cackshifter Posted February 8, 2010 Share Posted February 8, 2010 I have just bought a 90 to replace my 110 which was damaged in a crash. One thing I have noticed is the brakes don't seem very powerful. They feel OK initially with quite a reasonable 'bite', but then need a really good shove to do much more than check braking, and even with veins standing out on forehead with the pressure aren't impressive. I've checked the front pads and they have about 4mm, so nearly done, and the discs are below the minimum thickness, so yes it's time to sort that, but they shouldn't feel so dead at this stage. Calipers look quite good considering the age - the 110 had better brakes with far worse looking calipers. But I think it might be the power assistance that's lacking, so I was planning to measure the vacuum, courtesy of the EGR valve connection (it still has that). Does anybody have any idea what sort of figures it should show. Is there an easy way to test the servo to eliminate it from my inquiries? I though I might also just disconnect the pump and see if it felt any different (on an empty car park of course). Does the pressure valve ever go faulty ( though I can't see how it might affect the front brakes, and they must do most of the work) Regards Nigel Quote Link to comment Share on other sites More sharing options...
errol209 Posted February 8, 2010 Share Posted February 8, 2010 Does anybody have any idea what sort of figures it should show. Is there an easy way to test the servo to eliminate it from my inquiries? I though I might also just disconnect the pump and see if it felt any different (on an empty car park of course). Does the pressure valve ever go faulty ( though I can't see how it might affect the front brakes, and they must do most of the work) 0.5 to 0.7 bar, depends on the engine. The car park idea will show up if its working or not. If you mean the G valve or similar in the rear circuit - very rarely! Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted February 8, 2010 Share Posted February 8, 2010 General test is to sit with the vehicle not running, put your foot hard down on the pedal and build some pressure, then turn on the engine. You should feel the pedal give a bit more as the servo assist kicks in. Quote Link to comment Share on other sites More sharing options...
cackshifter Posted February 8, 2010 Author Share Posted February 8, 2010 0.5 to 0.7 bar, depends on the engine. It's a 300tdi. Quote Link to comment Share on other sites More sharing options...
cackshifter Posted February 8, 2010 Author Share Posted February 8, 2010 General test is to sit with the vehicle not running, put your foot hard down on the pedal and build some pressure, then turn on the engine. You should feel the pedal give a bit more as the servo assist kicks in. Thanks very much, I'll give it whirl. That'll give some idea. Nigel Quote Link to comment Share on other sites More sharing options...
martinspragg Posted February 9, 2010 Share Posted February 9, 2010 Had a similar problem and replacing the servo sorted out the problem. Quote Link to comment Share on other sites More sharing options...
nicks90 Posted February 9, 2010 Share Posted February 9, 2010 had a simillar problem and replacing the 10 year old brake fluid made a HUGE difference! Quote Link to comment Share on other sites More sharing options...
cackshifter Posted February 9, 2010 Author Share Posted February 9, 2010 had a simillar problem and replacing the 10 year old brake fluid made a HUGE difference! Maybe the rule should be "your brake fluid should never be older than your whisky". Thanks for the suggestions, I am about to have a look round. Quote Link to comment Share on other sites More sharing options...
errol209 Posted February 9, 2010 Share Posted February 9, 2010 It's a 300tdi. Higher value end then! Quote Link to comment Share on other sites More sharing options...
DaveSIIA Posted February 9, 2010 Share Posted February 9, 2010 The vacuum pump that feeds the servo tends to be past its best by ~120-150k miles, reducing servo assistance. Probably worth teeing in to the servo hose and checking the pressure (and how quickly it restores after brake application). The pump is an easier fix than replacing the servo. All the other stuff about discs, pads, fluid all being in good order still applies. Quote Link to comment Share on other sites More sharing options...
cackshifter Posted February 9, 2010 Author Share Posted February 9, 2010 Ok for your info,I measured the pressures; -0.3 bar idle, -0.5 bar with a rev. (I knew the EGR connection would be useful for something) . Put my British Standard thumb over the end of the hose and it didn't feel like a huge suck, our Dyson would have easily outdone it, but then I blocked the hose with a drill bit and the figures improved to -0.5 idle, -0.7 with a rev. That suggested to me that the servo was leaking, so I put a piece of hose on the servo connection, and tried sucking on it (ie with lungs) and I could pull air in no problem - it wouldn't hold any vacuum. So I've concluded that no.1 priority is change the servo and have ordered one. I take your point about the pump, it didn't feel impressive, so that may well be next on the list. Nigel Quote Link to comment Share on other sites More sharing options...
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