Bench test a C4 brake booster?
Thread Starter
Burning Brakes
Joined: Mar 2002
Posts: 1,065
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From: Kensington PE
Bench test a C4 brake booster?
We took a chance on a used brake booster that was working well on a car that was freshly scrapped. Unfortunately once installed it was leaking back into the passenger compartment.
Can this, or any future used boosters be easily bench tested?
BTW this was a 94 plastic model booster.
Can this, or any future used boosters be easily bench tested?
BTW this was a 94 plastic model booster.
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From: So. Cal.
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booster
I would give a good visual inspection on plastic body for cracks.
Corvette Mike
Corvette Mike
Drifting
Joined: Sep 2003
Posts: 1,363
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From: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
In therory, if you were to install the check valve into the brake booster (or if it's already installed), hooking up a mity-vac (or equivalent) to it via a hose, and pull a 15-20 hg of vacume, should at least tell if the plastic housing is sound.
Read the FSM before trying this for warnings (seem to remember something), but you might then be able to depress the shaft (which connects to the brake pedal) to verify no real loss of vacume (the depression should open up the back side of the diaphram to outside air, while closing off the vacume to the back side of the diaphram at the same time, sucking in the shaft, and not allowing any vacume to escape to back side of the brake booster.
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Read the FSM before trying this for warnings (seem to remember something), but you might then be able to depress the shaft (which connects to the brake pedal) to verify no real loss of vacume (the depression should open up the back side of the diaphram to outside air, while closing off the vacume to the back side of the diaphram at the same time, sucking in the shaft, and not allowing any vacume to escape to back side of the brake booster.
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Drifting
Joined: Sep 2003
Posts: 1,363
Likes: 7
From: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
Could be the booster shell (which when heated-up, seals a leak), but should hear a leak when cold and presume you've listened and not heard it (start, run for only a minute or so, turn off and listen).
Have you checked the vacume level at cold idle? Should be at least 15-20 hg.
If not, could be a broken vacume line, bad vacume 'check valve' (for AC controls), old PCV valve, intake manifold leak, throttle-body leak or butter-fly carbonned-up, or brake-booster's vacume hose routed to the wrong connector.
Last edited by theadmiral94; Aug 3, 2009 at 11:02 AM.
Team Owner
Joined: Feb 2006
Posts: 24,460
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From: sw Ohio
Could be the brake booster's check-valve, However, more likely it's something else. All the check-valve does is hold in higher vacume when lower vacume is present. Easy test is after car has been run, pull of the hose (don't remove the check valve), and depress brake pedal a few times, if pedal seems normal 1-2 depresses, check valve likely is ok (can also listen for any leakage or use a small piece of paper over hose barb to see if it holds the paper there, implying some leakage).
Could be the booster shell (which when heated-up, seals a leak), but should hear a leak when cold and presume you've listened and not heard it (start, run for only a minute or so, turn off and listen).
Have you checked the vacume level at cold idle? Should be at least 15-20 hg.
If not, could be a broken vacume line, bad vacume 'check valve' (for AC controls), old PCV valve, intake manifold leak, throttle-body leak or butter-fly carbonned-up, or brake-booster's vacume hose routed to the wrong connector.
Could be the booster shell (which when heated-up, seals a leak), but should hear a leak when cold and presume you've listened and not heard it (start, run for only a minute or so, turn off and listen).
Have you checked the vacume level at cold idle? Should be at least 15-20 hg.
If not, could be a broken vacume line, bad vacume 'check valve' (for AC controls), old PCV valve, intake manifold leak, throttle-body leak or butter-fly carbonned-up, or brake-booster's vacume hose routed to the wrong connector.
