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Discussion Starter · #1 ·
Is there a way of bench testing a power servo?
I've been offered to buy a unit from a forum member but unfortunately it's not on the car and the car didn't run so its unknown if the unit is fully operational.
Is there a characteristic that would be easily tested to see if it's holding vacuum or not? I mean what happens when you push the plunger in with the master cylinder removed, should it return under its own vacuum or something like that?
 

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yeah, should be easy to test if you can get the bench up to about 30mph!
Sorry cant ACTUALLY answer your question, but are you getting a good deal on the booster? is it not better to send yours off for rebuild - if you have one?
Depending on the type of booster a rebuild should cost $140-$170
 

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Discussion Starter · #3 ·
yeah, should be easy to test if you can get the bench up to about 30mph!
Sorry cant ACTUALLY answer your question, but are you getting a good deal on the booster? is it not better to send yours off for rebuild - if you have one?
Depending on the type of booster a rebuild should cost $140-$170

I'm in the uk so postage both ways would kill it. The booster for sale is about the same money as repair, which I'm fine with so long as it works!
 

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My friend from NAPA said brake booster is a big diaphragm, it needs to hold a vacuum .hook it up where it pulls vacuum off the car it should not leak down . I'll check it tomorrow.
I could also pull the one off "SnoWhite" put the other one on and TEST it on the lower 4.That's a lot of work.
I'll try my mechanic buddy , also have a friend at Auto Zone. Then I have a friend who has a friend that knows this guy who has a friend that has a cousin that has an uncle twice removed that has a friend..
I'll get it CHECKED OUT ..
 

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My friend from NAPA said brake booster is a big diaphragm, it needs to hold a vacuum .hook it up where it pulls vacuum off the car it should not leak down.
That's it. Easy is to plug the vac line from another running engine into it to pull initial vacuum. Rev the engine a few times (raise to mid-RPM and let the throttle snap shut) to pull max vac. Then hook a hand pump/gauge to it to monitor for leak-down.
:tup:
David
 

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Vac it down with the engine, pull the vac line from the check valve, hook your hand pump to the check valve. Give it a few squeezes and the gauge will top-out at whatever the booster is. Wait a couple minutes, vent the gauge, and do it again for a second reading.

David
 

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My friend from NAPA said brake booster is a big diaphragm, it needs to hold a vacuum .hook it up where it pulls vacuum off the car it should not leak down . I'll check it tomorrow.
I could also pull the one off "SnoWhite" put the other one on and TEST it on the lower 4.That's a lot of work.
I'll try my mechanic buddy , also have a friend at Auto Zone. Then I have a friend who has a friend that knows this guy who has a friend that has a cousin that has an uncle twice removed that has a friend..
I'll get it CHECKED OUT ..
no way, I know that same guy.. imagine that!
 

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OK.
I started the engine let it warm up while I was finding the vacuum gauge.
Pulled the line off "'SnoWhite"s booster checked the vacuum (normal @ idle). Pulled the small line going to the tranny put the tip to it. The needle started moving slowly toward( normal @ idle) .
Went into the shop got the Mercury booster laid it up fender well did the same test and got the same results.
I'm assuming it's good due to fact that "SnoWhite" will stop on and give you change..
 

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If the booster held vacuum for at least 10 minutes, then it should be healthy without obvious sign of impending failure. If the booster has a small leak (except the check valve - that's replaceable) faster than 2" Hg per minute, the booster will still work, but that indicates developing cracks or holes in the pliable parts (diaphragm and seals) or rust pinholes. That's why monitoring the pressure rise over several minutes after removing the vacuum source is part of the testing. HTH

David
 
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