elmscroft Posted March 10, 2015 Share Posted March 10, 2015 Hi All, Our Defender has just failed its MoT on: Brake efficiency 32%, Brake test imbalance 48% (OSR rear slower) brake application uneven Brake has no servo assistance Rear brake imbalance. Tester said it was the servo at fault, New servo fitted. Taken back no difference, no pass. Tester then said must be Vacuum pump, although it is only a couple of years old? Have fitted a vacuum gauge to the pipe from the pump and got the following readings: -30kPa (-8.86"Hg) at tickover -70kPa (-20.67"Hg) when revved I do have another secondhand pump I can fit, but I think readings are good. One way valve ok ( suck and blow) Pedal is firm and does not drop on start up. Not leaks from master cylinder (about four years old) Am a bit reluctant to go back to tester, until pedal sinks in start up, as, he may just keep suggesting next thing and so on. I have looked through the forum for this problem, but had no success. Truck only does 3-4k road miles a year and was fine last year. Any ideas or suggestions welcome. Thanks Mike Quote Link to comment Share on other sites More sharing options...
Rangy35 Posted March 10, 2015 Share Posted March 10, 2015 How old is the brake fluid, you may have seized calliper pistons, bad master due to the water in the fluid. Quote Link to comment Share on other sites More sharing options...
Chicken Drumstick Posted March 10, 2015 Share Posted March 10, 2015 Yeah not sure I'd have been looking at the servo first. What state are the pads/discs in? If they are worn unevenly that will need addressing. Seized calipers are pretty common too. Master cylinder is pretty cheap and easy to replace, so might be worth doing it while messing about with the brakes. Quote Link to comment Share on other sites More sharing options...
elmscroft Posted March 10, 2015 Author Share Posted March 10, 2015 Brake fluid good according to brake fluid tester, compared to brand new fluid. Will double check caliper. Thank you for your reply. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted March 10, 2015 Share Posted March 10, 2015 Inspect the callipers Quote Link to comment Share on other sites More sharing options...
Eightpot Posted March 10, 2015 Share Posted March 10, 2015 I'd also suspect calipers first- most likely rusted up pistons and maybe also the wiper seal is perished/rusted up/popped off so the piston can't move in and out easily. Take the brake pads out of one caliper at a time, pop something between piston & disc (spanner etc) so they dont come out all the way then gently press brake pedal - should be obvious if you have a sticky piston. If they're not too bad give them a good clean while they're popped out, put a smear of fluid round and ease them back in squarely. Quote Link to comment Share on other sites More sharing options...
elmscroft Posted March 10, 2015 Author Share Posted March 10, 2015 Rear calipers checked pistons moving ok Quote Link to comment Share on other sites More sharing options...
dirtyninety Posted March 10, 2015 Share Posted March 10, 2015 If the brake test shows the OSR brake is working inefficiently, clearly there is something wrong here. for the price of a new set of pads of discs Id just replace them to make sure it was all lovely and working! Brakes are important! Quote Link to comment Share on other sites More sharing options...
Souster Posted March 10, 2015 Share Posted March 10, 2015 My pedal doesnt sink on start up either. Have you got servo assistance though? Quote Link to comment Share on other sites More sharing options...
elmscroft Posted March 10, 2015 Author Share Posted March 10, 2015 Well according to the MoT tester 'no' but with a new servo fitted and the readings at the vacuum pump, I would say that end is ok. So now I'm thinking as suggested rear discs and pads may be new caliper on the offending side. Go to the identified area, as I assume all is ok at the front, servo and pump, must be doing something. Quote Link to comment Share on other sites More sharing options...
oneandtwo Posted March 10, 2015 Share Posted March 10, 2015 My money is on the servo, if the pedal doesn't sink then something is wrong. Despite being a new servo, In the past six months I have had two faulty new servos. The first one was a new pattern servo. This was so badly designed the mounting studs didn't go all the way through from the the master cylinder to the pedal box, so as soon as the brake was applied, the servo immediately flexed and lost all vacuum, with a telltale whooshing noise coming from the pedal box as soon as the pedal was touched. The next one was a Lucas TRW brand which had a poorly crimped joint which caused a loss of vacuum. Try spraying washing up liquid over the servo and see if it gets sucked in anywhere. The o ring seal to the master cylinder can sometimes be poorly seated. Quote Link to comment Share on other sites More sharing options...
Souster Posted March 10, 2015 Share Posted March 10, 2015 The seal between the master cylinder and servo isn't missing is it? Does the pedal sink eventually? Ie. Get softer? Quote Link to comment Share on other sites More sharing options...
elmscroft Posted March 10, 2015 Author Share Posted March 10, 2015 No air sound at all. Servo is genuine part, new 'O' ring was fitted. Thanks for your input. Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted March 11, 2015 Share Posted March 11, 2015 With the pedal not sinking on starting then you are looking initially at a lack of servo assistance, that's where I'd start as that's affecting all of the braking. The imbalances are telling you, as my learned chums above have pointed out, that your calipers are in need of an overhaul. Mo 1 Quote Link to comment Share on other sites More sharing options...
elmscroft Posted March 11, 2015 Author Share Posted March 11, 2015 Just to clarify if servo, would it not effect efficiency on the front? When I fitted the new servo, it came with a new O ring which I slid onto the plastic extension of the reservoir that goes into the servo, discarding,what seemed, a more shaped seal fitted to it. Is there any other way of testing the servo to confirm the new one (genuine part) is faulty old one is u/s. Thank you again for everyones input Quote Link to comment Share on other sites More sharing options...
elmscroft Posted March 15, 2015 Author Share Posted March 15, 2015 Well, just an update, All caliper pistons cleaned and lubed, new master cylinder, new brake fluid, cling film test done on servo, all ok. Pedal still doesn't drop on start up. So tomorrow off to MoT man to see what he has to say. Thank you for everyone's input. Fingers crossed. Quote Link to comment Share on other sites More sharing options...
cackshifter Posted March 16, 2015 Share Posted March 16, 2015 My money is on the vacuum pump or something round there, if the NRV is def OK. The last new Wabco pump I fitted pulled .8 bar ie 80kPa at tickover, it's knackered predecessor pulled 30. If the pedal feels like it has absolutely no give, that's a sign of no assistance. Of course you might have other issues as well. Could there be any sort of leak - if yours is a 300tdi it probably had a vaccuum take off for the EGR valve, are you sure that has been plugged when you take your readings? Maybe if you still have the EGR the solenoid control valve is stuck open? Quote Link to comment Share on other sites More sharing options...
elmscroft Posted March 17, 2015 Author Share Posted March 17, 2015 Hi, That's a figure I've been trying to find. ERG removed, but pipe securely plugged. Fitted a secondhand, pump that a friend was confident was ok, but poorer figure than mine. But now no was sort of figure i should be aiming for thanks. Quote Link to comment Share on other sites More sharing options...
elmscroft Posted March 19, 2015 Author Share Posted March 19, 2015 After one failed pump,new one fitted, and figure up around the 80kPa. MoT now in hand. Happy Days Thank you to everyone for their input. 1 Quote Link to comment Share on other sites More sharing options...
Jode Posted March 22, 2015 Share Posted March 22, 2015 Well, just an update, All caliper pistons cleaned and lubed, new master cylinder, new brake fluid, cling film test done on servo, all ok. Pedal still doesn't drop on start up. I hope lubed with brake fluid (or rubber grease) only! Quote Link to comment Share on other sites More sharing options...
Snagger Posted March 22, 2015 Share Posted March 22, 2015 My servo seems to have stopped working, but the car still stops on a sixpence. All the servo does is make the pedal easier to ress - it doesn't affect brake efficiency and certainly not balance. Go to a tester that knows what they are talking about - the clueless idiot you have at the moment knows nothing about brakes and could end up killing you. Quote Link to comment Share on other sites More sharing options...
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