Weak Brakes Issue

[NixEqnx]

Hi Everyone,

I'm a new member and here's my first of (many?) questions. I purchased a '83 K10 in April of last year, and have done quite a few things in it to get it into running condition, there are a few more functional items left (wipers, lights, rear shocks etc.) left, but mostly cosmetic issues. However, one thing i cannot figure out is my brakes.

I replaced the front calipers, rotors and discs, and left the rear drums alone (friend said they are fine) We ran all new brake lines. However, stopping from 5MPH to 0 is very difficult. From 60 down to 5 it's fine, works like a normal vehicle, but to get it down to zero, my foot is on the floor and my butt is off the seat holding it down.

Could this be air in the lines? I've tried bleeding the brakes twice, never really saw any bubbles. however, i also have filled up the fluid a bit and no matter how much i put in, the next time i check i seem to have the same amount of fluid (like a low point) so i might have a leak somewhere as well. i just don't see any leaks (i guess i really need to clean all the connections and check)

Do you think that the brake booster could be bad? Worth replacing the master cylinder + booster, or just try to clean the brake lines of dirt/grime, and see if i have a leak.

Thoughts?

Thanks in advance
~Nick

PS sorry if this is in the wrong spot, couldn't figure out where to post.

[philo_beddoe]

Had the same problem with my ford.  It was the booster, it felt like the "power" was gone in the power brakes.  Worked good at normal speeds, but not going slow.


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[zieg85]

It sounds like a master cylinder internal leak to me.  How is a total panic stop from 60?  An easy stop until you reach the point of "uh oh, I have to mash the brake pedal harder or I am not going to stop in time moment" could be the master with an internal leak.  If the brake booster is leaking vacuum your power assist could be going away.  Brakes are hard to diagnose over the internet so I would take it to a trusted mechanic and see what he/she says.

[NixEqnx]

panic stop from 60? knock on wood haven't done that yet. i have done some "heavyish" breaking at around 40MPH just to check that it they did work. i don't know my exact speed, as no gauges work except an aftermarket thermostat. (another reason i'm not driving around a lot)

Of course all my local shops, no one has a master cylinder + brake booster in stock. And the one shop that does have it in stock doesn't have a combo unit and only has the booster and a cylinder at another shop. Guess time to order online and spend my Saturday doing something else.

As for taking it to a mechanic, there isn't anyone in my neighborhood i know of that i trust. Always done everything myself due to my upbringing (hey it saves money right?) Anyway, $130 for a part isn't bad when it comes to safety.

[zieg85]

But if you are just throwing parts at it that may be wasting money you don't need to spend.

[Irish_Alley]

i would figure out also where the fluid is going to. it could be a bad wheel cylinder leaking fluid on the brakes.

[jaredts]

If you are losing fluid you will have problems.  You will have to find the leak(s).  If you don't see any fluid on the inside of your wheels/tires I would get a flashlight and look at every inch of you lines.  A rusted spot in a line can be just barely wet but cause issues.  Don't forget to look at the proportioning (combination) valve as well.  If it isn't leaking make sure the wire is plugged into it and that the brake light doesn't come on.  When I bought my truck the p.o. had unhooked the wire and the brake light wouldn't come on.  The valve was frozen with my back brakes locked out by the valve.

[NixEqnx]

Thanks for all the info guys. As the parts store didn't have it in stock i'd have to order so i didn't just buy the booster. One thing I should have done better was to clean the lines and then drive/inspect for fluid better. I just haven't had a chance to do too many things. Wife bought a bike that needs a carb rebuilt so that is currently taking up my garage workspace.

Hopefully i can do a clean on Thursday and see if there is any fluid elsewhere. The lines are all new so it might be a bad connection somewhere.

Note: as for the brake light on the dash, not much on the dash works except the voltmeter and some red light if it doesn't start on the first try. I bought it knowing it was going to be a project but a bit more than i can chew at the moment.

[Breadfather]

If you are losing fluid you will have problems.  You will have to find the leak(s).  If you don't see any fluid on the inside of your wheels/tires I would get a flashlight and look at every inch of you lines.  A rusted spot in a line can be just barely wet but cause issues.  Don't forget to look at the proportioning (combination) valve as well.  If it isn't leaking make sure the wire is plugged into it and that the brake light doesn't come on.  When I bought my truck the p.o. had unhooked the wire and the brake light wouldn't come on.  The valve was frozen with my back brakes locked out by the valve.

jaredts, how did you repair this issue?  I re did my rear brake system this weekend,(wheel cylinders, drums, shoes, hardware, new steel lines as the old ones broke removing them from wheel cylinders) when I was bleeding the rears, I noticed very little pressure, after a long time of gravity feeding them and triple checking the adjustment, i was convinced something else was wrong.  The brake light on the dash lights up and has been lit up since I bought it a couple weeks ago, and based on that and everything I have read online, I am convinced it is a prop valve issue.  I tried to get it to reset itself, by bleeding the fronts with the rears closed but no luck. As i was doing this, I noticed the drivers side front has low pressure but the passenger side front shoots out like a geyser when bled. So I am assuming this is another prop valve issue. Now how do I fix it?  I couldn't get the metal piston under the rubber boot to move with pliers or screwdriver or hammer.  Do I need to remove it and disassemble/reassemble? I've done brakes on these trucks many times and never had this issue. The brake light was on when I bought it last weekend and it looks like both rear wheel cylinders were leaking at some point based on the amount of gunk in the drums when I re did them.

[Irish_Alley]

could also be the rubber brake hoses. ive seen rust around the metal parts squeeze the rubber hose to restrict flow in both directions.

[jaredts]

My prop valve was seized.  I had to replace it as I couldn't find any seal kits or parts for them.