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Followup To
Question - I've seen minute leaks like that cause problems, but this had none prior to the rear line rusting out, and those I would keep getting air bubbles when bleeding. This has no air bubbles at all since the initial bleeding. I keep wanting to lean towards this centralizing the diffential valve. I used to an equalizer valve older Chevy products, but there is nothing like that on this vehicle. Does the RABS valve do that on this vehicle?
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Followup To
Question - OK, bled the front brakes, no bubbles, rebled rear brakes, rebled RABS valve, bled at master cylinder, results remained the same. We bled from back to front then front to back, results remained the same.
Thanks again for your assistance, like I said before I ran into this same problem a couple of years ago where I used to work and we changed EVERYTHING in the brake systems and didn't fix the problem, the boss's retired grandfather came in and worked on it, used an old power bleeder and after a few days of messing with it, took it to lunch for 3 hours and brought it back fixed. He claims he just bled it, but I didn't belief him then or now. Looked in my Chiltons manual and it says:
"It will be necessary to centralize the pressure differential valve after a brake system failure has been corrected and the hydraulic system has been bled."
My question is could this be the problem, and if so, how do I do it, cannot find any explanation in my Chiltons manual.
Thanks Ragu, for your quick response. Did what you suggested, got tons of bubbles, realized on pedal release was sucking air around threads of bleeder fittings, removed fittings and applied teflon tape to threads and rebled. No more air, continued to bleed rear brakes, still no air. Bled RABS valve, again no air. I haven't bled the fronts yet, bleeders are rusted in and front half of system wasn't opened. Shouldn't be air in the front, then, correct?? I've sprayed the front bleeders with penetrating oil in case you feel i need to bleed them. Do I need to do something different or a lot more?? We pumped the pedal several times at each bleeder
Thanks again for your help,
Hilton
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Followup To
Question -
95 f-250 rear brake line rusted out, replaced, bled brakes, right rear, left rear, good pedal. start vehicle, good pedal, then pedal fades, no leak, rebled system, no air but same problem. This is the 3rd truck i've worked on with same problem, went threw 2 gallons of fluid and changed every part on the one truck before it finally got fixed. does the air get stuck in a specific spot and is there a trick to getting it out?
Answer -
YES : take a glass bottle (see through) fill it 1/4 way up with brake fluid place a rubber vac hose about 1 1/2 foot long crack the bleader loose to were the fluid starts to com out.now place the hose on the bleeder and in the bottom of the bottle have someone just pump the peddle nice and slow when the bubbles stop coming out stop pumping take your foot off the peddle and tighten the bleader. start from the rt rear then left rear then rt front then left front. keep cking your fluid. good luck. let me know how it works out?
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yes the fronts have to be bleed too reasons 1)the old fluid is still there and the temp. level is low 2) you mite have trap air.
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we had a similar problem at my shop it was the rear wheel cyl.they were new but they had internal leaks the way we found this out was know matter how maney times we bleed the brakes we keep getting air. when we pulled back the rubber boot on the wheel cyl. we saw some brake fluid .the second thing was the rear brakes were never adj.when all was done it would put you throu the windsheld,
Answerwith out the truck running what i want you to do is pump the brake peddle till it gets hard then holding your foot on the peddle start the truck up and see if the paddle travles down.if so i want you to remove the master cyl and look behind it to see if it is wet.
