Technical Replacement Servo

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Technical Replacement Servo


New member
Jul 28, 2020
Hi all, I'm looking for guidance on selecting a replacement for the brake servo on my 2004 mk2b, 8valve active non abs.
There's a hissing sound from the inlet when the brake pedal is pressed. Idling is also affected by depressing the brake pedal repeatedly.
There is a number on the existing servo 4683384 which might be a Lucas part no.

The replacements I see are TRW or Bosch with a price from 100 to 300 quid.

Any idea what the correct replacement is?

Thanks in advance.
Not being funny but are you 100% sure it is the servo? The valve and plastic pipe just before it have been known to crack etc.
Also in the past I have know of the seal between the servo and the master cylinder to leak. The seal generally comes with a new servo but an expensive way of doing it.
We used to prove or disprove that seal by rubbing children's plastecine into the joint between the servo and cylinder, you could hear the air leak change. Not a permanent cure of course.
You may also be able to pin point it by placing a rubber hose to your ear and along the area you want to check to hear any hissing air.
Thanks for the pointers , bugsymike. I'll try the checks you suggested.