Brake problem
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Tuned
Joined: Nov 2006
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Brake problem
I'm hoping some one can give me a little guidance on this. While driving today, my brakes started acting different. I had one of those double pump moments, and on the second pump, brake pedal was hard as a rock. I had to try to push if through the floor to stop the truck. It is only noticeable if you double pump the brakes. Before anyone asks, yes I checked the brake fluid and it was full. Any suggestions would be helpful.
Lead Driver
Joined: Mar 2006
Posts: 5,097
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From: western SD
Check the vaccume pump. It should pull a minimum of 19 in. Pull the hose off the brake booster and check there with engine running. Does the heater/ AC defaut to the defrost when this happens?
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Tuned
Joined: Nov 2006
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Didn't get a chance to test vacuum pump yesterday. Brought the vacuum gauge with me so I'll do that today. But driving to work this morning the brake light came on, then went off about a minute later. Only came on once.
Lead Driver
Joined: Oct 2003
Posts: 8,476
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From: Madison, WI
Vacuum pump does not affect power steering (that must've been something else), unless it seizes entirely and shreds/throws the belt, at which point you have a LOT more going on. Warning light could be hydraulic issue, parking brake or vacuum pump, and with the hard pedal, vac pump is the prime suspect. That, or the hose from the vac pump to the distribution box.
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Tuned
Joined: Nov 2006
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Update
Replaced master cylinder today. Checked vacuum pump and a reading of 6 in Hg ( 15 cm Hg). Have to bleed the lines but do the vacuum readings seem ok?
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Lead Driver
Joined: Oct 2003
Posts: 8,476
Likes: 37
From: Madison, WI
That sounds like very low vacuum. Both the distribution box and the booster have a bit of vacuum reserve, so that's probably why the pedal gives some normal assist on the first push. But with the pump pulling such weak vacuum, the brakes probably exhaust that reserve quickly, and by the second pedal push, you're out of reserve and wham! hard pedal. If that measurement was right from the pump, before the distro box, then I'd say your pump is done for.
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Tuned
Joined: Nov 2006
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Unfortunately, this was my first time to replace a master cylinder. So I didn't know you were supposed to bleed it before installing in. I did bleed the brakes in the correct order. However, did not bleed the ABS sensor.
Forgive me, but I don't even know where the sensor is. If some one could tell me where it is, I would be greatful. Can I bleed the MC adequately now that it is already installed?
Forgive me, but I don't even know where the sensor is. If some one could tell me where it is, I would be greatful. Can I bleed the MC adequately now that it is already installed?
Lead Driver
Joined: Oct 2003
Posts: 8,476
Likes: 37
From: Madison, WI
There's no sensor. The truck uses the VSS as the sensor for ABS. You need to bleed the RABS _valve_, which is on the line going to the rear brakes, on the left frame member aprx. under the firewall.
For the M/C, you can disconnect the lines and hook up the little bleeder tubes (they should have come with the new M/C) and bleed it using the pedal. Then reconnect the lines and bleed all of the above.
For the M/C, you can disconnect the lines and hook up the little bleeder tubes (they should have come with the new M/C) and bleed it using the pedal. Then reconnect the lines and bleed all of the above.
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