probly wouldnt do much by itself. The car has fiberglass fenders and hood along with mustang gt springs, which made it sit kinda nose-high which is where I noticed the most toe change (when the suspension is in the bottom half of its travel), which I dont think would be any real concern by itself. The big kicker, I believe, was the Shelby drop. Each problem alone was likely not enough to cause a noticeable problem, but each compounded the other combined with the Shelby drop which is known to magnify other problems, i.e. bumpsteer. I put the control arms back in the stock location, recentered the center link (effectively making one side correct, and the other side an inch off), and bumpsteer on the corrected side was almost cut in half according to my measurements. I ordered a new center link and cut a half coil out of the springs, so when the CL gets here I can get the car re-aligned. As for the spindles, Ill take a chance that theyll be fine. Ive checked em over and measured everything I can and alignment shims are pretty even on both sides, so it seems unlikely the spindles are bent. If after an alignment the car still doesnt go straight, its gonna be one expensive way to roast marshmallows.

So the morals to the story here are:
1) measure (at least) twice, cut once
2) just cuz everything is new, doesnt mean its gonna work
3) just cuz you think it will, doesnt mean its gonna work
4) what can go wrong, will
5) if you want a fast/fun car and have minimal time/space/patience/sanity, for Crissake, buy one already finished!

CraigMBA · Jun 17, 2008

You should of cycled the suspension with the shock installed. It controls how much downtravel you have. I would suggest you do it again with the shock installed. It won't cost anything.

I guess what I'm trying to say is the bump steer you observed may not actually occur within the travel (that is limited when the shock is installed).

Since you are modifying the drag link a second time, I'd reinstall the shelby drop, and widen the old drag link to the correct length, and then bend the ends of the drag link untill you remove all of the bump steer. When you build the new one, bend it so that the ends are the same height as the sacrifical one. That way you can have the benifits of the shelby drop, stock ball joints, and a 'correct' bump steer curve. It won't cost anything other than time.

Decurion · Jun 18, 2008

CraigMBA said:
bend the ends of the drag link untill you remove all of the bump steer.

Hmm... thats not a bad idea. I just dont feel like taking the damn spring out again. Im kinda frustrated with the whole car, so I think Ill just leave well enough alone (assuming it works) and use the lesson learned on my other car.

Decurion · Jul 6, 2008

Looks like the center link was the culprit here. Im sure the shelby drop was contributing, but replacing the center link with one cut to the right dimensions has finally yielded a driveable car! I havent aligned it yet, but I set toe (caster/camber still way off, but even between sides) and so far it handles like a new car.

degins · Jul 6, 2008

bnickel said:
this is a common problem on early mustangs and falcons with granada brakes/spindles. is that what you have on your car? if so Degins has a granada kit specifically for the early cars that uses a different geometry spindle and if you already have all the rest of the parts i'll bet he'd sell you just the spindles.

if you don't have granada spindles it may have something to do with the control arm drop as the people who have done the granada swap and have this same problem only experience it after they've done the UCA drop, so maybe there is a problem with the drop itself or something.

Degins website is www.discbrakeswap.com BTW.

B,
I get regular phone request from guys who wonder if I sell the knuckles alone. My first question is, "does your car have an original Granada swap along with the Shelby drop, and are you experiencing bumpsteer". The answer is invariably, yes. I haven't receive similar request from users of Granada spindles without the drop. Draw your own conclusions.

And yes, the 65-66 geometry type knuckles are available separately.

Bump steer or... ?

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