Master cylinder and ABS Delete

[PlayingWithTBI]

Burb has JB7 and my sierra has JB5

I think my 88 C1500 has JB 0.1

 

[red98]

I'm a firm believer in replacing brake parts by rpo code. some rpo's are better than others and if you get into swapping brake parts because just they fit, could actually impair the brakes due to mismatched master cylinders with mismatched brake cylinders or calipers. so if someone wants to upgrade the brakes you need all of the parts for that particular rpo code.

sometimes people report good brakes after swapping in a 2002 tahoe mc.... but it just so happens to be of the right size for their rpo code.... meaning they kind of just got lucky. I think JB3 might be the ****** brakes found on a lot of pickups and they could benefit from an upgrade. otherwise the others just need to be fixed.

IMO of course but.... but it's simple hydraulics.

Al

So is the sales code simply referring to the different brake size setups? Or are there actual hydraulic differences in how they setup the brakes by RPO? Now I'm gonna go sort thru mine and find out which brakes I have - If I know I have a 14-bsf with 6-lugs, are all the brakes for that particular axle gonna be the same RPO?

Sorry if you don't know exactly, you just seem knowledgeable on this.

 

[thegawd]

no worries... I dont know all the differences but I can find some info... heres a pic i found that Someotherguy posted here...

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Richard

theres more info though...

 

[thegawd]

here is the thread that contains all the info.

JB5 JB6 JB7 JB8 Size Thread

Hello, After hours of looking around i can't find a thread that list all the sizes of the various brake components of JB style brakes. Please let me know if what i have so far is correct. I'm sure i have things wrong as all info is coming from other threads. JB5(6400lbs): 1.574" Bore MC Low...

www.gmt400.com

JB3 specs; Front disc 11.57 X 1" with 2 1/2" piston caliper
Rear drums 254 mm X 57 mm ( leading/trailing)
Vacuum-- Single Diaphragm
The easy way to identify JB3 brakes is the front rotor is solid not vented. It was also identified as JN3 in the service manuals.

JB5(6400lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 11.86x1.29
Rear Drum- 10x2.25
Vacuum- Double Diaphram
1 3/16" wheel cylinder

JB6(7200lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 12.50x1.28
Rear Drum- 11.15x 2.75
Vacuum- Double Diaphram(same as JB7)
1" rear wheel cylinder. 11' drum has self activating shoes, therefore does not require as much pressure as the 10"

JB7(8400lbs)Single rear wheel:
1.25" Bore MC(used in JB5 and JB6 Hydro Units)
Conventional Calipers 3.15" Piston
Front Disc- 12.50x1.54
Rear Drum- 13.00x2.50
Vacuum- Double Diaphram(same as JB6)
1 1/16 rear wheel cylinder

JB8(10000lbs)
1.312" Bore MC
Conventional Calipers 3.4" piston
Front Disc- 12.50x1.54
Read Drum- 13.00x3.50
Hydraulic Hydro Boost
1 3/16 rear wheel cylinder

notice theres conventional calipers and low drag calipers... that's another reason that these rpo codes are important... see that thread to learn the differences....

 

[red98]

here is the thread that contains all the info.

JB5 JB6 JB7 JB8 Size Thread

Hello, After hours of looking around i can't find a thread that list all the sizes of the various brake components of JB style brakes. Please let me know if what i have so far is correct. I'm sure i have things wrong as all info is coming from other threads. JB5(6400lbs): 1.574" Bore MC Low...

www.gmt400.com

JB3 specs; Front disc 11.57 X 1" with 2 1/2" piston caliper
Rear drums 254 mm X 57 mm ( leading/trailing)
Vacuum-- Single Diaphragm
The easy way to identify JB3 brakes is the front rotor is solid not vented. It was also identified as JN3 in the service manuals.

JB5(6400lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 11.86x1.29
Rear Drum- 10x2.25
Vacuum- Double Diaphram
1 3/16" wheel cylinder

JB6(7200lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 12.50x1.28
Rear Drum- 11.15x 2.75
Vacuum- Double Diaphram(same as JB7)
1" rear wheel cylinder. 11' drum has self activating shoes, therefore does not require as much pressure as the 10"

JB7(8400lbs)Single rear wheel:
1.25" Bore MC(used in JB5 and JB6 Hydro Units)
Conventional Calipers 3.15" Piston
Front Disc- 12.50x1.54
Rear Drum- 13.00x2.50
Vacuum- Double Diaphram(same as JB6)
1 1/16 rear wheel cylinder

JB8(10000lbs)
1.312" Bore MC
Conventional Calipers 3.4" piston
Front Disc- 12.50x1.54
Read Drum- 13.00x3.50
Hydraulic Hydro Boost
1 3/16 rear wheel cylinder

notice theres conventional calipers and low drag calipers... that's another reason that these rpo codes are important... see that thread to learn the differences....

I'm JB6 so I guess my squishy pedal and "just okay" braking performance are probably due to old hydraulics and O'reillys brake parts lmfao.

Still good to know it seems like I have one of the better braking systems offered that year, whoever built my truck had great taste.

 

[alpinecrick]

I'm a firm believer in replacing brake parts by rpo code. some rpo's are better than others and if you get into swapping brake parts because just they fit, could actually impair the brakes due to mismatched master cylinders with mismatched brake cylinders or calipers. so if someone wants to upgrade the brakes you need all of the parts for that particular rpo code.

sometimes people report good brakes after swapping in a 2002 tahoe mc.... but it just so happens to be of the right size for their rpo code.... meaning they kind of just got lucky. I think JB3 might be the ****** brakes found on a lot of pickups and they could benefit from an upgrade. otherwise the others just need to be fixed.

IMO of course but.... but it's simple hydraulics.

Al

Good info right there.......

 

[Erik the Awful]

JB3 specs; Front disc 11.57 X 1" with 2 1/2" piston caliper
Rear drums 254 mm X 57 mm ( leading/trailing)
Vacuum-- Single Diaphragm
The easy way to identify JB3 brakes is the front rotor is solid not vented. It was also identified as JN3 in the service manuals.

JB5(6400lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 11.86x1.29
Rear Drum- 10x2.25
Vacuum- Double Diaphram
1 3/16" wheel cylinder

JB6(7200lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 12.50x1.28
Rear Drum- 11.15x 2.75
Vacuum- Double Diaphram(same as JB7)
1" rear wheel cylinder. 11' drum has self activating shoes, therefore does not require as much pressure as the 10"

Good stuff! I have vented front rotors, so it looks like I have JB5 brakes, and all I need for JB6 is to replace the rear drum assemblies!

 

[MrPink]

My truck has JB5 and my brakes suck. I plan on doing the ABS delete with an adj prop valve and Cunningham Machine RR disc setup. More so for ease of maintnence. I do believe my booster/ master is failing and the front hoses need replaced anyway so I will replace the front and rear hoses at the same time.

 

[Pinger]

Pinger,

Thank you for the info. I didn't take the larger bore into account. Reality; I failed to read thru and fully understand the rear disc conversion instructions before I purchased and installed. It goes without saying I probably should have. if just to know the science/math behind it. Shame on Me.

At this point I've decided to purchase the front caliper upgrade and rear disc conversion to go with my already installed LS Mfg MC. "If your gonna do it, do it right! " Thanks for the assist.

As far as the GMT800 to GMT400, I've done a bit of light reading since your post and it seems the larger bore falls in line with the LF Mfg MC science. And.....im guessing the larger pistons in the front calipers address the small reservoir in the LS Mfg MC otherwise, they wouldn't recommend buying all three as a kit.

Thanks again

Another way to think about the hydraulic relationship between master cylinder and piston is to compare it to gearing. We downshift (small drives large (gear wheels)) when we want more force at the driven wheels. The same is true for the diameters of the pistons in a hydraulic system.

 

[red98]

here is the thread that contains all the info.

JB5 JB6 JB7 JB8 Size Thread

Hello, After hours of looking around i can't find a thread that list all the sizes of the various brake components of JB style brakes. Please let me know if what i have so far is correct. I'm sure i have things wrong as all info is coming from other threads. JB5(6400lbs): 1.574" Bore MC Low...

www.gmt400.com

JB3 specs; Front disc 11.57 X 1" with 2 1/2" piston caliper
Rear drums 254 mm X 57 mm ( leading/trailing)
Vacuum-- Single Diaphragm
The easy way to identify JB3 brakes is the front rotor is solid not vented. It was also identified as JN3 in the service manuals.

JB5(6400lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 11.86x1.29
Rear Drum- 10x2.25
Vacuum- Double Diaphram
1 3/16" wheel cylinder

JB6(7200lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 12.50x1.28
Rear Drum- 11.15x 2.75
Vacuum- Double Diaphram(same as JB7)
1" rear wheel cylinder. 11' drum has self activating shoes, therefore does not require as much pressure as the 10"

JB7(8400lbs)Single rear wheel:
1.25" Bore MC(used in JB5 and JB6 Hydro Units)
Conventional Calipers 3.15" Piston
Front Disc- 12.50x1.54
Rear Drum- 13.00x2.50
Vacuum- Double Diaphram(same as JB6)
1 1/16 rear wheel cylinder

JB8(10000lbs)
1.312" Bore MC
Conventional Calipers 3.4" piston
Front Disc- 12.50x1.54
Read Drum- 13.00x3.50
Hydraulic Hydro Boost
1 3/16 rear wheel cylinder

notice theres conventional calipers and low drag calipers... that's another reason that these rpo codes are important... see that thread to learn the differences....

Is the 7200 supposed to be the GVW of the truck? Mine is a half ton but it is the F44 half ton, I've never seen 7200 anywhere on it (even tho apparently my JB6 brakes are 7200), I think mine says 6600 or 6400.