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  #46 (permalink)  
Old 01-21-2013, 11:46 AM
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Alright got an update, I turned out the booster rod (between the booster and master) a bunch and tried to put the master on, no go, turned in the rod a little, better but still hitting the master, turned in more and it was flush but hitting the master just barely, turned it in just a hair more, master bolted up and not hitting the rod....
then adjusted the heim joint between the pedal and booster, turned it all the way in and there was no play, turned it back a little, now theres a little play, turned it just a hair more, now theres about 1/2" play (when I push the brake pedal it goes about 1/2" before I feel anything push on the MC).

Test drove it and its MUCH better but not right yet. I was able to slow down much quicker but still impossible to lock up the wheels (maybe because of the 454 motor and heavy truck with cheapo kragen pads??)

Should I adjust the booster again or look at better pads or what? I do have access to the depth gauge for GM boosters at my shop and can try that out also or is this as good as its going to get with the cheap pads, heavy truck, and massive engine??

I did notice that now under panic stops the engine stumbles a lot due to all the air being sucked up by the booster, maybe it needs some more vacuum to operate panic stops better?

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  #47 (permalink)  
Old 01-21-2013, 12:07 PM
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Glad we are making progress...

Does the pedal "pump up" when you are pumping the pedal, or does it stay at the same height every time you push it?

If you hold firm pressure on the pedal does it sink to toward the floor?

How high above the floor is the pedal when you are pushing on it hard?

If it stays the same and doesn't sink down, then try this...

Go into a gravel parking lot and drive about 15 mph and hit the brakes hard. If any wheels lock up, you will be able to see by the ruts in the gravel which wheel or pair of wheels it was.

Let us know what you find.
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Old 01-21-2013, 12:12 PM
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The stumble is more than likely a carburation issue and not due to vacuum.

It sounds like you are right on with the master/booster adjustment. Leave it as-is.

Cheap pads usually equal soft pads. Soft pads usually stop better cold than high performance pads. Don't get me wrong, there are some cheap pads out there that don't stop for a damn.

Lets keep working with what you have before you go and spend any more money.
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Old 01-21-2013, 02:00 PM
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when pressing hard enough to just stay stopped like at a light the pedal is about 5 1/2 inches from the ground (little less than 1/2 way from the at rest position), when pressing hard like for a panic stop its about 4 1/2 inches from the ground.

When pumping the brakes at idle the pedal goes down the same amount each time, when holding it down at idle it stays in position also.

Stopping enough to thrust me forward but not enough to lock up the wheels still.

Dont know ANYWHERE that there is loose gravel around here, ill keep an eye out but most of the places with gravel are construction areas and blocked off here in the city. Dont know if ill be able to find anywhere large enough to be able to do that gravel test, just with the weight alone I think the whole truck would slide anyway.
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Old 01-21-2013, 02:07 PM
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Now try this. With the engine off, press on the brake pedal and hold it down reasonably hard. Then, without lifting your foot, start the engine and tell me what happens.
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Old 01-21-2013, 02:08 PM
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That was the first thing I did when I starting dealing with this brake concern, pedal sinks, unless you want me to do it again. I have also pinched the brake hose from the intake to the booster and driven it, rock hard pedal then, I know the booster is working properly at that point.
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Old 01-21-2013, 02:11 PM
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What type of hose or line do you have connecting the booster to the engine?
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Old 01-21-2013, 02:13 PM
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reinforced rubber fuel line connected from booster to nipple on back of intake behind carb, pretty large diameter (standard gm valve on the booster so I am sure you know how large it is) also verified the hose is not leaking
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Old 01-21-2013, 02:21 PM
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Auto parts stores sell a special hose for brake boosters. It is described as 11/32" vacuum brake hose. It has a thicker hose wall and won't collapse internally, and being a slightly smaller diameter you don't typically need hose clamps if using it on a hose nipple fitting (though you can clamp it if you like).

For a hose run as long as yours (booster under the floor) I would recommend 3/8" hard line from the intake down along the transmission to near the booster, then a piece of vacuum brake hose from the hard line to the check valve on the booster.

At very least replace all the hose you have with the special hose.

Once all that is good, we can look at brake pressure at the wheels.
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Old 01-21-2013, 02:25 PM
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ill pick some of that up but in the meantime I have verified that this hose is NOT collapsing, in the meantime can I keep on checking the system with this hose? I just got off the phone with the parts store and they had to order it so I wont have it for a couple days.

Anything else to check also before going into specific wheel pressures?
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Old 01-21-2013, 05:15 PM
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This sounds like insufficient vacuum. How much vacuum do you have at idle?
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Old 01-21-2013, 05:22 PM
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19" vacuum at idle
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Old 01-21-2013, 05:27 PM
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So smooth as glass idle. That's not it, then.
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Old 01-21-2013, 07:59 PM
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The next question is how much flow of brake fluid you get from each caliper when you are bleeding the brakes. Do you get about the same volume of fluid at each bleeder screw when you are bleeding them?

If all that looks good, jack up the truck and get all four wheels off the ground. With the engine off, have a helper apply the brakes until you can't turn the front tires by hand and then have your helper hold the pedal in that position. Then go an try to turn the rears and see what happens. If the rear wheels will still turn, have your helper press harder to see if they can lock them up. Sometimes I will take off the tires and use a bar to turn the wheels. If the calipers are way out of adjustment it will show up with this simple test.

If the rear tires lock up first we can address that issue too.

Did you try locking up the brakes in gravel?

Let me know what you find...
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Old 01-27-2013, 06:37 PM
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hard pedal

I had a single sticking piston in a 4 caliper willwood front disk system recently that created a hard pedal and lack of clamp pressure ... I decided to rebuild the calipers with willwood seal kit and reassembly lube. The hard pedal problem disappeared as did the static brake drag I was getting.
If you havn't allready solved your problem, jack up the car and see if you have a wheel that wont spin when the brakes are not being applied.

If you find one, you have found a sticking piston or two or more....rebuild ( cheap and easy if the caliper has rebuild kit ... mine was 16$ for two calipers and assembly lube from willwood) or replace the calipers altogether.

Experts would insist you do both sides to keep things even...no matter which route you go...so I did...figuring if one side was sticking, the other was soon to follow so...why not.

Bo-peep 68 camaro 396BB.
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