10 replies to this topic

[maddogmcg]

Hello

Car spec  1993  mini sprite , engine 1330 cc stage 3 head hif44 carb 276 cam .

During my recent MOT ( car passed ! )  we noticed the engine revs changed and mixture dropped significantly  , from 6.5 to 1.6  CO  .When pressing brake pedal .

The tester suggested  a leak between servo and manifold causing unmetered air to enter manifold and weaken mixture .

 

I have yet to check for leaks  , i fitted a new master cylinder and rebuild the servo with a new seal kit before taking it for test .

 

I am asking if anyone else has had a similar problem and what was the cause  .

 

Thankyou

 

Neil McG

 

 

 

 

[Ethel]

It's possible, would have been handy to remove & block the hose while the gas analyser was attached.

 

The servo should hold vacuum for a good while with the engine off. This should be noticeable through the pedal and heard if you pull the the hose connecter from the servo body.

[maddogmcg]

Thanks Ethel

As hoses are very rigid its not easy to just pull one off its connector ,i removed the rubber grommeted pipe on the servo itself and there was still vacuum in unit after 2 hours of engine being turned off . im just gong to take car out for a spin and investigate leak .Ivw been wondering if it could be something to do with breather hoses but as it seemed related to presssing brakes it surely has to do with servo connections .

[andyapanel]

I had the grommet fail on the servo unit just before an MOT, causing the engine to hunt. If I wiggled it, the air leak was cured. I would check that before rebuilding the servo.

Good luck

[maddogmcg]

Thanks Andy

the servo rebuild kit came with a new grommet ,ive just removed the connection at the grommet and put my finger over it ,there is plenty of vacuum and the engine ticks over at less revs than when its connected and brake pedal pressed .

 

Everything points to the servo leaking somewherre ( ive checked the o ring between servo and master cylinder ,its new also ) .

 

Neither of the main mini parts suppliers have the newer servo in stock ,but ive seen plenty similar ones on e bay for land rovers and are less than half price of a mini one , anyone know if they are compatable .

[T.Harper]

Think BullMotif sell the new one for about £150.

[maddogmcg]

They advertise them but dont have stock

[MiniJosh92]

Not particularly helpful but I had exactly the same issues after fitting a rebuild kit to a servo. Ended up just fitting another used servo just to get out of trouble.

[weef]

Kind of sounds that a leak exists across the main diaphragm when the brake peddle is pressed allowing the air drawn in on the brake peddle side to pass the internal valve that isolates  the two halves of the diaphragm when the peddle is pressed. This more or less provides a direct path between atmosphere and engine inlet manifold. 

Suggest you strip and check the integrity of these components as brake performance will be compromised if this condition persists.

[maddogmcg]

I'll be the first to admit mistakes can be made ,i did rebuild it very carefully .maybe i didnt do something right .

I had a feeling this would be the next step ,i might be able to devise somesort of pressure test once its off the car .

Once its sorted i will post .

Thanks for the advice .

[weef]

Tee a vacuum gauge between the servo and the inlet manifold, servo side of the one way valve. Start the engine and note the gauge reading, this should indicate a healthy vacuum at idle, you may need to restrict the gauge pipe to smooth out the engine pulses, if the system integrity is intact . Now press and hold down the brake pedal. The gauge reading will initially dip then regain a reading close to the original if all is well. A low reading indicates that air is being drawn from the atmosphere side of the servo. Now release the brake pedal and observe the reading. It should return to that of the first. Stop the engine, the vacuum reading should be maintained, almost indefinitely, if not start looking for leaks.