Hey all,
I've been lurking in this forum for awhile now and today is the day I need some assistance. I tried to see if anyone else had this issue but I couldn't seem to find anything; that or I was just doing it wrong. So to start off I have a 2005 Pontiac Bonneville GXP and have had the car for roughly 2 years or so. It was originally my Dad's car and he had it for 9 years and loved it, but when he wanted to upgrade he passed the car down to me. I have loved the car forever and we have had our fair share of problems ie water pump going bad, upper radiator coolant hose exploding, vacuum hoses tearing apart and a couple other instances but nothing too major. The car has 159k on it currently and she keeps pushing on which is awesome. So back to why I am here. My current issue is that my rear calipers are not sitting correctly on the rotors which is causing a lot of travel in my brake pedal before it starts slowing down. I have been looking for a replacement set and it has been a bit more difficult than I thought it would be. I figured I should just replace all 4 calipers just because and my dad and I love doing projects together and its just more preventative maintenance I suppose. I would like the calipers to match the current red ones so I was either going to buy ones and spray paint them or try and find ones that already come painted. I have been looking at rock auto and there are some decent ones on there, but today I cam across a set of 4 on ebay that already come painted red and are pretty cheap, but in the "Fits this Following Year and Model" section it says that it only fits 2005 SLE and SSEi models. So here is my question, does the GXP share calipers with those models or are they different? As far as I can tell they look the same, but I would like to get a second opinion. I can send the link for them if I am allowed to. Also sorry for the long post, I wanted to intro myself just so I don't seem like a complete stranger.

well considering 2003 was the last year for the ssei i would probably say those might not be GXP brakes. i wouldnt be sure and maybe someone else might post different but maybe a link to them would help distinguish them

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2003 pontiac bonneville Sle with kenwood sound system. Upgraded tweeters, door speakers, deck speakers, kenwood sub and amp. Rage r20 18inch rims. Front and rear KYB shocks and struts. GXP Strut tower brace.. She's a work in progress still

GXP front caliper are unique to the GXP. The rears are identical to the SLE/SSEi but they have a different but larger bracket that allows for the use of a larger rotor.

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-Car Guy Carl
"Penelope" - 2003 SLE - 247k Miles
"Sydney" - 2000 Honda S2000 - 98k miles

Here is the link:
ebay.com/itm/291998498436?_mwBanner=1#vi-ilComp

Assuming the inner and outer brake pads are wearing evenly, I highly doubt that the calipers are the cause.
Much more likely would be lateral runout of the rotors.
What happens is the rotor keeps hitting against the pads, pushing the piston back in.
See this:
http://www.autozone.com/repairinfo/comm ... l%20runout

Rears are the same as Carl posted.

I am confused by the comment about the rear caliper not "sitting" properly. There are only two bolts (caliper pins) that secure it to the caliper bracket, so it fits over the rotor only one way. If you're referring to the "swept" area of the rotor, the pads will not sweep 100% of the available surface. Especially close to the rotor hat (the center section), as well as the outer edge.

If you're having long pedal travel, a couple things come to mind, going from simplest to most involved;

1) is the system properly bled? If their is air in the system, it will compress, giving the illusion of extra pedal travel before actual braking work is performed.

2) Is the rotor you have, the proper thickness?

3) Your caliper isn't "floating" properly. As mentioned, there are two caliper pin bolts (1 top, 1 bottom), that secure the caliper to the caliper bracket. The design of these pin bolts allows the caliper to slide, or "float" as the brakes are engaged/disengaged. When you press the brakes, the piston on the inboard side pushes out, which then causes the caliper and the outer pad to slide in, effectively clamping the rotor on both sides.

If these pins aren't propertly lubed/greased/etc, the caliper "freezes" and won't float freely, which can lead to quicker and excessive pad wear (particularly the inboard pad), which will then also give the sensation of extra effort needed to get the brakes to work as they've wore AND the caliper isn't "floating".

Typically, getting these pins out, cleaned of old grease and other crud on the sliding section of those pin bolts, and then regreasing, and upon reassembly, ensuring that the caliper can move freely in and out, you may not need to buy new calipers.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck

I rebooted and regreased my calipers and it has given them some new life. All you need to accomplish this is some grease and brake parts cleaner. It is a quick and easy way to save some money if it ends up being your fix. Plus it takes very little time.

_________________
-Car Guy Carl
"Penelope" - 2003 SLE - 247k Miles
"Sydney" - 2000 Honda S2000 - 98k miles

I never really thought about the slide pins. I replaced the rotors and pads little bit ago and I know I re-greased the slide pins front and rear but it wouldn't hurt to bleed the system and re grease the pins before I bought new calipers. I'll do that this weekend and I'll get back to you guys on it. Thanks so much for all of the help.