RaceCarRiot

i just installed a front set of STi 4 pots, and while they work wonderfully, the passenger side assembly keeps making this dish scouring noise whenever the car is in motion. and the worst part is, they make a HORRIBLE metal on metal screeching noise at 20 and 40mph.

so as soon as i pulled in my carport, i looked at the rotor to find a single small score. figuring that this was the problem, i disassembled everything again, only to find a matching score on the pad. i can't find anything loose, or rubbing against the rotor. the noise goes away under braking. the score isn't getting any deeper, and the brakes work fine -- no roughness or vibration coming through the pedal to indicate a problem.

anyone have any ideas? none of the yanks on this side of the pond can figure it out.

-adam-

Apple

just a few ideas to chuck in:-

are you sure both sides of the caliper are working and one side isn't sticking which means uneven loading on the disc? (should be less of a problem with opposed pistons rather than single sided calipers)

have you got any metal pickup from the disc in the pad (creating the groove)? (a lump of metal as opposed to the normal steel fibre in the pad)

are the discs warped / thin / are you getting dtv on them (vibration / pulsing as you first touch the brakes especially after lots of miles without using them)?

not implying you've bolloxed it, but are things installed OK - no bits missing eg like anti-squeal pads, rattle springs etc

haven't got a set of STi 4-pots - just general things to think about.

Apple

RaceCarRiot

i haven't had time to take it apart again this week, but the minor score hasn't gotten any worse. could it be the backing plates for the pads? i.e. the wear tabs that scrape against the rotor are bent too far in, and scraping against the rotor at certain points? can i run without those? it sounds like a thin piece of metal scraping across cement or something when it isn't screeching. also, now during low speed left turns (in a parking lot for example), it begins screeching, and it goes away as soon as the wheel is straight again...so the steering pushing out on that wheel is causing something.

so i guess i'll try removing those backing plates, if that's OK, and see if it goes away.

AndrewC

Have you upgraded from 2 pots and kept the original brake disk shield?

If so when the brakes get warm the shield will rub on the edge of the disk.

I this is the case take the shield off.

Andrew...

RaceCarRiot

Andrew -- that sounds like the most logical solution so far...people over on i-club insist that it's because i didn't put anti squeal compound on the backing plates, but that sounds much more logical, and would explain why the brakes have been silent the last few mornings until i've driven a few miles.

-adam-

Apple

reread your post - if noise goes away under braking then seems as though you've possible got a clearance / rubbing problem with the pads, e.g. leading / trailing edge contact

think of a record turntable and stylus - when record going correct way round, you've got trailing edge contact and stylus skims over surface. if record goes in opposite direction, stylus tries to dig in and if it can't (or doesn't snap) you've got leading edge contact - this can be one mode of creating brake noise. [I'm not into mixing decks and things working both ways but you get the idea with the stylus ]

when you put brakes on, you flatten pads against discs and have correct contact profile. check to see if your getting a chamfer worn on front or rear edge of pad - might indicate a piston not working 100% on one side of caliper rather than across caliper as before. could effectively be tapering off pads slowly.

all of the above might not show anything but you never know ;-)

Apple

PS finally - 100 posts methinks

edited for spelling and a few other bits

[Edited by Apple - 2/7/2002 1:25:03 AM]