Bump steer on Fox with 96+ Spindles

[SkurdalenFox]

I’ve got a ’92 with 98 spindles, stock LCA’s, Tokico struts, worn out springs, and a leaking 92 four cylinder rack/tie rod ends.

The car’s had a pretty bad bump steer problem since putting all new suspension parts on. I’ve attributed this mostly to the poor condition springs and rack. However, it has come to my attention that the straight armed 96+ spindles are a significant contributor to bump steer when on a FOX.

So, I measured the bump steer. I’ve got ~.3” of toe change in two inches of bump travel! That’s over ten times what Maximum Motorsports says I should shoot for according to their Adjustable Tie Rod Ends instructions. To get the geometry back into the appropriate range, I need to move the tie rod ends up, or the rack down. I’ve been looking at several options, and none of them seem too great.

I could change to 94/95 spindles with their higher TRE attachment point. The problem with this is the 94/95 spindles narrow the track over the 98’s I have by IIRC 8mm per side. I have a 96-98 length rear end, so the track in the front would be narrower than the rear – not cool. I suppose I could also upgrade to sn95 front LCA’s. But sn95 LCA’s are like IIRC 19mm longer than the FOX LCA’s. That'd make the front track a lot wider than the rear - not cool. I would also need a new anti-sway bar too correct? This option is beginning to look like a lot of money.

I could run a bump steer kit. According to some stuff I’ve read, even with the TRE all the way up against the spindle, I’ll still have noticeable bump steer. Some with 96+ spindles apparently end up running the bolt-through type, with the TRE on top of the spindle!

The other option I’ve seen is to use off-set rack bushings to lower the rack on the K-member. Like the preceding option, this apparently does not offer enough correction to eliminate bump steer to a large degree.

Before I throw $500 worth of springs, and rack at the car, I’d like to get this basic geometry problem fixed. Am I missing an option? Not noticing an obvious solution? Any suggestions, comments, cruel jokes?

[Italian LX]

. . . I need to move the tie rod ends up, or the rack down.
Does a '98 spindle drop the knuckle that far down?!? :eek:

[SkurdalenFox]

This is a 94 Spindle,
http://www.sn95brakes.com/old/94_modified_spindle.jpg

This is a 96+,

http://www.sn95brakes.com/old/96_spindle.jpg

I don't have anything but the 98 Spindles to measure, but from stuff I've read the 94/95 spindle moves the TRE connection point about 1" higher off the ball joint's pivot point than the 96+ spindle. From these pictures, 1" appears to be correct.

I wish I still had my old FOX spindles to compare it to.

Just looking at my car as the suspension articulates, it's plain to see that the TRE needs to mount higher, or the inner tie rod pivot point needs to move lower.

I’m no suspension expert, perhaps there is another way to reduce bump steer without moving either of these two points?

I’m not running a ton of caster either, only like 2 degrees. Obviously, more-er caster would equal worse-er bump steer in this situation.

[Photos from www.sn95brakes.com]

[Italian LX]

Obviously, more-er caster would equal worse-er bump steer in this situation.
Actually, more caster would raise the steering knuckle... this is what you want, right? :shrug:

[Italian LX]

What size discs do you have on the front? If you have something like the 13" Cobra set-up, I would recommend using the Steeda X2 ball-joints. They will raise your spindles up 1/2".

After I put the X2's on my coupe, I had to install a bump-steer kit (in addition to my off-set rack bushings) to drop my TREs down even more, In you're case, the ball joints should actually help your bump steer situation.

[SkurdalenFox]

Actually, more caster would raise the steering knuckle... this is what you want, right? :shrug:

Hmm, yeah but I was thinking that when the spindle is straight, that'd be true. But, as one turned, the height of the TRE at the knuckle would fall off as it arced. Even if the arc never fell below where it would be if the spindle had less caster, it seems like it could fall off faster, that is in a steeper arc, and that would make the steering less predictable. Does this sound right? :shrug:

Hmm, as I think about this more, the bump steer problem is a lot worse in curves. But I don't really know enough about suspension systems to know if the arc of the tie rod end is the cause or something else... or a combination of things.

I am running a Cobra brake setup with sn95 ball joints. With the sn95 BJ’s in lieu of the FOX BJ + stack ‘o washers, did I lower the height of the spindle/steering knuckle in relation to the BJ pivot point? I can’t seem to find measurements on this…

If I did lower the spindle with the sn95 BJ’s, it seems like X2 BJ’s would be right up my alley. That leads me to yet another question. I’ve heard that one can only replace BJ’s in an LCA once because manufacturers make replacement BJ’s housing bigger that stock to stretch out the hole in the LCA a bit so that it seats securely. Is this true?

[Sendero]

Sounds like you have a couple of different issues going on, so I'm going to address them individually.

Alignment

If I read your posts correctly you are only running 2* of (positive I assume) Caster. That isn't nearly enough by even Ford specs and has a very undesirable side effect of gaining positive Camber during compression.

Ford Specs
Camber: .6 Negative
Caster: 3.6 Positive
Toe-In: .25*

Recommended Street
Camber: 1.0 Negative (although I have mine set to 1.5 Neg with minimal tire wear)
Caster: 4.5 Positive
Toe-In: .5*

You should at least be running the "Recommended Street" settings if you have Caster/Camber plates. More positive Caster will make the steering wheel feel heavy in parking lots, but the car will be infinately more stable at higher speeds. Get the car realigned before messing with anything else or you could get into a "tuning loop" and chase the proper settings with money/time. If you can't get to these settings, you might have other issues.

Shocks/Struts

Since this was a former 4 cylinder car (or you swapped a 4 cylinder steering setup on a V8 car) I am assuming you have the 4 cylinder springs on the car. How much drop do you see in the front? With the extra 8mm track width of the 96+ Spindle I wouldn't suggest running anything less than a 1" drop in the front if you intend on running wide wheels/rubber unless you're ready to flare the fenders. (To keep from cutting tires at max compression and rubbing without rack limiters)

Possible Solutions


Get a "bolt thru" Bumpsteer Kit and mount the TRE on top of the spindle. Warning: Binding can occur!
Install Steeda X2 Balljoints.
Install *Aluminum* Rack Bushings
Install "taper bolt" Bumpsteer Kit
Get a MM K-member and install the LCA's in the lowered position.
Do any combination of 2, 3, or 4 until you get into a comfort zone.


Either way, you do need to at least get the car realigned (with you sitting in the drivers seat, it does make a difference) and install a bumpsteer kit. The bumpsteer kit comes with larger (more threads) TRE's because the stock Ford TRE's are maxed out with a 96+ Spindle.

[SkurdalenFox]

First, thanks for all your time and effort guys. I really appreciate it.

So, here’s my plan –

1. New springs - H&R Super Sports.
Currently, my CC plates are maxed out at ~2 degrees of positive caster. I’m pretty sure this has to do with a screwy spring issue because my rear LCA’s have around three inches of rise back to front. I probably did something stupid when I had it all apart like put 8 cylinder springs in the rear, and 4 cylinder springs in the front. Before my CC plates, I had .5 degrees of negative caster on one side and like .2 degrees positive on the other side! The CC plates are a band-aid stretched rather thin.

2. Get an alignment set to the recommended street setting that Sendero provided.

3. Then, re-measure the bump steer, and see where I need to go from there.

[Sendero]

If you don't mind, which C/C plates do you have installed on the car?

[SkurdalenFox]

Steeda Aluminum