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Post by Jens Munk on Aug 10, 2015 8:56:19 GMT
Hello,
I have just replaced the brake servo with a reconditioned unit on my PB, and it's like it sticks a bit. I.e. when I press the brake pedal, it needs a little pressure before it starts to move down, and when I brake to a stand still and take the foot off the brake pedal, it takes a second or so before the brakes release completely and the car starts to creep as normal for an automatic.
Is this normal for a reconditioned unit and will it go away on use? Or should I start to complain to get it replaced?
I did not have this problem with the old unit and it worked perfectly until the day it leaked all the brake fluid into the membrane compartment and quit working.
Thanks,
Jens.
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Post by Phil Nottingham on Aug 10, 2015 9:03:29 GMT
Not normal and can be caused by a sticking piston under the air valve
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Post by lagain on Aug 11, 2015 19:35:29 GMT
I would try to get it replaced.
Some years ago (oops, it must be 20) I replaced all the brake pipes with copper ones, in retrospect it was a silly thing to do as the originals were fine and now I have to keep polishing them !
I digress, as it was a complete overhaul I decided to use silicone fluid, which I would recommend, although it does mean cleaning out all the old fluid. They say that they are compatible, but they are not. I also had similar problems with the servo when I had put new rubbers into it and my conclusion was that possibly the bores were not as smooth as they should be for the rubbers to slide, although it all looked OK. I replaced the servo with a new one and every thing worked again as it should.
It would be difficult with a reconditioned unit to know how much work had been done to the servo,
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Post by Jens Munk on Jul 10, 2019 9:35:32 GMT
Following up on this thread....
I had hoped the servo would eventually become better when broken in, but it did not. So being very tired of it and my wife complaining about it as well, I went ahead and bought a new servo from JRW. Works like a charm now.
However, the culprit of the sticky refurbished servo is as suggested the little air valve piston. It can be grabbed with an inside circlip tool and you can feel the sticky behavior known from the brake pedal behavior.
The question is if this is fixable of if I should just dump it? Everything is nice, clean and the seal is obviously new - just too tight.
What do you think?
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Post by Phil Nottingham on Jul 10, 2019 19:00:48 GMT
It is fixable but will not last as long as a new one or anywhere near. Well worth dismantling to keep as spares or to rebuild in the future. Note later pistons are a different size. Do not leave as is as will seize up
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Post by djm16 on Jul 11, 2019 0:33:53 GMT
One of two things likely is causing the sticking:
coarse honing marks in the bore
different composition of the piston seal.
I presume you did not take the unit back to the rebuilder?
May be worth taking it partly dismantled to a brake parts specialist (a different one?) and see if they will let you try out a new piston seal on the spot, if give advice on how to correct the bore.
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Post by Jens Munk on Jul 11, 2019 6:53:25 GMT
The refurbished unit is also from JRW, but since I have had it for a couple of years, I don't think it is covered anymore. Also he is no longer selling the refurbished units - maybe for a reason....
Any good sources for piston seals?
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