m3g474rd Posted June 11, 2013 Report Share Posted June 11, 2013 Hey all am fairly new here, have been checking out the site for awhile to help with any issues I have run into and has been great. Now to the problem. I have been fighting with the brakes on this thing for awhile now and nothing seems to work. Had gone through 2 re manufactured master cylinders that were both bad, and then went with a brand new one. Spendy but it seems to be working fine. Replaced everything save for the adjusters in the rear, and even the NLSV. Have bled it oh about 20 times or more and nothing seems to be working. Pedal goes down to the floor when running and will stop the truck slowly, or if you pump a few times but never any real pressure. Thought possibly was the booster and tried plugging the vacuum lines for it and yes pressure, but no brakes. Have adjusted every brake to where they should be, at least according to the book. Till I cant free spin by hand then 2-3 clicks back. Any help would be most appreciated as kinda need the lil bugger to haul stuff and such :P Quote Link to comment
Z-train Posted June 11, 2013 Report Share Posted June 11, 2013 If there are no externals leaks,then the MC is by-passing internally.Replace the MC. Quote Link to comment
Radiant-Designer Posted June 11, 2013 Report Share Posted June 11, 2013 hmm did the 2 remanufactured MCs do the same thing? Is this a new issue or has it been ever since you replaced the MC? Quote Link to comment
Z-train Posted June 11, 2013 Report Share Posted June 11, 2013 If there are NO EXTERNAL leaks,the the MC is the only possible cause ASSUMING all other factors are equal. Quote Link to comment
m3g474rd Posted June 11, 2013 Author Report Share Posted June 11, 2013 one of the RM MC did the exact same, the other had issues with the bleeders on it being old and non working so we returned it. And yeah was thinking it was possible that the brand new MC could be bad but kinda hoping that wouldn't be the case. And no leaks that I can see anyway. Oh and Radiant this has been a ongoing issue honestly for the last couple years. Wasn't to bad when it started a pump or so and was fine, but then escalated to pedal to the floor Quote Link to comment
datzenmike Posted June 12, 2013 Report Share Posted June 12, 2013 You have air trapped in the system. Did you bench bleed the master before installing? Did you bleed the rears first then the fronts? open bleeder... pump pedal to floor and hold... close bleeder... let pedal up... repeat Quote Link to comment
m3g474rd Posted June 12, 2013 Author Report Share Posted June 12, 2013 Sure did Mike. Did the bench bleed before installing. Also followed a post you did for bleeding order. Which helped a lot. And yeah bled just like every other rig have worked on. Got me, my mom and uncle all going err what to try next Quote Link to comment
AceOfDiamonds0 Posted March 15, 2014 Report Share Posted March 15, 2014 A solution to this would be most helpful. My 77 620 is doing the exact same thing. 1 Quote Link to comment
ggzilla Posted March 15, 2014 Report Share Posted March 15, 2014 These symptoms can be caused by several different problems. So the solution that worked for m3g474rd may not solve your problem. Symptoms: "Pedal goes down to the floor when running and will stop the truck slowly, or if you pump a few times but never any real pressure." Potential causes include: * defective master (poor quality control) * pushrod incorrect length * air in lines * improperly adjusted brakes * spongy brake hoses * leaks What solved it for m3g474rd? Is the truck still sitting un-fixed? Or has he scrapped the truck? Quote Link to comment
kgrantkey Posted March 15, 2014 Report Share Posted March 15, 2014 You have air trapped in the system. I see where you bled 20 times. It sure acts like air in the system to me. I have also had a problem with new re-manufactured MCs that I got from Autozone (Cardone) i think. Quick funny story - my grandson that luvs the 620 (probably cause his feet reach the peddles) was gonna help me bleed the brakes. After a few tries and nothing happening I went to look at which peddle he was pumping. -The gas peddle!- I didn't make fun of him he was trying to help. We got it straight . Quote Link to comment
bonvo Posted March 16, 2014 Report Share Posted March 16, 2014 something i have noticed NO ONE has said yet is its a 620 with drums all the way around are the brakes adjusted correctly? that will cause the issues your having as well as impropperly bench bled master Quote Link to comment
datzenmike Posted March 16, 2014 Report Share Posted March 16, 2014 Have adjusted every brake to where they should be, at least according to the book. Till I cant free spin by hand then 2-3 clicks back. Any help would be most appreciated as kinda need the lil bugger to haul stuff and such :P Quote Link to comment
bonvo Posted March 16, 2014 Report Share Posted March 16, 2014 i some how missed that i would lean towards the master then Quote Link to comment
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