Kamphiker
South Florida (this 'aint paridise anymore)
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Joined: 07/09/2002
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Usually that valve have check balls inside and if trash gets inside will cause the balls to stick. Also corrosion form mositure in the brake fluid will cause the same thing.
Hopefully that will solve your problem and get you back on the road.
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Dugan7
Nationwide
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I am at yet another mechanic's this morning, and I relayed the suggestions I received, so they are checking into that. They're also saying that maybe the rear brakes could be out of kilter, and so that's causing the front brakes to overheat and lock. I don't think that's the case, because when it happened a few days ago, we'd only driven about 2 miles after the vehicle had been sitting for three weeks. Sounds like they're just shooting in the dark again!
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enblethen
Moses Lake, WA USA
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Joined: 01/05/2005
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Stay in touch!
Bud
Suzuki XL7 pushing Pace Arrow
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Gene in NE
Omaha
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Dugan7 - It sounds like the mechanics you have used so far are just replacing parts. Can you reproduce the symptom? Have you been able to figure out something that happened each time just prior to the brakes dragging? Something like going down a steep hill when you were resting your foot on the brake to keep the speed down? Dragging the pads for two miles can heat things up. Or bad front wheel bearings? It certainly acts like heat is the problem, because after it cools - things are normal.
How did you determine it was the front wheels? Were the hubs very hot? Careful touching brake components when it happens again - they can be almost red hot. The problem could be as simple as a non-fully retracting emergency brake. How often do you use the emergency brake?
2002 Trail-Lite Model 211-S w/5.7 Chevy
Gene
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Texas Jim S
Belton, TX
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The master cylinder has a internal vent that allows the brake fluid to return to the reservoir of master cylinder. As the brakes and fluid heat up the fluid in the system expands and if the vent is blocked the fluid won't return to the reservoir. The hotter it gets the more the brakes are applied. It has the same effect as you slowly applying more and more pressure to the brake pedal and will eventually stop the vehicle. If the vehicle has been towed either from the front or rear, it is possible a metal brake line was crushed. It sounds like you are just taking it anywhere and everywhere to have it fixed. I suggest that you take it to a garage that has competent mechanics that can properly diagnose the problem and not a shop that just replaces parts.
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j-d
Sunny Florida USA
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Joined: 09/04/2003
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Second Texas Jim.
If both front brakes are setting up on you, there is a very good chance that tiny pinhole in the master cylinder bore is clogged. There is a larger hole in the chamber that you should see squirt fluid up when pedal is released, but also a smaller one forward of the large one that ensures all pressure is dissipated. This is true of both chambers (one for front brakes, one for rear), but usually the rear will stay clear. Reason is that the rear drum brakes retract with spring pressure when you take your foot off the brake and that forces the fluid back to the master. On front disc brakes, the apply pressure is merely released but there is no actual return flow to the master. This allows that little hole to "heal up."
As previously requested, let us know what happened on this!
God Bless, jd
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Dugan7
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Thanks for the feedback and concern, everyone. Sorry I haven't replied sooner, but internet access has been spotty.
The folks at Aamco in Rhode Island replaced the rear pads, but that didn't affect anything. We decided the thing to do is go back to another Chevy dealer, but it's been really hard to find one that will work on RVs at all. We finally found one north of Boston, but they were very busy, and at first we were going to have to wait TWO WEEKS to get in. But now, we're set for Tuesday. By the way, out of the 7 shops we will have taken it to, this will be the third Chevy dealer. You'd think they of all people would know what they're doing!
In the meantime, the guys at Aamco showed us a trick that seems to relieve the symptoms temporarily -- when it freezes up, just loosen the fitting on the brake line at the side of the master cylinder to relieve some pressure (and lose some fluid in the process, of course). Anybody know anything more about this?
To answer you, Gene, there's no rhyme or reason to it. Sometimes it happens after the vehicle has been sitting a few days, and we're just starting out. Sometimes we've been driving for hundreds of miles, and it suddenly acts up while we're driving. It's definitely the front, because we saw it smoking once.
As for that hole in the master cylinder that a couple of you spoke of, I haven't been able to find it -- only the one hole in the center.
We're keeping our fingers crossed until Tuesday. Thanks again for all the input.
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Texas Jim S
Belton, TX
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If you open the bleeder valve on the master cylinder and it temporarily fixes the problem, then you are in effect opening the vent in the master cylinder. This vent IS NOT VISIBLE TO THE CUSTOMER. This is not a Chevrolet issue as it is the same with most cars and light trucks. If you have not replaced the master cylinder since it was new then it is probably overdue to be replaced. I recommend that you ask your friends, neighbors, and coworkers where the take their cars. When you have several people recommend one garage, then take your vehicle there. Tell them what you have had done and then STAY WITH that shop until you get it fixed. Jumping from shop to shop will do nothing but cost you money. Tell the garage that a qualified brake specialist has suggested that you may have a master cylinder problem. Good Luck.
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Spectramac
Monroe, WA
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Joined: 06/11/2008
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I've been fixing brakes (professionally) for years and your story even has me scratching my head. I'll echo some of the others saying the master cylinder is the problem (or at least is pumping and not releasing by some other physical issue). I was jumping up and down in my chair when I read about what some of these "shops" have been doing to you. Rear brakes causing the front to lock up????? Come on guys!!!
I heard you mention hydro boost. So the brakes are powered by the power steering pump, or do they have their own dedicated pump? Does it have that pesky electric motor that fires up if you hit the brakes with the engine off? I'm not sure where I'm going with this other than to get a better idea of the system in your rig...
I have heard of faulty master cylinders, was this a brand new unit or rebuilt?
* This post was
edited 10/02/08 11:56pm by Spectramac *
Malcolm
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T18skyguy
Eugene, OR
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Joined: 12/13/2004
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I'm gonna go with Enblethen. The part he is calling master cylinder compensating is also called the proportioning valve. It has springs and check balls in it that stick from rust. I think thats the problem.
Retired Anesthetist. Pilot with mechanic/inspection ratings.1996 Jayco C 22 foot with 460/Banks Powerpak/Bilsteins.Wife and daughter. Two cats which control my life. 1975 Ford F-250, 84 Coupe Deville, Thorp T18, tons of tools and tons of junk.
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