Servo not working

[whitesnake]

Hello All,
I have a problem with my series 2 servo not working, have replaced master cylinder, servo, reaction valve , and vacuum non return valve and have quadruple checked all hoses are correctly connected and not kinked, also removed piston from end of master cylinder that operates reaction valve cleaned and greased this and refitted.
But still no servo assist on brakes, at idle I have vacuum to both sides of the servo and on depressing the brake pedal it makes no difference, still vacuum to both sides of servo so piston not moving to assist braking.
I am now thinking it may be a problem with the metal lever at the end of the piston in the master cylinder that opens to operate the reaction valve piston.
What are your thoughts on this before I rip apart the master cylinder.
Apart from the servo the brakes all operate although requiring a lot of effort and concentration on braking distance

[christopher storey]

Another servo mystery ( there is a separate recent thread on this type of problem ) .I think that if you are still holding vacuum in both chambers of the servo when the pedal is pressed , then it is a vacuum sequencing fault , and not a hydraulic system fault . If the shuttle in the servo master cylinder were seized, then you would get the rear chamber going to atmospheric when the pedal was pressed , but no servo effect .

[Joes66]

If you have replaced the master cylinder and the complete servo and its attached slave master cylinder with new ones and you have vacume it should work
This assumes all the rest of the pipework is clear and free of any muck
And is attached correctly
And there are no other issues in the braking system
Its unlikely new units are faulty
Taking apart new units will also probably void any warranty
Joe

[malcolm]

I had an issue with my servo a while back. Although all the pipes looked good and not kinked, one of them was blocked internally (presumably with crud from the ages?) When replaced, the system worked fine. Might not be your problem, but simple to check at least

[caveman]

Is there a specific sequence for testing servo assist and vacuum lines etc?
I have a particularly heavy brake pedal, been like it since the day I collected it after restoration 20yrs ago and only done 6000 miles since. It made for an interesting drive over the Lecht ski centre yesterday and Friday, but with nothing to compare it to I’m not sure if the pedal force I’m using is ok or not. I know it’s not going to be like a modern servo but I thought I may as well check it out. Ive also been thinking about trying green stuff pads in my coopercraft front callipers to see if they improve.

[Joes66]

I recently replaced everything in the breaking system on my series 2
I had to really as it was all rotten or knackered
Only non standard part was the series 3 servo and slave master cylinder
I originally asked on this forum whether I should upgrade the brakes in any way as I was doing them anyway
The general consensus was to just put them back as standard
Which I did other than the servo from the series 3 which is a little more powerful
I can only say the brakes are excellent
Very responsive and certainly the best brakes I have ever used on a car from this age period
If I used a heavy foot or stood on them I would almost certainly end up through the windscreen or trashing the car
You shouldn't have to have a heavy foot
Unless I was going to fit a 300hp engine or go racing up and down mountain passes I wouldent change anything
Joe

[mgcjag]

Hi Steve...its easy to tell if your servo isnt working......find a safe place with a downhill slop...engine off and press brake a few times to empty vac tank.....then roll down slope and try your brakes......you then know how much force is required without a servo........start engine and repeat........you should need much less pressure to stop the car....Steve

[whitesnake]

Steve,
Pretty certain servo is not working correctly as at idle with engine running I have vacuum to both sides of servo, on depressing brake pedal this remains the same , no change to atmosphere at rear of servo to allow piston to move forward. Have now dismantled master cylinder and will refit with repair kit and am going to replace all pipes with silicone vacuum pipes although the old pipes were replaced with new about 3 years ago, if this does not work will move forward and put new seals in servo but the problem seems to be getting the rear of servo to go atmospheric.
Cheers Steve.

[mgcjag]

Hi Steve....i was replying to the other Steve (caveman) who jumped in on your thread....far too many Steve,s here ...all the best....Steve

[Joes66]

Why are people taking things apart and fitting seal kits these days?
Unless its for some originality reason on a car that goes to shows to be judged (and tbh I think safety over originality should come first) I just don't get it
Thats something we used to do when we had no choice and certainly not on a customers car unless you had cast iron insurance that you dident mind claiming on
Just buy quality new complete braking components
Half of peoples problems on here are due to this i am sure of it
Mucking about with old crap parts in braking systems seems insane to me
If I bought an old car and the owner told me he had fitted seal kits I would be horrified
Just like using old style braking fluid on a car that sits about most of its life
Its like begging for trouble
On cars that are probably worth in access of 50 grand and do 150mph I would want to be confident the car was going to stop
Even after having sat for months on end
I am going to ignore the cost side of this because if you have an e type there is zero excuse for a cost reason
I am sure I will get someone pointing out some new parts have been faulty, but then I have had brand new genuine parts that have been faulty
No reason to give up on treating your car to a nice new braking safety component because of one bad apple
Or others terrifying others on the rare occasion a batch of components have been a problem
These new braking parts like master cylinders are made in their thousands
You cant tell me they are all faulty or poor quality
Every time you touch an otherwise good or bad braking system you run the risk of faults and issues like leaking pipes that need tweaking up or a new part that may not be quite right
I have fitted hundreds of these parts to other peoples cars in my time
Sometimes i have had problems but you soon sort them out
My car after replacing all the cylinders etc with new parts has been fine and as pointed out above has excellent brakes
Only problem I had was a leaking new brake pipe on one of the rear calipers
I would also point out that where I have fitted seal kits, I have had some of them fail and leak, some of these seal kits can be of very dubious quality and no better than the ceap seals I have taken out
How long a seal kit been sitting about is a big problem and I've also had old seal kits re packaged in modern packaging
These experiences were years ago when the parts were not available
I was in my early twenties, chief mechanic at the maidenhead MG centre
And I can say we never fitted a seal kit unless it was calipers or for an unavailable cylinder of some sort
Even then the customer would have been fully informed as to the possibility of renewed failure of the part and signed a bit of paper to say he understood this
I was often asked to do so by customers to save a bit of money but it just wasent worth the risk or trouble if subsequently the part failed for whatever reason
Possibly killing soneone
In fact I remember a servo I was once was asked to rebuild because it wasn't available back then
The kit had a part missing that was needed and I was asked to just make the small part up
I refused, due to the above and the car was towed away from our garage to have it done round the corner by a local back street garage
No idea if the job worked out or the customer got himself killed
Let's face it, the companies and or those responsible for selling them in the uk would soon stop selling them and probably end up in court having killed someone if they were that bad quality
SNG Barrett for instance wouldent sell them for sure
These parts were always supposed to be disposable replaceable service items
You wouldent have had a garage of any worth putting a seal kit in anything unless they had to back in the day
Simply from the human error point of view you wouldent do it

I have written this in good faith, humour, and I hope constructive criticism
Just trying to part some of my past experience in the old car trade and having owned many classics
And hope it will prevent a lot of people loads of aggravation in the long run

Joe

[mgcjag]

Nice long rant Joe......i thought that you posted not too long ago that you had rebuilt all your calipers with seal kits....so have you now replaced these with new calipers?.......Steve

[whitesnake]

In response to Joe,
I am only renewing seals on my master cylinder as it was a new item about 3 years ago and I do not feel inclined to spend another £260 quid when all I wanted to do was open it up to check the lever operating the intermediate piston is not stuck or indeed the piston itself, all seals are correct replacements from SNG Barratt and all pistons and bores are unscored so where is the risk?
If this was and old item of course I would replace with new , as was done originally.
Cheers Steve.

[christopher storey]

I am afraid that Joe's response is a latter day technician's response - if it doesn't work throw it away and replace it with a new one. . There is no particular magic to hydraulics and their repair : what is required is orderly working practice and a very high standard of cleanliness, with total replacement really only required where there is damage or corrosion to the metal parts . Replacing cylinders with new ones as a matter of course has in present days become hazardous on occasions, because aftermarket parts are often of very dubious quality . And, frankly , I would rather trust my own practices than those of some unknown assembler on a different continent

[Joes66]

Hey..
Sorry wasn't meant to be a rant
Kind of went on when writing it
Just trying to put across some long term learnt knowledge that's all
And trying to save people time and grief
Was trying to explain myself with the length of it :)
I did mention in the rant :) that caliper piston seal kits have always been the norm
For most the replacement of a brake cylinder will probably be a once in a car ownership lifetime
Or at least it should be with the low milage our cars do
Not going to get into individual cases or those that consider themselves more competent than manafacturers at rebuilding things
But for most due to the consideration of safety,time and lack of knowledge, simply replacing the entire unit for a new one is by far the best course of action
And also the least likely to cause problems
Its not about wasteful practice really, just the best way to go
I hope what I have said will help some
Simply that
Joe

[caveman]

Thanks Steve (MCGJAG), I’ll give it ago.
Didn’t want to try that test coming down the highland pass on Saturday
Q. If I do find no (pedal) change, what is the next step when it comes to vacuum system/servo/brake diagnosis/test? Apologies if this is already out there.

Joes66, my brakes wouldn’t put me through the screen let alone feel as though I can lock them up with hard braking, tried that with people pulling out on me on way to E60!

I thought Coopercraft front callipers might be more effective hence the thought of fitting green stuff pads after my latest heavy pedal feel when driving……

[abowie]

I am afraid that Joe's response is a latter day technician's response -

I can see both sides of this argument having both restored and maintained my own cars and also worked for a business that restores and maintains other people's cars.

We have had a lot more trouble with rebuilt hydraulic items in the past than we do with new stuff. Especially wheel cylinders, which very often leak after rebuilds.

Despite trying the gamut of different repairers available in town we continued to have the same problems. Part of this I suspect is that the skills for rebuilding old parts, like making horse shoes, have gone with the retirement of the old guard.

Regardless, when running a business you need the repair to work the first time, both to keep your customers, and to avoid having to rectify problems for free. Add to that that the cost of rebuilt parts is frequently higher than new and new are much quicker to get, it became an easy decision.

In general, unless the owner specifies, we would always use new stuff if it was available, especially in critical areas such as brakes. And if they did insist, we'd make it clear that we had far fewer problems with the new stuff than the old and that they needed to keep that in consideration when making their decision.

[whitesnake]

Just an update on original problem of servo not working.
Now after dismantling master cylinder I can see the small plate at the end of main piston that should push the small piston to activate reaction valve is not seating correctly and the recess it should fit in is not there consequently it just jams up and will not go forward to activate reaction valve. Another example of poor machining, this was a brand new master cylinder bought 3 years ago from a main supplier.
So it looks like I will have to fit replacement after all. The good side is I can now see the problem and leave the rest of the servo alone.
Steve.

[mgcjag]

Hi Steve......have a close look at the small flap that operates the reaction valve piston......the edges are flat one side curved the other as if its been stamped out........i found that it only works if fitted the correct way around....cant remember which way that is......so probably oposite to the way you have it that dosnt work....Steve

[whitesnake]

Steve,
Yes have taken out small plate and filed it round at the bottom so that it will slide better and it seems to work.
What I am querying is should the first piston spring go up to the plate or be held back in the bore as my spring is at the moment, to me it makes more sense for it to be forward onto the small plate to keep it upright as the main piston bears down on it?
Regards Steve.

[mgcjag]

Hi Steve...this post may help viewtopic.php?t=15322