Low brake pedal

[Supercharged111]

Using the park brake lifts the adjuster mechanism--then applying the service brake "triggers" the adjuster. So you have to kick the park brake, release it, then kick the service brake pedal. Then repeat about a dozen times. Be prepared to do it another dozen times--or pull the drums and adjust 'em by hand.

You mentioned this in another thread, but my sequence is not what you have outlined above. I set parking brake, put truck in park, get out. When I get back in, I apply the brake, release the parking brake, and go. Does the above procedure apply to the 9.5" SF diff as well?

 

[letitsnow]

Most problems I’ve read about is low pedal, squishy also, but low pedal mostly. I’ve done Nbs master, rebuilt calipers, drilled and slotted rotors, rears as far as possible. All 3 stainless brake lines, rear whl only abs deleted and removed. Ok I’m a retired ASE certified brake tech. Still have low pedal, once they grab, hold that beer.! Here’s my hypothesis. Just for S&Gs. What woul happen if I got a spare brake rod from pedal to power booster, an welded 1/2 on to it.?

I've tried shimming the rod (1/16") on mine, and it made the front brakes drag slightly. After adding ss brake lines in front, a willwood prop valve, eliminated abs, all new brake lines, rear disc conversion - the brake pedal still goes down a bit farther than I would like. The brakes are great, but the pedal still goes down. When my stock master cylinder needs to be replaced, I am hoping to switch to a newer disc/disc one. That might help.

The low brake pedal combined with a brake light switch that isn't adjustable, that makes getting the trailer brake controller adjusted a bit of a pia. Not a big deal, but I wish that switch was adjustable...

 

[Schurkey]

These no air, pressure bled, rears adjusted to slight drag, never heard of twin leading shoe rear brakes, don’t know what that is.

MY MISTAKE, and I've edited the post to correct it. What I originally called "Twin Leading Shoe" rear brakes are in fact "Leading/Trailing Shoe" rear brakes.

What doesn't change is that THEY SUCK.

So far as I know, the Leading/Trailing Shoe brakes are used only on the 1500s. Even 6-lug 2500s had duo-servo rear brakes. I know this because I took off the 10-bolt 8.5 ring gear axle from my '88 and replaced it with a six-lug 14-bolt 9.5 semi-float axle from a 2500, and got the better duo-servo brakes in the process along with the heavier axle.

Leading/Trailing shoe brakes use IDENTICAL SHOES, and the adjuster mechanism is ABOVE THE AXLE SHAFT. The bottom of the shoes rest on a solid, fixed "block" attached to the backing plate. They adjust as I said--set the park brake, release the park brake, press on the regular brake pedal. (repeat a hundred times.)

The more-familiar DUO-SERVO brakes have primary shoes and secondary shoes, the primary is typically lighter-colored friction material that's thicker, softer, and shorter than the darker-colored material on the secondary shoe. The adjuster is a "floating" link (threaded, with a star-wheel) between the shoes at the BOTTOM (where the solid "block" would be on Leading/Trailing Shoe brakes.) They self adjust by braking firmly in reverse. It's a totally-different mechanism.

Pressure-bled means nothing in terms of "no air" on any vehicle with an anti-lock system or a vehicle where the master cylinder is tipped "up" in front. Both the anti-lock and the master cylinder can trap air that WILL NOT BLEED OUT via the wheel cylinders.

On my '88, the RWAL has it's own bleeder screw. I had a crappy, low, squishy pedal until I burped the ABS.

Sometimes a master cylinder must be tipped so that it's level--or even slightly down in front--to remove the last of the air through the compensating port(s) between the master and the reservoir. This may be done by jacking-up the rear of the vehicle to level the master, or by removing the master from the firewall or booster WITHOUT DISCONNECTING THE METAL TUBES, and just forcing the master down in front--then touch the brake pedal (vehicle raised in back) or tickle the primary piston with a Phillips screwdriver or wood dowel (Master disconnected from booster) until the bubbles transfer from the cylinder to the reservoir.

 

[Schurkey]

my sequence is not what you have outlined above. I set parking brake, put truck in park, get out. When I get back in, I apply the brake, release the parking brake, and go.

IF (big IF) you have leading/trailing shoe brakes, I think this will work, but the actual adjustment would happen the next time you use the service brake.

I need to find a photo of the GMT-400 rear brakes, because it's too cold out to pull the drum off of a vehicle, and work out the motion of the various adjuster components.

Does the above procedure apply to the 9.5" SF diff as well?

No, because a 9.5 axle probably (almost certainly) has Duo-Servo rear brakes that adjust every time you firmly apply the service brakes when backing-up.

 

[Schurkey]

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Leading/trailing shoe brakes, from the '88 service manual.

 

[eyeroc87]

I've tried shimming the rod (1/16") on mine, and it made the front brakes drag slightly. After adding ss brake lines in front, a willwood prop valve, eliminated abs, all new brake lines, rear disc conversion - the brake pedal still goes down a bit farther than I would like. The brakes are great, but the pedal still goes down. When my stock master cylinder needs to be replaced, I am hoping to switch to a newer disc/disc one. That might help.

The low brake pedal combined with a brake light switch that isn't adjustable, that makes getting the trailer brake controller adjusted a bit of a pia. Not a big deal, but I wish that switch was adjustable...

Thanks for info on shined

 

[eyeroc87]

Thanks for that info, that’s good stuff, your right I have trailing shoe, adjuster above axel (brilliant) am doing the brake release thing that’s was suggested. Everything else was do. Guess I’ll live with low pedal, but good brakes. Thanks for all your responses.

 

[Schurkey]

Thanks for that info, that’s good stuff, your right I have trailing shoe, adjuster above axel (brilliant) am doing the brake release thing that’s was suggested. Everything else was do. Guess I’ll live with low pedal, but good brakes. Thanks for all your responses.

Once you get the rear brakes adjusted, you should NOT have a low pedal. The problem is that "nobody" uses the park brake regularly, which leads to the rear brakes getting further and further out of adjustment. Then re-adjusting the brakes becomes a major project.

 

[Supercharged111]

I use the parking brake daily and brake downhill in reverse daily. Explain why my 1500 with a 6 lug 9.5" diff still sucks.

 

[Schurkey]

I use the parking brake daily and brake downhill in reverse daily. Explain why my 1500 with a 6 lug 9.5" diff still sucks.

Do you have leading/trailing shoe brakes, or duo-servo?

I'd expect duo-servo, but I don't know for sure.

The adjuster(s) could be seized, the star-wheel teeth could be worn. The brake hose could be restricted*. The proportioning valve could be defective. The shoes could be glazed or just "crappy"--cheap, low-friction linings.

Are the drums oversized? They're metric-sized, but typically allow for (the metric equivalent of) .060 "cut" oversize plus another .030 of wear. I've seen folks with drums so oversized that the metal gets thin and distorts, and/or heat-checks.

Grease on the linings from defective wheel seal(s)? Brake fluid on the linings from leaking wheel cylinder(s)?

Do the front brakes work properly? Do you have the crappy Kelsey-Hayes RWAL? Does the RWAL work properly?

There's about two dozen reasons for brakes that suck. Maybe more.

*I've been burned personally by brake hoses that plugged. One vehicle was easy--I was doing a disc-brake conversion with used parts, and the front calipers wouldn't bleed because the used hoses I pulled off the donor vehicle were both swollen shut. Two others had the rear hose plug (gradually) with the result that the braking power was poor, and REALLY POOR at low speed in snow--the rear wheels would drive the cars forward at idle even though the front wheels were locked and sliding (therefore no steering!) I got multiple lessons in how important rear brakes are. This was when I started replacing plugged rubber hoses with steel-braid-over-Teflon brake hoses.