Servo/ Master Hissing

[Guest bloke]

any one else experience this?

 

seems 2b coming from small opening on bottom of master where meets servo when brake pedal is pressed??

[chris27]

Hi Mate

 

seems like you've got a air leak in the servo . I had the same happen a few weeks ago. A quick trip to the scrappies and about £10 should sort it

[Big Jim]

When you say "it hisses" do you mean, all the time, when you press the pedal, or when you release the pedal?

[Guest bloke]

brakes are rock solid but when you press the pedal it hisses/ sighs a bit

 

before the fluid was in the brakes it was more pronounced

 

had a look at the junction between the servo and master and there seems to be a small appeture in the middle?

 

if the servo leaks, then the vacuum is affected, would this make the efi lump run non smooth/ hunt/ cut out at idle?

[Guest chris brown]

if the servo leaks, then the vacuum is affected, would this make the efi lump run non smooth/ hunt/ cut out at idle?

In a word "yes" as you are sucking air directly into the manifold. cant remember if there is a seal (O ring) between master cylinder and servo. Haynes no help. if there is not then as Chris says a trip to the scrappies is called for but if there is suposed to be a seal the try replacing it.

[Guest rizla]

cant remember if there is a seal (O ring) between master cylinder and servo.

 

yep there is meant to be a large 0 ring there chris

[Guest chris brown]

thanks Riz

[Guest bloke]

cheers chris27, jim, chris an riz,

 

off to the garage to have a look

 

had a look and seperated the master from servo - no o ring between?

 

when brake pedal pressed, same noise and a fine jet of air comes from the servo apperture (now open as master seperated) -do you think this means the servo's dead?

 

will try blocking the vacuum pipe by replacing it with a bolt in the plenum to see if the lump will idle soon...

[Guest bloke]

any ideas...?

[Guest Phil Slater]

I've had a similar noise and tried the bolt in the hole test and it didn't make any diiference to the lumpy idle - so I'm not sure if the hiss is evidence of a problem . I traced the lumpy idle to a faulty throttle control valve sorted that out with a replacement from the scrappers.

 

Having said all that I should point out I haven't tried the brakes in ernest yet.

 

Phil Slater

[Guest bloke]

cheers phil, yep bolt in hole (spare sump plug) to no avail!

 

how did you trace your engines prob to the throttle control valve?? i would like to sort the coughing lump to a clean brum...

 

was wonderin if the hissing is the servo balancing to atmospheric pressure or something??

[Guest Ant]

A couple of suggestions. First off seperate the engine hunting problem from the servo hissing problem (if it is a problem). Block off the vacuum outlet _completely_ on the manifold (PTFE tape on the bolt is probably needed) and then approach the idle problem. Unusual running and hunting at idle is down the the air bypass valve 99% of the time.

 

All servo's hiss when the brakes are actually applied as the vacuum is "used up" in helping you to press the pedal.I guess this is where Jim's question is leading to.

 

With the servo line disconnected suck some air out of the tube and hold a bit of a vacuum in the servo. Lung power is sufficient. If it holds the vacuum then its fine. If the vacuum disappears within a few seconds then your servo is faulty.

 

A question about this seal too ... There's no air or fluid passed from the cylinder to the servo or vica-versa why fit a seal? I don't understand that bit.

 

Ant

[Guest Phil Slater]

I had exactly the same thought, that it could be the vacuum equalising once the engine stopped.

 

With regards to the idle problem, it was a process of elimination really.

 

Using the info in the files availalble from the NW hoodies site I used a multimeter to check the throttle position sensor and the air flow meter. I was fairly certain they were OK. With Longboaders help we came to the conclusion that as the engine was "hunting" it was running too rich and assuming the engine management chip was OK that implied the idle contol valve might be involved. I did all the soaking in solvent etc, as recommneded, to clean it, but it didn't help . So, in the end went and got a replacement from the scrappy. It didn't make the slightest difference :angry: :angry:

 

I then separated the solonoid from the valve on the replacement unit and found it was dead. As the valve on the replacement unit looked in better nick than on the original we took the working solonoid off that and in retrospect made one good'n out of two badn's, as the car ticks over relatively well now. In comparing the two valve sections I think the end "cover" of the shaft from the valve that is operated on by the solonoid was damaged and causing teh problems.

 

I hoping it just needs a bit of fine tuning of the idle mixture I to get it "perfick".

 

HTH

 

Phil Slater

[Guest Battery Bill]

Bloke

If you decide you need a servo, are you going to Stoneleigh because we have one you can have.

See we are nice chaps arn't we Ant

[Guest Simon cooper]

Hi Bloke,

I give you my 100% guarantee that you servo is stuffed!!

There is a seal that is not replaceable inside the servo that has perished. The servo is sealed and you cannot get into it. However, although not naughty but if the MOT man sees it, it is a fail, but run a fillet of silicone around the joint master to servo and smooth it with a wet finger. WARNING !!!! Do not run the engine till the silicone has hardened. He He.

This is perfectly safe but ultimately you need a servo.

Just as a mater of interest, it was also common on the old Montego's and Maestro's, but you could buy a kit for £4 to fix it, I think old henry wants a ton plus for a new one.

All the best

Simon