Replaced rear shoes, too much travel

[Three504spd]

1994 Blazer 4wd.
Replaced rear shoes, standard procedure, now I have alot of travel, feels like the rears take forever to grab and the brake light is turning on and off.
Will bleeding the brakes fix this or did I Fubar something.
Daily driver so any help would be appreciated.

 

[magimerlin]

Adjust them then.... pull the wheel back off 1 at a time.. adjust the star adjuster till the shoes just start to drag on the drums... repeat on other side. Put all back together. Enjoy properly adjusted rear brakes.

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[RichLo]

^ what he said.

and/or if your parking brake works, pump that a few times and that should auto-adjust them

 

[sewlow]

^ what he said.

and/or if your parking brake works, pump that a few times and that should auto-adjust them

That may work. But...the auto-adjusters do no not work all that great on these trucks.
The problem is with the notches on the adjuster wheel.
They're too big. By the time that the shoes wear down to the point of the adjusters doing their job & ratcheting up to take up the slack, the pedal is so low that it's nearly at the floor when the brakes finally do
engage.
...and, for some reason GM redesigned the rear brakes so that the adjuster is at the top, as opposed to the way they were for years before with the adjuster at the bottom. Could that be the cause of the problem? Maybe. Maybe not. But my experience with the previous design, GM brakes never had this problem with the auto-adjusters.
Then just to top it off, GM eliminated the window on the backing plate which the previous design had to allow for manual adjustment. Not even a knock-out provided.
Remove the wheels & then the drums just to adjust brakes? Even my ole man, a fleet maintenance mechanic for over 45 years, was shaking his head over that one. Kept saying all I had to do was to punch the knock-out to get to the adjusters. Had to actually physically show him. All he had to say was, "Sure glad I ain't working on this **** anymore!"

 

[east302]

Then just to top it off, GM eliminated the window on the backing plate which the previous design had to allow for manual adjustment. Not even a knock-out provided.
Remove the wheels & then the drums just to adjust brakes?

What’s strange is that the service manual implies that there is a knockout of some sort in the backing plate. I have not noticed one and don’t understand why they would have deleted an adjuster opening. It may be that the axle flange is in the way.

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[94burbk1500]

What’s strange is that the service manual implies that there is a knockout of some sort in the backing plate. I have not noticed one and don’t understand they deleted an adjuster opening. It may be that the axle flange is in the way.

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I did mine earlier this year and I swear there was an adjustment window on mine. Maybe you guys got friday trucks?

 

[El Tigre]

I installed a 10# residual pressure valve that seems to keep the shoes from retreating all the way. Proper adjustment is key,and there is a tool that measures the drum like a caliper. The other side of the tool is a pass/fail space that gets one really close (if not at) where it needs to be...

 

[Schurkey]

Drum brakes with self-adjusters at the bottom (Duo-Servo) may self-adjust when braked firmly in reverse. This WILL NOT WORK on drum brakes with the adjusters at the top (Leading/Trailing shoes).

Drum brakes with adjusters at the top may self-adjust when the park brake is applied and released, then the service brake is applied. The park brake "*****" the adjuster, the service brake "pulls the trigger". Depending on how far the adjustment is from correct, it may take several repetitions. Damned pain in the ass. I happily upgraded my K1500 from the dreaded leading/trailing brakes (adjuster at the top) for 6-lug K2500 duo-servo brakes (and rear axle assembly) with adjuster at the bottom.

With EITHER system, one notch on the adjuster wheel is damned sure NOT the difference between normal brake pedal and pedal-near-the-floor.

If a residual check valve doesn't allow the "shoes to retreat all the way" you've screwed-up the brakes. The shoes MUST retract properly or the self-adjuster won't work right. Residual pressure valves were NOT intended to prevent full retraction of the shoes. They're intended to maintain a slight positive pressure in the wheel cylinders, so air cannot be "sucked" in when the brake pedal is released. Wheel cylinder seals are primarily intended to keep fluid in--not to keep air out. On most vehicles, having the master cylinder mounted a couple of feet above the wheel cylinders is all that's needed. The height difference provides some minimal pressure in the wheel cylinders.

I've also run across guys who adjusted the park brake cable too tight, that won't allow the shoes to retract properly, and therefore also screws-up the self-adjuster. ALWAYS adjust the service brakes before adjusting the park brake.

And while rear brake adjustment is PROBABLY the cause of low brake pedal and the brake light illuminating, it is entirely possible that there's air in the system. Adjust first, re-bleed if the adjustment doesn't fix the low brake/brake light.

 

[El Tigre]

My experience over many years with GM "self adjusting" drum brakes is that I always ended up adjusting them myself. Or,self adjusted brakes... Bahahahahaha....

 

[Gibson]

Drum brakes with self-adjusters at the bottom (Duo-Servo) may self-adjust when braked firmly in reverse.

Yep,, the key word is "may".
All these trucks are at an age where the brake parts are showing wear. If the little "ridge" on the adjusting lever is worn, (kinda rounded off,) and the teeth on the star-wheel are worn, then the lever won't turn the wheel properly.
It's also really important that the threads, (both male and female,) on the star-wheel parts are really clean and smooth acting, some rust or grit will impede their rotation, and screw-up the self-adjusting properties.
A bit of disc-brake lube on the threads is good practice,, it doesn't take much.
When all the parts are smoothly operating, the Duo-Servo system works quite well to adjust the brakes when you back-up and stop.