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Brake probelm query


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'84 90 truck cab with

rangie disk rear axle.

new pads

new braided flexible pipes

new mastercylinder

new vacuum servo

new pad pins

Its not a loose wheel bearing.


brakes work extremely well for intial depressions of the pedal, assistance appears lost with repeated braking.

on repeated pressing of the brake pedal either moving or stationary the pedal goes hard on about the 4th pump of the pedal and its akin to loosing the power assistance.

Checked and changed:

Brake vaccum pump produces a good suction on the end of the hose to vacumm servo (enough to make finger go red - is this enough?)

Not brake fade as it happens when stationary.

Various parts changed as above over time as above.

any thoughts?

does the m/c plunger length need changing or brake vacuum pump not creating a big enough vacuum - and how would you check it?

thanks in advance for your thoughts.

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Jase - it had that plastic white male connector in the top of the new vacumm servo which the pipe went onto, i used the exisitng old pipe.

For what it's worth.

I'd be tempted to re-bleed the system just in case you still have air in it, from your description the rest seems OK.

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Either :

Air in system, over bleeding can excite and cause air to jam in even when you have flushed and flushed


Servo, disconnect pipe and see if any different


Master cylinder fluid creeping past seal

Try clamping off the rear brakes on the flexy and drive and see if any different, then do the same with fronts, do be F carefull, but it can identify front / back / neither prob area


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Try clamping off the rear brakes on the flexy and drive and see if any different, then do the same with fronts, do be F carefull, but it can identify front / back / neither prob area


Check with the supplier of these braided hoses to make sure this is safe.

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I'd check the plastic valve that goes into the servo from the vacuum pipe. Air should only be able to pass one way through this. I had similar symptoms to yours James. I cheked the valve and was quite freely passing both ways. Once it was replaced, the problem was solved.

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checked the plastic valve going into the servo, can't blow into it and can only suck for 1/2 a suck(!) if that exists! so i guess its working correctly.

chekced the pressure of the vacuum on the end of the hose again not sure its strong enough but have nothing to compare it to!

Putting my finger over the end it holds the pipe on and there is no hissing etc so connections to pump and pipe are OK.

i am concluding that the vaccum pump is not sucking enough.

anyone got a MPN for one?

It is the only bit of the system that hasn't been changed!

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i was quoted £4 each for those, so which should it be £4 for each rotor or £4 for all 4?

Sorry James, got me fingers muddled :(

the bits for my vacuum pump came to £24.36 including vat

4 x blades @ £4.20 each = £16.80

1 x 'O' ring @ £2.94

2 x gasket @ £1.00

from my local independent LR parts supplier. :i-m_so_happy:

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OK just done an hour or so on the beast,

servo valve only works one way, so thats OK(you can suck but not blow into it)

valve on top of vacuum pump removed, cleaned refitted, that works one way eg you can blow into it but cant suck out of it.

rotors and O ring and gasket repalaced. to be honest the old ones looked ok. made sure the rotors slid easily as well.

check pipe, condition is good and no blockages etc.

So more questions - am i right in presuming there should be oil in there to aid movement of the rotors?

If the engine is running and you pump the brake pedal - what should it do, work upto hard after small movement. then slowly drop again to noraml braking position?

On the shaft that drops in to the block and has the drive pinion up the middle of it (the bit undr the vacuum pump) which way round does it go back in? there is a slot on the one of the three sides near the top which i presume is to allow oil movement, this lines up with the one in thetop part i guess?Anyone taken one apart and know? And no id didn't check it when i took it out it look symetrical and i didnt see the slot. i thnk it goes to the rear. and yes it will go back on in three other locations!

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To test the servo

Engine off, press the pedal a few times to kill any residual vacuum

Hold the pedal down and start the engine.

You should feel the pedal give slightly as the vacuum builds and increases the fluid pressure, which causes the pipes to expand a bit, the linings squash up slightly and so on.

This effect will not be very pronounced if you have braided hoses as they don't give as much as rubber ones.

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yep thats what it does, goes hard after pumping up then sinks a bit when the engine is started.

It also does it when the engine is running! which i put down to the fact that the pump isin't sucking enough. Should it?

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I had this yonks ago on an old Cortina. In the end (as Tim alluded to in his post) it turned out to be the hose. You could blow through it OK and it seemed fine, but after a couple of pedal depressions the inner wall was caving in. Leave it a while and it would expand again.

In view of all the other things you have changed it may be worth trying a new bit of hose.


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