[ROVERNET - UK] Re: rovernet Digest, Vol 29, Issue 1

Phil philhodge at northsound.net
Tue Apr 5 15:19:18 BST 2005


I have had the very same problem with the recent rebuilt of my brake master
on my 3500S. I believe Eric is correct in his diagnosis. The reaction valve
in the 3500S system is on the master though, rather than the booster units.
It, therefore, controls all four brakes ie. if you jack up the wheels, you
will find, unlike Eric's case, all four (three in your case) wheels will be
locked. Another symptom I have is that if I pressed lightly on the brakes,
they will stay on lightly and continue to slow the car for about 10 to 15
seconds then release. Further, if I stepped very hard on the brakes (best
when fully stopped as, when moving, this manouver tends to interest police
and scare other drivers), they released instantly. I cleaned out the
reaction valve cylinder when I rebuilt my master and therefore, rust is not
the problem. I believe it is caused by an overly large ring seal on the
valve plunger. This lends to make the plunger sticky enough not to return
after light pressure on the brakes have moved it a short distance forward.
The vacumn has little pressure when trying to return it to its resting
position after the brake are released. It works just fine with heavy
pressure on the brakes and a longer travel which results in more pressure
to return the valve once the brakes are released. I have not yet found a
smaller replacment for this ring seal so have not tested this theory but
this thread has made me decide to try my wornout,  seal to see if the
problem is remedied. Ruth informed me that it is only a dust excluder anyway.

Good luck with your brakes, hope not to read about it in the papers,

Phil Hodge

>Hi all.
>Many thanks to all who have made suggestions re: my brake problems.
>As it turns out, the right rear brake line was about to burst, with a 
>big fat bulge in it (thanks for that suggestion, Bill D.), so I 
>replaced it with a spare I had.  I get no braking action from the left 
>rear, but can bleed fluid there. That side brake line looks pretty new. 
>So I'm suspecting the caliper is bad on that side. However, I've now 
>discovered that all three working calipers are binding after braking. 
>they bind, then after a while relax. The odd thing is that they only 
>bind when the car is running. If I roll down the driveway with the 
>engine off, they don't bind. I'm wondering if this suggests the problem 
>is in the servo/slave binding up, or if I could have a problem with my 
>recent master cylinder rebuild? Or if this may have something to do 
>with the brake failure switch at the 5-way junction. Ruth Burgess 
>described its function to me the other day, but I don't know if it 
>would serve to prevent fluid from backing off and releasing the 
>calipers for some reason?
>When I first depress the brake pedal, I get full action, as if the 
>servo is working. When I let up and depress the pedal again, I get a 
>hard pedal at the top of the stroke--very little movement.
>Any thoughts?

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