Grunt from brake servo

Hi folks,
As I wrote earlier, my Mk2 lost it’s brake fluids during 6 month winter hibernation. No obvious leaks, so I (and you) guess it went to servo.
Now I added fluid and started engine. At first brake pedal went straight down but after couple of pumps it now feels pretty normal, no spongy.
But there is a short grunt like sound from servo when brake is pressed. Listen the video.

If I close the air pipe of servo air valve with my finger, the grunt disappears. So is it air valve membrane? Or what? Everything worked fine 6 months ago.
It seems usual suspects do not sell air valve repair kits. So do I need to buy whole servo? Is the cheaper uprated brake servo LR18230 ok, or do you recommend the original servo C19612E?
I haven’t driven the car yet, so not sure how brakes behave.
Thanks for any advise,

Have you confirmed where the fluid went to? If its sitting in the servo I would suggest at some point it’s going to be drawn back into the intake. At that point you will need to be in fresh air as the cloud of smoke will obscure the surrounding area :slight_smile: BTDT

Hi Kopi

Did you get to the bottom of the noise? I have just fitted a new servo for similar reasons and when I started everything up I have a grunt or a “chuff” when pressing the brake pedal?
It might be me being extra sensitive, as it has just gone back together and the bonnet if off, so any noise would be louder than normal?
I have not got the car back on the road yet - maybe later today, so this is just when on axle stands in the garage


Not yet, I ordered a new servo, should arrive next week. I’ll let you know how it sounds after servo swap.

I got the car back on the road, and have two observations…

  1. The grunt is air being drawn into the servo intake through the filter. If I put a finger over the hose is goes away, but finger is sucked onto the hose.
  2. Probably not related, but I have quite some considerable brake imbalance after changing the servo. The right hand front is locking up on a dry road long before the left (LHD car). I can see how this can be related to the servo swap, but I did change brake pipe? I changed the master cylinder to the servo, the servo to 4 way connector and the two pipes to the front calipers, as well as swapping the flexible lines for braided lines as they were rubbing on the chassis. I have beled the system twice and cannot see any air at all - any ideas on what this might be?


Yes, like I wrote, I noticed the same. But it did not make that noise before, at least not as loud.

For your second problem, I can’t think anything else than air in the LH line.

Still waiting parts for my repair. Removed old parts today. Servo has fluid in it, can hear it splashing when turning servo around.

One wheel locking/operating before the other is normally a caliper piston hanging up in the bore. You might need to O/Haul BOTH calipers.

Lubricate all contact points of the slides and pad “wings” with antiseize to prevent future binding of the pads against the rotors. Hope that makes sense, you don’t want metal to metal on any moving parts of the brakes.


OK, now I have done my brake servo and master cylinder repair. Quite a job, 4 hours to remove old ones, 9 hours to put back new ones, partly because my own mistakes (vacuum hose cut too short etc.) partly because not compatible parts (master cylinder fork, see my web page).
Now everything works fine, brakes are as good as before if not better. Little “chuff” can be heard if listening next to servo but not so loud grunt as before that you could hear it to cockpit. I guess that “chuff” is normal when air rushes into vacuum chamber.
Quite a lot air in pipes, specially in the first/longest line, LH rear.


Thanks, I guess I will stop worrying about the “chuff” and focus on the brake in-balance.
The calipers are quite new Zeus twin pot ones, so think I will start with the bleeding - was a bit worried that did not get as much air out as I was expecting first time.


I have the same sound from the servo I just fitted , brakes work fine , don’t notice the grunt on the road , just in the garage .
Brakes work fine , as before , see how it goes , may put the old one back on , if there is a problem .
I have removed the air tank , but that is not related to the grunt , have a one way valve in the air supply line !

Hi Ian and Kopi

I have been driving mine and the brakes are working well, I think the balance issues I mentioned above were in my mind or due to the terrible road surfaces around Somerset. I popped the car on the local MOT stations - behind my profile picture with the thatched roof - and the brake balance was good.
The grunt is still there when the bonnet is open and I am listening, but from inside the car I don’t hear it anymore!


Thanks for the update David , I do not know the history of my servo , but by the look of it , it has not done much work .
Long as my brakes work I can live with a little grunt , unless one day I have nothing to do :smile: