Front Brake Locking Goblin

[dna9656]

I have never had to replace a master cylinder or a booster, I count myself lucky because it's one of the worst stories shade tree guys tell. Once upon a time I was ASE brake certified, trust me, it wasn't much of a test; but anyway my 2006 Avalanche has the hydro boost, does this 2007 not have the hydro boost? If it does could it be the issue? The spacer theory intrigues me, I found one of those spacers that's supposed to increase performance behind the air what ya call it valve in front of the intake, I think they just increase the volume that you have to fill with additional vacuum; I don't see how that works but anyway the water pump wouldn't fit as the hose nipple on top wasn't clocked correctly with that blue (finely machined BTW) chunk of aluminum. I'll post a pic one day, maybe we can figure it out I donno.

So far as jury rigging, brakes ain't the place to be doing that, you use the right parts of good quality and replace anything you question. There is no feeling like stepping on your brakes and they don't work. First you say it (S - -T) then you do it (in your pants) trust me. I have installed calipers upside down (now that some one else had done it I don't feel so bad) on my 71 Monte Carlo, they don't bleed well as the air stays in what then became the top of the caliper. Try bleeding brakes on a motorcycle, the old school way, it's really tough. I bought a power (Pneumatic) bleeder, you're done in no time!

[richard wysong]

master cylinders are easy if you bench bleed them often times you can just bleed them by cracking the lines at the master. pressure  bleeder makes it so easy too. very often systems will gravity bleed as well if you leave the cap on the master loose and open the bleeders 1 ata time

[Stratton_Silverado1500]

Update: I checked a couple of other vehicles and couldn't find a spacer between the booster and firewall, and couldn't find evidence of this part online. It's still possible I threw away a spacer with the original booster core. But without a good path forward other than putting on yet another booster—a fairly reliable part—or a third new master cylinder, I did what worked the first time and gave the pushrod a few turns to shorten it. She's driving fine and I've made it from Charleston to Kentucky so far en route to Utah. 

If there are further developments or knowledge gained, I'll update this thread. It wasn't the start-to-finish SOLVED post I'd hoped for, but oh well. Even the dealership just wanted to throw another booster at it. Sometime in the future I may pop a GM booster and master cylinder combo in to see if that does it. 

[richard wysong]

Have a safe trip! I think its only the booster thats causing the problem, Its very possible you ran into a batch that were boxed with the wrong part # on the box or the push rod misadjusted at the factory. if it's working good now I would leave it alone, thats not an easy job changing the booster, I'm not sure I could even do it anymore trying to get  up under the dash isn't as easy as it was when I was younger and skinnier

[Stratton_Silverado1500]

Thanks Richard! It took me about an hour just to get the top right bolt out of the firewall the first time. And the clip on the brake pedal can be a pain to get back on. But I can swap the whole thing in 20 minutes now. Partially why I balked at 3 hour labor charge for a booster change at the dealership. 

 

The Cardone replacements did all come from the same shop. All things considered there's a good chance you're right about a bad batch. 

I appreciate the help along the way! 

[richard wysong]

safe travels