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A bad master cylinder from Autozone?

R

realsquash

1/2 ton status
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I've replaced the entire brake system on my truck, lines, propvalve, calipers, and master cylinder. No leaks, things seem to bleed out fine, no air. For some reason the primary side of the master cylinder doesn't seem to be building much pressure. I even went so far as to plug the port and press the brake pedal... No change! For some reason I just can't get that working.

Is my logic flawed? When I blocked the secondary i got lotsa feedback on the pedal 1/2 way down, right when it was pushing the secondary piston.

Andy /forums/images/graemlins/eek.gif
 
Yes, it was bench bled and i also rebled it in the truck just to eliminate that as a possible problem.

Andy
 
could be bad, wouldent suprize me, my buddy once got a caliper for his c-j7 that was cracked and just sand blasted over, they don't really care sometimes /forums/images/graemlins/deal.gif
 
My dad had a very good thought on master cylinder problems:

If pressure isn't being built, and the system is bled, there is only one place in the entire brake system that can bleed pressure without externally leaking. /forums/images/graemlins/smile.gif
 
Yeah I hear ya. I picked up another one today at lunch and I'll know tonight. I also ordered up a pressure gauge from Mcmaster carr for some more fun testing if this doesn't work. A friend of mine went through 3 alternators until he got a good one from "the zone". I think I need to head to NAPA tonight....

Andy
 
I got 2 dead power steering pumps from them then went to Napa and haven't had a problem sine... I still have the autozone starter on my truck and it goes out about every 6 months so I take it back and get a free new one.
 
Autozone and Napa get their power steering pumps from the same company so the only thing you got by going to Napa is a more expensive version of the exact same part. (AFIAK, ftcollinsram can chime in here but I believe Napa carries Cardone as well, who is pretty well known in this market)

With a master cylinder I would highly recommend a new one as opposed to a remanufactured unit as the quality is typically much higher.

I have had good luck with all of Cardone's products.

The most common reason that a new power steering pump will come back is that the system is not flushed. It's kinda like an automatic transmission--if one pukes and you put in a new one but don't flush out the cooler, it will fail soon afterwards.

Not saying this is the reason yours did, and everyone gets some bad apples sometimes, but Cardone as a whole makes a very high quality reman product in my opinion so you shouldn't be having problems with one unit after another.
 
The pump I received from Napa was a different brand then the ones from Autozone (hd a sticker stuck to the pump stating manuf., was not cardone).

Anywho, yeah my system was brand spanken new when all this happened, hoses and all. And even then I flushed 2 quarts of fluid through it into a bucket before using it.
 
Like I said, everyone gets some bad apples once in a while I suppose. Cardone is supplying GM now though so I'd say their quality isn't really all that shaky.
 
Well I picked up another master from another autozone today and swapped it into my truck. Whaddaknow, i have brakes! playing with the first one on the bench confirms what I felt in the truck. It was like the pistons were catching something or the seals were not functional.

Now my problem is that I bought a master cylinder for the "JB6" system which I think is for drum-drum brakes. So I went back tonight and bought the master for a JB8, a 78 K30, and it doesn't fit my booster /forums/images/graemlins/angryfire.gif My bad, I just didn't check. The JB7 system master looks good tho, I'm going to play with that one tommorow. I've got chevy 3/4 ton calipers front and rear now and this master doesn't seem to like that.

Andy
 
Do you know for a fact that is the right one to get? Does it bolt to my old 76 vacumm brake booster?

Andy
 
Oh, nevermind. If you've got the newer booster you need a cast iron master.

Screw that idea, try the 3/4 ton master and see how it works out.

AFIAK, if you had a stock cast iron master you have to run that unless you change boosters. Same with the aluminum ones if you happen to go the other way around.
 
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