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04-07-2007, 04:20 PM
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#1 |
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Problem Child
 
Join Date: Sep 2005
Location: Kettering Ohio
Posts: 1,248
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brakes
I was looking at brakes today at autozone for the 78 how do i tell if it is jb7 or jb8 brake system.It i a one ton 4wd
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1972 gmc sierra grande 350/350 a/c soon`to get a new 350  I Survived Norwood 
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04-07-2007, 08:05 PM
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#2 |
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The Crazy Machanic
Join Date: Jan 2007
Location: Nokesville Va
Posts: 1,437
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Re: brakes
i think its a rotor sizes might say in your info in the dash.
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*1986 Sliverado longbed 400 small block mean as hell, 700r4 trans (5 speed coming one day) * 1970 chevelle 2dr sedan Latest update June 24 2007.  *1957 4 door stationwagon - pink all original needing a good restore (body great, floors bad)  newest additions 1965 shortbed fleet great granddads. Been told im nuts to bring it back from the dead (still going to happen) plans-all stock with a turbo 292 inline 3 speed column shift. and thats it big block 427 and 5 speed trans and ford 9 inch theyhave no home yet thinking what to put them in and a 79 c60 trash truck um no idea i have one
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04-10-2007, 12:37 AM
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#3 |
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Until Seventy Times Seven
Join Date: Feb 2005
Location: Rocky Mountain Front Range
Posts: 1,301
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Re: brakes
The JB7 system runs a vacuum boost with 1.28" front discs and 2.5" rear drums whereas the JB8 system uses the hydroboost setup with larger discs (1.53") and larger drums (3.5").
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boxRODz 1983 C10 SWB Fleetside When two halves is gone, there's nuthin left. Two nothings is nuthin. That's mathematics son. You can argue with me but you can't argue with figures. Two half nothings is a whole nuthin... |
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04-10-2007, 01:54 AM
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#4 |
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glamoros piece o' lowlife
Join Date: Mar 2007
Location: Redford, MI
Posts: 1,164
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Re: brakes
True that, however I guess somewhere in the '80s things changed cause my hydroboost module that came off an '80s 1-ton diesel has to use a JB7 master cylinder (for a '79 C30), the JB8 one that's supposed to fit it has a bore in the piston that is too deep for the hydroboost rod. I'd suggest just pulling a wheel and measuring yer current rotors, they will be thinner than the brand new ones but they will still give you an idea of what to get. Check the rear drums too, just to make sure.
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The more I drink, the more I drink, the more I drink... diesel, reg cab, long bed, 4 across the rear, single stack, wooden stakes, and lotsa lights - the Hay Express |
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06-02-2007, 01:50 PM
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#5 |
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Problem Child
Join Date: Sep 2005
Location: Kettering Ohio
Posts: 1,248
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Re: brakes
does it make a differance in telling that it has a dana 60 in the front.Also whne measuring the rear brake does 3.5 inches the meauserment of the shoe width or the drum width
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1972 gmc sierra grande 350/350 a/c soon`to get a new 350 I Survived Norwood
Last edited by cory321; 06-02-2007 at 01:50 PM. |
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06-02-2007, 01:58 PM
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#6 |
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glamoros piece o' lowlife
Join Date: Mar 2007
Location: Redford, MI
Posts: 1,164
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Re: brakes
dunno about the front axles I'm running the JB7 hydroboost master cylinder for a 1-ton with my half-ton rotors and calipers without any issues. The 3.5" should be shoe width, you will need to pull drums for that and that can be pretty nasty depending on yer axle's rust developments. Really best way would be to pull a front wheel and measure the rotor thickness, if it's about 1.5" you should have the JB8, and if it's around 1.25" it's the JB7, but even then I'd check with the actual part dimensions at AutoZone cause stuff gets mislabeled sometimes. As I said, I have to run a '70s JB7 master cylinder on my '80s JB8 hydroboost system, and I only figured that out cause I had measured the bore depth of the original hydroboost master cylinder in the junkyard.
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The more I drink, the more I drink, the more I drink... diesel, reg cab, long bed, 4 across the rear, single stack, wooden stakes, and lotsa lights - the Hay Express |
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06-02-2007, 03:29 PM
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#7 |
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Problem Child
Join Date: Sep 2005
Location: Kettering Ohio
Posts: 1,248
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Re: brakes
Thank you I'll measure the front rotors tonight
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1972 gmc sierra grande 350/350 a/c soon`to get a new 350 I Survived Norwood
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