More brake issue...
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Senior User
Joined: Feb 2008
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More brake issue...
Asked this over in the 89 forum and diddnt really get anywhere. I finally got the brakes working good on the truck about a month ago, drove it cross country and haven't had any problems. Now Ive got one. About half the time I go to use the brakes, the pedal will go almost all the way down, and then get very firm, at which point the brakes start to catch, but its nowhere near good enough. When it does this, I can hear a vacuum leak inside the cab. Sometimes it will do this, sometimes not. Everything in the brake system is new except the wheel cylinders which looked ok last I saw them, maybe leaking slightly(its on my list), and the booster. Any help?
Postmaster
Joined: Apr 2008
Posts: 4,802
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The brake system is hydraulic, the brake booster is vacuum, no amount of vacuum leaks will cause a sinking pedal. Any and all pedal travel issues can be traced to hydraulic issues, in your case it's either the rear wheel cylinders or the HCU for the RABS. Wheel cylinders leak, pull your drums and pry the rubber caps off the ends of the wheel cylinders and see if you see any traces of brake fluid there. The HCU can bypass internally, to check for that you lock its accumulator piston in place - you do this by removing the large hex cap from the front end of the HCU and pulling the spring, then replacing the spring with a bolt of suitable length and diameter, and finally reinstalling the hex cap - a locked piston will not allow pressure bleed off the main line to the rear wheels even if the dump valve is leaking internally, so if your pedal feel improves while the piston is locked it's time for a new HCU (or you can leave yours locked, and learn to brake without RABS assist).
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