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10-21-2013, 02:35 PM
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#1 |
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Registered User
Join Date: Jul 2012
Location: Ocala,FL
Posts: 129
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87 GMC Sierra power brake master cylinder bore size?
Hey guys, just picked up am 87 GMC over the weekend. Brake pedal if very mushy, pedal travels very far, and it seems to stick or come up slow.
I was thinking about replacing the master cylinder and re-bleeding the system. Autozone.com sells 2 with different bore sizes. 1.57 and 1.41 Bore. Besides this they both look the same. Does anyone know which one would work best? Or should I remove the one that's currently on the truck to verify? Thanks! Joe |
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10-21-2013, 04:13 PM
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#2 |
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Registered User
Join Date: Feb 2007
Location: Memphis MI
Posts: 1,851
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Re: 87 GMC Sierra power brake master cylinder bore size?
Look at your brake code on the SPID in the glove box. Bore size is relted to braking power which is given by the code, JB_ usually is the first two letters.
__________________
1987 2 ton  1982 250/TH350 beater in progressDad's 1981 3/4 L6 3 on tree posi and no options, awaiting restoration or scrappingPlus a mess o' tractors |
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10-22-2013, 09:35 AM
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#3 |
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Registered User
Join Date: Jul 2012
Location: Ocala,FL
Posts: 129
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Re: 87 GMC Sierra power brake master cylinder bore size?
Thanks! I checked out the sticker in my glovebox. Code says 9J50. So is this considered the JB5 brake system?
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10-22-2013, 10:24 AM
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#4 |
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Registered User
Join Date: May 2009
Location: Motor City
Posts: 9,193
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Re: 87 GMC Sierra power brake master cylinder bore size?
I happen to have the brake system release chart for a 1987 R truck:
 Your brake code of J50 (the "9" is a dummy code/place holder) would equate to JB5. The master cylinder bore diameter looks to be 28.6 mm, which would be 1.12 inches...which doesn't match either of the Autozone offerings... I wonder if they are measuring something other than the internal bore - like the external diameter that mates with the booster. Those vary on whether the master cylinder is QTU (Quick Take Up) vs Non-QTU. K
__________________
Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/ Last edited by Keith Seymore; 10-22-2013 at 10:31 AM. |
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10-22-2013, 10:50 AM
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#5 |
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Registered User
Join Date: Jul 2012
Location: Ocala,FL
Posts: 129
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Re: 87 GMC Sierra power brake master cylinder bore size?
Thanks for the info! I just checked Advance Autos website and they offer two units. (For JB1 & JB3 brake codes) Measuring 1" & 1.13" diameter.
Looks like the 1.13" JB3 should be the one I need right? Heres the link to it. http://shop.advanceautoparts.com/web...new#fragment-2 |
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10-22-2013, 12:16 PM
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#6 | |
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Registered User
Join Date: May 2009
Location: Motor City
Posts: 9,193
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Re: 87 GMC Sierra power brake master cylinder bore size?
Quote:
That chart is what we referred to in order to release parts for production. It was the "gold source" for all the other documents that flow from it (service releases, for example). K
__________________
Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/ |
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10-22-2013, 12:54 PM
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#7 |
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Registered User
Join Date: Jul 2012
Location: Ocala,FL
Posts: 129
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Re: 87 GMC Sierra power brake master cylinder bore size?
Great! Thanks again for the help!!
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