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06-17-2022, 05:55 PM | #1 |
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BIG A#$ Brakes dilemma..
Hello everyone,
So I just picked up a 1984 C20 that used to be an old railroad truck. You know the ones that actually drive on the rails. (and no it doesn't still have the train wheel things on it. lol) But it does still have the inverted or reversed 19.5 steel wheels that narrow the width so the tires match the rail width. So here is my dilemma. It has MONSTER brakes on it. The front disk's are 13" and the rear drums are 15" It has no brake pedal pressure. I believe the master is shot. I pulled it off and it has a 1.5" bore on it. The spid has no code for brakes or even a listing of the brakes. I thought it would be the JB7 or JD7 but that only has a 1.25" bore. It is a cast iron master with the small chamber in the rear of it. It has a pretty big booster on it so i'm thinking that this is some special combo that was maybe converted by the rail company or ordered that way but not listed. I don't want to just throw a new style 1.5" bore plastic style on it and have it not work proper. Or just get a new booster and master from a JD7 and it not be enough for this Huge combo. Any suggestions as to how I would look up a master by bore size and see if I can match it? I've been all over the net to no avail. Maybe one of you guys has come across this before. Any help would be appreciated.
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If you ain't living life on the Edge.... Your taking up entirely to much space!!!! My 64 Stepper Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=586792 Last edited by MadRatt; 06-17-2022 at 06:07 PM. |
06-17-2022, 06:34 PM | #2 |
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Re: BIG A#$ Brakes dilemma..
Where’s the pic of the master and booster?
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06-17-2022, 06:34 PM | #3 |
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Re: BIG A#$ Brakes dilemma..
Nothing I could find on line from this end but what about taking the old MC apart and measuring the piston. Any numbers on the old one? pic of it.....pics of the rear drums also---never heard of a 15'' drum. What rear axle is in it? pic of that also
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06-17-2022, 07:30 PM | #4 |
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Re: BIG A#$ Brakes dilemma..
First things first.
Tell me about that Hodges Hauler it is sitting on. After that I'll pull the brake charts out. K
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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/ |
06-17-2022, 10:03 PM | #5 |
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Re: BIG A#$ Brakes dilemma..
1989 c3500 ext cab with a 454.
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If you ain't living life on the Edge.... Your taking up entirely to much space!!!! My 64 Stepper Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=586792 |
06-17-2022, 10:05 PM | #6 |
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Re: BIG A#$ Brakes dilemma..
What are you wanting to do with the truck? If it were mine, and I was considering using it as a mobile toolbox, I would scrounge junkyards and find the correct stuff to put it back to a typical stock configuration. It depends how much you value the 'coolness' of the railroad setup, though.
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1987 C6P V20 truck, 2010 LMG 5.3, AFM delete, 2010 Camaro exhaust manifolds, 1997 nv4500, 1991 np241c, hydroboost, 2005 14bff axle & driveshaft, drop-n-lock gooseneck, 4.10 gears, stock suspension, rims, and tires. Still a work in progress. Any questions or suggestions are welcome! |
06-17-2022, 10:14 PM | #7 |
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Re: BIG A#$ Brakes dilemma..
I'm planning on pulling it out tomorrow. Letting it soak with penatraiting oil over night. I'll see then if any #'s are visible and take some pic's. The rear end is a 14 bolt with a G80 locking diff. Drums show 15" outside diameter measuring with a tap measure laying on my back underneath. 😆 the front rotors must actually be 12.5" not the 13" I thought. Measured them looking thru the rim with a tape measure.
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If you ain't living life on the Edge.... Your taking up entirely to much space!!!! My 64 Stepper Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=586792 |
06-17-2022, 10:22 PM | #8 | |
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Re: BIG A#$ Brakes dilemma..
Quote:
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If you ain't living life on the Edge.... Your taking up entirely to much space!!!! My 64 Stepper Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=586792 |
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06-18-2022, 01:06 AM | #9 |
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Re: BIG A#$ Brakes dilemma..
So in other words it's just a regular 3/4 ton with 13'' drums. Looks like a semi-float rear which also came as a 14b with a 9.5 ring gear as opposed to the 10.5 full float rear. the only thing really special is the rims and tires
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06-20-2022, 10:53 PM | #10 |
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Re: BIG A#$ Brakes dilemma..
Nice.
Now that that is behind us I can focus on your question at hand. a) It's vacuum boost? Not hyroboost? b) Any idea of what the GVW of the vehicle is? This might be a good juncture to remind you that if you send the GM Heritage Center your VIN (and $50) they can tell us what the original option content was, as it left the GM factory. c) C20 pickups could be had with JB6/JD6 or JB7/JD7. Front rotors are shown as 12.5" in all cases, the largest rear drum is 13" diameter (that would be at the friction surface, not the outer most visible flange of the drum. Master Cylinder bore is 28.6mm (ie, 1.13") for JB6/JD6; 31.8mm (or 1.25") for JB7/JD7. Make sure you are measuring the bore of the piston/seal itself, not the outside diameter of the casting. If it doesn't match that stuff then the system was changed by the upfitter, after the fact. I really can't comment or say what they might have done. Pics of the m/c and booster, and rear drums would sure help. K
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Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/ Last edited by Keith Seymore; 06-20-2022 at 11:14 PM. |
06-23-2022, 03:38 PM | #11 |
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Re: BIG A#$ Brakes dilemma..
Thanx for the reply Keith.
I found a master after some digging that seemed to match. It was an i.d. of 1.25. I never had to measure for one of these before. Thought I needed to measure the O.D. that went into the booster. It is a vacuum boosted set up. I had a hell of a time finding one once I identified it. Rockauto was out of stock. Autozone showed unavailable anywhere as well as Advanced. O'reilley crossed to one that was backwards from what I needed. Ended up getting one from Amazon in the Cardone brand. Fits but seems now I have a caliper problem. Pedal still is just an air ball even thou I can see fluid moving in the master. I think a caliper is stuck. That will be the next adventure. Probably do new calipers and new wheel cylinders to make sure everything is good. Just gotta wait on some help to move the truck safely to where I can work on it with some air tools that reach. No brakes is hard to move around by yourself. lol
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If you ain't living life on the Edge.... Your taking up entirely to much space!!!! My 64 Stepper Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=586792 |
06-23-2022, 04:23 PM | #12 |
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Re: BIG A#$ Brakes dilemma..
A quick thing to check is that the front calipers are installed on the correct sides. They're almost identical, except for the bleeder hole location. If installed left-on-right and vice-versa, the bleeder will be at the bottom of the caliper piston chamber instead of at the top, and won't allow you to bleed all the air out. Edit: That's on the 1980's K20 trucks with JB7 brakes. I can't say for sure if the C20 trucks of the same era have the almost-interchangeable calipers as well, or not.
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1987 C6P V20 truck, 2010 LMG 5.3, AFM delete, 2010 Camaro exhaust manifolds, 1997 nv4500, 1991 np241c, hydroboost, 2005 14bff axle & driveshaft, drop-n-lock gooseneck, 4.10 gears, stock suspension, rims, and tires. Still a work in progress. Any questions or suggestions are welcome! |
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