Was towing 14,000# yesterday and a 40 mile hilly narrow backroad trip.

3/4 through the trip I get a hard brake pedal, took both feet to stop truck :eek: (no power brakes but had power to steering).

Did this 8 times while stopping and last time I was on brakes hard and something let loose in pedal and I slid the tires (power brakes came back on).

Was fine rest of way and today on way to work.

I assume a valve somewhere or ???

F/CMVSS Noncompliance - Brake Hydro-Boost Relief Valve Seal Fracture #04004A - (Jun 18, 2004)

04004A - Brake Hydro-Boost Relief Valve Seal Fracture

2003-2004 Cadillac Escalade, Escalade EXT, Escalade ESV

2003-2004 Chevrolet Silverado, Avalanche, Suburban, Express

2004 Chevrolet Tahoe

2003-2004 GMC Sierra, Yukon, Yukon XL, Savana

2003-2004 HUMMER H2

THIS BULLETIN CANCELS AND REPLACES BULLETIN 04004, ISSUED JUNE 2004. THE INSPECTION PROCEDURE IN THIS BULLETIN HAS BEEN REVISED TO INCLUDE ADDITIONAL STAMPED NUMBERS ON THE HYDRAULIC BRAKE BOOSTER. ALL COPIES OF BULLETIN 04004 SHOULD BE DESTROYED.

Condition

General Motors has decided that certain 2003 and 2004 model year Cadillac Escalade, Escalade EXT and Escalade ESV; Chevrolet Silverado, Avalanche, Suburban, and Express; GMC Sierra, Yukon, Yukon XL, and Savana; HUMMER H2; and 2004 model year Chevrolet Tahoe vehicles fail to conform to either Federal/Canada Motor Vehicle Safety Standard 105, "Hydraulic and Electric Brake System", or Standard 135, "Light Vehicle Brake Systems". These vehicles may have a relief valve bore within the brake hydro-boost module that is not to specification. An out-of-specification bore could result in fracture of the relief valve o-ring seal within the module. If this happens, during brake applications the driver may be able to hear an engine compartment noise similar to the sound that occurs when the steering wheel is turned to a full stop position. The driver could also experience a slight increase in steering efforts while braking and parking. Under certain driving conditions, a fractured seal may require a slight increase in the applied brake pedal effort to achieve the same vehicle deceleration rate as prior to the seal fracture. If this were to occur, it could result in a vehicle crash without prior warning.

Correction

Dealers are to inspect the hydro-boost module and replace the relief valve, if necessary.


This may be worth looking into...

Thanks Max P for this valuable info! ;) Thankfully mine did not fall into this grouping and has not displayed any problems in this area.

Tim,
You've had a bunch of these trucks. Is that the first failure you've had?

"General Motors has decided that certain 2003 and 2004 model year Cadillac Escalade, Escalade EXT and Escalade ESV; Chevrolet Silverado, Avalanche, Suburban, and Express; GMC Sierra, Yukon, Yukon XL, and Savana; HUMMER H2; and 2004 model year Chevrolet Tahoe vehicles fail to conform to either Federal/Canada Motor Vehicle Safety Standard 105, "Hydraulic and Electric Brake System", or Standard 135, "Light Vehicle Brake Systems". These vehicles may have a relief valve bore within the brake hydro-boost module that is not to specification. An out-of-specification bore could result in fracture of the relief valve o-ring seal within the module. If this happens, during brake applications the driver may be able to hear an engine compartment noise similar to the sound that occurs when the steering wheel is turned to a full stop position. The driver could also experience a slight increase in steering efforts while braking and parking. Under certain driving conditions, a fractured seal may require a slight increase in the applied brake pedal effort to achieve the same vehicle deceleration rate as prior to the seal fracture. If this were to occur, it could result in a vehicle crash without prior warning."

Thanks, may be something to look at but my steering was OK and like I said it is working OK now.

I'd think a blown seal would cause trouble all the time.

Would both feet classify as slight increase ):h

Just got off phone w/ dealer and he wants to deal on my 05 that came in.

I'll have to ? service about it.

Tim,

Years ago I did some testing with Chevy on ABS malfunctions. We had a similar problem. It took both feet to stop the car. Finally the problem corrected itself. They suspected a faulty ABS sensor.
With these diesels the hydroboost is certainly suspect.
Doug

look at the hydroboost system is my answer too.... I bet if you trade it off on your 05, the problem will go with it..

I just don't want someone else to get it and not know about brakes.

The pedal seems kind of odd acting, some pulse and more mushy than before.

Tim, I would start by checking the recall to your truck. Have it done if it applies (duh) and then take it from there. Might be hard to guess if it dont act up, but my first guess would be booster failure.

Dave, my first failure and on D/A #8, hope #9 does as good as the others.

Eric it is doing it a lot more, I should get the 05 Wednesday.

I'm almost sure it is booster trouble since steering is OK.

1 out of 8 isn't too bad.

You still suck. :D

What's the 05 gonna have?

We'll I'm keeping the 04.5 since GM doesn't have much rebate money, was close to $6000 difference.
So dealer is ordering me another 05 for next year and we'll try it again.

Dealer checked brakes and found a TSB on cleaning the front ABS sensors so that is what they did.
We'll have to see what happens.

Eric could u post the serial #s listed in the TSB that u edited in the earlier post or is available some where else.

I didn't get to check my serial #.

Thanks, TIM