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No Brakes!!!


Cruzn620

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well i put the truck (79 620 KC) up on stands today. i thought that the calipers were frozen up, but preliminary tests ruled that out. all of a sudden, i had brake pressure! when i started the truck though, all pressure was lost. my reseviors are full of fluid, i have bled the brakes once, everything seems to be hooked up right, though i'm not sure if there is a hose clamp on the line going from the intake mani to the brake booster. could i be loosing that much vacuum there? any other ideas? thanks!!

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Just to clarify, you tried the brakes while the truck was up on stands? While it was off? Was there no pressure at all with the engine running, or was it just really weak?

 

Have you actually checked the vacuum line for cracks or kinks or whatnot, and do you have clamps at both ends, tightened well? Have you actually checked how much vacuum you have in the line with the car running?

 

I really don't have any idea what it could be... Have you tried bleeding the brakes to make sure the fluid is getting through all the hoses? How does the brake pedal feel? Only thing I could think of is maybe the vacuum is being applied to the firewall side, rather than both, or perhaps a valve is clogged and not releasing pressure or something... The booster is the only thing that comes to mind that could be affected by whether or not the truck is running...

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brakes are kinda a fun thing to diagnose when they dont work, everybody always misses the one common thing. the master cylinder. it works all the time no matter what, you can stop a vehicle whether its running or not, you should get a good firm solid pedal after just a coupla pumps. id check the back of it and see if its leaking. then id follow the lines down and check for a springer. then id check the lovely old rubber hoses that like to crack and clog. then last is the caliper/operating cylinder. if the slider is not seized and the piston in the caliper works, the bottom end is fine. replace the master. now the fun part. when working on drums. the operating cylinder has to be checked with 2 ppl to do it right. remove the drum, and only one!! get a buddy in the cab and one that will follow directions exactly. no idiots or funny guys here. place 2 decent sized flathead screw drivers against the backing plate ridges, and touching each shoe. then tell buddy to very slowly press the brake. both sides of the operating cylinder should move pretty near equal. dont let it go to far out, or youll need to replace that operating cylinder. thats where having a trusted buddy comes in. if only one side works, then the cylinder is screwed and needs to be replaced. you cant turn the drum by hand when brake pressure is applied, even tho one side is screwed. the brake effort of that one side is approx 30%. thats why you may not stop, but still have pressure. hope that helps. i see it all to often at work.

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thanks for all the help guys. i couldnt build this truck without all of you! my brake hoses up front are pretty much junk. there is electrical tape wrapped around them!!! i have new ones on order, though on the old one, i didnt see any leaks. I think i have a wheel cylinder leaking on the drivers side rear, as there was oily residue on the rear of the drum when i bled them a few weeks ago there, but not on the other side. i didnt bother bleeding the system again with the brake hoses in the shape they were in. as far as the feel, when the truck was turned off, the pedal felt good. when the truck was running, it fell 95% to the floor, then i had some brakes on that last 5%. basically to drive it, i had to shift down til i got to about 10mph...my brakes could stop the truck from 10mph on down. other than that, they were useless. i dont think i have a problem with the "bottom" end of my brakes because with the front wheels off the ground, hitting the pedal would stop the wheels when i turned them by hand. i'll be down to work on it thursday and friday, i'll post my findings. thanks again for all the help!

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parking brake? does it work?

it doesnt use the hydraulic pressure of the MC.

 

replace ALL: the rubber lines; MC; wheel cyliders; rebiuld the calipers (or replace too)

 

safety first!

 

and what shady said about testing the cyliders, i just put the drums on 1/2 way to watch the motion

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If your front lines are that soft, I would replace all of your soft lines on the brakes while you're at it, they obviously haven't been replaced in a looong time, so it would be good to do it now while you're thinking about them.

 

Also, check your wheel cylinders to see if they are leaking or not. I had to rebuild my rear cylinders because they were leaking and I couldn't find replacements.

 

Just saying it's better to be safe.:)

 

EDIT: Sorry hang 510, I didn't read your post until after I posted, but I will leave this up to reinforce what he said

 

 

IOW, Your brakes are important.:D

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  • 3 weeks later...

little update...i got the new hoses on today and bled the system. i have good pedal feel, but didnt run the truck to see how it was when it was running. That leaky wheel cylinder didnt have as much pressure when i bled it than the other side did, so that is on my list to replace when i get some more cash putting into the datto fund. i was messing around in the cab and notice that the e-brake was on....this thing has been on since i bought the truck!!! so yeah...my shoes have to be shot! Im going to replace those too because the truck rolls fine with the e-brake on! LOL!!! now when i put the rear shoes on, will i get my e-brake back, or will it need other work? thanks

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