Squarebody 73-87 Brake Upgrade

[buffydores]

Just wanted to share my experience in brake upgrades. For the half tons there's a factory brake upgrade available to us. There's a big piston caliper (JB7/JD7 - 13" - 3-5/32" piston diameter) that increases the clamping force by 15% over the standard smaller piston caliper (JB6/JD6 - 11" - 2-15/16" piston diameter). The big caliper showed up in the mid 80s 3/4 ton trucks. It's a bolt on. Starting in 1979, they started using the 10mm banjo bolt. Earlier than that, the banjo bolt was like 7/16". So pre 79 trucks might require a new set of lines coming off the frame to the caliper.

As far as brake pads, I've started to run EBCs Ultimax 2 pads for the D50 GM calipers. These suckers are rated GG friction, which is top notch. They have the cold bite you need in a daily driver. They also have the break in coating that helps get the pads seated to the rotor real nice. I can stand my Blazer, running heavy 35s, on its toes.

If you're running a heavy setup, and you don't want to go hydroboost, this is the ticket.

And please, please follow the break in procedure. Probably the most important aspect of the upgrade.

[Hammered 77]

Interested. So do these require 1" or 1 1/4" rotors and does your 15" wheels still fit?

Rick

[buffydores]

Originally Posted by Hammered 77

Interested. So do these require 1" or 1 1/4" rotors and does your 15" wheels still fit?

Rick

Everything works fine. Same rotors. Bolt on. Just need to consider the brake line change if your lines are pre 1979.

I'm assuming on the wheels though. I'm actually running 16" wheels, but the only difference I can see on the calipers is the larger piston.

[buffydores]

Update: Checked the clearances. No difference. 15s are good to go.

[Hammered 77]

Thanks for checking.

[Hammered 77]

What brakes do you have on the rear axle? Are you still running shoes or did you add disc to the rear?

[aggie91]

Originally Posted by Hammered 77

Interested. So do these require 1" or 1 1/4" rotors and does your 15" wheels still fit?

Rick

Originally Posted by buffydores

Everything works fine. Same rotors. Bolt on. Just need to consider the brake line change if your lines are pre 1979.

I'm assuming on the wheels though. I'm actually running 16" wheels, but the only difference I can see on the calipers is the larger piston.

The JB7/JD7 calipers require a 1 1/4" thick rotor.

[buffydores]

Thanks Karl. I see that factory rotors are 1-1/4". Why would anyone run a 1" rotor?

[Hammered 77]

I don't remember what year it started, but some of the light duty 1/2 tons came with 1" rotors.

[aggie91]

Originally Posted by buffydores

Thanks Karl. I see that factory rotors are 1-1/4". Why would anyone run a 1" rotor?

At some point GM started putting 1" thick rotors on the trucks as a light duty brake system. I think it was around 1981, I had an '84 that came with a V6 & TH400 that had the light duty brake package. I upgraded to the JB5 system with the 1 1/4" rotors up front (for 2wd, you have to swap the spindles to do this, I did when I put on the dropped spindles) and went with the 2 3/4" wide drums in the rear. Not sure why GM did it, but they did.

SO, if you have the 1" rotors and don't want to replace the spindles (2wd guys) to use the 1 1/4" rotors, then this upgrade is not for you.

[Low Elco]

This is a cool idea and all, but how would you spec that out at say, O'Reilly's or AZ? Just ask for '77 3/4 ton calipers?

[aggie91]

Here is what you need to tell AZ or O'Reilly:

1985 Chevrolet C20 (3/4 Ton), 2wd, 5.7 engine
Front Calipers for Heavy Duty brake system, 13" rear drums

For reference:
Front Right Caliper is a ACDELCO #18FR649
Front Left Caliper is a ACDELCO #18FR650

These require the 10mm banjo bolt and hose

Ask for the front hoses for a 1985 C10 with the heavy duty brakes.

[buffydores]

Such great info. This is gonna be helpful for a lot of folks.

[SCOTI]

Also..... The 1/2 ton HD drum set-ups are more common under Burbs & Blazers if anyone is searching for the backing plates.

[SBTork]

Great info, thanks for the heads up!!

[Low Elco]

Right on, thanks! Dig this- so I go over to a friend of my kid's shop who is a big 4x guy. We start talking trucks, and I mention this idea. He says, oh yeah, I have a pair on the shelf over there- used them once. You want them? 20 ea, with pads. not only that, but we tore our new truck down, and danged if it doesn't have the big back drums on it! Ha-HA! Gonna be stoppin' good now, fellas! imagine with the Hydroboost!

[bondobob]

OK I get that bigger thicker discs and bigger and wider drums give you more stopping power for hard braking but do I really NEED to do this on my 84 short bed? It will add unsprung weight don't forget. My 82 K10 stops great with the big brake set up (locks the rear under heavy braking) but that's quite a bit heavier. If you guys feel it's definitely worth it on all street trucks I'll do it. I need to buy the correct dropped spindles and all new parts anyways. Looks like the proportioning valve and booster/master all gets changed. Small point: the single booster is better looking than the dual. I'm sure this has been hammered on before so thanks for your patience.

[Keith Seymore]

Originally Posted by bondobob

OK I get that bigger thicker discs and bigger and wider drums give you more stopping power for hard braking but do I really NEED to do this on my 84 short bed? It will add unsprung weight don't forget. My 82 K10 stops great with the big brake set up (locks the rear under heavy braking) but that's quite a bit heavier. If you guys feel it's definitely worth it on all street trucks I'll do it. I need to buy the correct dropped spindles and all new parts anyways. Looks like the proportioning valve and booster/master all gets changed. Small point: the single booster is better looking than the dual. I'm sure this has been hammered on before so thanks for your patience.

I don't think so.

My '87 was a daily driver for 30 years and was picture perfect in terms of pedal feel/travel/decel, even with all of my commuting, parts chasing, light hauling and trailering.

K

[buffydores]

I only did it because I'm running 35" tires and needed more clamping force to get full lockup.

[Ski-me]

Nice info and thread. Are you saying a nice improvement over the original? I'm also running 35's and would be nice to slow it down a bit better.

Thanks for the great info!!

1985 Chevrolet C20 (3/4 Ton), 2wd, 5.7 engine
Front Calipers for Heavy Duty brake system, 13" rear drums

For reference:
Front Right Caliper is a ACDELCO #18FR649
Front Left Caliper is a ACDELCO #18FR650

These require the 10mm banjo bolt and hose

Ask for the front hoses for a 1985 C10 with the heavy duty brakes.

[buffydores]

Originally Posted by Ski-me

Nice info and thread. Are you saying a nice improvement over the original? I'm also running 35's and would be nice to slow it down a bit better.

Definitely do it. It's cheap. It works. I love these EBCs Ultimax 2 pads.

[Ski-me]

Originally Posted by buffydores

Definitely do it. It's cheap. It works. I love these EBCs Ultimax 2 pads.

Did you touch your master cylinder? I'm debating about swapping in a new one now.

My current MC is a 1-1/8" bore (18M217 or 19176456). Wondering if I went to a 1-1/4" bore (18M422 or 19176314).

My pedal still goes almost to the end when braking so think I may need to also replace my MC. New SS lines to calipers and also a new Vacuum Booster, from a few years ago.

My Blazer has the RPO code JB5.

[buffydores]

I did not change the master cylinder.

[Ziegelsteinfaust]

Originally Posted by Ski-me

Did you touch your master cylinder? I'm debating about swapping in a new one now.

My current MC is a 1-1/8" bore (18M217 or 19176456). Wondering if I went to a 1-1/4" bore (18M422 or 19176314).

My pedal still goes almost to the end when braking so think I may need to also replace my MC. New SS lines to calipers and also a new Vacuum Booster, from a few years ago.

My Blazer has the RPO code JB5.

A larger bore master cylinder will give you more brake at any one point of pedal travel. It will also be firmer due to displacement of said fluid.

It all comes down to personal taste. On how you like your truck set up

On my Camaro I used a smaller bore master to get more progressive feel out of it when I actually get to race it. Making corner braking much safer.

[1968k20]

Did you ever find a low-miles Suburban?