Home » Public Forums » GMCnet » Brake booster replacement
| Brake booster replacement [message #305725] |
Sun, 21 August 2016 15:31  |
tgeiger
Messages: 518
Registered: February 2006
Location: kansas city
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Ok, got the new brake booster in and it's working great, but my brake lights are constantly on. Any ideas of what caused that?
Tom Geiger
76 Eleganza II
KCMO
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| Re: [GMCnet] Brake booster replacement [message #305729 is a reply to message #305725] |
Sun, 21 August 2016 15:49  |
James Hupy
Messages: 6806
Registered: May 2010
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The pressure is unequal between the front and rear braking systems. You
most likely have air in the brakes someplace. The brake warning light is
actuated by a spool valve switch in the distribution valve. As long as the
spool valve has equal amounts of fluid pressure on both sides of it, it
remains centered and does not actuate the switch. When the pressure varies
between sides, the spool valve moves towards the low pressure, and actuates
the light switch. Bleeding the brakes should fix the problem, if the spool
valve sticks, then you likely have crud in the distribution valve. Flushing
might cure it, or replacement of the distribution valve might be required.
Remember you are dealing with a system, all the parts need to be good, or
none of them are.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Aug 21, 2016 1:32 PM, "tom geiger" wrote:
> Ok, got the new brake booster in and it's working great, but my brake
> lights are constantly on. Any ideas of what caused that?
>
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| Re: [GMCnet] Brake booster replacement [message #305730 is a reply to message #305729] |
Sun, 21 August 2016 16:09 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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James Hupy wrote on Sun, 21 August 2016 15:49The pressure is unequal between the front and rear braking systems. You most likely have air in the brakes someplace. The brake warning light is actuated by a spool valve switch in the distribution valve. As long as the spool valve has equal amounts of fluid pressure on both sides of it, it remains centered and does not actuate the switch. When the pressure varies between sides, the spool valve moves towards the low pressure, and actuates the light switch. Bleeding the brakes should fix the problem, if the spool valve sticks, then you likely have crud in the distribution valve. Flushing might cure it, or replacement of the distribution valve might be required. Remember you are dealing with a system, all the parts need to be good, or none of them are.
Jim Hupy
Salem, Or
78 GMC ROYALE 403 He said light[s]. I thought that meant the brake lights that tell drivers behind your vehicle that your brakes have been applied.
The pedal is not retracting all the way, or the switch is staying on because it needs to be adjusted or replaced. Should be an easy fix.
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| Re: [GMCnet] Brake booster replacement [message #305731 is a reply to message #305729] |
Sun, 21 August 2016 16:04 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Jim,
Either you or I mis-read Tom's problem -- I think it's the brake lights on
the rear that are staying on, not the dash warning light.
Tom,
In case I'm right:
The slight differences between the two boosters probably resulted in the
brake light switch being misadjusted. It's just to the right of the
steering column, up high, actuated by a tab on the brake pedal shaft. A
real PITA to adjust, but I'm afraid that's what you'll have to do.
Ken H.
On Sun, Aug 21, 2016 at 4:49 PM, James Hupy wrote:
> The pressure is unequal between the front and rear braking systems. You
> most likely have air in the brakes someplace. The brake warning light is
> actuated by a spool valve switch in the distribution valve. As long as the
> spool valve has equal amounts of fluid pressure on both sides of it, it
> remains centered and does not actuate the switch. When the pressure varies
> between sides, the spool valve moves towards the low pressure, and actuates
> the light switch. Bleeding the brakes should fix the problem, if the spool
> valve sticks, then you likely have crud in the distribution valve. Flushing
> might cure it, or replacement of the distribution valve might be required.
> Remember you are dealing with a system, all the parts need to be good, or
> none of them are.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
> On Aug 21, 2016 1:32 PM, "tom geiger" wrote:
>
>> Ok, got the new brake booster in and it's working great, but my brake
>> lights are constantly on. Any ideas of what caused that?
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Brake booster replacement [message #305738 is a reply to message #305735] |
Sun, 21 August 2016 16:18 |
James Hupy
Messages: 6806
Registered: May 2010
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Ahhh crap. It was me. I did misread it. But my answer still stands correct
IF IT IS THE DISTRIBUTION VALVE. More than likely you are right about the
pedal switch.
Jim Hupy
On Aug 21, 2016 2:14 PM, "Jim Kanomata" wrote:
> Can be your master cylinder.
> difference in pressure of front and rear cause the piston to be pushed in
> one position.
>
> On Sun, Aug 21, 2016 at 1:31 PM, tom geiger wrote:
>
>> Ok, got the new brake booster in and it's working great, but my brake
>> lights are constantly on. Any ideas of what caused that?
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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>
>
>
> --
> Jim Kanomata
> Applied/GMC, Fremont,CA
> jimk@appliedairfilters.com
> http://www.appliedgmc.com
> 1-800-752-7502
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| Re: Brake booster replacement [message #305740 is a reply to message #305725] |
Sun, 21 August 2016 16:37 |
tgeiger
Messages: 518
Registered: February 2006
Location: kansas city
Karma: -1
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Will look at that switch. Is it pretty straight forward on it's adjustment? Got the repair manuals to refer to if there are instructions in there.
Tom Geiger
76 Eleganza II
KCMO
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| Re: [GMCnet] Brake booster replacement [message #305753 is a reply to message #305747] |
Sun, 21 August 2016 18:37 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Emery,
I wish mine DID work that way, like the throttle's "passing gear" switch,
but it doesn't -- it's got to be adjusted by moving the two hex nuts on its
threaded shaft. I hope Tom's is like yours.
Ken H.
On Sun, Aug 21, 2016 at 6:29 PM, Emery Stora wrote:
> Tom
> The switch is self adjusting. Just push it toward the pedal. When you put
> on the brakes and the pedal goes back up it will adjust properly.
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Brake booster replacement [message #305760 is a reply to message #305753] |
Sun, 21 August 2016 19:32 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Ken
You are probably right on this. I haven’t adjusted mine in many years. I may be confusing it with another vehicle.
After I think about it I believe the switch is in combination with the cruise control release so it likely does use nuts to adjust it.
Emery
Stora
> On Aug 21, 2016, at 5:37 PM, Ken Henderson wrote:
>
> Emery,
>
> I wish mine DID work that way, like the throttle's "passing gear" switch,
> but it doesn't -- it's got to be adjusted by moving the two hex nuts on its
> threaded shaft. I hope Tom's is like yours.
>
> Ken H.
>
>
> On Sun, Aug 21, 2016 at 6:29 PM, Emery Stora wrote:
>
>> Tom
>> The switch is self adjusting. Just push it toward the pedal. When you put
>> on the brakes and the pedal goes back up it will adjust properly.
>>
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