yet another rattling heat shield question - plus slotted rotor noise

[lee]

When I searched the rattling heat shield problem, most people seemed to have it occur during light acceleration. My rattling is mostly only during moderate speed decelleration, i.e., foot off the gas around 45 mph is the worst spot.

So before I put the car up on jackstands, anybody want to offer alternatives I should check while I'm under there...would really be frustrating to tighten up the bolts to find the noise unabated.

Also, for those reading this far, I hear the brake pads dragging (slotted rotors) during some conditions. Any fix?

I used to never hear these things, but that was because of several things - the biggest fix being new tires which reduced the interior noise immensely. Also, haven't been playing the stereo as loud - while I listen to my new transmission (well actually a junk yard 4.11 with 29K miles, but hopefully you get the idea). And before you suggest it, yes I guess I could just turn the volume up again, but every once in a while my wife rides in my car and insists the SVX be like any other "normal" car - whatever that means.

[SVXer95]

If the dragging noise you hear from the slotted rotors is faint clicking, it is normal. I have put 40k miles on like that with no problems.

[lee]

Originally posted by SVXer95
If the dragging noise you hear from the slotted rotors is faint clicking, it is normal. I have put 40k miles on like that with no problems.

I was just wondering if other slotted rotor owners noticed this. around 40 mph it sounds almost like metal lightly dragging - most like what would happen if the inner shield had been bent in and barely touching except for this rythmic nature that I think is the slots hitting the leading edge of the pad. I can put on the brakes and it goes away...and it's not always there. I'm wondering if it's how well the pads retract after an application. might be time to pull the calipers and regrease the slides. I also considered putting a chamfer on the leading edge of the pads and give that a whirl, but that's a shot in the dark.

[SVXer95]

I do not know if you are familiar with brake operation, but the way the pads retract are as follows. The rotor has runout in the design that 'knocks' the pads away. I am not sure, but I imagine there is never a time when they fully retract. It is my guess that this slight contact is what causes the noise. Now noticeable due to the slots.

Let me know if your adjustments make a difference.

[Beav]

Most rotor specs only allow for .003" lateral runout, any more will lead to brake vibration. The caliper piston retracts slightly by way of the lathe-cut seal (read: square cross section.) The seal twists as the piston extends and when hydraulic pressure is released the seal relaxes, pulling the piston back into the bore. Slight pad/rotor contact is both normal and expected. Any additional clearance would create a low brake pedal as calipers, by way of their relatively large bores (in relation to the bore diameter of the master cylinder), require a large volume of brake fluid to operate.

One might consider the flexing of the rotor/hub assembly against the pads during cornering as a way to push the pads away from the rotor, but then again it just leads to a pedal drop and is not a design consideration for proper brake release.

Humidity, heat, friction material condition and construction and rotor lateral runout or thickness variation can cause the symptom. Pads that are sticking in the mounting bridge may tend to not relax away from the rotor. If the rotor has a couple thousandths of runout it can cause a slight noise as it wobbles through the pads. The slots may tend to make the symptom a bit more pronounced as the slots tend to 'scrape' across the pads.

[Landshark]

my slotted rotors don't make any noise. squealed a little, but removing the AXXIS Ultimate pads fixed that.

go to Home Depot (or similar store) and get some large hose clamps in the plumbing sections, and use them to quiet the heat shields. better and easier than removing them......

[SVXer95]

Originally posted by Beav
Most rotor specs only allow for .003" lateral runout, any more will lead to brake vibration. The caliper piston retracts slightly by way of the lathe-cut seal (read: square cross section.) The seal twists as the piston extends and when hydraulic pressure is released the seal relaxes, pulling the piston back into the bore. Slight pad/rotor contact is both normal and expected. Any additional clearance would create a low brake pedal as calipers, by way of their relatively large bores (in relation to the bore diameter of the master cylinder), require a large volume of brake fluid to operate.

One might consider the flexing of the rotor/hub assembly against the pads during cornering as a way to push the pads away from the rotor, but then again it just leads to a pedal drop and is not a design consideration for proper brake release.

Humidity, heat, friction material condition and construction and rotor lateral runout or thickness variation can cause the symptom. Pads that are sticking in the mounting bridge may tend to not relax away from the rotor. If the rotor has a couple thousandths of runout it can cause a slight noise as it wobbles through the pads. The slots may tend to make the symptom a bit more pronounced as the slots tend to 'scrape' across the pads.

Well, I guess my auto-tech class was wrong. Always good to know the facts.

I don't know about Lee's case, but my noise is very very slight. I can only here it with the window down driving past a solid wall.(so the noise reflects)

[Beav]

Originally posted by SVXer95

Well, I guess my auto-tech class was wrong.

Sorry to hear that, maybe you can get a refund.

[lee]

Thanks all.

After reflection I suspect a couple of things:

First, and I'm so ashamed, on my pad swap I did not replace any seals...I have no idea when/if the PO had it done...it may be the "lathe cut" action is soft?

And, I can't remember what I did for pad mounting, probably got in a hurry and just stuffed the pads in there without proper cleaning & greasing of parts (again, with head hanging...I bought caliper grease but just noticed the tube is still in its package, so....).

can you guys ever talk to me again

Given the above admissions, I wonder if I actually tightened down all the heat shields properly when I did the 4.11 swap...thank god I live in Florida...or they'd be coming to take my license away soon for being senile.

[nordique14]

When you check for rattling heat shielding, do more than just check to see if the bolts are tight. I was getting a rattling sound a few months back. I checked all the bolts and all were on tight. When I tapped all the shielding, I found one of one of the curved pieces was slightly loose even though the bolts were nice and tight. I removed it and put more of a bend in it so it was tight against the pipe. Reinstalled it and the rattle went away.

Matt

[Ron Mummert]

Given the above admissions, I wonder if I actually tightened down all the heat shields properly when I did the 4.11 swap...thank god I live in Florida...or they'd be coming to take my license away soon for being senile. [/B][/QUOTE]


All I can offer, Lee, in that I'm already borderline demented anyway, is that I've had my heat shields "tightened" twice in four years by my friendly "fix-anything" auto mechanic. No charge if I let him change my oil. I think he jambed some asbestos stuff in a few cracks somewhere, but all's quiet enough to hear the digital clock ticking.

Ron.

[SVXer95]

Originally posted by nordique14
When you check for rattling heat shielding, do more than just check to see if the bolts are tight. I was getting a rattling sound a few months back. I checked all the bolts and all were on tight. When I tapped all the shielding, I found one of one of the curved pieces was slightly loose even though the bolts were nice and tight. I removed it and put more of a bend in it so it was tight against the pipe. Reinstalled it and the rattle went away.

Matt

I envy all of you that live in a land free of rust. My frozen bolts don't tighten, they break

[Earthworm]

Originally posted by Ron Mummert
but all's quiet enough to hear the digital clock ticking.

Funny, I thought that was the dash popping.

[Beav]

The seal I'm referring to is the caliper piston seal. You wouldn't have replaced it unless you rebuilt the calipers. If the seal isn't leaking it's action is probably just fine. However crud builds up inside the caliper bore and on the piston, either of which can inhibit the seal's ability to pull the piston back.

[lee]

Thanks Beav, I knew which seal you were talking about....I'm just ashamed I was so lazy in my install. I remember going out to buy the caliper grease, now I find the package unopened, etc. The excuse I'm telling myself is my wife probably wanted me to do something/go somewhere, and I just short-cutted the job.