Author Topic: Brake Pads for JB7 System  (Read 4176 times)

Offline Jon87V20

  • Frequent Member
  • **
  • Posts: 268
Brake Pads for JB7 System
« on: July 16, 2018, 01:04:52 AM »
This weekend, I was replacing my front rotors/hubs, calipers, and pads on my '87 Suburban V20 with the JB7 brake system (verified with the glovebox service sticker).

I noticed that my old pads had a "lip" of brake pad material along the top edge of the pads where it hadn't been making contact with the rotor. Likewise, the rotor had a raised stripe around inner circle where the pad wasn't touching. I know I have the correct calipers, but it looks like I was running the wrong pads before.

I took them back to Autozone (I won't be going in that place anymore for a lot of reasons) and swapped the "MKD52S" pads out for the "MKD153" pads. Unfortunately, those pads don't cover the entire surface area of the rotors either, and the holes in the outer pads are too big for the caliper pins.

I'm not sure what to do here. Can anyone help me out with a part number I can use for Oreilly's, Napa, or even Chevrolet? I'm going to take these pads back again and try someplace else. Ordering some online isn't really an option right now because this is my commuter several days a week and I need to get it roadworthy again immediately.

Thanks!
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 18979
Re: Brake Pads for JB7 System
« Reply #1 on: July 16, 2018, 05:35:45 AM »
The 153 pads should be the right ones. Maybe the wrong rotors or calipers were installed?


,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Jon87V20

  • Frequent Member
  • **
  • Posts: 268
Re: Brake Pads for JB7 System
« Reply #2 on: July 16, 2018, 08:22:58 AM »
Vile, the calipers I have are the "C530" and the "C531" calipers. Are those the correct ones? The rotors I bought were these ones from Oreilly's "56287RGS".

These are the same rotors that were on the truck before as they had the same issue with the pads. I really hope these aren't the wrong rotors as they were $83 a piece and I bought new bearings and seals for $50. I don't think they'd accept that stuff back...
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 18979
Re: Brake Pads for JB7 System
« Reply #3 on: July 16, 2018, 05:30:15 PM »
You might want to check the fitment with the other calipers. They are a smaller diameter piston but have a wider back. You can dry fit one and see if you do in fact have mismatched parts.
,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Jon87V20

  • Frequent Member
  • **
  • Posts: 268
Re: Brake Pads for JB7 System
« Reply #4 on: July 18, 2018, 10:08:38 PM »
I'm stuck again. I think I finally found the right combo of calipers and pads. The front calipers that correspond with having 11 inch rear drums and the MKD153 pads seem to be the correct setup. However, now I can't get the brakes to feel right. I've bled them out a few times now, but the pedal still feels close to the floor and I can get it to touch the floor if I'm performing an emergency stop. As far as I can tell, I don't have any leaks and the Master Cylinder seemed fine prior to this job.

Any advice on something I may be overlooking? Is it possible the Master Cylinder could not be functioning properly now?

Thanks.
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 18979
Re: Brake Pads for JB7 System
« Reply #5 on: July 19, 2018, 06:10:42 AM »
Are the rear brakes properly adjusted?
,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Jon87V20

  • Frequent Member
  • **
  • Posts: 268
Re: Brake Pads for JB7 System
« Reply #6 on: July 19, 2018, 08:33:48 AM »
I'll have to check them out. It's just weird because before I changed all the parts out, the pedal was still a few inches from the floor and couldn't be pressed all the way down.

If I remember correctly, you move the adjuster screw until you can hear the shoes barely scraping on the drum. Is that right?

The drums don't seem to be contributing much, so hopefully that will help. The reservoir for the rear is always full so I don't think they're leaking.

I'll check the adjustment on those today and report back.
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline Jon87V20

  • Frequent Member
  • **
  • Posts: 268
Re: Brake Pads for JB7 System
« Reply #7 on: July 21, 2018, 09:04:25 PM »
So I'm completely baffled at this point. I've bled all four wheels out A LOT. There's definitely no air in there. However, the pedal is still almost touching the floor.

When the engine's off and the booster isn't active, the pedal feels normal and goes about halfway down. When the engine is running, it goes all the way down.

I've checked the front calipers over and over and can't find anything wrong. There isn't excessive travel from the pistons or anything. They are barely extended. When the pedal is pressed, everything clamps down and cannot be moved. There's no leaks anywhere either.

The only other thing I imagine can be an issue at this point would be the Master Cylinder. It just seems so unlikely that it would be fine before this brake job, and suddenly have issues now. I have noticed some corrosion running downward on the brake booster like there was fluid leaking down there at some point, but it's been like that as long as I can remember.

Is it possible it's the master cylinder? Is there anything else that could be causing an issue here? Can the proportioning valve create weird problems like this? It just seems like with fresh rotors, calipers, and pads that the pedal shouldn't be able to physically go down that far before the pads wouldn't allow it. Like I said, the pistons are not over-extending and look fine.

Something else worth mentioning is the bleeder screws seem a bit janky on these new calipers and wobble a bit when you open them during bleeding. It almost seems like fluid is coming up out of the bleeder screw threads. Could this just be a faulty caliper? There's no air in the system anymore. If there is I don't know how to get it out.

I'm getting desperate. I really need to use this truck all next week!
« Last Edit: July 21, 2018, 09:06:43 PM by Jon87V20 »
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 18979
Re: Brake Pads for JB7 System
« Reply #8 on: July 22, 2018, 07:04:48 AM »
Did you pull the drums off and check the rear brakes yet? Make sure you pull back the boots on wheel cylinders to peek in there for any evidence of fluid. Are the shoes properly adjusted? Master cylinder internal leak will usually result in pedal creep however the wrong master cylinder will result in a low pedal. Did you replace the master cylinder? Which one is on there? Try running the one with the plastic reservoir after you inspect everything.
,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Jon87V20

  • Frequent Member
  • **
  • Posts: 268
Re: Brake Pads for JB7 System
« Reply #9 on: July 23, 2018, 04:51:23 PM »
I ended up getting a new Master Cylinder. It seemed to help a bit. It's drive-able, but there must still be a bunch of  air in there someplace. The pedal gets resistant sooner, but you can push through it easily.

Thanks for all the help, Vile!
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208