Brake servo gone again?

[soldave]

Am wondering if someone can help confirm what I think is my brake servo gone again in my Éclat, 18 months after a rebuild. Context is the car has been off the road for a month, during which time I've done timing belt, bled brakes, and a couple of other little bits of maintenance.

Went out for a drive the other day and the brakes just felt wooden and I was really having to put some pressure on them to slow down. If I'd needed to get close to locking up the brakes then my foot would have been in the engine bay with the amount of force needed! Did a bit of testing on the following:

• Non-return valve - working as it should
  Vacuum line from servo to engine - no leaks, not collapsed
  Driving with vacuum line plugged but disconnected - Brakes feel even harder to stop
  Bleeding - done again using the old 2-person method

I also took a video yesterday where you can hear a constant hissing sound in time with the engine when the brake is pressed, and the engine nearly die (admittedly it was a cold engine with no choke). See https://www.youtube.com/watch?v=S58M8jl1bkc.

My guess is that there's a leak in the servo causing the brake feel, the sound, and the extra air being pulled into the engine when it should be a vacuum is causing it to nearly die when cold and foot on the brake.

Does this theory seem about right? If so then it's a frustrating second rebuild inside 2 years but will have to be done to get back on the road.

[rbgosling]

Sounds a reasonable diagnosis, but I'd double-check the vacuum supply to the servo before digging into the servo itself.

If you can hear a hissing, using a tube with one end stuck in your ear as a sort of stethoscope may help isolate the location.

[Alan_M]

I think your diagnosis may be correct.
I had similar in a Mercedes many moons ago -£1100 for a new servo!!! Ouch!!!

Richard’s suggestion of using small tube to listen is a good one to confirm.

[Marten]

Am wondering if someone can help confirm what I think is my brake servo gone again in my Éclat, 18 months after a rebuild. Context is the car has been off the road for a month, during which time I've done timing belt, bled brakes, and a couple of other little bits of maintenance.

give the brake pedal 10 pumps and then start the engine with your foot on the brake. If the servo works the pedal should go down.

Check for seized calipers

[soldave]

Sounds a reasonable diagnosis, but I'd double-check the vacuum supply to the servo before digging into the servo itself.

If you can hear a hissing, using a tube with one end stuck in your ear as a sort of stethoscope may help isolate the location.

Good call. I will check that. But would that cause the engine to die with the brake pedal held down, if it's a problem with the amount of vacuum itself?

[MetBlue]

Sounds very much like pressing brake pedal opens up the vac pipe to atmosphere (which it shouldn't).
Try running engine at tick over and just pulling the vac supply pipe off. If engine behaves same as hitting the pedal, you boosters Donald Ducked.

[soldave]

Just wanted to revisit this to round it off. So I took the servo off the car and it rattled a little when I shook it. Not a great sign! Manipulated the input shaft on the servo, which made a loud clock sound and then the servo just stayed in activated. Would have been quite unfortunate had that happen when I was driving!

Replacing it with a Land Rover servo with a modified fork but the car is off the road for a while now I think. A door hinge pin replacement has turned into me waiting for window frames to be manufactured again now.

[soldave]

Thought I'd update on this as a few people are talking brake boosters elsewhere.

Has the Land Rover one in my car for a while now with an extended input fork. Adjusted the output rod by feel on a stopped car and think I've got it there or thereabouts so no drag when braking but slight depression gives me brakes.

I've found a couple of things though. The braking feels super light first of all. Like very little pedal pressure is needed at all to give me some braking, but it needs quite a bit of travel it seems to get strong brakes.

Secondly is that I can't really get the brakes to lock. If I stamp on them on a dry road I can get to the point where it feels they are right about to lock but they don't. Doesn't feel like they need further bleeding but might try it again sometime. Not sure if that's the general experience with the Land Rover servo though.