So this has been an on-going issue with our GXP for 3 years now. The car just takes brake fluid. I've looked at it, had a shop look at it, there are absolutely no leaks anywhere, it just needs to be filled up every few months, takes a least a cup of fluid. My only conclusion is that the M/C is poorly sized for the front calipers, and as the pads wear it takes more fluid than say the SSEi does, because of the extra volume of fluid. It's been more pronounced since we had the fronts rebuilt with new pads and rotors this spring, but it's always been an issue.

Anyone else experience this?

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Bye Bye:

RIP sandrock

No.

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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

Maybe it's just thirsty?

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Will
88 Cutlass Ciera Brougham International | 120k mi | White w/ Dk Claret Int. | Roller to be S2 L67/4T65E-HD | 1 of ~5100 3.8 FE3 Int'l series
91 Riviera | S2 L67 Swap/4T60E | 127K mi | Antelope Met. w/ Tan Int. | Saved From Death By Crusher
92 Bonneville SSE | L67/4T60E | 77K mi | Med Slate Grey w/ Two-Tone Grey Int. | Low Miles Time Capsule
92 Lumina Z34 | LQ1/4T60E | 177k mi | Torch Red w/Grey Int. | Rusty In Odd Spots
99 Tahoe LT | L31/4L65E | 276k mi | Spiral Grey Metallic w/Grey Int. | Truck for Truck Things and Portable Concert Hall
03 Park Avenue Ultra | 212K mi | White Diamond Met. w/ Shale Int. | Southern Time Capsule
05 Acura RL | 155K mi | Carbon Grey Pearl w/Ebony Int. | The Super-Hooptie Daily

Never had to top up the GXP while I owned it.

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Jerry /// Past: 95 SSEi (June 2010 COTM) -- 04 GXP (July 2011 COTM)
91 Honda Civic Wagon DX 2WD (fuelly) -- 208,000km -- 92hp -- Autocross Warrior
09 Lexus LS460 AWD -- 94,000km -- Daily Driver
09 White Hot G8 GT -- 155,000km (fuelly) -- LS3 Cam -- GM LS3 CNC Ported Heads -- Kooks 1 3/4" Long Tube Headers -- Solo Catback Midsection -- Hooker Maxflow Mufflers -- Pat G Tune -- Rotofab Intake -- Tein S-Tech Springs -- GXP FE3 Dampers -- BMR Subframe Cradle Inserts -- BMR Subframe Connectors -- Forgestar F14 Gold 18x9 +40 -- Michelin Pilot Super Sport 245/45/18 -- Maverick Man Carbon Fiber Spoiler

Is the pedal spongy at all? Wondering if the master cylinder may be leaking into the booster.

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*Gone, but not forgotten* - Black 2000 SSEi, HIR Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, 180 degree thermostat, HS 1.9 rockers, LSx yellow springs, Intense FWI, PCM, shift kit, push rods, and 3.4 Pulley. ZZP Power Log.

That was my thought as well. Even a firm pedal though could still be the master cylinder leaking by. Maybe remove and inspect the brake booster vacuum line for any signs of brake fluid.

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Ryan

2003 Bonneville SSEi - The Black Mirror SOLD!
2002 Bonneville SE - The Mutt Complete 2004 SLE interior, drivetrain, and body harness swap, ECC swap, HUD swap, black GXP wheels, GXP headlights and tinted tails - SOLD
2003 BMW 540i M Sport, 2001 BMW X5 4.4i, 2010 GMC Acadia, 2017 Grand Design Imagine 3150BH
1982 Cutlass Supreme - The fun one

Yeah, I hadn't thought of that. Pedal is nice and firm.

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Bye Bye:

RIP sandrock

Firm for how long? When the 95 lost its master cylinder it had a firm pedal initially when you stood on the brakes, then you went "one steamboat... two steamboat... thre--HOLY *shoot*!"

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Jerry /// Past: 95 SSEi (June 2010 COTM) -- 04 GXP (July 2011 COTM)
91 Honda Civic Wagon DX 2WD (fuelly) -- 208,000km -- 92hp -- Autocross Warrior
09 Lexus LS460 AWD -- 94,000km -- Daily Driver
09 White Hot G8 GT -- 155,000km (fuelly) -- LS3 Cam -- GM LS3 CNC Ported Heads -- Kooks 1 3/4" Long Tube Headers -- Solo Catback Midsection -- Hooker Maxflow Mufflers -- Pat G Tune -- Rotofab Intake -- Tein S-Tech Springs -- GXP FE3 Dampers -- BMR Subframe Cradle Inserts -- BMR Subframe Connectors -- Forgestar F14 Gold 18x9 +40 -- Michelin Pilot Super Sport 245/45/18 -- Maverick Man Carbon Fiber Spoiler

Firm indefinitely.

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Bye Bye:

RIP sandrock

x3. I figured Ed would be able to identify a leaky line, or other obvious leak just reading title, and author. But thought maybe he was ooverlooking the seal behind the m/c.

I had one leak on my old 1st gen s10, and it also held a firm pedal. Maybe loosen the two bolts and take a peak behind the m/c to see if the booster looks wet from brake fluid.

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92 Olds 98. L67, Gen 3 M62, 2.55 pulley, FWI, PLIM, 1.8 YTs.