So, where's the fluid gone.....?

[PeterK]

Can you try someone else's car to check that what you're now experiencing isn't normal ?. You've just gone from dodgy servo to new, and there will be more pedal travel with an effective servo.

If pumping the pedal doesn't cause the pedal to gradually get firm with less travel, then I would discount air in the fluid. If travel is too great, then is the sleeve in the master cylinder exactly the same ID as standard ?

[reb53]

The servo has always been fine.
I got it re-conditioned after finding all the fluid gone from the master cylinder after the car had been laid up for the Winter. ( see 1st post).
I'm well used to what it should feel like as I've had it for 37 years.
I suppose the company re-conditioning the master cylinder could have changed the bore size but it seems unlikely.
I'm thinking there's lost motion in the servo but I don't know enough about how they actually work to form any theories.

[billwill]

Are the master cylinder bores now narrower than they used to be. If so they have to move a bit further to displace enough fluid into the calipers for the same movement as before.

If not it sounds as if you still have some air in the system somewhere or your pedals are not pressing the master cylinder as short a distance as it used to be.

Check if the pedal rod on the master cylinder has any free play and adjust that. The rest position of your refurbished master cylinder might be different than it used to be.

[rcraven]

Could it be wear in or around the clevis pin between the pedal and the cylinder rod?

[saildrive2001]

I found that you have to go around numerous times to get all the air out. I would do around three rotations of bleeding all the calipers, then leave it for a day to let the air collect, then repeat the process. I have tried vacuum bleeding but found the old tried & true method of using a helper to push the pedal down whilst you open the bleed screw works the best.

[reb53]

Thanks for the replies so far.

My understanding of the re-sleeving process is that the bore is machined out and a new stainless tube pushed in, retaining the original bore size and, apparently, usually retaining the original piston as they "don't wear".

If, for some reason, the bore had been changed I would expect the pedal to have a different travel than before.
Not the current situation which is, "nothing, nothing, nothing.......phew ! at last ! "

The clevis pin was well inspected/checked for wear and is the original one so nothing is changed there.

Even though I went around bleeding it a couple of times I'm thinking that now that it's settled I'll go around it a few more times in the next couple of days.
I assume nothing special, ( bleeding wise ), is required for the servo ?
I just plumbed it back in and then went from wheel to wheel as per the book.

Cheers
Ralph.

[reb53]

No amount of bleeding has made any bleeding difference.

Spoke to the bloke who did the servo rebuild,who, after a bit of discussion, said " I know what you're talking about, we had another one that did that"

Something to do with a couple of little seals that now need more pressure to operate than they did before.
Whether or not it is possible to replace them with some others, and have it all still work, remains to be seen.
So it's going back and we'll see how good he is.
It's basically unusable at the moment so something has to be done.

What is slightly worrying is that in response to my question " don't the kits have the appropriate type seal ?", he said "there are no kits".
I thought, " Oh yes there are, what are you using.......?".

Ralph.

[rgh0]

I had something similar about 10 years ago with a rebuild of the servo on my plus2. In the end I disconnected the vacuum line and put in high coefficient pads and drove it without any boost for a few years. One day I decided to reconnect the vacuum line and try it with boost again and the long pedal travel before the boost came in had gone away. I guess the seals they use need more pressure like he says to get the shuttle that controls the boost to move enough but after a while they free up. I never did pull it apart to understand the issue as its worked perfectly now for the last 8 years.

cheers
Rohan

[robertverhey]

Hmm gotta say the reconditioner's response isn't inspiring confidence (in me anyway). Some of those seals are definitely not "off the shelf" items.

While the booster's in for another service, why not try bridging the pipe work with a short length of flared pipe with female 3/8 unions? See if it will bleed okay and whether the pedal returns to normal without a booster. That would help narrow the problem down. The old adage about "only adjust one thing at a time" may be at work here, there may be an issue with your newly overhauled m/c......

Way back in the past, I had a similar issue with a Corty, which remained a mystery and from (dim) memory I solved it with a threaded adjustable m/c pushrod, which took up the mysterious slack that had appeared.

Robert

[reb53]

Thanks guys, all food for thought.

The idea of an adjustable push rod has crossed my mind but I'm not sure that it would help as it appears that the problem is one of having to apply more pressure than before, before the brakes start to work.
So I've lost the ability to gently brush the pedal to bleed off a little speed.
All the finesse has gone and, as you know, that's the whole point of the car.

I'll see what the re-builder comes up with. Might suggest he gets one of the Ebay kits out of the UK as surely they will have exactly the right bits in them.
Cheers
Ralph.

[Chancer]

Decades ago I rebuilt a servo as kits were then available, i think that it was on a Viva.

The drum had a piston with a rope seal rather than a diaphragm and the new seal was tight, perhaps I should have soaked it in oil, anyway the effect was a slow lazy servo.

You would approach a junction and brake, the pedal would feel hard and unservoed so you had to push much harder, the car would then slow progressively and all of a sudden stand on its nose as the servo cut in, you let off the pedal and it was another couple of seconds before the brakes released.

It was my everyday commute car and I couldnt fix it till the weekend so had to adapt my driving technique, it was a real game of strategy to be able to come to a halt exactly where I wanted to.

I have also mucked around in the past with adjustable pushrods, often you need an upper pedal stop for it to work in taking out lost motion, it was particularly effective on MK1 golf and sciroccos, however be very very carefull as you can end up with the brake pressure not releasing.

[billwill]

Thanks guys, all food for thought.

The idea of an adjustable push rod has crossed my mind but I'm not sure that it would help as it appears that the problem is one of having to apply more pressure than before, before the brakes start to work.
So I've lost the ability to gently brush the pedal to bleed off a little speed.
All the finesse has gone and, as you know, that's the whole point of the car.

I'll see what the re-builder comes up with. Might suggest he gets one of the Ebay kits out of the UK as surely they will have exactly the right bits in them.
Cheers
Ralph.

??
Did you put new brake pads in and they have not bedded in yet?


Definitely try your system without the servo, as Robert suggests, by make a bridge pipe for where the servo used to be. That should tell you for sure whether the problem was in nthe servo or was in the rest of your braking system.

[reb53]

The pads aren't new, been in for years but plenty of life left in them.

To make up a by pass pipe I'll be running around town to get it done, and when fitted I'd still have the hard pads in so I suspect I'd be completely confused.
Also, by the time I'd done that the servo could be back with the overhauler.
I remember now that when I was talking to him he mentioned the pressure needed to activate "the tipping valve" (?) as most likely having changed.
So, we will see.....

Ralph.

[AHM]

Ralph,

You are right to send it back to the rebuilder, it should work properly, and it sounds like he is doing his job so far.

It sounds like he is talking about the air valves, and I don't believe even the genuine kits had parts for those.

With my brakes I get a very slight lag after the servo rebuild - I'm expecting that it will improve as things bed in.

[billwill]

Under the circumstances I would probably ask the servo re-builder to make up a 'servo-substitute' pipe for me so that if the redone servo still does not fix the issue, you can try an unassisted system to see if that gives you any clues as to what is wrong.