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73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: Logan80 on February 02, 2014, 06:29:34 PM
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I've got a 1980 1-ton 2wd Chevy truck with the Hydroboost brakes and it's got an issue. The pedal seems to be easily pushed nearly to the floor and it doesn't do much of anything as far as braking is concerned. You get some feedback in the pedal if you push it hard when the truck is sitting idling in the driveway, almost feels like ABS (which it's obviously not).
I'm hoping it's a master cylinder and not the actual hydrobooster. The power steering fluid is full and power steering works just fine. If you REALLY mash the brake pedal down it'll cause minor belt squeal similar to turning to full lock and trying to turn farther, which leads me to believe that the hydrobooster is actually functioning.
Has anyone had a problem like this? Likely master cylinder?
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Loosing a master cylinder with hydro boost brakes feels nothing like loosing it with the standard vacuum boost power brakes. If you had brakes but now don't and there is no leaks it is more than likely a bad master
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I have the truck so that I can sell it for a family friend who now lives out of state. From what I was told it was fine when it was regularly used last, but it's been pretty much sitting for a couple years.
It most definitely has pretty much no brakes. You can move it at driveway speeds, but if you try to drive at even 25mph it gets real exciting trying to stop...
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Are you sure the problem is not at the wheels?
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Ditto on the above..
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Well, I haven't experienced wheel cylinders or calipers causing pedal feedback like this before. Is that a common thing?
If you push the brakes firmly while idling it pushes back and pulsates almost like ABS...
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Sounds like air in the lines...
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stupid question and kind of being a smart butt, but you do have fluid in the reservoir?
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Yes, it's full of fluid, and the power steering fluid is also full.
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You have a sneaky by-pass in your master cylinder. Sometimes a by-pass in the master doesn't always manifest itself. Once I was pulling a car onto a rack after a very short test drive for a "check brakes" ticket. I could hear the metal to metal on the first brake apply, so I headed to the rack, but when I tried to apply the brakes to stop over the rack the pedal went to the floor, and I darn near had a collision with the tire machines.
That pulsing you feel is the result of the fan belt undulating rapidly under the strain of you pressing hard on the pedal. If you were to point a timing light at the Hydroboost pump belt while someone was pressing hard on the pedal you'll see what I'm talking about.
If your not using fluid just replace the master.
Good luck,
P.S. It is possible the energy the causes the pulsing originates inside the hydroboost pump resulting in a undulating fan belt. I never really gave it that much thought. I do know that the pedal pulsation is common while standing on the pedal.
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I replaced the master cylinder and the brakes then seemed ok. However the driver's side started dragging pretty bad on my little test drive around the neighborhood.
Replacement calipers aren't terribly expensive and I want the truck to be safe, so I replaced both calipers. When I went to bleed them the passenger side bled fine, the driver's won't allow any fluid out.
I even disconnected the brake hose from the caliper and still cannot push any fluid out, the pedal does not go to the floor like it should. I have a new driver's side brake hose, just haven't gotten a chance to change it yet. It's dark and raining when I get home from work, not idea conditions to crawl under a truck and try to figure out how to change this hose...
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For sure your next step is change out the brake hose.
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Ok, so I replaced the hose and that was definitely the issue causing it to not bleed.
Right now I have two new calipers, one new hose, and a new master cylinder.
I can't get it to bleed all the air out however. I've just been trying to bleed the front and it's gotta be sucking air someplace, but I'd think that would also mean it's leaking fluid. I can't find anyplace where fluid it getting out or air is getting in.
It's tough because during the hose change of course fluid spilled all over the place, I cleaned it up the best I could but you can't get it all 100% clean/dry. It makes it tough to find any potential leaks...
Any ideas where I should look next?
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have you opened the rears yet? i always crack the bleeders and gravity bleed them then i ise the brakes to finish the job or a brake bleeder