Borked Master Cylinder??

[Cheggers]

Hi All,Please can you help with a diagnosis...?The brakes on the Triumph suddenly went a bit "odd" yesterday. They still work well (in fact, they feel more progressive than before), but the pedal is almost in the carpet when braking, whereas they used to be very "high".There are no obvious leaks from calipers, wheel cylinders or flexible pipes. When the problem first happened I needed to topped up the brake fluid which was very low, but since then there's seemingly been no further loss of fluid (after approx 10 miles of stop/ start driving).The brakes won't bleed, permanently seeming to have air bubbles in the fluid to all 4 wheels.The main thing that's leading me to the Master Cylinder is that there are bubbles coming up into the fluid reservoir when you pump the brakes.Any ideas??Thanks chaps!!

[Rusty Pelican]

Does sound like the master cylinder , theres a one way valve type effort in them , ( more like a rubber seal ) this stops fluid being pumped into the reservoir when you brake , hence your bubbles , just a guess mind

[M'coli]

HAve you tried pumping the pedal? If the pedal rises on the second pump, sort the master cylinder.

[Richard]

HAve you tried pumping the pedal? If the pedal rises on the second pump, sort the master cylinder.

Surely badly adjusted brakes would have the same effect?Replacing the master cylinder seals is cheap, relatively easy and worthwhile so it wouldn't hurt to do that- especially if they are single circuit brakes. You should inspect the whole system too, paying particular attention to the adjusting mechanisms. Check the front wheel bearings too. Play in the front wheel bearing pushes the pads back in and therefore requires more travel to apply the brakes.Master cylinders tend not to appreciate a significant increase in travel, it forces the seals into an unused section of bore, which can be rough.

[Cheggers]

HAve you tried pumping the pedal? If the pedal rises on the second pump, sort the master cylinder.

It does, so I will...many thanks guys.

[CIH]

You can test the mastercylinder by clamping all 4 flexi hoses. If the pedal is anything other than rock solid it's probably the m/cylinder.

[25v6turbo]

2000,S suffer from the brake master cylinder leaking interenally into the servo,and filling that up!!So you don,t notice where the fluid is going,i would also remove the sevo if changing the master,just to see??Its happened several times on a few 2000s i,ve owned(over 30!)

[Cheggers]

2000,S suffer from the brake master cylinder leaking interenally into the servo,and filling that up!!So you don,t notice where the fluid is going,i would also remove the sevo if changing the master,just to see??Its happened several times on a few 2000s i,ve owned(over 30!)

You may well be onto something. The fluid must have gone somewhere!!Do you know if a MC repair kit would sort it, or is it a whole new Master Cylinder job??

[25v6turbo]

You could try a repair kit,but i would try and source a MC to be honest.

[Cheggers]

Cool, thanks for the help.