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| Assessing a coach - purchased! Brake re-do not enough [message #213093] |
Tue, 02 July 2013 22:28  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Ai yi yi. The honeymoon is over and I never left the driveway. Despite multiple twelve hour days, still no brakes. New master cylinder, front lines, front calipers and pads. Rear brakes driver side were close to correct, passenger side adjust lever wasn't even hooked up, midwheel star was so far out it was useless for e-brake. I learned about the little button on the combination valve to bleed with. Got it all together, fired up the motor (first time from main tanks instead of gas can in floor because filler hose was shot on front tank)and the brakes were hard as a rock and barely would stop me in the driveway. I can't jog backwards to adjust parking brake because the regular brakes just don't work. I don't think the combo valve is bad, because neither end is stopping, and pedal feels all wrong.
So I am figuring the vacuum/power booster is bad. Intended to check for vacuum at booster, but I couldn't get the vacuum hose off by MC on first attempt for fear of damage. Maintenance manual mentions an air filter in the troubleshooting (page 5.13) is that serviceable? Anything else to look at on booster or other suggestions? Is there a part number for a booster that I could get locally?
Upside after brake test disappointed - messed around with air system, found a third leak and seems to pump and hold pressure. Is it normal for the "lower" setting to just vent right there at the control? I laughed it surprised me, but it lowered all right.
If you're still reading...I repacked the rear bearings when I was in there. couldn't get hub off drum to replace broken wheel stud - do that later. greased as many fittings as I could find in front, I think I missed one at bottom of steering column. and I couldn't find zerks on the lower ball joints. cut the ground wire at the buzz box and removed it. Anyone have a spare/unused/used newer style converter they want to sell? Looks like my macerator pump is corroded/dead. I may try to disassemble it and get it going. the gate from black tank to macerator assembly is frozen, but gate posterior seems fine, so I can use gravity in the mean time. I put in a new thermostat to be safe and very pleased with how the old one looked upon removal. found several bad vacuum hoses, worse one to the distributor advance. Pulled driver side back wall out, it was just disintegrated pressboard under the laminate. Blanket box I'm sure will be the same. Roof leaks and interior plumbing haven't even been started yet to stop water intrusion. I have a significant exhaust leak at a junction just ahead of the main entry door. I'll get that looked at as one of my first test drives. Is there a web page that shows how to remove dash components? I want to check idiot light bulbs (door open is only one that lights, including brake and generator lights as far as I can tell) and my radio lights up but doesn't play and I want to see if the amp is fried- must remove first. Dash fan blows really low no matter the setting - switch or some resistor thingy likely?
Feel free to comment and suggest solutions on anything, but the brakes are the most welcome feedback at this point...
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213096 is a reply to message #213094] |
Tue, 02 July 2013 22:54  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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Good idea on supplemental vacuum. I tinker with computers as well, and I used to put two side by side to use a power supply. Might be able to pull a vacuum off something else (my truck) to test...but getting the hose off at booster without breaking the fitting is tomorrow's start for testing...
Thanks
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: [GMCnet] Assessing a coach - purchased! Brake re-do not enough [message #213100 is a reply to message #213096] |
Wed, 03 July 2013 00:28 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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If you are worried about breaking the plastic 90 fitting for vacuum off the booster when removing the stuck hardened hose you might try inserting a slender 90 degree pic in between the hose and plastic fitting and gently working it around the fitting to un stick the hose. If that is sketchy , slit the hose on the fitting and carefully free it then re trim the hose.
If the braking force and response do not change between engine on and off my bet is booster or vacuum to booster
Todd Sullivan
Sully
77 royale
Seattle
On Jul 2, 2013, at 8:54 PM, Tyler <tilertown@hotmail.com> wrote:
>
>
> Good idea on supplemental vacuum. I tinker with computers as well, and I used to put two side by side to use a power supply. Might be able to pull a vacuum off something else (my truck) to test...but getting the hose off at booster without breaking the fitting is tomorrow's start for testing...
> Thanks
> --
> 1975 Eleganza
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213108 is a reply to message #213093] |
Wed, 03 July 2013 02:43 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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You sure have a list of stuff to work on. Since you listed brakes first, let's talk about them. If you replaced the master cylinder, did you bench bleed it before installing it and connecting up the lines? Did you bled all of the lines in the order listed in the book?
Assuming all of the above was done lets look what is next. Did you manually adjust all 4 for the rear brakes. I would jack it up and start adjusting each wheel using a brake adjustment tool.
http://www.opentip.com/Tools-Home-Improvement/Kd-Tools-Brk-Adj-
Tool-p-3608465.html?utm_source=PriceGrabber&utm_medium=CPC&utm_content=MIS-KD287&utm_campaign=CSE
I tighten each wheel until it locks the shoes against the drum and you can not turn the wheel by hand. Then I back it off a few clicks until I can spin the wheel and you just barely hear the brakes shoes rub on the drum.
Once all 4 are adjusted correctly, have someone step on the brakes while you try to turn each wheel by hand. If that works then you can assume that you have rear brakes adjusted correctly.
The rears must work correctly before the fronts will engage. This hold off action is done by the combination valve. If the rears will lock up then try the fronts by hand while someone steps on the brake.
If all of that works correctly and you still can not stop the coach then I would look at the power brake booster. You mentioned that you can not get the vacuum hose off. Actually the hose attaches to a 90 degree plastic fitting. That fitting is actually a check valve and it just pushed into the power brake cylinder. It just pulls out and is much easier to remove than trying to remove the hose from the fitting / check valve. . Also when you remove the fitting you should hear it hiss if there is stored vacuum in the booster. If there is no hiss, you need to verify that you have vacuum at that check valve with the engine running. If you do have decent vacuum then the booster is probably leaking / bad.
If you end up needing a power brake booster, Call Jim K. at Applied GMC or Jim Bounds at GMC Coop. They both have sensitized brake boosters that fit the GMC. Mine came from Jim K. I do not think you will find one locally. The GMC booster is slightly different than one on a car. I know of no other vehicle that it fits.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213117 is a reply to message #213093] |
Wed, 03 July 2013 07:23 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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Thanks for info -
I bench bled the new MC, but I'm not convinced I did it completely. I've done lots of pads and rotors, but this was first MC - I activated the plunger probably twenty times, and let it bubble up, and it was just doing a little fountain of pure fluid up the center (I used supplied plugs, not fittings with a hose to recirculate).
I adjusted the rear brakes by: parking brake off I could spin with my foot, and parking brake on I adjusted star wheel to where I could not spin it.
Heading out to test vacuum stuff after breakfast, hoping it is simple, because if I have to order a booster that officially kills the July 4 shakedown cruise.
Pulling the check valve out straight and using a pick around the rubber are great tips, thanks.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213123 is a reply to message #213093] |
Wed, 03 July 2013 08:24 |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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Senior Member |
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I know what you're going through. My rear brakes didn't
work until I got a pressure bleeder and replaced the
rusted brake lines.
Good Luck,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213125 is a reply to message #213093] |
Wed, 03 July 2013 08:46 |
lance
Messages: 190
Registered: December 2004
Location: Vancouver, WA
Karma: 0
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Did you order the sensitized booster that is on several of the GM sites? Amazing improvement in stopping power. If you did not order this, I strongly recommend you change your order. The cost is about the same. Get the new one, not the modified one. Good luck. It sounds like you found the problem. Let us know what the final solution turns out to be.
1974 Palm Beach
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213127 is a reply to message #213117] |
Wed, 03 July 2013 09:08 |
GMC Cruse
Messages: 606
Registered: June 2009
Location: SE Michigan
Karma: 3
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| Tilerpep wrote on Wed, 03 July 2013 08:23 |
Thanks for info -
I bench bled the new MC, but I'm not convinced I did it completely. I've done lots of pads and rotors, but this was first MC - I activated the plunger probably twenty times, and let it bubble up, and it was just doing a little fountain of pure fluid up the center (I used supplied plugs, not fittings with a hose to recirculate).
I adjusted the rear brakes by: parking brake off I could spin with my foot, and parking brake on I adjusted star wheel to where I could not spin it.
Heading out to test vacuum stuff after breakfast, hoping it is simple, because if I have to order a booster that officially kills the July 4 shakedown cruise.
Pulling the check valve out straight and using a pick around the rubber are great tips, thanks.
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If you don't already have one, here's a test procedure.
http://www.mbmbrakeboosters.com/index.php?option=com_content&view=article&id=12:what-to-do
Mike K.
'75 PB
Southeast Michigan
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213134 is a reply to message #213093] |
Wed, 03 July 2013 09:36 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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I know that brake pedal feel you are talking about. rock hard, but does not stop. I would not be so quick to point at the booster. I think that is just the way the gmc pedal feel with any sort of problem with the brakes.
call up Jim Hupy, get his break bleeder, you will not be disappointed in it.
then you know 100% that your brakes got bled properly. plus it is way easy to use!
http://bdub.net/jhupy/
that will eliminate all of second guessing yourself on the brake bleeding. plus, if you replace the combo valve, or take apart any piece of the brakes. it will make the job so much nicer when it comes to re-bleeding the brakes at any time in the future.
I have pulled my brakes apart 3 times since I got the pressure brake bleeder. I have yet to remove the pressure bleeder after closing up the last bleeder screw, and not go into the cab to find a good pedal.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: [GMCnet] Assessing a coach - purchased! Brake re-do not enough [message #213148 is a reply to message #213134] |
Wed, 03 July 2013 12:17 |
Jim Bounds
Messages: 842
Registered: January 2004
Karma: 0
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If the booster is connected to the motor and the vacuum line to the booster from the motor is good-- and there is vacuum at the booster--- fire up the motor, watch your vacuum gauge and pinch off the vacuum line, your cavuum should go up. Listen at the driver floor, you should be able to hear a hissing sound, when the line is pinched off the hissing will stop.
I have not seen a rock hard pedal without the problem being the booster
Jim Bounds
------------------
________________________________
From: Jon Roche <lqqkatjon@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Wednesday, July 3, 2013 10:36 AM
Subject: Re: [GMCnet] Assessing a coach - purchased! Brake re-do not enough
I know that brake pedal feel you are talking about. rock hard, but does not stop. I would not be so quick to point at the booster. I think that is just the way the gmc pedal feel with any sort of problem with the brakes.
call up Jim Hupy, get his break bleeder, you will not be disappointed in it.
then you know 100% that your brakes got bled properly. plus it is way easy to use!
http://bdub.net/jhupy/
that will eliminate all of second guessing yourself on the brake bleeding. plus, if you replace the combo valve, or take apart any piece of the brakes. it will make the job so much nicer when it comes to re-bleeding the brakes at any time in the future.
I have pulled my brakes apart 3 times since I got the pressure brake bleeder. I have yet to remove the pressure bleeder after closing up the last bleeder screw, and not go into the cab to find a good pedal.
--
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213228 is a reply to message #213093] |
Wed, 03 July 2013 21:51 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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Knowing I could pull the check valve straight out let me do some testing. Yesterday when the brake shake failed, I turned my attention to the air lines, found three leaks and repaired them right in front of the brake booster. It held 80 pounds of pressure overnight! So, when I re-inserted the vacuum line in the booster with engine running and the hissing began again, it confirmed bad booster. As hot and frustrated as I was, the "better in the driveway than the roadside" timing of discovery was good. I have the power level panel to use as a dash door, but I still think I am going to have to cut something to get that bottom left bolt off the booster from the inside. tips?
Still chasing electrical oddities, i'll post that question under the "assessing coach 12 volt" thread I started a while back.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213231 is a reply to message #213117] |
Wed, 03 July 2013 22:01 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Tilerpep wrote on Wed, 03 July 2013 07:23 |
Thanks for info -
I bench bled the new MC, but I'm not convinced I did it completely. I've done lots of pads and rotors, but this was first MC - I activated the plunger probably twenty times, and let it bubble up, and it was just doing a little fountain of pure fluid up the center (I used supplied plugs, not fittings with a hose to recirculate).
I adjusted the rear brakes by: parking brake off I could spin with my foot, and parking brake on I adjusted star wheel to where I could not spin it.
Heading out to test vacuum stuff after breakfast, hoping it is simple, because if I have to order a booster that officially kills the July 4 shakedown cruise.
Pulling the check valve out straight and using a pick around the rubber are great tips, thanks.
|
The parking brake has nothing to do with adjusting the brakes unless the cables are adjusted too tightly and interfere with normal operation.
Leave the parking completely brake off and adjust them as I explained in the previous posting. It really sounds like you need to adjust the rear brakes correctly first before you look at anything else. Your booster may not be bad.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213236 is a reply to message #213231] |
Wed, 03 July 2013 22:36 |
Phantom2
Messages: 94
Registered: September 2012
Location: Springfield, IL
Karma: 0
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Ken, read how he adjusted the brakes, He said: he adjusted the star wheel with the parking brake on.
Tilerpep wrote on Wed, 03 July 2013 08:23
Thanks for info -
I bench bled the new MC, but I'm not convinced I did it completely. I've done lots of pads and rotors, but this was first MC - I activated the plunger probably twenty times, and let it bubble up, and it was just doing a little fountain of pure fluid up the center (I used supplied plugs, not fittings with a hose to recirculate).
I adjusted the rear brakes by: parking brake off I could spin with my foot, and parking brake on I adjusted star wheel to where I could not spin it.
Heading out to test vacuum stuff after breakfast, hoping it is simple, because if I have to order a booster that officially kills the July 4 shakedown cruise.
Pulling the check valve out straight and using a pick around the rubber are great tips, thanks.
Larry Hopkins
75 Avion
Springfield, IL
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| Re: Assessing a coach - purchased! Brake re-do not enough [message #213254 is a reply to message #213236] |
Thu, 04 July 2013 02:37 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Phantom2 wrote on Wed, 03 July 2013 22:36 |
Ken, read how he adjusted the brakes, He said: he adjusted the star wheel with the parking brake on.
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Yes I read that. The problem is with the parking brake on the shoes are not all the way retraced. We have no idea how far the parking brake pulled on the shoes. Did it pull the shoes .010" or .250" ?
The parking brake cables need to be fully relaxed (no tension at all) before adjusting the shoes. Then the shoes need to be adjusted with just enough clearance do not drag and cause heat build up on the drums.
Keep in mind that master cylinder was originally designed to only move 2 wheel cylinders. On a GMC we are moving 4 with the same piston size and stoke. It works on 4 only if the rear brake shoe clearance is near close. As the shoe clearance is increased the brake pedal moves toward the floor. The combination valve prevents the front brakes from working until the rears have made contact and some hydraulic pressure is built up. So improperly adjusted rears will affect all 6 wheel brakes.
He may indeed have other brake problems like the booster or bleeding but the rear brakes still need to be adjusted correctly to have a correctly functioning system.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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