Home » Public Forums » GMCnet » brake light... and questionable brakes
| brake light... and questionable brakes [message #70637] |
Tue, 12 January 2010 12:22  |
cal clements
Messages: 18
Registered: October 2009
Location: athens, ga
Karma: 0
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Junior Member |
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greetings you all:
maybe this has something to do with below freezing weather here in georgia, or maybe not... but i notice that my brake light has come on. indeed, the brakes do seem a bit weak. it is hard to say, however, because i get used to driving my truck and other cars, such that the GMCs reduced braking is always a bit of a surprise.
i do notice that some squealing does happen when the brakes are applied harder (in the back left wheels).
i notice that the master cylinder has fluid.
what steps might i take to troubleshoot this?
cal.
The Green Pickle
1977 GMC Palm Beach
Athens, Georgia
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| Re: brake light... and questionable brakes [message #70638 is a reply to message #70637] |
Tue, 12 January 2010 12:28  |
jwillard
Messages: 118
Registered: May 2004
Location: Silver City, NM
Karma: 0
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If the noise is "scrapping" rather than "Squealing" I'd get the rear brakes looked at.
Otherwise, they are probably way out of adjustment. That will turn on the light (It's good your's works. :>) ) Once they're adjusted up a few hard applications of the brakes should reset the light. Make sure you keep a close eye on fluid level.
Jeff Willard
Silver City, NM
1973 ex-Glacier
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| Re: brake light... and questionable brakes [message #70641 is a reply to message #70637] |
Tue, 12 January 2010 13:06 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| cal clements wrote on Tue, 12 January 2010 13:22 |
greetings you all:
maybe this has something to do with below freezing weather here in georgia, or maybe not... but i notice that my brake light has come on. indeed, the brakes do seem a bit weak. it is hard to say, however, because i get used to driving my truck and other cars, such that the GMCs reduced braking is always a bit of a surprise.
i do notice that some squealing does happen when the brakes are applied harder (in the back left wheels).
i notice that the master cylinder has fluid.
what steps might i take to troubleshoot this?
cal.
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Cal,
That indicates an imbalance between the brake systems front to back. This can be a leak in either system or a failure internal to the master cylinder. (Read WD0AFO of 03 January and related entries.) In any case, operation of the vehicles is not advised. - DUH.
I do not recall if the switch used in the coaches is self resetting. If it is not (some please fill this in), there may have been a temporary imbalance that has cleared. Unfortunately, this was probably caused by a real problem.
You say the master cylinder has fluid. Are the cells the same?
About the only test that does not require experienced touch, is fortunately a simple one. Pop the top off the reservoir and have someone step on the brake. Some fluid will come back, but not much should. If a bunch more comes back in one than the other, it is a master cylinder failure.
No Luck?
Now top up both sides of the reservoir, and with the engine running, stand on the brake pedal.
Does it creep down?
-If it does not, you might not have a leak or it might be very hard to find.
-If it does go down - even very slowly - there is a leak. You might as well pump it up a couple of times and make it easy to find. You already have a mess to clean up in any case.
That is about the end of the cheap and easy diagnostic.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: brake light... and questionable brakes [message #70647 is a reply to message #70641] |
Tue, 12 January 2010 13:56 |
cal clements
Messages: 18
Registered: October 2009
Location: athens, ga
Karma: 0
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Junior Member |
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hi matt:
thanks for these steps. i will follow them all soon, when i can grab an assistant. but one thing i noticed right off: no, the two cells in the master cylinder are not the same. the front cell was empty. the back cell was full.
what does that indicate?
cal.
The Green Pickle
1977 GMC Palm Beach
Athens, Georgia
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| Re: brake light... and questionable brakes [message #70649 is a reply to message #70647] |
Tue, 12 January 2010 14:53 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| cal clements wrote on Tue, 12 January 2010 14:56 |
hi matt:
thanks for these steps. i will follow them all soon, when i can grab an assistant. but one thing i noticed right off: no, the two cells in the master cylinder are not the same. the front cell was empty. the back cell was full.
what does that indicate?
cal.
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Cal,
That is not good. (I just bet you figured out that much already.)
In the original installation (who knows what POs have done), the front cell is the rear brakes. That is bad because the rear brakes should never have the change of fluid level that one should expect from the front (rear reservoir). Ergo, it is very likely that there is a leak in the rear portion of the brake system. The rear brake system should be carefully inspected for leakage. This may require removing the drums. That is not a huge job, but if you don't see the leak along the line, you do not have a lot of choices here.
Do you have some brake fluid?
If yes, fill the front reservoir and pump the brakes a few times and see if the pedal feels different. The master cylinder may self bleed enough to get by. Filling the system is only damage control at this time.
In normal service, the level in the front reservoir should not change much at all. The rear can be expected to go down and that is the compensation for the wear of the pads in the front disk brakes.
Does(did) the brake pedal "pump up" very much in normal prior to recently?
That could indicate that the rear brakes where in need of adjustment (the automatic adjusters have never been all that great and a manual adjustment may be required).
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: brake light... and questionable brakes [message #70669 is a reply to message #70641] |
Tue, 12 January 2010 19:03 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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""I do not recall if the switch used in the coaches is self resetting. If it is not (some please fill this in), there may have been a temporary imbalance that has cleared. Unfortunately, this was probably caused by a real problem. ""
It is self resetting but as you say, it's not going to reset until the original cause is fixed.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] brake light... and questionable brakes [message #70691 is a reply to message #70669] |
Tue, 12 January 2010 20:42 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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G'day,
Ken Henderson has a series of annotated photographs on the Photo Site which
show how he removed the 130 psi feature to the rear brakes before the fronts
got pressure. He noted that his was "pretty cruddy" when he took it apart.
http://www.gmcmhphotos.com/photos/showphoto.php?photo=5317
If you like you can start on the picture below and follow what he did step
by step.
http://www.gmcmhphotos.com/photos/showphoto.php?photo=5314
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Bob de Kruyff
Sent: Wednesday, 13 January 2010 12:04 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] brake light... and questionable brakes
""I do not recall if the switch used in the coaches is self resetting. If it
is not (some please fill this in), there may have been a temporary imbalance
that has cleared. Unfortunately, this was probably caused by a real problem.
""
It is self resetting but as you say, it's not going to reset until the
original cause is fixed.
--
Bob de Kruyff
78 Eleganza
Chandler, AZ
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] brake light... and questionable brakes [message #70809 is a reply to message #70691] |
Thu, 14 January 2010 14:28 |
cal clements
Messages: 18
Registered: October 2009
Location: athens, ga
Karma: 0
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Junior Member |
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today i tried the following:
1. i loaded the front compartment of the master cylinder with brake fluid.
2. my wife pressed the brake pedal.
3. i watched large bubbles emerge. then small bubbles. then, after a number of pumps, a rather solid fountain.
4. putting the cover back on, i tried driving forward and back at low speeds. the brakes are much improved.
5. the brake light is now off.
i decided to see what the master cylinder does in my chevy truck, for comparison. indeed, when the brake pedal is pressed, quite the fountain of fluid emerges. (splattered all over).
from this, i conclude that the master cylinder is working (for now). the question, i suppose, is "will the front cylinder's fluid leak out?" i shall watch for this.
how does that sound to you all?
with best wishes and thanks for your help,
cal.
The Green Pickle
1977 GMC Palm Beach
Athens, Georgia
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| Re: [GMCnet] brake light... and questionable brakes [message #70810 is a reply to message #70809] |
Thu, 14 January 2010 14:55 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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There are better ways of troubleshooting these things Cal. But what
the heck, it worked:>)
On Thu, Jan 14, 2010 at 1:28 PM, cal clements <calclements@yahoo.com> wrote:
>
>
> today i tried the following:
>
> 1. i loaded the front compartment of the master cylinder with brake fluid.
> 2. my wife pressed the brake pedal.
> 3. i watched large bubbles emerge. then small bubbles. then, after a number of pumps, a rather solid fountain.
> 4. putting the cover back on, i tried driving forward and back at low speeds. the brakes are much improved.
> 5. the brake light is now off.
>
> i decided to see what the master cylinder does in my chevy truck, for comparison. indeed, when the brake pedal is pressed, quite the fountain of fluid emerges. (splattered all over).
>
> from this, i conclude that the master cylinder is working (for now). the question, i suppose, is "will the front cylinder's fluid leak out?" i shall watch for this.
>
> how does that sound to you all?
>
> with best wishes and thanks for your help,
>
> cal.
>
>
> --
> The Green Pickle
> 1977 GMC Palm Beach
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
'76 EII
Sierra Vista, AZ
Urethane bushing source
www.bdub.net/ferguson/
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| Re: [GMCnet] brake light... and questionable brakes [message #70818 is a reply to message #70809] |
Thu, 14 January 2010 15:44 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Cal,
Something caused the fluid in the master cylinder to "leak out" if you did
not troubleshoot and find the reason for it to do so then it is reasonable
to assume it will "leak out" again.
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of cal clements
Sent: Friday, 15 January 2010 7:29 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] brake light... and questionable brakes
from this, i conclude that the master cylinder is working (for now). the
question, i suppose, is "will the front cylinder's fluid leak out?" i shall
watch for this.
how does that sound to you all?
with best wishes and thanks for your help,
cal.
--
The Green Pickle
1977 GMC Palm Beach
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GMCnet mailing list
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_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] brake light... and questionable brakes [message #70833 is a reply to message #70818] |
Thu, 14 January 2010 20:40 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Robert Mueller wrote on Thu, 14 January 2010 13:44 |
Something caused the fluid in the master cylinder to "leak out" if you did not troubleshoot and find the reason for it to do so then it is reasonable to assume it will "leak out" again. ...
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Correct,
Brakes do not "USE" brake fluid and shouldn't need "topping off." The reservoir feeding disk brakes will drop as the pads wear, but the reservoir should be large enough for this.
Look for the leak while the coach is safe at home.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] brake light... and questionable brakes [message #70869 is a reply to message #70833] |
Fri, 15 January 2010 09:57 |
cal clements
Messages: 18
Registered: October 2009
Location: athens, ga
Karma: 0
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Junior Member |
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yes--thanks! i'll look for a leak. i'm a new owner of this GMC such that i don't know how full/empty the reservoir has been. now i have a data point from which to determine the rate of the leak.
am i right in thinking that it could be in one of three zones--
a) the master cylinder and regulator
b) the lines
c) the drums
The Green Pickle
1977 GMC Palm Beach
Athens, Georgia
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| Re: brake light... and questionable brakes [message #70892 is a reply to message #70637] |
Fri, 15 January 2010 17:38 |
fred v
Messages: 999
Registered: April 2006
Location: pensacola, fl.
Karma: 0
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Senior Member |
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i agree. a leak of that magnitude will be easily spotted with wet brake fluid on the frame or dripping out the back side of the rear brake drums. you shouldn't even have to have someone stepping on the pedal while you look.
Fred V
'77 Royale RB 455
P'cola, Fl
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