New failure mode for the brake accumulator

[Chris Wright]

Well, I guess I've found a new failure mode for the brake accumulator, or at least one I hadn't read about before.

Three or four months ago the brake warning light started to intermittently come on. Now the pressure switch had been replaced and was good, so I checked the accumulator by pumping the brakes to discharge it back into the reservoir and the level came up normally and then fell back, not quite to the bottom of the screen, as the bomb recharged when the engine was restarted. Now i thought I had remembered the level dropping below the bottom of the screen but I figured I was remembering wrong. That should have been my first clue.

It's not the switch, or the bomb, so at this point I'm afraid it might be a sticky regulator ($$$$ ), so i flushed the hydraulic system and used a little ATM varnish remover but no luck.

So months pass and it becomes less and less intermittent. At this point it nearly has the classic symptoms of a bad bomb so I check it again. This time the level is only down about an 1-1/2 from the top to start with and it only rises about an inch when the brakes are pumped.

Very strange, it's as if the bomb has only lost part of its charge and it's taken 3 or 4 months to leak out. So now it is pretty obvious that the bomb is bad so I get a new one from steve and sure enough, that fixes it (as I sigh in relief, better $72 then $375!). :)

[MVX11V]

Holy thread resurrection! I have had this flickering brake light for a while, once I thought whatever it was causing it had stopped as it was off for a few days... but then it came back. It's never on when the engine is cold and then it would appear that it gets worse as the journey continues to the point where it would seem that it is coming on and going off over bumps in the road however, trying to make it come on or go off by deliberately going over bumps does't work!
There is the other issue too... my brakes start to seize up in stop start traffic like they are being over pressurised and the brake pedal goes like rock. Breaking free from the traffic and getting a good run appears to cool things down and the brakes return to normal. Unfortunately I got caught in a few hours worth of traffic and toasted the front discs as I was unable to pick any speed up because the brakes were binding too hard, causing them to warp.
I've done the pumpy pumpy test on the fluid levels and that checks out, I've also changed the fluid with no result but I still have the power pump making this labouring noise when on full lock and it whines sometimes after a long run.

This car had a hard, neglectful life and I'm on the downhill side of exchanging every part and of course these parts I haven't visited yet! Are the intermittent brake light and locking up and pump whining issues all contributing to the same problem?

It's next on my list of repairs. I read somewhere a while back that the seals in the master cylinder go hard and when they get hot i.e. stuck in traffic with near on constant brake use, they can seize the system by not operating correctly... is that viable?

[ron]

Master cylinder seizing is a common problem when it gets hot. What side is your brake M/C on?

[MVX11V]

It's all on UK passenger side.

[ron]

Your car was made before 9/86 as, from then on, the M/C was moved to the R/H side which, in theory, improved the brakes efficiency as they didn't have all that lost motion from the linking torque shaft.

Unusual for the M/C to get hot on the L/H side as the exhaust heat is on the right.

Your problem could be a number of things. Flex hoses can deteriorate and not allow pressure release is just one. M/C seals, caliper seals etc.etc.

[MVX11V]

Useful information there. As with other issues it has had, I am expecting a total rebuild of the system due to it apparently having exceeded it's useful life rather than just replacing parts at random in the hope that it will sort itself out... and if I change out a good part then hey, I have a spare!