Squirrely under medium-hard braking?

Gents,

First I'll detail the setup of the car, and then detail the problem I am having...

Xida/AST f700#/r400#
14mm msm rear sway
1.125" tubular front sway
adjustable end links
Hawk HP+ brake pads and ss lines

Alignment settings:
Front camber: -2.5
Rear camber: -2.2
Caster: 6.2/L, 6.0/R
Toe F/R 0/0
Ride height measured from ground to pinch weld: 4.25"/F 4.5"/R

*Alignment bolts are original, car is 2000 model.
Had the alignment done back in october, car felt freaking awesome. Hit a few events, had some fun with the car here and there.

The issue I'm having now is unstability under medium to hard braking. The front end of the car gets very squirrely under braking. I have to hold the steering wheel like a vise to prevent the car from jerking left or right.

I tried multiple stops in an empty parking lot today. Basically the wheel jerks quickly between left/right/left/right/left right. A few times, the car jerked to the left only, a few times to the right only. The ground was relatively flat. After multiple repeated hard stops, the car starting braking straight and solid.

Also the last few times I drove the car, I heard an occasional light clunk under braking.

I'm wondering if my alignment bolts are just out of whack and need to be replaced? I'm under the impression those are used to set camber - would them being loose also affect toe? I don't think the calipers are sticking because I think that would cause the car to consistently go to one side under braking - right? Do the HP+ act funny when they are cold? My experience with them is that they don't bite as hard when cold, but they shouldn't feel like alternating L/R ABS that randomly turns on or off.

Thoughts?

Check/clean/lube caliper slider pins.

Meh. Sounds about right to me. Any alignment that made the Miata behave well for autocross tended to make it a "handful" under braking on the streets I drove on. My compromise was to run much softer sidewall tires on the street. Go try some hard stops on smooth surfaces with relatively little camber to them (like the Bush service road through Plano (Since I don't know what you're near). Vise-like grip may indicate there really is a problem, but I wouldn't expect it not to wander a bit as the front tires try to follow the road contour.

And when my alignment bolts slipped, it wasn't a "light" clunk. I recall POS running for the hedgerows once at Pennington...

^If it was alignment related, wouldn't it be squirelly/darty without braking?

I'll go ahead and clean and lube the calipers, I needed to do a little brake check up anyways.
I'll check the alignment bolts too while I'm under there for looseness.

I was thinking that it was possible that when the front squats (ever so slightly) under braking, perhaps I was possibly going into a toe-out condition if the alignment was off causing the instability. I got the 1 yr alignment pkg @ TTW, so I'm going to take it Tuesday to double check the spec and see if anything has shifted.

^Lube your front sway bar bushings while you're under there.

Matched set of tires??

I know my car with its crappy old ass daily driver tires doesn't like panic braking on the street even with its ABS. ;)

Quote:

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Originally Posted by POS Racing

Matched set of tires??

I know my car with its crappy old ass daily driver tires doesn't like panic braking on the street even with its ABS. ;)

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Yeah, Hankook RS3s all around with 2 autox's on them.
I got under the car and didn't find any looseness in the adjustment bolts... none that I could immediately see..


However I did discover that the front left wheel has been rubbing against the front sway, which has apparently shifted ever so slightly from its original position.
I also discovered that the same wheel has rubbed through the stainless steel brake line outer clear coating. Found that the driver side wheel has done the same very slightly on that line.

The SS lines came on the car when I bought it. Not sure if the rubbing on the brake lines is new or not, it's not that clean. Did some reading up on SS line install, and found that they should be clocked at a certain angle so that the line tucks away between the A arms when the wheel is turned, mine doesn't.

Add to the list of items to change ::Fist::

If all the alignment settings check out, I might request a slight tad of toe in for some added stability....

You might check for uneven pad transfer on the rotors. When you put the pads in:
1. Did you use new rotors? - If so did you clean them with soap and water to remove the protective coating (per my NAPA guy) and then brake cleaner?
2. If used rotors - did you sand the rotors to remove existing transfer per the Hawk instructions?
3. Either - did you bed the pads per the Hawk procedure?
4. Did you use your parking brake after an autocross run? Uneven cooling could cause uneven transfer or warp the rotor.

Also, how old are the wheel bearings? I had to change mine per Vorschlag pre DE inspection at 135k.

Quote:

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Originally Posted by sammm

^If it was alignment related, wouldn't it be squirelly/darty without braking?

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Different wheels are loaded at different times....definitely could be the alignment. Old, stretched eccentric bolts could be a problem.

What are your damper settings? If you have the car full-soft the rear will unload hard and dance around. I know you auto-x guys love soft shocks, but that doesn't always work on big-boy suspension.

I've got it set at "3" all the way around.
I'll head over to TDR tomorrow to grab some lines and new pads. Picked up new rotors yesterday. This stuff looks like it needed to be changed anyways.

I noticed it's a bit more pronounced on bumpy roads - how prone are these cars to bumpsteer? My car is low, but it's not retarded low.

Just wanted to give an update incase anyone has similar issues...

I replaced the rotors, pads, and lines. The car already had HP+ pads, old fluid, worn down rotors.... now running brand new rotors, new HP+, new lines, and fresh fluid.
The braking was great before, but is holy shit amazing now... WOW!

However, the brakes still did not solve the twitchiness.

Had it at TTW today to check alignment... every setting was way off! Caster was at 3 degrees, 3/32nds toe out... just totally f'ed settings. I think the first alignment was done right after the new suspension was installed, and the suspension settled a bit since then. AJ worked his magic on it, put it back into spec. OH MY GOODNESS... feels like a whole other car now, and feels like it did the first time I got it aligned.

Anyways, I fell back in love with the car after getting annoyed with how it was handling.

Good deal...enjoy!

Oh I am... drove it to the office today... found my self with a smile on my face driving in...

or maybe because it's Friday??