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Username Post: JB6 and JB7 Brake difference        (Topic#236358)
Abowsman 
Forum Newbie
Posts: 40

Age: 31
Loc: Atlanta
Reg: 02-18-10
02-24-10 09:02 AM - Post#1868627    

Whats the difference in JB6 and JB7 brake systems on these ttucks. And how do i know which i have?

 
gchemist 
Senior Chevytalk Moderator
Posts: 21783
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
02-24-10 11:38 AM - Post#1868706    
    In response to Abowsman

JB6 76 88 BRAKE SYSTEM,VAC PWR DISC/DRUM
JB7 76 88 BRAKE SYSTEM,VAC PWR DISC/DRUM

http://www.73-87.com/chevy_ids/rpo-hk.htm#rpo-j

Does your truck have a brake booster? Front disc brakes? Rear drums?
'83 Silverardo XST - ZZ4 powered
'96 GMC Jimmy LS Ret. @236651 miles


 
Abowsman 
Forum Newbie
Posts: 40

Age: 31
Loc: Atlanta
Reg: 02-18-10
02-24-10 12:00 PM - Post#1868712    
    In response to gchemist

my truck has the hydro-boost system. Fromt disc and rear drum.
I have heard it is based on the GVW of the vehicle. I am replacing the brake calipers and thats where the question came.
The only difference i am aware of in the calipers from the 70's trucks is the size of the banjo bolt.
I am sure there are some internal differences like the size of the piston or something like that.

 
Abowsman 
Forum Newbie
Posts: 40

Age: 31
Loc: Atlanta
Reg: 02-18-10
02-24-10 12:03 PM - Post#1868716    
    In response to gchemist

When i was at the parts store they are offering two different part numbers for an 83 k20 chevy. And it depends if i have a jb6 or jb7 brake system.

 
gchemist 
Senior Chevytalk Moderator
Posts: 21783
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
02-24-10 12:19 PM - Post#1868722    
    In response to Abowsman

1" or 1.25" rotors. Measure the width.

The rear are two differents sizes too. I can't remember at the moment.
'83 Silverardo XST - ZZ4 powered
'96 GMC Jimmy LS Ret. @236651 miles


Edited by gchemist on 02-24-10 12:20 PM. Reason for edit: No reason given.

 
Abowsman 
Forum Newbie
Posts: 40

Age: 31
Loc: Atlanta
Reg: 02-18-10
02-24-10 12:24 PM - Post#1868724    
    In response to gchemist

I believe the fronts are 1.25
The rear is a 14bolt and i am putting disc brakes on it.

 
gchemist 
Senior Chevytalk Moderator
Posts: 21783
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
02-24-10 03:34 PM - Post#1868833    
    In response to Abowsman

The 1.25" rotors are on Heavy Half, 3/4 ton and up trucks.
'83 Silverardo XST - ZZ4 powered
'96 GMC Jimmy LS Ret. @236651 miles


 
Bill K.b 
Senior Member
Posts: 4196

Loc: upstate NY
Reg: 10-24-05
02-25-10 07:37 AM - Post#1869176    
    In response to gchemist

If it's readable I check the RPO sheet, as it will have the brake system right on it.

I think from having a couple half-ton Subs apart the JB7 shoes are like 3 inches wide, and the others narrower. I know the one diesel sub I took apart I couldn't re-use any of that stuff because it was different from my truck.
Those who can, do. Those who can't, criticize it on the internet.

1988 G20 van 5.7L - driver.
1993 3500 dually 5.7L NV4500 - tow truck
1991 G20 van - parts truck

Plus cars for swap and sale
&yes, I once tried a frame swap on a 51 Chevy.


 
Abowsman 
Forum Newbie
Posts: 40

Age: 31
Loc: Atlanta
Reg: 02-18-10
02-25-10 01:59 PM - Post#1869373    
    In response to gchemist

yes mind is a 3/4 ton but the auto parts stores still bring up both options of JB6 and JB7 brakes.
I checked the glove box, door jam, and under the hood for the build sheet but its nowhere to be found. The only thing in the glove box is a sticker that says something about not putting a camper in the bed of the truck.


 
Abowsman 
Forum Newbie
Posts: 40

Age: 31
Loc: Atlanta
Reg: 02-18-10
02-25-10 02:02 PM - Post#1869374    
    In response to gchemist

I replaced the front brake rotors, pads and calipers all at the same time. When putting it all back together the calipers and pads were pretty snug fitting around the rotors. I am guessing this is just because the pads and rotors are both unworn and at their max thickness. I used the JB6 brake calipers because thats what they had in stock.
Anyone done this before and had similar results.

 
85ChevyTow 
Member
Posts: 28

Loc: s.e. Louisiana
Reg: 03-05-02
03-08-10 03:56 PM - Post#1876358    
    In response to Abowsman

The Jb7 Brake calipers are bigger in size and take a bigger pad and will bolt in place of the jb6. The brake lines are different and will not interchange so you evidently got the right parts.

 
Abowsman 
Forum Newbie
Posts: 40

Age: 31
Loc: Atlanta
Reg: 02-18-10
03-09-10 06:15 AM - Post#1876745    
    In response to 85ChevyTow

just curious what is different with the brake lines. I did also replace the brake lines with braided lines. Is it the banjo bolt size different or something else.

 
85ChevyTow 
Member
Posts: 28

Loc: s.e. Louisiana
Reg: 03-05-02
03-09-10 11:18 AM - Post#1876908    
    In response to Abowsman

If I remember correctly,the Jb6 brake line kinda resembled a T where it bolted to the caliper. The Jb7 line was like round where it bolted down to the caliper. I have an 84 swb 4x4 with 3/4 ton axles and I'm going to upgrade to the Jb7 when I swap in my 4.10 axles. When I'm winching something heavy, the brakes won't hold with my 33"s and I'll be going to 35"s soon. The next time you're in A-Z or Napa get them to pull up the pics and show you the difference between the calipers an lines and you'll see the difference.

 
Abowsman 
Forum Newbie
Posts: 40

Age: 31
Loc: Atlanta
Reg: 02-18-10
03-10-10 06:46 AM - Post#1877400    
    In response to 85ChevyTow

Well now i kinda regret not going with the jb7 brakes. I have 37's on there now. I replaced the calipers, rotors and pads all at the same time and when i first assembled all the parts i could barely get the caliper and pads on the rotor. Have you ever run into this problem? I think it was just because everything was at its max thickness. I made sure the first few trips were short because the brakes were rubbing and causing alittle extra heat. They seem to have loosened up now though.

They stop my truck just fine even pulling a 30' boat. No winching though. I am getting ready to put disc brakes on the rear and i may put the jb6 calipers on the rear and put jb7's up front. That may also help balance out the braking and may not need a proportioning valve for the rear. Any thoughts on this???

 
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