1987 V10 4x4 Power Brake Problem Need Help

[scorpion1110]

Thanks in advance for your ideas.

Picked up an 87 Silverado 4x4. new GM motor, fresh 700r4, new exhaust - priced right but had been sitting awhile. Got it running right and then a brake line blew. So I replaced:

• Front calipers, rotor, pads
• Front hoses
• Rear wheel cylinders, hose and shoes
• new stainless brake lines
• new proportioning valve
• New Master Cylinder
• New parking brake cables

I did not replace booster.

Bench bled master cylinder. Checked all lines for tight connections. Then bled brakes the old way, two man pumping Master Cylinder. Got firm pedal. Fired it up, booster pulled vacuum and pedal went to floor. Re-bled - same thing.

Sprung for Mityvac vacuum bleeder. Bled brakes twice more. Firm with engine off. Fire it up and you have pedal almost to floor. it will stop but it feels like far too much travel.

Assumed answer would be air in system. Have bled these at least 4 times. Checked all connections again and think the lines are tight and not pulling air. Added silicon grease around bleeder screws so I would not pull air at bleeders.

So:

is it possible booster is bad? maybe a diaphram issue? Ordered a new one just in case. Can here a "whoosh" sound when I depress pedal like pumping air but its inside cab. Figure the last thing you dont check is usually the problem.

Assuming that the PB Booster isnt the issue, is there a way to pressure test the system? Perhaps add a fitting to the old MC reservoir lid and add some compressed air and check for any leaks?

I have bled brake systems a zillion times and have never not been able to get a firm pedal- This truck is driving me nuts.

Any ideas or suggestions will be greatly appreciated.

Thanks! S

[motornut]

I'd try getting the rear shoes closer to the drums
does the Ebrake work?

[scorpion1110]

Ebrake works. We adjusted rear shoes until you could just feel drag on the rear drums. is that correct?

Thanks, S

[motornut]

Originally Posted by scorpion1110

Ebrake works. We adjusted rear shoes until you could just feel drag on the rear drums. is that correct?

Thanks, S

sounds about right hard to say tho,myself I'd try a bit more drag/pressure
you can always back it off after,and they will still need to seat

[donut]

Try unplugging the vacuum from the booster and see if the brakes firm up. Whoosh on my booster meant dead. As usual, ymmv.

btw, welcome.

[scorpion1110]

Thank you guys for helping me! I really appreciate it.

I disconnected the vacuum line to the booster and the pedal firmed right up. I am thinking that the booster might be bad. i will replace that tomorrow.

We adjusted the parking brake yesterday but I dont think its grabbing quite enough. So we will also pull the drums and add some more adjustment to the shoes and tighten up the EBrake.

I will post the results.

Thanks, S

[SkinnyG]

I adjust drums until there is a noticeable drag at the drum, as in: it takes ~effort~ to turn it with one hand.

Don't worry about any alleged "friction." Your single hand trying to turn the drum is nothing in comparison to 3800lbs of truck rolling at 60mph.

[donut]

I usually tighten rear brakes until I feel light drag, then do the back up, hit the brakes to let the brakes adjust where they want. Once the rear shoes are "set", then adjust the e brake cables.

In my younger years, I did make the mistake of getting adjusters backwards. Backing out of parking spots actually backed of the brakes, had to pull the drum and flip the adjuster back around.

[scorpion1110]

Well it looks like it was actually a combination of items.

I replaced the booster and noticed a slight improvement. Then I pulled the drums and re-adjusted the rear brakes. I didnt have them adjusted right. After I readjusted, pedal was perfect. Drives great and brake is where it should be.

Thanks for all of your assistance Guys, you were a huge help.

S