9 replies to this topic

[Old Bob]

Do these valves fail and if so, can you please describe the symptoms?  I am trying to eliminate all possible problem areas on a new brake system and that is the only one which still concerns me.  Logic says (to me) that a failure would just result in unbalanced braking, but could it generate other problems?

 

Thanks all.

 

Bob

[Ethel]

FAM7821,  it isn't a pdwa strictly speaking: that stands for "pressure differential warning activator" and was connected to the brake test switch before the fluid level float hobbies.

 

The most likely failure would be to just seize, causing the rear to lock under hea. braking.   Note that if you swap to the yellow band master cylinder from an earlier, common bore, type you need to swap the connections over - the, larger, bottom bore is for the rear brakes.

[Old Bob]

Thanks Ethel.  I am unsure how the valve works, but I seem to have a problem which makes little sense to me.  Set-up is with new yellow band master cylinder, all new pipes etc.  Brakes have been bled several times (by myself with an Easibleed, by foot pumping and also by a well respected professional).  In every case, pedal pressure is fine for a few hours, then goes soft.  There is no obvious fluid loss and no bubbles when re-bled.  The only thing in the system which hasn't been replaced is the valve, because I couldn't see how that might cause such a problem.  Now I am starting to wonder - hence the question.

 

Regards,

 

Bob

[samsfern]

Could be the master cylinder starting to fail?

[cal844]

try doing a servo vacuum test?!

 

pump the pedal, hold the pressure on whildt starting the engine?!

[Old Bob]

Thanks Guys.  New master cylinder just replaced with another new unit so hopefully that eliminated any potential issue there.  And no servo so it isn't that either.

 

Really, for such a simple set-up this is causing me an awful lot of grief!

 

Bob

[Dan]

  It doesn't sound like the normal fault from the FAM valve, as Ethel says when that fails you normally get the rear locking up and so you tend to swap ends.  Are you using normal mineral fluid?

[Old Bob]

  It doesn't sound like the normal fault from the FAM valve, as Ethel says when that fails you normally get the rear locking up and so you tend to swap ends.  Are you using normal mineral fluid?

 

Yes Dan, fresh Castrol React.

 

Bob

[Dan]

Oh, very important, which Castrol React exactly?

 

 

  Actually, forget that.  It's probably not important.  It's just that all the React products apart from SRF are marked as 'not to be used in systems specifying mineral oil' but DOT 4 is DOT4.

Edited by Dan, 26 September 2013 - 08:50 PM.

[Old Bob]

Even more confused now Dan!  Label says 'Castrol React Performance DOT 4'  The small print does say 'not to be used in systems specifying mineral oil' but I assumed (always dangerous I know) that this did not include bog standard systems like yellow band master cylinders.

 

Regret now not having used racing blue..........

 

Bob