5 replies to this topic

[Richard_]

Hi all -

 

I now have my 1989 998 Racing green edition in standard trim running quite smoothly.

 

On switching off I notice a hissing sound coming from the servo which lasts about 10 secs then stops.

I disconnected the servo and blanked off the vacuum hose at the manifold end - and no hiss.

I have replaced the plastic vac hose with new rubber vac hose and something still hisses.

I haven't taken the car out on the road yet due to lack of paperwork so it's hard to assess brake servo operation.

 

Whilst the hiss is not a problem in itself - I wonder if I have a problem within the servo somewhere. Possibly the O ring seal against the brake master?

Does anyone know if this sound is normal? or is there a loss of vacuum occurring which might cause a loss of braking assistance?

 

Many thanks.

 

[RooBoonix]

It's not normal. Did you replace the rubber grommet/seal in the servo body where the vacuum pipe elbow attaches? Part no, NAM8569

[Ethel]

It's possible, the servo should hold on to its vacuum without the engine running. Roo's suggestion is the sensible place to start - you could also see if holding the brake pedal down makes a difference

[Richard_]

No - and it seems pretty wobbly in relation to the steel servo body. The old plasticky vac hose had gone very rigid.

Tried to buy one from minispares but couldn't find one. That part number should really help - many thanks.

[RooBoonix]

http://www.minispare...ic/NAM8569.aspx

 

Limited stock apparently. Cheap part, seems the most sensible place to start before digging much deeper

[Richard_]

Found the grommet on mini spares and ebay. Have ordered one. 

Brilliant super-fast assistance as ever from the forum - thank you!

Edited by Richard_, 26 April 2021 - 12:02 PM.