brake booster check

[blackandbluefj]

ok did the search thing and cant find my answer. fsm says to check the booster have the truck running and with pedal pressed turn truck off and if pedal stays its good. well my pedal doesnt stay is this the check valve bad or do i just get a new booster


thanks all


Bryon

[Wile E Coyote]

The booster diaphragm could be shot=new booster. However, b4 damning the booster, check where the booster mounts to the firewall and the MC for leaks.(There should be thin gaskets) Check the vac hose for cracks, and if the check valve is like the one in my head, you can check that by blowing/sucking air through it. Apply vac with a MityVac or similar tool. That's all I've got for now.

[rchalmers3]

Yeah, I don't understand the FSM method, sounds like the diagnosis will mis-lead you. Here's a better method:

1) Use a vacuum gauge to test the dead head vacuum being supplied to the booster. Pull the hose off the check valve and test the vacuum available right there at the end of the hose. You may need to rig some stuff to make a small vacuum hose seal the end of the hose going to the booster. Use a tool like Wilie mentioned: A vacuum pump with gauge that will tell you if the booster is receiving adequete vacuum. If the booster is receiving full engine vacuum, great, go to the next step. If not, hunt down any leaks or restrictions affecting the booster receiving full vacuum from the engine.

2) Using your vacuum pump and your accumulated attaching adaptors, connect your pump to the booster and pump it like crazy for 30 seconds. You should see a rise in vacuum. If it rises a little or a lot your booster is sealing and I must ask why you think it's a problem! If you don't see a rise, go to the next step.

3) Finally, you will need to build a "Tee" into the booster vacuum hoses to connect your gauge and watch the vacuum during operation. Proper operation should look like your engine vacuum readings being present at the booster most the time, changing only briefly when you depress the brake pedal and rebuilding vacuum quickly. If the vacuum present is less than engine vacuum readings taken during step one, your booster has a leak and you need to repair or replace the booster assembly.

Boosters can leak from the diaphram or the seals. Diaphram leaks lose vacuum constantly while seal leaks occur more during pedal movement.

SOR and other mud vendors have rebuilt boosters available on core exchange basis.

Hope this helps!

Rick

[ellington12]

here's a link to a good PDF article from toyota regarding booster operation. the second link is a great source for boning up on general mechanical principles etc.

http://www.autoshop101.com/forms/brake05.pdf

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