I am using a set of stock calipers in addition to the Roe slotted 14" upgrade on the front, and slotted 13" on the rear. I decided to order a set of red powdercoated calipers for both the GTS and the SRT. Well, today I got around to switching out the ones on the GTS. I changed them out, and then bled the brakes(RR,RL,FR,FL). I took them for a test drive and noticed that the pedal felt really stiff.(kinda like when you turn the engine off while you are still coasting and you don't have any power assist) I would have to really stand on the pedal to get the fronts to start howling.
After letting the car cool down, I re-bled the brakes and went back out to test them. At first, the pedal was just as hard, but I thought that maybe everything needs a little time to get "seated" or something. I took the car out to the proving ground, and did several slow down cycles. After stopping from a decent speed a few times, the pedal seemed to soften up a little, meaning that I was feeling a little more power assist. Then I found that the FL wheel would lock up way before the FR. I thought maybe it needed a little more time to do it's thing, so I did a few more cycles. Nothing changed. Also worth noting, for the most part, the brakes felt pretty strong(even though the FL was locking too soon) but a couple of times, it went back to that "loss of power assist" feeling.
I'm not sure where to go from here, so does anyone with brake experience have any advice? Thanks.
Gary...wonder if you got some trash in the system from the newly powdercoated calipers (blasting media, coating flakes, etc), might have caused a blockage in or around the prop valve.
Another thought is this...I had a set of big Wilwoods coated for a C5 customer of mine recently and the piston bores on one side of the caliper came back out of round....pistons would hang going back into the caliper.
HOS,
Thanks a bunch for the advice. I am thinking about taking the FR (red) caliper off and reinstalling my factory (black) caliper, to see if maybe just that one is defective. If I can't get to the bottom of it, I may just send these back, and go back to stock. This is turning into a PITA.
Chuck,
No, I flushed the system, and bled them twice, and I am still having issues. Now, this is exactly what happens:
I get the car up to lets say 70mph. I hit the brakes pretty hard, and everything feels pretty good. The pedal is soft(I feel the power assist) and the car slows down pretty strongly. Once I get down to say 35mph, the pedal gets hard, as if I shut the engine off, and the brakes "fade". I have to practically stand on the pedal to get to threshold once this begins to happen. Then when I do get momentary lockup, it's only the front right brake that locks up. I think I am going to reinstall my factory calipers, and if that clears it up, just send these others back. It's not worth all of this shit.
Do you suggest anything?
Thanks.
Oh yeah, BTW, I bought them from VenomBlue500 on the other board. He said that they had all new seals in them.
Chuck,
Thanks for the advice. I misspoke a minute ago. It's the front left that locks up. There is definitely something up with it. The car doesn't stop nearly as easily as it did before. One thing to note, I took the pads off and I could have put the inside pad on the outside, and vise versa. Excuse my brake ignorance, but do pads mate to their surface, and since I could have switched them from one side of the rotor to the other, would that make them less effective? I did not scuff them of the driveway, because I thought that was only necessary when you are installing new pads.
Gary,
Debris from powdercoating wouldn't work it's way upstream, so the proportioning valve is not likely. You've bled multiple times (in the rear) and this is the most common issue my 40mm caliper customers have. Due to the horizontal depth of the caliper, because it includes the parking brake mechanism, it very often traps air and you need a short drive to jiggle all the air towards the bleeder valve. But you're bound to be beyond that.
Your description of "good brakes then hard like a stone" sounds more like your power assist is going away mid-event. The assist works off engine vacuum, which as you describe, would go away with the engine shut off. It's even more unusual in that under braking, your foot is off the gas (right?) so intake manifold vacuum is at it's highest.
Ignoring the left or right front locking issue for now, it sounds like something in your vacuum assist/power brake booster isn't right. Is the large diameter vacuum hose from manifold to booster attached well? Is the check valve in the booster (the round black plastic thing the hose attaches to) working? Is the hose pinched, cut, or leaking? Is the hose soft and maybe collapsing under very high manifold vacuum?
You just had the calipers powdercoated. Was the area around the brake hose attaching location coated, and now the copper washer has crushed the coating and it's leaking? Is the fluid reservoir full (maybe you are leaking fluid just enough that you are losing pressure?)
Can you replicate the problem by pushing hard on the brake for 20 seconds in the driveway? In any of these, does the red brake light come on? (If not, then it's not likely anything to do with the calipers or fluid.)
It sounds like you have one of these "little" things that is hard to find rather than a "big" thing that needs replacement. Big help I am, huh? Good luck.
Tom,
Thanks a bunch. I have set aside wednesday to look things over. I will be sure to go through all of your suggestions. I have only bled the rear twice. I will be sure to try that one more time before I go into other things.
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