[ROVERNET - UK] more 3500S brake questions

Bill Daddis magnet at roverclub.org
Mon Apr 4 02:23:18 BST 2005

On 3 Apr 05, at 15:27, peter king wrote:

> 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?

Sounds like a classic case of either the master cylinder (or possibly 
but less likely) the servo not returning to its rest position after the 
pressure is released.  Unless the piston in the m/cyl returns 
completely, the pressure in the system is not released.

With foot off the brake, there should be a little free play in the pedal 
linkage -- little is the operative word here.

Having said that, I have had brakes bind on because of swollen 
hoses.  On a brake application, the pressure from the servo is 
sufficient to force fluid into the wheel cylinders, past the restriction in 
the hoses, but on releasing the brake,the pressure from the wheel 
cylinders (due to the run-out of the discs pushing the pistons back a 
bit) isn't enough to overcome the restriction.  But this would 
probably show up whether or not the engine (i.e. servo) is running. 

P6 rear brakes don't have a lot of piston movement, and if the self 
adjuster isn't fully functional, the piston will hit its stop before any 
mechanical force is applied to the brake pad by the rocking lever.  
See if moving the hand brake lever on the unservicable rear caliper 
will result in any braking action.  If it does, the problem is likely to be 
hydraulic.  If not, it's mechanical.


 -- Bill D.

Aurora, Ontario, Canada
The Toronto Area Rover Club

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