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| Brakes [message #303359] |
Sun, 10 July 2016 10:58  |
jor
Messages: 43
Registered: June 2016
Location: Tucson
Karma: 0
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Went to dump this morning and lost most of the braking system going down a steep hill (a bit butt clenching). I noted brakes fluid puking out of the front area of the master cylinder. It's the type without a regular vacuum canister. I've never messed with one of these. Anyhow, I managed to get the GMC back in my driveway and I guess I'll remove that master cylinder and try and figure out what's going on. I tried pumping the brakes but I don't see any more fluid coming out.
One thing that I noted when I bought the GMC a few weeks back is the brake pedal seems close to the floor. The PO advised me that it was typical of these rigs with the six wheel disc system.
Anyhow, just looking for some advance info from anyone that may have experienced a similar issue with this master cylinder. Thanks.
jor
John O'Reilly
76 Eleganza II (quad bags, disc brakes w/ reaction arm. 3.70 gears, manny trans, headers, Patterson dist.)
Tucson, AZ
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| Re: Brakes [message #303360 is a reply to message #303359] |
Sun, 10 July 2016 11:33  |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Senior Member |
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I had the exact same failure this year. The solution is to replace the master Cyclinder AND the brake combination valve. The combination valve has failed, probably do to internal rust from water in the DOT 3 or 4 brake fluid. JmK has both in stock. Available from other vendors also.
While you are in there, you might check your front brake hoses for age. If original, replace them as well.
Retreading your post, I think that your master Cyclinder, if OEM, might be too small for a six wheel disc system. Think about using a P-30 as a replacement. Search the forum for further information, my system is stock.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] Brakes [message #303375 is a reply to message #303359] |
Sun, 10 July 2016 13:42 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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John,
If you have the 6 disc system, I tend to look at the master cylinder as
being defective.
The previous owner is correct about the peddle travel being longer.
I think you have the Power Master unit that use the Electric pump.
Look at it and advise me.
I have used that system back in 1990 and had similar experience.
On Sun, Jul 10, 2016 at 8:58 AM, John O'Reilly
wrote:
> Went to dump this morning and lost most of the braking system going down a
> steep hill (a bit butt clenching). I noted brakes fluid puking out of the
> front area of the master cylinder. It's the type without a regular vacuum
> canister. I've never messed with one of these. Anyhow, I managed to get the
> GMC back in my driveway and I guess I'll remove that master cylinder and
> try and figure out what's going on. I tried pumping the brakes but I don't
> see any more fluid coming out.
>
> One thing that I noted when I bought the GMC a few weeks back is the brake
> pedal seems close to the floor. The PO advised me that it was typical of
> these rigs with the six wheel disc system.
>
> Anyhow, just looking for some advance info from anyone that may have
> experienced a similar issue with this master cylinder. Thanks.
> jor
> --
> John O'Reilly
> 76 Eleganza II (quad bags, disc brakes w/ reaction arm. 3.70 gears, manny
> trans, headers, Patterson dist.)
> Tucson, AZ
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Brakes [message #303405 is a reply to message #303375] |
Sun, 10 July 2016 21:22 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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John, I had recently converted back from a Power Master to what Dave Lenzi
provides. My Power Master pump failed and to try to find another is nearly
imposible. When I did find a unit it was simply less expensive to have
Dave Lenzi modify a brake booster and replace the master brake cylinder.
On Sun, Jul 10, 2016 at 12:42 PM, Jim Kanomata
wrote:
> John,
> If you have the 6 disc system, I tend to look at the master cylinder as
> being defective.
> The previous owner is correct about the peddle travel being longer.
> I think you have the Power Master unit that use the Electric pump.
> Look at it and advise me.
> I have used that system back in 1990 and had similar experience.
>
> On Sun, Jul 10, 2016 at 8:58 AM, John O'Reilly
> wrote:
>
>> Went to dump this morning and lost most of the braking system going down
> a
>> steep hill (a bit butt clenching). I noted brakes fluid puking out of the
>> front area of the master cylinder. It's the type without a regular vacuum
>> canister. I've never messed with one of these. Anyhow, I managed to get
> the
>> GMC back in my driveway and I guess I'll remove that master cylinder and
>> try and figure out what's going on. I tried pumping the brakes but I
> don't
>> see any more fluid coming out.
>>
>> One thing that I noted when I bought the GMC a few weeks back is the
> brake
>> pedal seems close to the floor. The PO advised me that it was typical of
>> these rigs with the six wheel disc system.
>>
>> Anyhow, just looking for some advance info from anyone that may have
>> experienced a similar issue with this master cylinder. Thanks.
>> jor
>> --
>> John O'Reilly
>> 76 Eleganza II (quad bags, disc brakes w/ reaction arm. 3.70 gears, manny
>> trans, headers, Patterson dist.)
>> Tucson, AZ
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
>
> --
> Jim Kanomata
> Applied/GMC, Fremont,CA
> jimk@appliedairfilters.com
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: Brakes [message #303534 is a reply to message #303359] |
Wed, 13 July 2016 16:44 |
jor
Messages: 43
Registered: June 2016
Location: Tucson
Karma: 0
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Member |
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OP here. I'm on the right track. I bought a P30 master brake cylinder, bracket and sensitized vacuum booster from JimK. Took me awhile to get the old bracket off as I had to remove the leveling lever plate. Would have been a lot easier if I could have gotten up there from under the dash but I sure couldn't see any way to do it without actually removing the dash! Anyhow, I plan on bench bleeding the cylinder and I'm hoping I won't have to bleed the brakes.
I now have two Power Master units - the one that failed and an extra that came with the GMC. Does anyone need one?
jor
John O'Reilly
76 Eleganza II (quad bags, disc brakes w/ reaction arm. 3.70 gears, manny trans, headers, Patterson dist.)
Tucson, AZ
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