New hydroboost, still spongy pedal

6speedsd

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Replaced the hydro on the 03 work truck. Was leaking fluid out every seal and barely had brakes. New one went on this morning, reused the master. Pedal gets firm engine off, but it is soft with it running. You can mash the pedal and it'll hold, but if you barely release pressure, it surges towards the floor. Fluid is full...brake and PS, we did brakes on the rear a couple weeks ago and bled all 4 corners then. No PS issues that are obvious. If its air in the pressure lines, will it purge itself out with a little time, or is there a procedure to bleed the PS system?

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DEEZUZ

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Make sure you don't have a seized caliper pin or caliper somewhere
 

6speedsd

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I had the rears off a couple weeks ago and all was good with those. We rebled the rears today but got sidetracked and didn't do the fronts. No air in those. Jacked up the front end, held the brake and did lock to lock with steering a couple times, did not help pedal feel. Pedal is slow to return to normal position....it comes up on it's own, but its slow. Tested the new booster by holding the brake and cranking the truck...while turning over the pedal went to the floor but never returns. (Mine drops then kicks back up when the truck fires). Pumped the pedal to get it firm with engine off then held for 30 seconds...best I can tell it doesn't seep off like the master is bypassing internally. Fluids are full, no leaks. It will stop now with the new booster, but pedal goes almost to the floor before it bites.

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6.0 Tech

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Have you tried bleeding the master? Did it get tipped upside down when doing the hydroboost? If so, it more than likely has air in it.
 

6speedsd

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Had the old man go hold the pedal engine off this evening. He says its sweeping down to the floor, so it's getting a new Master tomorrow. Will report back afterwards.

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