Topic: Whats wrong with my Brakes ????

[locked 4x4]

Ok so for the last couple of weeks I have been pulling my hair out trying to find the gremlin in my brakes.

So what I am working with is and 82 toyota pickup.  It has an aftermarket GM master cylinder and a stock booster.  The axles are dana 44's out of a scout.  The front has a single piston calipers and the rears are just drum brakes.  

For the last year the breaks have always worked flawlessly.  However, a couple weeks ago I was wheeling the truck and the front breaks went out.  The back breaks still worked though and every time I came to a stop they would lock up and I would skid to a stop.  

I figured the master had gone out so I went and got a new one, bench bled it, and installed it.  I bled the breaks and all I could get was mushy brakes.  Continued to pull things apart.  Ended up putting new wheel cylinders in the rear axle.  Also replaced the break pads all the way around and still had mushy breaks.  I then replaced the master again thinking I might of had a dud, bench bled it and bled the whole system again and still mushy breaks.

I gave up for a while and today I tried again to find the gremlin.  Ended up adjusting the pads in the rear axle until they were so tight that I could barley turn the tire by hand.  Bled the whole system again.  Didn't see any signs of air coming out of the system.  However the truck still has mushy breaks.  Every time I come to a stop my brakes go all the way to the floor and the truck just slows down gradually.  I just don't get it because before the brakes had no trouble locking up.  

My booster seems to be working still because I can feel it kick on when I start the truck.  If I pump the peddle and start the truck the brakes do settle a little more.  

Any ideas would be greatly appreciated.  I have put a disgusting amount of break fluid through the system and I am out of ideas what else could be wrong.  I can't see any signs of leaks in the brakes. soooooooooo

  :headscratch:WHY WON'T MY TRUCK STOP???

[Doable]

Still sounds like air in the system. Sometimes bleeding the brakes give trouble for me and my buddies and we just drive the truck a little bit on the dirt roads to "bounce the air bubble" around that may be in the lines and bleed the entire system again. Most of the time this works for us. Good luck let us know what it takes to fix it.

[locked 4x4 [OP]]

Yea I went on 1 trip so far with no breaks and did enough bouncing around to snap a driveline and pop a tire.   Have bled the breaks again since then and it is still spongy.   Its just so bizare because on all of my other truck re breaks have been so easy.

[Cheesemaker]

Are you getting rebuilt master cylinders, or new?  What condition is your rubber brake lines in? 

[locked 4x4 [OP]]

Both masters are from Autozone.   They appear brand new but they may be rebuilt.  I don't see how I could have 3 bad masters though.  The break lines are name brand steelbraded lines.  No visible wear.   I was talking to a buddy and he suggested that it may be the calipers on the front axle.   I don't know how these would fail though.  They are not leaking fluid and when I bleed them air dosent seem to come out any more.

[emsvitil]

Adjust the brake pushrod

[Sparkplug]

ive had this a few times. Might sound crazy but I crack the line coming out of the master, and have someoneone pump, i wait ill i see fluid come out and as its coming out, i close the line. I do this to bohth of them, and they usually hav air in them, even if i bench bled it beforehand. Worth a shot

[OOPS]

If you do not bench bleed the MC before you put it on, you will have air trapped in it.

[locked 4x4 [OP]]

Adjust the brake pushrod

I dont see how it would move all of the sudden.  Also when I took the master cylender off of the booster it appeared to be making contact.  Although at this point anything is possible.   Ill put it on my list of things to check again.

[locked 4x4 [OP]]

ive had this a few times. Might sound crazy but I crack the line coming out of the master, and have someoneone pump, i wait ill i see fluid come out and as its coming out, i close the line. I do this to bohth of them, and they usually hav air in them, even if i bench bled it beforehand. Worth a shot

Ill give this a try.  Deffinately sounds like a possibility.

[locked 4x4 [OP]]

If you do not bench bleed the MC before you put it on, you will have air trapped in it.

I bench bled both new masters before I put them in and its still the same problem with mushy breaks.  I even jacked the back end of the truck up so that the master cylender was level and tried bleeding the system and still couldnt get a firm peddle.  

[emsvitil]

I dont see how it would move all of the sudden.  Also when I took the master cylender off of the booster it appeared to be making contact.  Although at this point anything is possible.   Ill put it on my list of things to check again.

The recess in the new cylinder may not be as deep as the original.   

If it's not as deep, the brakes will be slightly on, covering up the bypass hole in the cylinder.

[locked 4x4 [OP]]

   

If it's not as deep, the brakes will be slightly on, covering up the bypass hole in the cylinder.

Can you explain this more.   It is the same model master I replaced it with so the depths of the whole should be the same.

[emsvitil]

Can you explain this more.   It is the same model master I replaced it with so the depths of the whole should be the same.

It should be the same, but might not be...

[locked 4x4 [OP]]

Well I ordered new front calipers.  They should be here tomorrow.  My plan is to install those and bleed the calipers.  Then im going to try cracking the line at the master cylinder and bleed it their.  If i still cant get peddle, the master is coming off again and I am going to check if I can adjust the rod somehow.   

[BHT12]

 
weird.. im subscribed.. i want to know what outcome is.. all i can think is front calipers if theres no fluid dripping

[locked 4x4 [OP]]

Well I put new calipers on and the brakes work.  Still don't understand why though.  The old calipers were moving but they just weren't applying enough pressure.  The new calipers seem to work great.  They may need to be bled a bit more but the brakes are working again so I'm stoked.