Spongy brakes

[dbt01]

Originally Posted by spyder

The level needs to be halfway up the neck. Any dot 4 fluid can be used/mixed. Why was it so low? a T4 will do it quicker and better to a degree, but not a must in my experience .

Agree Spyder. In my experience an occasional problem of an ABs or brake-warning light still displaying after a repair can be fixed via a T4, although often a battery disconnect-reset is enough. Doesn't happen often anyway.

Can't see how it can help a soft or spongy pedal. A pressure bleed does not need a T4 as such as far as I am aware?.

David

[ianbstag]

It may be a bit of an urban myth, but my old school mechanic swears that brakes should be bled with the ignition on, to power the abs unit.

I've never heard it before, but it sort of makes sense if you think about it. (probably a load of rubbish, who knows?)

[clf]

This has been discussed at length many times before, but I havent read a definitive answer to it.

THESE are just some of the relevant threads. It is a lot of reading, perhaps someone can recall a thread with a definitive answer

an interesting THREAD HERE and ANOTHER

I can see how the ABS unit could become involved in a sinking/spongy pedal, but cannot understand how just having the ignition on will eliminate it from the symptoms. To elinimate it, I would have thought the ABS would need to be activated (ie that pumping feeling you get when brakes are pressed in an emergency stop situation)

[ianbstag]

He may well be mistaken, but he witters on about the abs unit needing to be on because once powered up, certain valves inside are opened, something to do with initialisation.. (to be honest, I stopped listening to him, it all got very technical)

Always leaves the car with a firm pedal though, so I can't complain :-)

[clf]

Originally Posted by ianbstag

He may well be mistaken, but he witters on about the abs unit needing to be on because once powered up, certain valves inside are opened, something to do with initialisation.. (to be honest, I stopped listening to him, it all got very technical)

Always leaves the car with a firm pedal though, so I can't complain :-)

I cannot say if he is mistaken or not, I do think he is onto something especially if you read what Russ says in the thread HERE, and it kinda makes sense. But I am not sure how the ABS pump works, but cannot imagine it opening and closing with the just the ignition on. Although I imagine as I said, the pump needs to be activated, ie pumping, to make a difference.

[oldie]

Filled reservoir to just below "Max" mark. Press the pedal a few times, all seems firm. Engine on, pump pedal to the floor four times. Engine off. Fluid level now just below the "Min" mark. That seems quite a lot of fluid to disappear.

[3disco]

You must have a leak,perhaps if not visible outside the car going into the servo!

[spyder]

Following this thread as my fluid level went lower than expected without warning on my diesel, seems OK now.

I had a similar problem with my SDI 2.6. On a long rather fast trip on a national road I suddenly had a burst of power, a big explosive noise and lots of smoke. I pulled over found nothing wrong and finished the trip without further incident. Still lost brake fluid though.

Turned out, as below, the fluid was leaking into the brake servo and sucked up via the vacuum pipe into the inlet manifold.

Could not get another servo, so sold the car.

[oldie]

I suspect the master cylinder. A sudden loss of braking performance, loss of fluid, car's been largely idle for four years (brittle seals?). My hands are biggish, if I can get one under the reservoir will I be better informed about the condition of the cylinder? Are the cylinders the same as those for the v6?

[dbt01]

Originally Posted by oldie

I suspect the master cylinder. A sudden loss of braking performance, loss of fluid, car's been largely idle for four years (brittle seals?). My hands are biggish, if I can get one under the reservoir will I be better informed about the condition of the cylinder? Are the cylinders the same as those for the v6?

If you have checked for leaks at all four corners, and rubber hoses to same, and the the ABS unit and front-aft piping run then it cannot be anything other than the servo/master cylinder. If fluid is being lost and not visible anywhere then it must be being leaking in/into the servo and either still sitting in there (lots of room) or being eaten by the vacuum feed back to the V8 surely?? Older BMC/BL stuff did it regularly, my MGC and a Cooper-S did it, but never heard of it in recent times though?

IF I'm right then its not good news maybe, David :-( .

Get onto Brian (scooter) at Dreadnought and see what he may have in stock? Pick his brains whilst your on! Maybe even the two-sixties shop via Tim? (Don't know to what extent the units are ZT or even 75 compatible, other than claims here that the master cylinder is the same as regular ZT or 75 2.5 Tourer).

David