 | Home > Technical > Servo or vac pump? |
 
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| Rickydodah Member Since: 14 Jul 2014 Location: East Sussex Posts: 1091  |
I'd have said anything in excess of 0.5 negative bar would be sufficient to work the servo. What's it like if you keep your foot on the brake and allow the vacuum pump to build up a good head?
 I started with nothing and still have most of it left! |
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20th Sep 2015 10:51pm |
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| Cupboard Member Since: 21 Mar 2014 Location: Suffolk Posts: 2971  
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You're never going to get more than -1 bar gauge vacuum pressure, at least not at sea level.
You might do in a submarine, but you're limited by atmospheric pressure of about 1 bar. Remove all the air and you've just got the atmosphere pushing in. |
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21st Sep 2015 11:48am |
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| g-mack Member Since: 07 Jan 2014 Location: northumberland Posts: 1967
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so you are checking the vacuum from the pipe that enters the servo yea? and you can here hissing in servo? i would say its the servo thats gone!
if your getting -1bar at pipe just before entering servo the pipe and vac pump are probably fine. this of course is MHO  My 109 thread
my youtube channel |
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21st Sep 2015 1:24pm |
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| jst Member Since: 14 Jan 2008 Location: Taunton Posts: 8053  
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Change the servo. Get a disco one in there from disco with abs, it's bigger, better for repeat braking Cheers
James 110 2012 XS Utility 130 2011 M57 bespoke Camper 90 2010 Hardtop 90 M57 1988 Hardtop |
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24th Sep 2015 7:12pm |
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| donmacn Member Since: 06 Nov 2017 Location: Nth Scotland Posts: 1845
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Thread resurrection!
On my 300tdi 110 the brakes 'aren't wonderful'. On checking at the monent, the pedal doesn't drop when the engine starts, so I'm going to be looking at issues with the servo/vacuum pump/hose. The car is 24 y/o and I'd have to wade through a lot of paperwork to see if the pump was ever replaced. I know I did the servo myself, but that could be several years ago. So, the point of reviving this old thread - is the suggestion above to use a Disco servo still valid? Is it an easy fit, and does anyone have a part number?? Cheers D Donald 1994 Defender 300Tdi 110 SW - owned since 2002 - 230k miles and going strong (The 'rolling restoration' or tinkering thread: http://www.defender2.net/forum/topic58538.html ) 2000 Range Rover P38 4.0L V8 in the past.. RR classic - fitted with 200Tdi 1984 RR classic - V8 with ZF auto box 1993 Discovery 300Tdi not to mention the minis and the Type 2 VW camper... |
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26th Aug 2018 10:14am |
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| jst Member Since: 14 Jan 2008 Location: Taunton Posts: 8053
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its a direct replacement and something we fit on off roaders and autos as a matter of course. the bearmach std def replacement one will also do the job as will an ABS one from defender or Disco tdi. Cheers
James 110 2012 XS Utility 130 2011 M57 bespoke Camper 90 2010 Hardtop 90 M57 1988 Hardtop |
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30th Aug 2018 6:04am |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720 
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Sounds like the servo, buy a cheap vacuum pump (mityvac or similar) and connect to the servo, you can put a vacuum to it manually and see if the servo works - obviously it'll only work once before you use the vacuum up and have to pump it again. If you can't make a vacuum your servo is leaking.
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30th Aug 2018 6:30pm |
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| donmacn Member Since: 06 Nov 2017 Location: Nth Scotland Posts: 1845
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Thanks guys,
I did own a Disco 2 way back when, but it was brand new and only had it for a few months. I'm sure I must have, but I don't really remember looking under the bonnet much - are we talking all models of Disco for this, or up to a particular model? ZSD - thanks for that - a good plan, and I never know such testers existed. The mityvac look a wee bit pricey for something I might only use once. Do you reckon this would do the job? https://www.amazon.co.uk/dp/B07F7XXMQG/ref...9f427e8ea3 Donald 1994 Defender 300Tdi 110 SW - owned since 2002 - 230k miles and going strong (The 'rolling restoration' or tinkering thread: http://www.defender2.net/forum/topic58538.html ) 2000 Range Rover P38 4.0L V8 in the past.. RR classic - fitted with 200Tdi 1984 RR classic - V8 with ZF auto box 1993 Discovery 300Tdi not to mention the minis and the Type 2 VW camper... |
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30th Aug 2018 7:28pm |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720
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Genuine Mityvacs are really expensive, but there are plenty of generic ones. That Amazon one will be ok, it might not last long but it'll do the job for now.
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30th Aug 2018 8:04pm |
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| donmacn Member Since: 06 Nov 2017 Location: Nth Scotland Posts: 1845
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Well, I might get a vaccum pump for future use, but had a chance today to take a closer look.
The vaccum pump on the car is definitely working. With the pipe disconnected from the servo I could hear it chuffing away, and it would pull my thumb quite tightly onto the end of the pipe. For a pressure of -1bar (I think, roughly??) I suspect it's OK The servo? Visibly cracked along the bend in the pressing by both master cylinder bolts. I've also realised that my 'spare' in the garage is also split. So, temporarily fixed the current one with some 'dum dum' and gorilla tape, and I can feel a difference. Not a startling difference, but a definite improvement. So the question is which is the best servo to get that would fit onto the standard pedal box and master cylinder? That would be the 'easy' option. If there were another servo which would give significantly better assstance, but which would need the brake lines to the master cylinder remade, then I'd consider that. Donald 1994 Defender 300Tdi 110 SW - owned since 2002 - 230k miles and going strong (The 'rolling restoration' or tinkering thread: http://www.defender2.net/forum/topic58538.html ) 2000 Range Rover P38 4.0L V8 in the past.. RR classic - fitted with 200Tdi 1984 RR classic - V8 with ZF auto box 1993 Discovery 300Tdi not to mention the minis and the Type 2 VW camper... |
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2nd Sep 2018 5:08pm |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720
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You could probably take them to bits and weld the crack back up.
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2nd Sep 2018 9:11pm |
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| donmacn Member Since: 06 Nov 2017 Location: Nth Scotland Posts: 1845
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^^ Never thought of that
Have you tried this? When you say 'take them to bits' do you mean taking the servo itself to bits? First glance I'd have thought this would be a little tricky as they seem to be a 'press and tab' manufacture. But I can see how a line of weld along the crack might well work. Still though, my wife's car is a Skoda Yeti. Going from that into the Defender, the Def brakes are really poor. If there's a fairly straightforward way to improve them I'd think about it. Donald 1994 Defender 300Tdi 110 SW - owned since 2002 - 230k miles and going strong (The 'rolling restoration' or tinkering thread: http://www.defender2.net/forum/topic58538.html ) 2000 Range Rover P38 4.0L V8 in the past.. RR classic - fitted with 200Tdi 1984 RR classic - V8 with ZF auto box 1993 Discovery 300Tdi not to mention the minis and the Type 2 VW camper... |
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3rd Sep 2018 5:36pm |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720
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I've not looked closely at Defender servos, and an 80's one may not be the same as my Puma. But I have rebuilt a 90's Mini one. It's a kind of twist the two halves and it pops apart thing, It's not threaded as such, it's more like a bayonet with wedges on it.
You might be able to just weld it from the outside. The heat should be far enough away from the diaphragm not to harm it, at the end of the day you haven't got a lot to lose if it doesn't work. |
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3rd Sep 2018 6:51pm |
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