[Externet]

Hi.
An idling engine with healthy normal vacuum... Will the brakes booster pull the pedal in all the way by the sole action of the vacuum if there is no master cylinder attached ?
(Trying to find out if my booster has a too weak or too strong spring inside)
Miguel

[yesgo]

No.
That situation is usually caused by an overadjusted or improper pedal rod, wrong angle, or defective air valve (seal).

http://www.procarcare.com/includes/c...6/26Fig11.html
There may be an additional air valve spring to hold the air valv/pushrod assembly closed, not pictured.

Edit -oops, air valve spring is #26.

[Henry Highrise]

(Trying to find out if my booster has a too weak or too strong spring inside)
Miguel[/QUOTE]
Why?

[Externet]

Hi.
Because I just replaced the booster + mastercylinder + calipers with "new" (remanufactured) and pedal is now hard, and I want to discern which one is bad; if a binding master or a wrongly rebuilt booster.
With the mastercylinder unbolted and apart from the booster, the pedal is not "supersoft" with engine idling, but goes smooth all the way in and returns slowly.
With the master cylinder attached, there is some hurdle resistance after the first ½" of pedal travel; another ½" past that hurdle point, the rest of the travel is only hard. Brakes apply well and does not pull to any side, system is well bled.
The last possibility is something wrong with the calipers. Or two problems -binding and hard-
Miguel

[yesgo]

Do the usual booster checks first... with master attached. Key off, pump pedal to release any vacuum. With foot on pedal, start engine and pedal should sink. Cut engine and pedal should remain w/o pushing back until you let off.

Or you could also try checking the booster with a vacuum pump to see if it holds vacuum, and also inspect the 1-way check valve.

It should never apply the brakes by itself... I thought that was what you meant.

If it passes all those tests, the booster should be okay... should.