Opinions welcome - brake issue

On a recent longer trip, just once or twice the brake pedal sank nearly to the floor, and on releasing and reapplying - pedal was back.

My opinion is an internal leak in the master cylinder, but it's not reappeared since, nor when applying pressure can i get the pedal to sink to the floor.

If it's useful info, LHD fitted with servo.

It didnt feel to me like brake fade, but I'm open to any views or experience anyone else may have.

 

Things going wrong in the servo ?

 

Had exactly that a few weeks ago! On a long trip.

I immediately thought brake fade but my experience in the past with that (on a track) was not pedal to the floor - just not stopping!

I'm swapping out the master cylinder as it is still the orginal, and on stripping the old one down it was pretty grim in there!

If you're interested, I have a new LHD servo master cylinder I bought in error a couple of years ago!

 

I'm sure you've checked the fluid level...

 

And this isn't a sophisticated sales pitch! Just coincidence!

 

Mine did something similar, but was more consistent.
Despite seemingly spending ages adjusting the rear brakes, a recent re-adjustment ( more in hope than expectation) …. my brakes no longer have the double press panic, if traffic suddenly slows on a motorway journey.

 

Drop the master cylinder back a bit and feed a long cable tie down into the servo and see if there is any brake fluid on it when drawn back out .

 

Oh yes - there's no visible leaks either

 

Explain further please - do you mean detach the MC and servo?

 

Yes if the master cylinder is leaking it will leak out into the brake servo.

 

Undo the two 8mm nuts (13mm spanner size) that hold the master cylinder to the servo and pull away from the servo until you can get a cable tie into the bottom of the servo to check for brake fluid deposits .

 

Right-o skip, gotcha.

Again, there doesnt seem to be any drop in fluid level, unless these one or 2 occurances have put 1/2 a thimble in.

thanks all for advice - I'll try and find time at the weekend for a look-see

 

I’d check rear adjustments first.

 

Thanks - would badly adjusted shoes not manifest all the time though? Perhaps not under light braking, but surely the same result with the same pedal pressure?

 

Who knows but worth checking and adjusting first

 

^^What he says.
Adjust all the rear shoes just to within a gnats of catching.

 

Yes it would and the pedal wouldn't go almost to the floor unless they were really badly adjusted.

 

I’d take the drums off, and clean everything first.
Then adjust them. Could be low fluid level? Air bubble moving about?

 

Thanks, I think I'll check MC first, the drums (when I last did shoes) are pretty well adjusted, and I always chuck loads of fluid through when I bleed so I'm confident there's no air in there. I'd expect spongyness with any air in the system, and as this seems so sporadic I'm ruling it out for now...but I'm always prepared to be wrong.

 

There could be water in the servo. The breather under the front seat could be suspect and could have let water in causing similar symptoms.