soft brake pedal / pedal drops / pedal pump - Pontiac G8 Forum: G8 Forums -
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post #1 of 5 (permalink) Old 06-25-2019, 03:51 PM Thread Starter
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soft brake pedal / pedal drops / pedal pump

For so long I've been searching for my soft brake pedal problem, I think I finally knocked it. Posting this in case anyone else has the same issue. I searched so many posts and found a few with the exact same thing but no solutions. Now I cant find those posts, so making a new one.

Problem: slowly as I put miles on the car, I needed more and more brake force on the pedal to get enough stopping power. Driving the car every day I think I got used to it. But if I drove a different car I could really notice how much force I'd need on the G8 to get good braking. With enough force the brakes worked fine, it was just getting shocking how hard I'd need to press. Also if I was coming to a stop at a light or stopsign, I'd notice after I came to a stop the pedal would sink a little then get firm again. If I was slowly coming to a stop, and for some reason I'd get off the brake and back on quickly, I'd notice it was nice and hard after a "pump" where the pedal would slowly be sinking and if it went up a little it was hard like it should be. I've changed the pads and rotors many times while this problem was slowly getting worse and worse and no change, I've bled the brakes and even fully swapped out the fluid a twice and no change. Sounded like a classic master cyl problem. After searching here many times, I found a lot of posts with people with almost the same problem and quiet a few changed the master cyl and had no change. So I kind of let it go.

A few weeks ago I decided to check my front pads, even tho they were not that old I felt a very slight grind. One of the pads was worn much more at the top than the bottom, meaning one piston was doing a lot more work than the other. And I think I kinda remembered last time I changed pads a similar problem but not as bad. I assumed the pin was just drying a little and lubed the hell out of them.

Since my car almost had 90k miles, and I've had nightmares on old cars chasing caliper problems, I replaced the front calipers and threw in new lines. Problem gone, brakes feel nice and tight even with light pressure and no more fade after you come to a stop.

My theory: the pads were wearing uneven top to bottom causing the pad to get that slanted wear. But when you drive the whole pad would push back. Now you're on the brakes and only half the pad is touching the rotor, and the pedal slowly drops down with weak line pressure as the second piston is still moving on the uneven pad. Once the slanted pad is fully against the rotor with one piston out more than the other I get the line pressure goes up to what it should be.

Or I'm totally wrong. lol

If you have the problem I had, and your miles are getting high, you might want to check your calipers and make sure the pads are not bound up, the pistons not bound up, the pins dry and bound up. Anything that could be causing uneven pad wear top to bottom.
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post #2 of 5 (permalink) Old 06-26-2019, 11:21 PM
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Here is my theory: you had air in the line(s)
You bled the brakes again problem gone.
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post #3 of 5 (permalink) Old 06-27-2019, 06:48 AM
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Guessing the wear at the top of a pad was due to a caliber piston out of wack so the whole caliber assembly gets replaced. Was it the pad on the piston side?
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post #4 of 5 (permalink) Old 06-27-2019, 09:10 AM
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Uneven wear is most likely from lack of lubrication on the caliper slides or caliper bracket clips. The firm pedal is from Bleeding the brakes. Now what colour was that brake fluid? My guess it is the original brake fluid and Should be flushed out for fresh.

'09 PBM GT. #2 "Time to start modding again"
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post #5 of 5 (permalink) Old 06-28-2019, 10:47 AM Thread Starter
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The brakes had been bled many times while this problem happened. Fluid was pure gold at the end of every bleed, went thru a whole bottle even after the bubbles stopped so overdid the bleed to get air out. I always assumed not doing the ABS pump (need tech tool) was a factor, but after I changed calipers I couldnt do the ABS pump either, so I dont think that had anything to do with it.

The pedal was firm, once it got to the bottom. It was like you got some brake firmness, the pedal would slowly drop another inch, then better firmness. And while this happened the brakes didnt bite until you got that high pedal pressure at the end. Now I never get that feeling of hitting a hard pedal, then it drops again an inch once the car gets down to idle. Always assumed it was a master or booster problem, thats what it felt like.

I cant remember which pads they were that were worn at angle (top to bottom), inner or outer. But it was only one side. I went thru two sets of pads where it happened, each time the pins were lubes with synth grease, top and bottoms of pad where it slides lubed also. Always replaced clips. Maybe I had a piston problem? Dunno, either way problem is gone and brakes have been fantasic since replacing calipers.
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