Master Cylinder question

[Todd Z]

OK,



I believe my master in my 03 is going on me, but not 100% sure....



I replaced front brakes last week.... Calipers a year ago.... Stainless lines 3 years ago.... Bleed system, changed fluid. Re bleed system. I am 100% there is no air.



1) During a slow normal stop the pedal is firm and you will go through the windshield if you press slightly harder. Onced stopped you can push like heck on the pedal and it gets soft...but if you release its ok.



2) During a fast stop ( Not panic) the pedal goes low, the truck seems to take a longer time to stop almost coasting.... Pump pedal, gets firm and truck stops OK to me...



3) Panic stop, the pedal almost slams the floor.... the truck doesn't even want to stop, like the brakes are non existant.... pump pedal or push harder and the truck seems to slow down.....



the only thing to add is the truck blew out rear pads (ALL worn evenly) about 6 months ago...



I replaced all 4 at the SAME time !!!! WTF !!! LOL



Any input please....



I was going to replace the master this week.....



Thanks



Todd Z

 

[Chad Merry]

Mine does the same thing. Let me know what you find.

 

[Willie Anglin]

Rule of thumb I always use, if you can pump up the brakes and hold and the the pedal does not go down it is not the master cylinder 95% of the time. Master cylinder will bypass most of the time if it is bad and leak down when pressure is being applied.

 

[Todd Z]

prch,



I agree, But i wonder if there is a worn spot in the middle some where causing the fast stop it doesn't seal right away,,, the 1 way gasket in there ya know.....



This is why i hate things like this.... LOL



Todd Z

 

[Kevin Palmer]

Try this,,,



Once stopped, release the pedal a bit and then put slight down pressure on the pedal. So basically your doing a little hic-up kind of thing with the pedal. But not aggressive, just a little bump (release) and then gentle press back down.



If the pedal continues to go down, then the master cylinder is defective.



Wheat happens is, the fluid bypasses the end seal and travels along the shaft and back into the fill area. So no leaks (actually, internal leaks but you can't see them).



As a general rule, this is more prevalent when the fluid is warm..

 

[Jeremiah Morgan]

Sounds like a Master to me!

 

[EddieS'04]

That is exactly how my brakes acted, when. I tried using speed bleeders. Put the oem bleeders back in, all is well.

 

[Richard L]

Todd Z,

Since the rear brakes blew out, I would suspect that you have a problem with the rear brakes that sounds like you have air, a leak or bad rear calipers. When you push the pistons back in to fit the new pads it pushes the piston back over the possibly corroded sections of the piston bore and the can damage the seals.



You can stop very well at low speed because the front brakes are doing all the work. When you try to do a panic stop, the fronts can't stop without some assist from the rear brakes and they are not working properly.



I would check the rear brake calipers for leaks, flush some of the fluid from both rear brakes and see what the fluid looks like. If it's dirty and nasty looking, you need to flush all the brakes and try the brakes again, but you may need to replace or rebuild the calipers if they have become too corroded inside.



If the fluid comes out clean, then I would look at the Master Cylinder. The best way to test the brakes is with a hydraulic pressure gauge (you can probably rent one). You can test pressure at each wheel and the master cylinder and that will tell you what you need to know.



The last area could be in the ABS system. I have not messed with them, so I can't tell you how to test the unit?



Many years ago I had a similar problem with my Honda and it just needed to have the fluid flushed because the old fluid had absorbed water and water turns into steam and steam can compress just like air. and it only does it on panic type stops.



...Rich

 

[Todd Z]

Rich,



The rear calipers are new too and flushed the fluid 2 times, once the old way and 1 time with a machine at the dealer.....



I am gonna replace the master as i got a new Wagner one for $50.00 shipped to my house.... If that doesnt work I am burning the truck to the ground.... the brakes were SOO mint from about 20K to 80K..... Now its just a headach.,.......



I feel I sold the wrong truck this year.... its heart breaking.....



Todd Z

 

[Richard L]

Todd,

Are those Brand New calipers, or rebuilt?? If new, they should be fine, but if rebuilt, they may have had a defect that was not caught when they were rebuilt.



Anyway, I hope the master cylinder fixes it.



...Rich

 

[Todd Z]

Me too...... Yes Brand new.... I don't play with rebuilt UNLESS I rebuild it.....



Changed the master today and completely blead the system again !!!



Gonna give it a few days of my driving to see how it goes !!



Todd Z

 

[Richard L]

I prefer to use facotry rebuilt calipers from an autoparts store like AutoZone, NAPA, PepBoys, etc. They often give 50K miles to lifetime warranties and I have never encountered a bad one yet...but I'm sure occassionaly one bad apple slips through. :grin:



Good luck with the Master cylinder and let us know how it works out. One thing I forgot to mention was bleeding the master cylinder. if you sucked in air when you bled the brakes, that air will stay trapped in the master cylinder and could also cause the symptoms of air in your rear brake lines?? I hope you know that you should bench bleed the master cylinder before you put it on the truck? Bleeding the brakes does not always get the air out of the master cylinder.



...Rich

 

[Todd Z]

OMG thats been my issue all along,,, really, I was supposed to do that ??.....



insert sarcasm smiley here.....



:rofl:



Todd Z

 

[Richard L]

Todd,

I was not trying to be sarcastic, just helpfull...You posted that you were having a problem and I tried to help with a solution even if that meant going over some of the basics that you already knew. The number of people who don't know that you should bleed the Master Cylinder, or simply forgot to, might surprise you.:grin:





...Rich

 

[Richard L]

Oops, I double clutched that one and posted twice.

 

[Willie Anglin]

So Todd what's the verdict? Enquiring minds want to know.

 

[Jeff Harwanko]

Yeah Todd, any news? I'm having the exact same problem, and it's driving me crazy...

 

[brian brown 3]

still no answer? did he run into a wall and can't come back on? haha.. just kidding!



Brian