 | Home > Technical > diagnosing brake servo |
 
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| I Like Old Skool Member Since: 23 Feb 2015 Location: Manchester Posts: 762   
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Pull out the vacuum hose from the servo and check the vacuum pump is working with the engine running (put your thumb over the end and it should get sucked on). If this is ok then put it back in and run the engine for a minute before turning off and pulling the pipe out. The servo should hold vacuum for a while and if you don't get a whoosh/hiss of air rushing in when you pull the pipe then the servo is leaking.
The servos are a bit crap and do split where the master cylinder mounts but the cracks are usually hidden so only really visible when you pull the cylinder away. Just had to replace mine on my old TDI last year after thinking for a year or two previously that the brakes perhaps weren't 100% (still passed MOT though!) and it was much better after the new servo. |
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10th Apr 2023 3:26pm |
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| miker916 Member Since: 25 Oct 2022 Location: Fife Posts: 47  
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thanks for the help, so it looks like i have some sort of problem but not with the servo:
With the engine running and vacuum hose disconnected from the servo i can feel it sucking when i put my finger over the end. Connected the hose back to the servo and left the engine running for a minute, switched engine off and pulled the hose out - air came rushing out the servo. But when i pump the brake pedal and hold it down as far as it'll go then start the engine the pedal dosent move down at all. I tried this about 10 times and it was the same for 9 tries but one try after starting the engine, the pedal did sink. |
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10th Apr 2023 3:53pm |
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| geobloke Member Since: 06 Nov 2012 Location: Nottinghamshire Posts: 4390
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Your brake servo is failing or has failed internally I am afraid. By replacing it you will have your pedal back again.
I have recently been through a similar fault finding experience in Miffy which led to the replacement of the servo. To give you an idea now Miffy's brakes are good enough to hang you from the seat belts. |
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11th Apr 2023 7:33pm |
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| miker916 Member Since: 25 Oct 2022 Location: Fife Posts: 47
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thank you, a new TRW booster is on its way. Fingers crossed it fixes the issue
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12th Apr 2023 8:12pm |
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| landy andy Member Since: 15 Feb 2009 Location: Ware, Herts Posts: 5416 
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How much is the servo costing?
Is there an uprated option that others have used? |
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12th Apr 2023 8:22pm |
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| geobloke Member Since: 06 Nov 2012 Location: Nottinghamshire Posts: 4390
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There is not really an uprated version. But... there is one that has a slightly bigger internal volume made by County. The housing is more square than the LR item. This is the one that I bought as I was curious that others had said the extra internal volume provided better braking efficiency. I am not sure about that, but thought I would give it a go and Miffy's brakes are superb.
https://www.ebay.co.uk/itm/114248028555?ha...R6bf6O_uYQ |
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12th Apr 2023 8:42pm |
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| landy andy Member Since: 15 Feb 2009 Location: Ware, Herts Posts: 5416
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Thanks. Notice that is non abs so may give them a call. Just not happy with my brakes, and have swapped most other things. Servo appears ok, but may swap out
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12th Apr 2023 10:26pm |
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| geobloke Member Since: 06 Nov 2012 Location: Nottinghamshire Posts: 4390
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Hope you get it sorted
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13th Apr 2023 9:49am |
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| Porny Site Sponsor Member Since: 31 Aug 2009 Location: Sutton Coldfield - West Midlands Posts: 787 
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£192 + vat inc UK postage for a TRW/OEM ABS spec brake master cylinder
They do fail internally, but most commonly they spit where there master cylinder bolts on (more common on none ABS) IRB The home of the first modified Keswick Green 90 - and the first 2.4 Puma through both the 200bhp and 550Nm barriers. www.IRBdevelopments.com www.facebook.com/irbdevelopments www.integrated316.com www.facebook.com/integrated316 |
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17th Apr 2023 1:03pm |
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| miker916 Member Since: 25 Oct 2022 Location: Fife Posts: 47
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it was the TRW one i went for, only cause autodoc are doing it for 97 + VAT just now
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17th Apr 2023 1:20pm |
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| Porny Site Sponsor Member Since: 31 Aug 2009 Location: Sutton Coldfield - West Midlands Posts: 787
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That's cheap! IRB
The home of the first modified Keswick Green 90 - and the first 2.4 Puma through both the 200bhp and 550Nm barriers. www.IRBdevelopments.com www.facebook.com/irbdevelopments www.integrated316.com www.facebook.com/integrated316 |
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17th Apr 2023 1:24pm |
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| miker916 Member Since: 25 Oct 2022 Location: Fife Posts: 47
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it wa the servo, was cracked where the master cylinder bolts to it
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20th Jun 2023 3:56pm |
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| I Like Old Skool Member Since: 23 Feb 2015 Location: Manchester Posts: 762
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I win
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20th Jun 2023 11:46pm |
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