How much vacuum should a brake booster be tested to?

 

typical car engine pulls between 6-16 " of vacuum.
a typical vacuum test is called leak back test.
pull vacuum on component with gauge attached, say 14"
now isolate the test component, from vacuum source.
it should continue to hold same value, for several minutes.
if it drops off right away you have a leak.

 

Thanks 69Vett.
I am having some brake issues on the 82. Brakes will stop car but I am close to having no more pedal. Front calipers replaced by the previous owner. I had the master cylinder replaced. I do not think it is the booster but wanted to check it and did not know what vacuum to use.

 

if you have almost no pedal, you have other problems.
you should be able to bleed the brakes, with car off and have rock hard brake pedal with plenty of pedal travel left.
someone else replaced calipers, and master cylinder, ... these are clues.
I would start with a proper brake bleed of all wheels. do this until you get good pedal.

 

Don't feel You are the only one to have this same situation. Using the search feature will find a lot of info bleeding brakes. Either the previous owner installed the wrong parts which caused the problems You now have, or, He had the same issue and started throwing parts at it to fix it. Keep in mind there are two bleed screws on the rear Calipers.

 

Thanks all for your input.
I will do my research on the search function of CF for the brake bleed.
This is why I like this forum because of people like you and your input.

 

Tested booster to 17 hg/in for 5 minutes. Test good. Pulled vacuum test on running engine to booster 16 hg/in. Pulled back tires and inspected rear of car. Gravity bled rear brakes. Fluid dirty. Gravity bled until clear fluid.
On the rear pads the RR are worn at an angle from the back to the front and LR has the same but not as bad. Thickness of pad is about twice the thickness of the piece they are attached to. Rotors are in good condition. Will check runout.
Is this normal wear?
What would be a good brake pad replacement and caliper if needed?

 

FROM EXPERIENCE.

Seeing how you just bled the brakes and the fluid is clean. I would test the brakes and see how well this improved your brake issue.

When you were gravity bleeding the calipers...did you notice any AIR coming from a specific caliper or calipers???

Also...how well did you brakes feel when you had the master cylinder installed???? It takes quite a bit of time to just bench bleed the master cylinder. So it depends if the person doing the work took the time...or has a pressure bleeder which will force brake fluid through the brake system under pressure....which for me...is the only way to do this. Gravity bleeding does not work well if there is air in the master cylinder....which is why bench bleeding needs to be done properly.

If your brakes feel better and the pedal is higher up. I would write down the DATE and MILEAGE and drive the car. When and IF the problem surfaces again...see how many miles you went until the issues surfaced again.

If you go 10,000 miles....then the system would seem to need only bleeding to correct it.

If you go 500 miles...then that is when I would dial indicate all bearings and rotors.

As for your brake pads wearing un-even. That can be a caliper/piston issue and if these pads are on the calipers that were NOT replaced by the owner...then it may be necessary that they would be replaced along with the rubber hoses and possible steel lines in the rear.

Rotor thickness is important. A new rotor is 1.250" The minimum that the rotor can be re-surfaced to is 1.230" and if it is thinner than 1.215" it is junk. Measure one inch from outer circumference in several spots.

If replaced pads..there can be a chance that a caliper can leak after doing it so do not be surprised. This is due to pushing the piston back into an environment that may still be contaminated with crud and sludge...even though you bled it til it was clean fluid...the crud can still be in there.

I do not install and "fancy-dancy" brake pads on car that are daily drivers. The regular organic or semi-metallic pads seem to work just fine. If you are more aggressive of a driver than up-grading to a metallic pad may work better for you.

When it comes to calipers....I install the lip seal design. You can search the forum for so many discussions on which way to go...O-ring design or lip seal design.

DUB

 

Thanks DUB.

Brakes feel about the same after the clean fluid. Fluid that came out was dirty. Unable to see bottom of red solo cup after 1/2" of fluid in bottom.

After MC installed brakes felt about the same. MC replaced because it was rusty and around the top would stay wet.

Will replace calipers and hoses. Steel lines look good.

Caliper rotors with micrometer, both rotors were 1.25" measuring 1" from outer edge in 6 different spots. Note, rivets where drilled already on both sides.

 

Were the brakes better BEFORE you had the master cylinder installed????

DUB

 

Brakes before MC change out we're about the same as after. Just not that good feel stopping power for 4 wheel disc.
New calipers and pads ordered. NAPA remanufactured calipers (Delco caliper). Pads are NAPA premium.
Will let you know.

 

Calipers, hoses and pads arrived. Checked calipers and installed pads and hoses. Had no issue installing calipers over disc. Installed brake lines. Gravity bled RR inner then outer, LR inner and then outer. Have good brake pedal but have not made a test run yet.
Question, how do you adjust the emergency brake pads? I know it is thru the hole in the disc, but how do you rotate the disc to adjust the proper drag?

 

The problem with you messing with the parking brakes has to do with if they are still original or not. By turning the rotor...and have the lugs on and snugged down well so the rotor stays tight to the spindle. Turn the rotor until you can see the adjuster wheel at the bottom...somewhat. IF it is not shiny stainless steel...it may not turn due to age, rust and brake dust.

Insert a flat blade screwdriver and raise the handle away from the floor....this causes the shoes to be spread out by the adjuster. I keep doing this until it stops and the rotor will not turn...then I back it off 7 to 9 teeth and check it.....then I get under the car and adjust the cable so that the parking brake hold on the 14 click.

Problems you can encounter:
The lever for the parking brake will seize and hold and not release even though you have released the handle. Rotor need to be removed to deal with this issue...which may be a bit of fun if it has seized and there is a ridge in the rotor that will hold up the shoes and not allow then to slide off the inner portion of the rotor. Removing the parking brake cable from this lever may help...so you can manually move the lever.

The springs can be aged/rusty and thus will not retract...so when they are stretched out...they stay in that position.

The primary and secondary (cross-over) cables are stretched and you loose the ability to adjust the parking brake under the car.

The rear ( cross-over) cable is seized in the metal housing at each trailing arm.

Back to your brakes. Did you check your bearing and rotor run-out at each wheel? This is an important step that should not be overlooked.

DUB

 

DUB, thank you for all the input.
When I pulled the rotors I was able to inspect the emergency brake assembly. The pads looked OK. I did not take the assembly apart but did clean and lubricate behind the pads. I pulled up on the emergency brake lever and the pads opened. Released and the pads relaxed. Did this several times. Lever movement made the cables move where they are attached to the brake. I was able to rotate the adjusters on the bottom all the way in. Just needed to reset adjusters for brake to hold.
Did not check bearing runout after re-installing rotors. Did check rotors runout - 1.25"
Road tested disc brakes. They were very good.

 

Glad to read that your brakes are better.

(Bold area in your post)
This was the rotor THICKNESS....correct??? And NOT the run-out.

IF you are not going to check and correct bearing and rotor run-out...make sure you write down your mileage and DATE. So if and when you have a problem...you have a time line an mileage to go off of to aid in finding a possible problem. Just a bit of advice.

DUB

 

DUB,
Correct 1.25" on rotor.
Is the bearing and rotor run-out in the SM or AIM?

 

This thickness is getting close to DISCARD. You can NOT resurface them...because they are below 1.230"...BUT they are barely above the 1.215" MINIMAL THICKNESS.

The information is in the service manual.

DUB

 

DUB,
I thought 1.250" was considered good for rotor runout?
Will use Service manual for info.
Thanks,
Bikergems