Diablo Posted October 22, 2012 Share Posted October 22, 2012 Typically whenever first starting up, but also after ~1min of slow/stationary traffic, when you brake, the pedal is fairly solid and there seems to be a fair reduction in braking efficiency. As soon as the revs increase, braking returns to normality. I'm guessing this is pointing towards a knackered servo or vacuum pump or similar, but not sure where to start? Quote Link to comment Share on other sites More sharing options...
mmgemini Posted October 22, 2012 Share Posted October 22, 2012 Start by looking closely at the front of the servo. Where the master cylinder mounts. Look for cracks towards the bolys. The cracks can be hard to see. HTH Quote Link to comment Share on other sites More sharing options...
western Posted October 22, 2012 Share Posted October 22, 2012 300tdi servo's seem to suffer this cracking around the brake master cylinder mounting bolts, 200tdi & earler vehicle seem to be fine. Quote Link to comment Share on other sites More sharing options...
Yostumpy Posted October 22, 2012 Share Posted October 22, 2012 if you do see 2 cracks, a temp bodge, is to clean up the metal surface, then cut 3 thin strips of gaffer tape , each one progressively wider, and lay them over the cracks, and rub down to seal. DON'T laugh, this works a treat, as the crack is sucking the tape into the holes. mines been like it for 6 months now, got anothr 6 months till mot. One other thing, if the EGR has been removed ( if it had one) check the vacuum pipe coming out of the servo unit. If it has a 't' peice and a 'thin' pipe trailing off somewhere, make sure the end of this is blanked off, other wise you're losing vacuum. Quote Link to comment Share on other sites More sharing options...
Diablo Posted October 23, 2012 Author Share Posted October 23, 2012 The engine is a 200tdi, though not original. I presume the brake set up is 200tdi as well, but not completely certain. Quote Link to comment Share on other sites More sharing options...
Tanuki Posted October 23, 2012 Share Posted October 23, 2012 Engine-revs dependency makes me think either your vacuum-pump is weak, or you've got a small leak on the vacuum-circuit. When engine's running slowly there's insufficient "suck" being fed to the servo. A few brake-applications will use up the vacuum stored in the servo-reservoir and then the pedal goes hard. When the revs are increased, the amount of 'suck' from the vac pump goes up so normal servo operation is restored. Quote Link to comment Share on other sites More sharing options...
Simon Smith Posted October 23, 2012 Share Posted October 23, 2012 My 200Tdi creates plenty of vacuum at idle, in fact if you pump the pedal without the engine running until the pedal goes hard and then start the engine, you can feel the pedal go down just on cranking on the starter. My last 200Tdi was just the same, and both had servos that would hold a vacuum for several hours if you didn't touch the pedal. So I am pretty sure that there is a leak somewhere, If the pump creates a vaccum at higher speeds but the vacuum fails as soon as you slow the engine speed I think the pump is fine but not keeping up with the leak. Had the same problem on my Series 3 and replacing the NRV and it's rubber grommet fixed it. Quote Link to comment Share on other sites More sharing options...
Off Road Toad Posted October 23, 2012 Share Posted October 23, 2012 300tdi servo's seem to suffer this cracking around the brake master cylinder mounting bolts, 200tdi & earler vehicle seem to be fine. Sorry to jump in but I'd just like to add a thank you for this! I've had poor brakes for ages and just checked my servo and lo and behold there's a crack! Steve Quote Link to comment Share on other sites More sharing options...
Diablo Posted October 23, 2012 Author Share Posted October 23, 2012 I guess I'm starting to get a list of suspects together then! Is the NRV on the hose? Can't remember the exact layout at the mo. Quote Link to comment Share on other sites More sharing options...
western Posted October 23, 2012 Share Posted October 23, 2012 if the servo is a large diameter & master cylinder bolts are offset, thats the same as the 300tdi servo, so check for cracks anyway around the studs as noted above. Quote Link to comment Share on other sites More sharing options...
western Posted October 23, 2012 Share Posted October 23, 2012 Sorry to jump in but I'd just like to add a thank you for this! I've had poor brakes for ages and just checked my servo and lo and behold there's a crack! Steve your welcome. Quote Link to comment Share on other sites More sharing options...
Simon Smith Posted October 23, 2012 Share Posted October 23, 2012 It's the plastic fitting on the end of the hose which plugs in to a large grommet on the servo. LR part number 18G8953L according to my parts drawing, includes the NRV and the grommet. Quote Link to comment Share on other sites More sharing options...
Diablo Posted November 4, 2012 Author Share Posted November 4, 2012 Well, finally (!) had a chance to get a look at this. No cracks evident. Though a very mildly leaky brake cylinder is. Think I'll replace that rather than rebuild. Might as well order a new NRV whilst I'm at it, and hope that one or the other cures the problem. Quote Link to comment Share on other sites More sharing options...
Diablo Posted November 21, 2012 Author Share Posted November 21, 2012 Rebuilt the master cylinder at the weekend, and whilst that issue is now fixed, the one linked to the vacuum still persists. I tested the vacuum pump at the same time, and got readings of 5 ins Hg at idle, and up to 25 at high revs. Is this what it should be pumping at? Quote Link to comment Share on other sites More sharing options...
western Posted November 21, 2012 Share Posted November 21, 2012 closest I can find is for TD vac pump [same as Defender 200tdi vac pump] manual says at 2500 rpm vacuum is 0.8 bar Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted November 21, 2012 Share Posted November 21, 2012 It shouldn't vary with revs - it'll just take longer to get there at lower revs. Suspect the vacuum pump. Quote Link to comment Share on other sites More sharing options...
Diablo Posted November 22, 2012 Author Share Posted November 22, 2012 But the vac pump's output (or should that be input?!), will vary as it's driven off the engine, which is linked to the revs? Or am I reading this incorrectly? Granted the vacuum in the servo shouldn't change. Off to find a bar to inches of Hg conversion table now then.... edit: 1 inch of Hg is 0.03386 bar. At high revs I was getting around 20/25 inches Hg. At the above rate, 0.8 bar is 23.63 inches of Hg. so it appears that, at those revs anyway, the pump is ok. Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted November 22, 2012 Share Posted November 22, 2012 It's a piston pump (sort of). So each 'stroke' will move a certain displacement. Therefore, any revs should give you maximum vacuum - assuming all is well and nothing is leaking. However, if the diaphragm is leaking or the spring is giving up then you're constantly pumping against a leak, or it's not pulling/returning properly - faster revs will pump faster therefore giving more vacuum. Think of it like a hydraulic pump driven winch. Even at idle it'll still pull to the maximum rating, just it'll take longer to pull (assuming the engine doesn't stall of course) If you're not getting any vacuum at idle then your pump is knackered, or you have a leak somewhere else. Given that you've ruled out the latter, your pump must be knackered. Easy way to test - pull the vacuum pipe off. Start the engine and let it idle. Stick your finger over the end. If there's no (or very little) suck, it's knackered. If it's pulling a good vacuum you'll know about it. Quote Link to comment Share on other sites More sharing options...
Diablo Posted November 22, 2012 Author Share Posted November 22, 2012 That's what I tested. I pulled the pipe off the non-return valve, and shoved a vacuum gauge in there, giving me around 5 inches Hg at idle, progressing to 25 at about 3000 revs. Still worth testing it at source I suppose. The only things left, other than pump, are a dodgy hose (unlikely, but a cheap replacement), dodgy NRV (new one in the post somewhere), or the servo is leaking somewhere (casing, diaphragm, elsewhere), as described in your second paragraph. Quote Link to comment Share on other sites More sharing options...
western Posted November 22, 2012 Share Posted November 22, 2012 It's a piston pump (sort of). So each 'stroke' will move a certain displacement. it's a rotary vac pump, the 4 vanes inside can be bought seperately & replaced, AEU2718 x 4 just remove the top cover, pull the old vanes out, fit new vanes, refit top cover.http://www.lrseries....=AEU2718&page=1 Quote Link to comment Share on other sites More sharing options...
cackshifter Posted November 22, 2012 Share Posted November 22, 2012 If it's any help a brand new Westinghouse 300tdi pump generates about .8 bar just beyond idle. When knackered about .3 to .5 , (and it's surprising the difference it makes to the pedal). Quote Link to comment Share on other sites More sharing options...
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