Brake failure temporarily !!!

AndersDK · Post by **AndersDK** » 09 Jun 2006, 14:55

steviewonder7 wrote:Thanks to your reply Anders.If I read you correctly,if my abs is causing this braking problem,it would be safe to immobilise the abs from the braking circuit and use the brakes like a conventional car if need be?

Thanks steve

Yes - no problem.

steviewonder7 · Post by **steviewonder7** » 09 Jun 2006, 17:28

O.k Anders that gives me piece of mind.I'm driving the car now with a degree of caution,not a positive way to drive with potential brake failure possible i know.I almost dont want to drive the car,but its my only transport at the mo and I will try driving without the abs fuse in place tommorrow.

thanks for your comments folks always a pleasure to read and learn from lots from the forum postings.Its a great forum.
Cheers Steve

Dave Burns · Post by **Dave Burns** » 10 Jun 2006, 10:52

A sensor somehow producing more signals than normal for any given wheel speed, is not very likely to do so in the way a truly faster rotating wheel would, extra or spurious signals would be just that, eratic, and just as the software contains data of how rapidly a wheel can be slowed normaly without locking, it should also know that a spurious signal can't mean that the car has suddenly doubled its speed, and act as though the other wheels have all instantly become slower at rotating and release their brakes, any such eratic signals must be ignored or at best cause a fault state and the abs be shut down.

I'm not saying that erronious signals from sensors can't somehow confuse the abs computer, only that I think it couldn't happen in this way, if it could it would be a horrificaly designed piece of engineering.

If this car doesn't have anti sink then it has a flow diverter valve, all the oil from the pump is shared between the suspension, steering and brakes, the job of the FDV is to split the output from the pump between the steering and the main accumulator for the brakes and suspension, but allways to favour the accumulator for the obvious reason, the FDV can develop problems of its own due to dirt entring the valves, could be a situation where a fault in one system causes a problem in an adjacent system.

Dave

jeremy · Post by **jeremy** » 11 Jun 2006, 00:08

I agree Dave that without anti-sink this car must have a flow divider valve, which will provide a feed for the power steering and for the suspension/brakes.

I have had a flow divider problem which actually turned out to be incorrect assembly with the ball bearing relief valve being incorrectly assembled. the steering functioned properly but the pressure for the rest of the system was unreliable and the warning light would come on especially in the first few miles.

Stevie - does the warning light and the stop light come on when the car is being driven?

Is the accumulator sound - this can be tested by running the car for a couple of minutes at normal height, turn off the engine and sit in the boot. The back of the car should sink then rise again after 30 seconds or so.

If the car doesn't rise the accumulator sphere probably needs replacing - and what I think may be happening is that the brake lines are full of gas from the burst sphere. When the brakes are applied the gas in the lines must be compressed - and the only available supply is the direct pump output - which is not very great and causes the delay - then the pump pulses are felt as a reaction on the doseur valve - hence the pedal pulses.

Simon - I still think certainly the early ABS systems are switched by the pedal switch - certainly on a BX there is a connection to the ECU - which would not be needed if the valve block was able to sense anything. Most of these devices are rather crude when you get to the detail.

Gregg1100 · Post by **Gregg1100** » 11 Jun 2006, 13:52

Hi,
Car has antisink and hydractive2. Like I said, once pedal pushed for first time after reversing--key word--reversing, brakes don`t work until second dab on pedal. Doesn't do it driving forward at all. Anyone any ideas./
Thanks,
Greg

jeremy · Post by **jeremy** » 11 Jun 2006, 19:41

Gregg - is the rear anti-sink sphere the original? - if so its probably the source of the problem. In fact the anti-sink sphere doesn't prevent sink but provides a supply of pressurised LHM when the valve opens. This in turn is needed as the twin outlet pump has little output for the brakes and suspension, and when the valve opens there can be a collapse of pressure in the system or parts thereof.

You should test your accumulator by the sit in the boot test as well.

steviewonder7 · Post by **steviewonder7** » 12 Jun 2006, 17:22

Thats interesting about the flow diverter valve Dave,I shall look into that.The
only thing is off-hand do you know where this valve might be situated on my model of car as at the moment i dont know where it is ?

Jeremy, the stop light does not come on when I'm driving ,only when I turn the ignition on does it light up.
I shall test the accumulator tommorrow.Saying that, the accumulator is only 9 months old and would be a little suprised if its succumed already.

thanks again for your thoughts on the subject
Steve

jeremy · Post by **jeremy** » 12 Jun 2006, 18:36

Flow diverter is the FIRST component in the circuit after the pump.