soft and hard brake pedal????

[bdydrp97s10]

ive replaced all the hard line and rubber lines on my 68 c10, put a new master cylinder on it

and when the truck isnt running it has a good brake pedal, but when i start the truck and the booster has vacuum the pedal gets soft for some reason..

its nowhere near as hard as when the truck isnt running, the pedal goes almost all the way to the floor and then i can feel the pedal pressure a little bit..

im scared to take the truck on its maiden voyage with the brake pedal like this... any ideas what is wrong

and the lines are beld, they have been bled like 4 times just to make sure.. no air bubbles are coming out anymore.

[LONGHAIR]

Still sounds like air in the lines to me. The pedal is hard when the truck is not running....but when you get the added pressure from the booster you are able to compress that little bit of air.

Did you bleed all of the air out of the Master Cylinder before installing it?

[bdydrp97s10]

yes i bench bled it and it seemed to help it a bit..when i put it back on the truck i beld the brake lines again

any other ideas

[bdydrp97s10]

could it be booster problem??

what does a bad booster feel like?

[LONGHAIR]

Usually they feel like you don't have one at all.

I still think it is air.
You could try "gravity bleeding"

Open the master cylinder, make sure that it is full, leave the top off.
Crawl under the truck an open all of the bleeder screws....
Do NOT touch the brake pedal, in fact stay out of the cab.
All of the bleeders should begin to flow when you open them, at least a little.
Now just let it run for a while, but keep an eye on the master cylinder! You cannot let it run dry, just add a little as needed. After you have gone thru some fluid, start closing the bleeders. Start with the right rear and work your way up to the left front last.
After this, you should be good to go...

[bdydrp97s10]

i tryed the gravity bleed, to no avail.

still the same pedal.. ill try to conventional bleed one more time and see where we stand

[bdydrp97s10]

conventionally bled the brakes and it has a good pedal while the engine is off but when its on its kinda crappy... i know there is no air in the lines... so im stumped

now im not saying the brakes dont work because i dont know.. they may stop the truck just fine but i dont want to risk driving it and the brakes not working well

[protrash64]

When I bagged my 'burb I had this issue...turned out I smashed the rear brake lines...thought they were 1/2 a$$ed out of the way and they werent. When I fixed everything it worked fine.

Have you tried putting your truck in gear??????? Running.

[bdydrp97s10]

Originally Posted by protrash64

When I bagged my 'burb I had this issue...turned out I smashed the rear brake lines...thought they were 1/2 a$$ed out of the way and they werent. When I fixed everything it worked fine.

Have you tried putting your truck in gear??????? Running.

no im scared to.. will that change anything??

im really sure none of my lines are smashed, but ill look again

[Sammy]

After replacing lines, bench bleeding, gravity bleeding. It still took me 7 or 8 times to bleed the entire system.

[protrash64]

Originally Posted by bdydrp97s10

no im scared to.. will that change anything??

im really sure none of my lines are smashed, but ill look again

Cant really do anything unless you have an object in front of you....just to see if you're getting any grab. I just remember the feel of my pedal changed once I threw it in gear......just pop it back out if there is an issue.

[62LS1]

I'm not fast enough at typing to enter in a bunch of ideas, so I'll start with a simple suggestion. Go to www.cardone.com and join their ProTech club. It's free and then you get access to their ProTech bulletins. There are a number of them on diagnosing problems and several dealing with brake bleeding. You may have to search a little to find the right bulletin, but I quickly found one bulletin that shows how to narrow your problem, starting with the master cylinder, then working your way through each wheel to see where the actual problem lies. (I think it's still air in the system.)

Good luck.

[VDOG]

This is what I used today. It works, but my problem I bleed the rear for about 40 minutes total on the right rear, and it still had air bubbles.
The front took only 5 seconds to give a solid flow.

[dammitmitchell]

you have neutral and a working cable run emergency brake..
be patient, test drive within REASON in the neighbor hood or a parking lot with low traffic (highschool on saturday, not walmart on payday)and be sure...
remember the MOST BIASED OPINION is your own..
and your perception is your reality,
not trying to offend or upset you , if i have i apologize not my intent, but we have ALL freaked out over "nothing" before.. you never know until you check..
if you get issues use neutral and use your e-brake a click at a time you should know before even leaving your street if it is okay,,
after all these repairs the feeling you have now might be the correct one... especially if you have repaired parts that caused degradation in your braking system..
(same issue when i did my axle swap)
good luck

[dammitmitchell]

p.s. if you do a :pump pump bleed method" remember to keep the cover on.. my shiny new suspension lost paint and now looks ghetto because of that mistake

[70C10Toejam]

What carb and how old??? May sound like an odd question, but my brakes varied, while running, not a running/not running issue. But while rebuilding my carb, I replaced the very cracked vacuum choke pull-off, and just about put myself through the windshield with the extra(all I should have had) vacuum. brakes are a whole new beast now.

[panhead57]

may sound wierd but stick with me on this. We had the same problem when we did the brakes on my older brothers burb. I sat there for a good hour scratching my head on it before I called one of my buddys from work. His suggestion was to bleed the system with the engine running, worked for us thats my .02

[Longstep70]

Originally Posted by 70C10Toejam

What carb and how old??? May sound like an odd question, but my brakes varied, while running, not a running/not running issue. But while rebuilding my carb, I replaced the very cracked vacuum choke pull-off, and just about put myself through the windshield with the extra(all I should have had) vacuum. brakes are a whole new beast now.

Ok, this post has me thinking - I have new disc brakes with a brand new booster and master and have bench bled the master and bled the lines several times. i still get a soft pedal at the top of the travel before it firms up and this post made me sit up and take notice because i have an issue with my vacuum advance line fron the base of my TBi setup - when i disconnect the line it makes no difference to the timing. It seems like I have no vacuum advance right now - if i have a similar issue would the (potentially) lower vacuum reduce my booster input?

-Andy

[70C10Toejam]

Originally Posted by Longstep70

Ok, this post has me thinking - I have new disc brakes with a brand new booster and master and have bench bled the master and bled the lines several times. i still get a soft pedal at the top of the travel before it firms up and this post made me sit up and take notice because i have an issue with my vacuum advance line fron the base of my TBi setup - when i disconnect the line it makes no difference to the timing. It seems like I have no vacuum advance right now - if i have a similar issue would the (potentially) lower vacuum reduce my booster input?

-Andy

The vacuum advance depends on if you use ported or manifold vacuum. Ported means no vacuum unless you press the go fast pedal. If it is manifold vacuum, then there is always some vacuum present. But a leak could affect the amount of boost available.

[Tony@AirRideTech]

There is no doubt the pedal will be firmer with the engine off. My money is that the push rod that was supplied with the brake kit is too short and not fully engaging the master cylinder.

[hwyix]

I would pressure bleed several times. You replaced some many things it is going to take a while to get the air out.

I have never had good luck with the gravity bleed way. Have a friend pump, then open the brakes up only seems to work well after almost all the air is out.
Pressure bleed it.

[Super73]

When I went from manual brakes to a boosted system, at first I was usure I even had brakes until I actually went for a quick ride. They worked fine but it felt like they went to the floor. It took a little to get used to. Now I'm going back the other way to shave weight.

[cajundragger]

it is also prossible your pulling too much vacuum.

[85sqbdy]

Just a shot in the dark here, but you stated that you went to a power brake setup. I recently went the other way on my 85 c-10 trying to cut some weight and ended up with a super stiff pedal. After going through the whole replace parts and bleeding about three gallons of brake fluid through the system phase, I looked at the brake pedal assembly itself. I noticed that the pedal had no free travel at all and was alot closer to the seat now. On a huntch, I measured the distance from pedal pivot point to master cylinder and compared it with a friends manual set up. My pushrod was too long. I made my own pushrod from a grade 8 bolt with the head cut off and a clevis on the pedal end so i could adjust the length. Seems to be working alot better with the shorter rod. Is it possible that yours is too short or maybe the point at which it attaches to the pedal is a different spot making the pedal ratio not great enough. Did you look to see if the pedal is down to the pedal stop when the brakes are fully applied? If so, you may not be getting all the braking you could be. I'm not sure if the setups are similar or not. I've heard that some factory setups use different pedal ratios to save money on the production line. Just a couple of ideas to think about.

[bdydrp97s10]

ok guys i got it "figured out"

I replaced the proportioning valve and replaced the booster with a new one and bled the hell out of the lines..

they are fixed now.. not sure what the problem was but its fixed after i put those new parts on..