Brakes soft after changeing both front and back.

[77Impala]

Two days ago I hear what sounded like metal on metal when stopping my truck. Today changed both front and rear brakes and found nothing to be metal on metal. But did find both rear cylinders leaking. Left just a little bit, and the right was soaking wet.

Before changing I had what I call a firm brake pedal. After changing the pad, shoes and wheel cylinders I have soft brakes. I have bleed them so I have all new fluid, I have changed the master cylinder thinking something may have traveled up from the calipers and damaged it. I have readjusted (for what I know how at the moment) the rear shoes.

The pedal is firmer than this afternoon but not what it was this morning.

Bled from RR, LR, LF, RF. Then master cylinder, ABS bleed valve, RR, LR, LF, RF 2 times.

Is there a procedure of adjusting the rear shoes? I hate the high adjusters that these trucks have, I wish they were the low ones like my Impala. The adjusters were frozen when I replaced the shoes but I was easily able to get them working again.

One trick I just was not in the mood for tonight was to try backing it up and stomping on the brakes. I will try that tomorrow.

Is there anything I am missing?

 

[AbramF_496]

Will be kinda hard to find it going through the thread so go on google and type in
Brake fix or brake mod gmt400
It'll be quicker to find good luck !!!
Reversing. Usually works n makes the rear lower adjusters do their job n tighten up

Another problem that I had come across was a broken emergency brake cable!

Ya once I replaced and tightened it up my brakes were back to normal


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[skylark]

One small change in your procedure. "Bled from RR, LR, LF, RF." It should be RR, LR, RF, LF. I doubt this is the whole problem though. My money is on rear brakes being way out of adjustment.

 

[polar]

This^. The key is to start with the farthest away bleeder, and work your way to the front still keeping distance to the master on your mind. Another thing is that you might have not gotten all the air out of your abs


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[michael hurd]

You still have trapped air, and the rear brake shoes need to be adjusted up before trying to bleed the system. Did you bench bleed the master cylinder properly before installation? You need to stroke it slowly, and wait 10 seconds or so between strokes.

You may go through a few liters of fluid before getting acceptable brakes. GM uses a tool to cycle the ABS system while bleeding. If you can't access or are unwilling to take it to a shop, you can do it the poor man's way. If you have a gravel road nearby or snow covered area, and you can safely get there: brake hard enough to activate the ABS, then bleed the system after that. Keep repeating drive and bleed with ABS activation and you should get all of the air out and have a nice firm pedal.

Chances are with high mileage, the MC was getting worn anyways, and it's not like they are expensive to replace. As mentioned, tapping the front calipers before bleeding with a rubber mallet can dislodge air bubbles.

Hope that helps you out.

 

[77Impala]

Thanks everyone. In a while I will be taking the truck and doing some reverse stops to finish tightening up the rear brakes. Also at first yesterday after changing the brakes I had no park brake but by evening after manual tightening the back brakes I had some park brake being applied.

From that I will see how firm the pedal is. If needed, or who knows, for kicks and giggles I may still try one more bleeding. I do have a part gravel road at my work I can use to activate the ABS unit.

 

[michael hurd]

Guaranteed there is still air in the system, you need to bleed that out to have effective brakes. Brake fluid is cheap, driving into someone because you can't stop is never cheap.

Yes, assuming that everything is in working order, backing up and applying the brakes will self adjust the rear brakes tighter.

 

[michael hurd]

When bleeding, take nice deliberate slow strokes on the pedal and wait 10 seconds or so between pumps to avoid fluid aeration.

 

[skylark]

You need to stroke it slowly, and wait 10 seconds or so between strokes.

Thank you Michael! I just convinced my wife that we need to bleed the brakes!

 

[77Impala]

Yup still need to finish bleeding the system. Auto adjusting the rear brakes helped a good bit but still have about 1 1/2 inch of more travel than I am use to. Hopefully I will have some help later today.

On the slow strokes are you meaning to: open the bleeder, have the helper slowly push the pedal to the floor and hold, tighten the bleeder, reset brake pedal, wait 10 seconds and repeat? Or pump slow for say 6 -10 strokes than on the last open the bleeder?