Dugan7
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The master cylinder was replaced in April of last year -- about 8 months before the problem started.
What the mechanic at Aamco loosened was not a valve, it was just the nut connecting the line to the master cylinder. And fluid sprayed out, indicating that pressure was being relieved. The brakes freed up after that. I don't know if that makes any sense, but that's what happened.
The reasoning that Aamco offered for focusing on the rear brakes is that they were indeed really weak, and therefore the front brakes were doing all the work, and possibly overheating. I didn't really expect this to solve the problem, mainly because it sometimes happens when we're just starting out, before the brakes CAN overheat. But I figured if I needed rear pads I should get them anyway, and pray that it did fix the issue. It didn't.
There is nothing like that "pesky electric motor" you describe, Spectramac, so I assume that means the brakes are powered by the power steering pump. (I'm no mechanic, as you no doubt have guessed.) Does this mean that fluid level or some defect in the power steering pump could be the culprit??
Let me clarify that my wife and I are on the road fulltime. And we have been for 16 years. (Our son, who just turned 18 and moved out, grew up on wheels.) So there is, alas, no way I can have a regular mechanic. Sometimes its really really REAAAALLLY hard to find a mechanic who'll touch an RV at all -- in some places, you have to be towed in before they'll make an exception. So we've had to just find the best available service we can wherever we break down. We do use Good Sam's Roadside Assistance plan, but Sam is no good for something like this.
Anyway, when we go to Chevy on Tuesday, we're going to take along a list of all the repairs that have been done and when, so they won't be starting from scratch. And when this is all over (surely it will be eventually!) we're going to look at getting some refunds, particularly from the other Chevy place who replaced the hydro boost unit for over 1000 bucks, when apparently it wasn't really needed.
Thanks again for everyone's illuminating comments. I'll keep you posted.
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Dugan7
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By "Roadside Assistance Plan", I meant mobile mechanic service. Good Sam, of course, is still good for towing when needed.
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rockhillmanor
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All I can add to your post is today I found out that it was my emergency brakes that have been draggin NOT the MH brakes.
Same thing, everyone kept checking the front brakes and the backs and none of them saw that it was the rotor and calipers from the emergency brake that was allowing the damaged piston to inch out after it got hot from driving.
When cold you didn't notice it, but boy you sure would after you had been driving for awhile. No smell of fire just the MH bogging down.
31 ft Four Winds
Chevy Tracker 4x4 Blue Ox
We must be willing to get rid of the life we've planned,
so as to have the life that is waiting for us.
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Spectramac
Monroe, WA
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I would put another master cylinder on it and give that a try. Sounds like something inside it has gotten sticky and not letting the pressure return to the top tank every time. The only other thing I can think of is if the pedal linkage is not letting it come back all the way or something like that...
I'm usually not just a parts replacement type mechanic, so I would even go so far as to tear apart the master cylinder and look for the problem.
* This post was
edited 10/04/08 01:50pm by Spectramac *
Malcolm
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Dugan7
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The mention of pedal linkage makes me realize there is something I neglected to mention. After this most recent repair session at Aamco, when we got the vehicle back, the brake pedal was loose, and didn't spring all the way back. We went back into the shop the next day, and they did some adjustment on it and it's a little better, but they said they were pretty stumped about it, and we'd probably have to have Chevy look at it. But this was the first time there'd been any problem with the pedal except for it getting hard at times--a couple of times, this happened just before the brakes locked.
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TreeSeeker
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>What the mechanic at Aamco loosened was not a valve, it was just the nut connecting the line to the master cylinder. And fluid sprayed out, indicating that pressure was being relieved.
Because of this symptom, logic would indicate that the problem is either in the master cylinder, hydo-boost or the pedal linkage. One of them is not letting the fluid back into the master cylinder to relieve the pressure.
I think this would eliminate the proportioning valve, calipers, and rubber hoses. If it was any of those, then the unrelieved pressure would be downstream of them and not upstream.
Since you have replaced the master cylinder, it is less likely to be that, but still possible. Something loose in the fluid could have plugged even a new one. Or, if is was a rebuild, then it may not have been properly rebuilt.
Since you also have a new hydro-boost then that is probably not the problem.
This leaves the pedal and hydro-boost linkage as the most likely problem, particularly since you mention issues with the pedal. It could be that you have actually had two problems. One that was fixed sometime during this ordeal and another that was introduced during the process of fixing the first problem. Or, it could be that the pedal linkage was the problem all along, and when the hydro-boost was replaced they still didn't adjust the linkage properly.
As long as you are getting fluid squirting out from the brake line fitting (after applying the brakes), the problem has not been solved. That is the best diagnostic tool you have.
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Dugan7
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Yesterday, I had a chance to verify that loosening the nut on the master cylinder to relieve pressure really does work. I could actually hear the brakes groaning as they released their grip.
Today, I am back at the Chevy dealer's near Boston, trip number 7 in an effort to cure this ailment. The service manager just came into the waiting room and told me that there is most likely a defective seal in the master cylinder, and they want to "start" with that. (Didn't I already start many months and many dollars ago??) So we're keeping all fingers crossed.
What really amazes me is that all of these mechanics seem to be just guessing.
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Dugan7
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Okay, they replaced the master cylinder, and I am cautiously optimistic. The reason is that we just drove to Hartford last night (100 miles or so) without incident, and for the last few days, we hadn't been able to go more than about FIVE MILES at a time. So maybe this really did the trick!
HOWEVER...
There's still the pedal problem, and the story there is more problematic. It seems that when the Chevy dealer in Missouri replaced the booster, the new unit did not come with a push rod, and so the old one was reinstalled, and it's a bit too short. But it can't be replaced now, because --wouldn't you know it -- they don't make them anymore. The service manager at the Chevy we went to yesterday said he'll make a couple of calls and try to locate one, but he sounded doubtful, and suggested that I do some searching on my own. I don't know where to look except auto salvage yards, and even then I'd probably have to buy the entire booster, and still might not get a rod that's the right size. Anyone have any suggestions?
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TreeSeeker
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Maybe a machine shop. They might be able to make one.
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Cool Mike
Mendocino. Calif.
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Do you know who makes that Hydro-boost system? GM and Ford dont make much or any break parts anymore, all that stuff is imported. And that's where I would start looking.
The incompetence of some of these mechanics is unbelievable. At best there parts changers, and the customer gets stuck paying for all the parts until they accidentally hit on the bad component, and no one fixes anything anymore, its all replace.
2001 27' Four Winds Class-C E-450 V-10.
Buick Park Ave Ultra, Ford Ranger PU, JD 500 backhoe.
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