Bump steer fix, spaced versus new hole relationship

[nathaninwa]

Hey guys, I spent most of today mocking up and cycling my suspension to cure a huge bump steer problem. I've installed a mustang 2 rack and thought the initial setting was good, till I started having issues at the track over 150mph

 

My initial reading gave me darn near 15/16 tow out under power. So after looking st the data and finding the static, braking and non launch acceleration height I was able to plot all this. I found raising my rack and adding a 1/2 ball joint strut spacer netted me the best results at 1/16 toe in, in both directions

 

So my questions is, if I drill or slot the cross member for the raised position that 1/2 inch, will it be the same as the mockup spacer I have and I'll be able to take it out?

Edited June 11, 2017 by nathaninwa

[74_5.0L_Z]

Pictures and plots of  your data would be helpful.

[RebekahsZ]

Is the spacer causing wheel clearance issues? If not, there are 2 ways to install an adjustable bumpsteer kit onto a Z. 1), reem the steering knuckle to fit a pinto tie rod and use a pinto bumpsteer kit from the round track guys, or 2) get a bumpsteer kit from Arizona Z Car, which has the correct taper for a Datsun tierod. Dave has just come out with them and they do not appear on his dated online catalog. Several companies make the 1"-ish spacer that goes between the strut and the knuckle. I'm surprised moving the rack up isnt giving you harmonic balancer clearance trouble. Insofar as slotting of the crossmember to raise the inner lower control arm points-I found that this enhanced my bumpsteer, and returned my inner LCA pickup points to the stock location. The guy above 74.... is most knowledgeable about rack relocation, and may also have a Mustang rack. JMortensen may have raised his rack too and he is running an LS motor like you and I do. 74... has a lot of autocross track time too; both guys have really worked hard on their setups.

Edited June 11, 2017 by RebekahsZ

[nathaninwa]

Ok. I'll post a shot in bit after a cup of coffee

 

I don't have any plot data, just a bunch if info written down on paper of static position, versus compressed and the rebound hieght my car travels at down the track

 

I currently have a 14 inch, 125lb spring up front which maybe helping with nose lift after the launch. That's combined with a 90/10 drag strut. I have some material to make a splitter to help with bringing the front down, and I can get some 70/30 struts for my application. I'm running 3rd gen comaro struts, but can't fit the adjustables from how I mounted them. So I'm ordering some 12 inch 150lb coils for some testing

 

I am running an LS, but it's setback in the chassis, and the manual pinto rack has tons of clearance

 

And I have reamed my steering arm for the pinto balljoint. But from the overall width of the pinto rack, I'm not sure there is enough thread on the inner tierod, versus getting the bump steer kit installed safely

 

In the beginning I wanted power steering, so I installed the Forester rack, but then decided that I wanted the manual system back. Since the 240 rack was gone, and buying one used and rebuilding it was more money than the pinto rack, I installed the pinto setup. After looking at pics I thought I was close to the stock position when welding in the mounts

 

So yesterday I spent most of the time trial and erroring different spacing and positions. My initial setting would give me almost 3/4 inch toe out on the rebound hieght the car drives.

 

I then spaced the balljoint down, the LCA arm down in various positions. Finally I found a setup that gets me 1/16 toe in and 1/16 toe in at both positions of compression and ride height rebound

 

That setup is, pinto ball joint in positions with no spacers bolted up. LCA is spaced 1/2 inch down. I moved my rack up as far as I could within the bushing slot I can fix the rack positions easy, I'm at the point of either buying a 1 inch LCA spacer and machine it down to a 1/2 inch or just Drill a new hole in the cross member for the LCA pivot and bolt the arm to the spindle again.

 

I can't really drill the member in the car, so it needs to come out.

 

Running a full 1 inch spacer gives me 1/16 toe in on compression but 3/16 toe in on rebound

Edited June 11, 2017 by nathaninwa

[nathaninwa]

My pics are not loading for some reason. But I just did some more testing.

 

Raised rack and no LCA spacer it went all wonky again

 

So I took the bolt out of the LCA pivot and put a pc of 1/8 rod in there and raised it, and toe for the one side went 1/4 in and out

 

So I lowered the pivot point, and now it's 1/8 toe in compression and rebound

 

Maybe more low would work. I'll see about more testing

[nathaninwa]

Got this just about sorted. Pulled the cross member, welded on new slotted rack mounts, slotted the control arm mount and ended up fabbing my own caster rods. Turned out alright, and initial garage alignment shows 1/16 toe in at ride height and at rebound height I get 1/4 inch toe in

 

I'll make a few 1/8 mile hits on this setup, collect some data and get the car aligned proper

 

 

 

[nathaninwa]

Well, got thencar aligned, ended up with .16 degree of toe through the travel, 1/2 degree of camber and 7 degrees of caster. I went 8.86@171.7 last night and car drove 95% better. Had some input but nothing sketch at all!

Edited July 2, 2017 by nathaninwa