Another brake squealing problem!!

[CapSS92]

Hi all, I am having an issue with a newly installed setup on a 55 2 door sedan. Everything is brand new and is as follows: Hydraboost setup from ABS Power Brakes, CPP chrome master cylinder with built in proportioning valve, front 12" disc brakes with single piston iron calipers (standard mail order conversion kit), and C5 rear disc conversion using Kore3 brackets.
I just started putting some miles on it to get everything worked out and it has run fine for about 150 miles. Then suddenly the other day I get a massive squeal when I put a light foot on the brakes. It sounds like when you blow into a Coke bottle. Kinda like a loud humming sound rather than a squeal. Reminds me of a school bus. If I stomped on the brakes it would stop. Then I did a couple of hard stops and the sound went away for a while and then returned. And it only did it after 20-30 minutes of driving. I parked it for 10 minutes and it worked fine for another 15 minutes and then started again. And then it got worse. It started making the noise as I was driving with NO brake application. If I stepped on the brakes kinda hard, the noise semi-stopped.
So for now I parked the car. I took the rear wheels off and there is brake dust everywhere on the rear. I haven't checked the temps with a temp gun but that is my next step. I did try adjusting the prop valve per the instructions from Classic Performance Parts but to no avail. I read some threads here on the board and I'm thinking maybe it's a brake rod issue but I don't understand why it seemed to pop up suddenly. I am going to try loosening the master cylinder bolts and add a washer between them and the hydroboost to see if that helps. Am I headed in the right direction? Any suggestions would be greatly appreciated. Thank you guys.

Alex

[Apogee]

Alex, it looks like the only thing you're running from us are the rear conversion brackets, so what are you using for pads and rotors?

I also tend to think that you have a residual pressure issue due to the excessive brake dust and presumably temps, however you may just have dusty pads, so that's not necessarily a definitive indicator one way or the other. The fact that you're getting noise without the brakes applied would indicate that even though you may not be applying them at the pedal, that doesn't mean that you don't have either a pushrod or Hydroboost issue. As for the noise(s), can you tell whether it's coming from the front, rear or both?

First thing there would be to make sure everything is installed and torqued properly as failure to do so can result in odd harmonics. You indicated that this is a newly installed setup, however at the end of your post you mention the issue popping up suddenly...which is it?

Tobin
KORE3

[CapSS92]

Hi Tobin, thank you VERY much for your reply. I am using C5 calipers and pads from Autozone. They sell them assembled with abutments and all clips. All I had to do was mount them onto the bracket. I made sure that the rotor was centered and that the caliper had equal spacing on both sides. As for the rotors I am using Raybestos C5 rotors cross drilled and slotted. The noise is coming from the rear. I added some washers between the MC and hydro and the noise seemed to stop happening while driving with no brakes applied. I cleaned off all the rear today and took it out for another drive. No more noise while driving but it happened while braking after about 10 miles of driving on the freeway and only while applying light pressure as I was either coming to a stop or just pressing them as I was going about 10 miles an hour. If I stepped on them hard, there was no noise. And the rear wheels had a light coating of dust again. It doesn't seem to happen when I first use the car or if it's been sitting for an hour or so. As for the setup, I consider it newly installed as I just finished the car and it's only got about 100 miles of driving on it, spaced out over the course of a year. When I first started driving it to shake out all the bugs there were no issues. I hadn't run the car in about 3 months and just started driving it again at the beginning of this month when the noise started.
I had also adjusted the MC prop so there was little or no pressure to the rear and I still had the noise when braking. I'm beginning to wonder if it's not the pads or a stuck caliper. Any way to check?
Again thanks again for your help Tobin. I'm just extremely frustrated with this.

[John Wright]

Do you think the firewall flexed, or maybe the pushrod has bent?
(for it to act right at first, but is happening all the time now)

[CapSS92]

I checked both areas and they seemed fine. The pushrod came out straight when I checked it.