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Old November 29th, 2006, 01:28 PM   #1
Strangler
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Default Hydroboost brakes- no pressure to rear?

I converted my FF 14 bolts brakes to disc, using 78 K25 calipers and rotors on my 97 K2500. When I did this (4 months ago), I threaded the stock rear brake line into a small adapter (to change thread) and then into the caliper.

I bled the brakes like any other vehicle... pump, pump, pump. hold, bleed.

I then did the front when I put the Dana 60 under it. Changed the brake lines (to longer ones), filled the m/c and pump pump pump , bleed.

Brakes worked great! They were a little strong in the rear with the disc, but they worked great for 4 months. I then developed a squeal in the rear, which was caused by gear lube leaking from the hub seal, onto the rotor.

I dissasembled the axle, brakes and hub to repair.

Upon re-assembly I cracked the stock hardline when the caliper slipped out of my hand, so I ran to the parts store, bought some line and replaced the lines from the rear axle "T" to the calipers.

The M/C never ran completely dry.

I filled the m/c, and proceeded to pump and bleed as usual...... nothing.

I now have very little pressure at all. I disconnected the lines at the "T" and checked again.... with someone hitting the brake I still have very little pressure thru the line. I reassembles the lines and gravity bleed everything, then used a mity-vac, then tried bleeding as usual, and I still have no pressure- the pistons arent even moving in the calipers.

The pedal blows right thru the first half of its stroke, and is SSLLOOOOWWWW to return.

Any ideas? What did I do wrong? How do the proportioning valves work- could it be "stuck" and not allowing pressure to the rear?

When my assistant has the brakes pumped up, and I crack the bleeders, fluid just peeters out, instead of spraying whether the engine is running or not.

Ideas? Bueller? Bueller?
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Old November 29th, 2006, 02:31 PM   #2
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On the front of the prop valve you will see a button like, Pull it out with some pliers and let fluid flush thru while gravity bleeding (keeping the master full). It could be gummed up and not allowing the valve to move inside.
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Old November 29th, 2006, 06:05 PM   #3
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I think your not re-charging the master at the begining of its stroke. it sounds like you have flow, but the master is not returning far enough to take in more fluid. check your brake light switch to see if its holding the pedal down some. it maybe just enough to cause this head ache. secondly use the power booster. when you cycle the system the accumulator lets you get between 5-8 pumps under power with the engine off.
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Old December 11th, 2006, 12:10 PM   #4
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your a retard he has hydro boost brakes not vaccume boost
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Old December 11th, 2006, 12:16 PM   #5
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you need to eliminate the problem at the source, first cheak for preasure at the rear port of the master cylinder, then work back the first place without preasure,it will be the problem. It also saves you money by not just being a parts changer.
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Old December 11th, 2006, 12:28 PM   #6
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you need to eliminate the problem at the source, first cheak for preasure at the rear port of the master cylinder, then work back the first place without preasure,it will be the problem. It also saves you money by not just being a parts changer.
i know this guy hes my Neighbor he knows his shit
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Old December 11th, 2006, 05:36 PM   #7
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your a retard he has hydro boost brakes not vaccume boost
who were speaking too?
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Old December 11th, 2006, 08:34 PM   #8
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who were speaking too?
just a guess but I think it was directed to you.
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Old December 12th, 2006, 08:37 AM   #9
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Is the brake light on the dash illuminated?

Inside the proportioning/combination valve there is a spool valve that moves to one side if the brake pedal is depressed while there is no pressure in one of the brake channels (Front or rear), such as what could happen if one side developed a leak... OR if you happened to push the pedal to the floor while bleeding the brakes... There would be pressure in te front, but not in the back, so the valve moved toward the back.... Usually this illuminates the brake warning light.

Sometimes the valve is designed to block further flow to the channel with no pressure... in effort to stop the loss of brake fluid. The valve is SUPPOSE to reset itself, but I have heard they sometimes dont and need to be reset manually.... Like KillerB said. Look for the button or nub in the front side of the combination valve and try to pop it back out.
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