CRX - Violent shaking under breaking

[bvondran]

All,
First time poster, but I've lurked here for a long time. I need some help.

I did a pdx this weekend at Nelson
Ledges and my car developed a violent shaking under light braking before the kink. It was an up and down oscillation, not a side to side shudder like warped discs. And it was violent at times, like I could see the dash oscillate up and down. There was a slight vibration under braking for 12, but nothing like before the kink.

The car is an 88 crx prepped for ita. New front pads (hawk dtc 60) and new front rotors. Rears are old and could be the culprit I guess.

What about ball joints or bushings, could they be causing such an issue? Or maybe the pads are cooling down too much?

Any help would be greatly appreciated.

Thanks,
Brian

Edited for additional description.

[Ed Funk]

I'd check shocks and CV joints.

[jumbojimbo]

I'd quit braking before the kink. And listen to Ed about possible causes.

[Tom Blaney]

I believe it could be a number of items but in order of importance I'd check

Lower Ball Joints
Radius Rod Bushings (yes I do make the best replacements)
Tie Rod Ends (but if it's up and down it's less likely)
Front Shock's for Bump setting then Rebound
Front Springs should be 500lb to 800lb rate depending on your driving style (with rears going from 750 to 1000 in proportion)
Upper Spring mounts (perhaps)

[tom91ita]

double check that the caliper mount bolts are tight. the two bolts that connect the caliper to the knuckle sometimes are not tight enough and can be loose.

[Knestis]

I had kink-related violent shaking but it happened after I misjudged a pass about dawn at the Longest Day, catching a slow car right at the apex. I lifted, went off backward driver's left, and didn't stop sliding in the wet grass until I was over the access road and down past the workers' station at the last turn onto the straight...

:)

K

[bvondran]

All,
thanks for the replies. I'm thinking lower ball joint as I just replaced the driver's side axle and may have buggered up the ball joint a little. I was debating whether to replace it when I replaced the axle, and probably should have. If that doesn't fix it, I'll continue down the line until a) I've fixed it, or b) I've spent all my money!

Yeah, I know I need to grow some cojones. I'm just starting to make the transition to road racing from autocrossing, and only getting out once or twice a year doesn't help.

Jim, you guys in ITC had a great race on Sunday. I work sound when I'm not pretending to be a driver. It was great to watch you guys have a good battle for the lead.

Thanks,
Brian

[zchris]

Brian, you might just have not bedded the pads in incorrectly. Common in race pads. I have installed new PFC pads and gone out to qualify and had the wheel shake so bad I thought a wheel was going to come flying off. Take some Scotch Brite pads and buff the rotors. Go back out and warm up the brakes with a few moderate stops followed by a couple off theshold braking stops and then let it all cool down. You may find thats all it is. A friend of mine who liked Hawk pads tried a set of PFC in his Miata and had the same result and just assumed the PFC are no good. He just did not bed in properly. Hope this helps.
Chris Howard

[SamsRX7]

Most automotive shops will let me put my car on there rack for free as long as I slap one of there stickers on the car. Contact a shop up the street, preferable not a franchise and see if you can use there rack? This is always helpful to have access to.