Squarebody 73-87 Brake Upgrade
 

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.

Re: Squarebody 73-87 Brake Upgrade
 

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

Rick

Re: Squarebody 73-87 Brake Upgrade
 

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.

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

Thanks for checking.

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

Still running drums. Most of the work is done on the front end. Not saying upgrades in the back aren't helpful. They just don't move the needle as much.

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

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.

Re: Squarebody 73-87 Brake Upgrade
 

aggie 91 what issues (if any) did you run into changing to 2 3/4 brakes in the rear? Any wheel fitment problems? Was it just a matter of changing the brake shoes, drums, and cylinders?

Thanks
Rick

Re: Squarebody 73-87 Brake Upgrade
 

No wheel issues at all.

The brake upgrade requires changing the backing plates. Those are what sets the width of the wider shoes to the inside. The axle placement and the face of the drum (wheel mounting surface) does not change.

Change the backing plates, new shoes, new hardware, new wheel cylinders, and new drums. That's it.

Check out this thread...Title is 12 bolt Drum Brake Upgrade, but same goes for the 10 bolt in these trucks...same parts are used...
http://67-72chevytrucks.com/vboard/s...d.php?t=692672

Re: Squarebody 73-87 Brake Upgrade
 

Thanks, so before I go any further i'll need to find some backing plates.

Re: Squarebody 73-87 Brake Upgrade
 

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?

Re: Squarebody 73-87 Brake Upgrade
 

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.

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

Great info, thanks for the heads up!!

Re: Squarebody 73-87 Brake Upgrade
 

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!

Re: Squarebody 73-87 Brake Upgrade
 

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.

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

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.

Re: Squarebody 73-87 Brake Upgrade
 

Did you ever find a low-miles Suburban?

Re: Squarebody 73-87 Brake Upgrade
 

I found plenty. I just changed my mind. My middle boy wants a square body suburban when he gets old enough. He's 10. In a couple of years, I'll get one and start working on it with him.

Re: Squarebody 73-87 Brake Upgrade
 

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

Re: Squarebody 73-87 Brake Upgrade
 

^^^ Cool, thanks!

Re: Squarebody 73-87 Brake Upgrade
 

I just picked up an 72 k10, 6.2, barn doors!

Re: Squarebody 73-87 Brake Upgrade
 

Suburban

Re: Squarebody 73-87 Brake Upgrade
 

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.

Re: Squarebody 73-87 Brake Upgrade
 

I did not change the master cylinder.

Re: Squarebody 73-87 Brake Upgrade
 

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.

Re: Squarebody 73-87 Brake Upgrade
 

Wilwood makes a nice aluminium caliper for C10's. Its pricey, but looks good behind the right wheels.

Re: Squarebody 73-87 Brake Upgrade
 

Does anyone know if these 3/4 calipers are "low drag"? The 3/4 ton uses a cast master cylinder and my understanding is none of the squarebody cast iron master cylinders were quick take up. Which would mean the calipers are not low drag?

Re: Squarebody 73-87 Brake Upgrade
 

i know, older thread... anyone here use these calipers with Mcgaughys 2.5 drop spindles with 1 1/4 rotors?

Re: Squarebody 73-87 Brake Upgrade
 

Looking to do this on my 78 and hoping to verify the part numbers:

- napa total eclipse 3 5/32" piston calipers CAL SE4674 & CAL SE4673
- napa pads CAL SE4674 (should i use ebc ultimax 2's? cannot find the right part)
- napa brake lines UP 38065 & UP 38066
- 2 banjo bolts for calipers