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74 620 Brake Booster Repair: Sticking Pedal on Release & Loud Clicking

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First, a little vent:  So many internet posts showing how to "repair" a booster.  They all go like:  take the booster off and install the new one - a typical Stack/eHowToo/FixIt "Smart Phone" response.  Duh!   I guess "replace" is not glorious enough a term.


OK I'm done... here we go:




It took a while to figure out just what was causing this problem.  Symptoms:

  • Power brakes worked
  • Loud Click when releasing pedal pressure accompanied with pedal "sticking" before the click and "releasing" after the click.
  • Sometimes after heavy brake application, pedal would stay down and continue braking until jabbing the pedal cause the click and subsequent release.


Removed booster and it seemed to work just fine by hand w/engine vacuum.


Installed and still clicking.


Under dash, tried to see just where the clicking was occurring and found it:  the Valve Operating Rod (rod to pedal) was sticking/binding in the Diaphragm Plate Assembly (large protruding cylinder VOR goes into:  As the pedal was released, the DPA would move out of the booster and when the click occurred, the VOR popped maybe 3/16" out of the DPA.  (the "free play" of the VOR in the DPA is small at maybe 1/16")  This "popping out" is not supposed to happen - something was sticking or binding.


So I took removed the DPA rubber boot, felt seal retainer, and felt seal exposing the valve assembly and slopped it down with Teflon dry lube (didn't know what lube I should have used - it was Garage Door Lube.)  Also slopped some by the Push Rod on the master cylinder end.  (Of course now I see that the FSM outlines how to repair the booster!  And it looks like the Parts Manual shows no internal parts for the booster - am I missing something here?)


Problem solved and booster works properly.

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