Unusual brake problem

[casper171072]

Had the 1.5 out for a run today now the snow has gone. And I came to brake and the pedal went almost to the floor with no brakes. Pressed it again and perfect all braking resumed. Did it again some miles later each time a gentle second dab and all braking and pedal pressure is perfect. The pedal pressure is generally very strong and does not move under pressure. I’m not aware of any leaks in the system. In all my years of classic car ownership I have never experienced this before.

[2robert4]

I have suffered this problem myself and found after much head scratching it to be worn Master Cylinder rubbers. I honed the Master Cylinder bore slightly using a home made tool and rebuilt with new rubbers and the problem has not appeared after two years. Hope this is of some help?
NP

[casper171072]

Many thanks for that I will give it a good look

[johnmann]

Mine has been like that for a while. I have been working round and renewing all the wheel cylinders and am hopeful that the latest change (front offside) has cured it.

[canuck]

My experience, and not only on the Riley is that over time the seal in the Master cylinder deteriorates. This is just enough that the fine rubber  edge of the seal reverses on itself and temporarily jams.  This coupled with a 'blemished' cylinder bore over time this will fail permanently. A tap of the pedal usually gets things moving again but remedial work is required.

Not knowing the age or maintenance your brakes have received over the years, I suggest you have a gander at the flexible hoses at each front brake back plate and the rear axle. These have been known to collapse from the inside, (rubber deterioration) and will cause a similar or worse symptom of the brake locking on.

Brakes are verrrry important.

Have fun, let us know what you find

Bruce

[casper171072]

I will have a look soon and let everyone know thanks. Just going out put another post on as everything I seem to touch seems to be going wrong at the moment 😊

[tjt77]

Air in system.. common when the cars sit awhile.. usually enters via the brake master cylinder at push rod end.. it may be wise to replace the seals in your master cylinder of they are above 7 yrs old/50k miles .. its always wise to change the brake fluid every couple of years especially if you live in an inclement climate.. brake fluid is hydroscopic.. ( absorbs moisture) and this will eventually cause problems .. as a standard test, bleed a bit off from one of the rear wheels via a clear 3/16" tube into a glass jar.. and check it for colour and contaminants.. if its anything other then clean and the colour of american beer ..( almost clear to pale amber) change the fluid . and bleed the whole system..

[casper171072]

I got it sorted now. I was forced to getting it done when one of the front brakes started binding. I stripped the master cylinder. First I found the brake fluid was defiantly off in some way it easy almost luminous green and very cloudy. The the piston was stuck in the cylinder, had to take it to my garage for them to blow it out with the air gun. When I stripped the cylinder the main rubber seal looked perfect until compaired with its replacement. It had ballooned in size but was perfect in shape and form which was clearly causing the piston to stick in the cylinder. New rubbers and fluid and hey new brakes 👍

[canuck]

Good sleuthing and wrenching!

Nice to be able to stop when needed.

B