Brake pressure increases rpm

[Concrete-crusher]

Hi when I was having the Mot test last week , we got to the part where you hold down the brakes. I noticed this caused the rpm to increase by about another 300 rpm

Can anybody tell me if this is normal , or is it a symptom of an vacume leak or something

Elan s3 with webers


Thanks in advance.

[Elanconvert]

not normal on mine....

could be pedals interfering...?

oversize shoes...?


ok not helpful, I know.....

fred

[AHM]

Not normal - It is a symptom of the air valve not sealing.

What type of servo?
How hard were you pressing?

[Concrete-crusher]

Hi thanks ,it's a replacement servo bought new from Christopher Neil about 15 years ago , the cars done about 300 miles since then as it's been stood up , so I'm not surprised if something is sticking.

I was pressing the pedel hard

Is it something that will cure , or is it likely to get worse ?

Steve

[AHM]

,it's a replacement servo bought new from Christopher Neil about 15 years ago

What type of servo would that be?

[Concrete-crusher]

Here is a picture , as I'm not sure about types.

[rgh0]

Sounds like an air leak in the servo vacuum control valve when it is activated by the brake pedal leading to air leakage into the engine via the servo vacuum line

cheers
Rohan

[Concrete-crusher]

Thanks , one last question , is it a user serviceable part , I ask because I tried servicing the original servo with the service kit , and it never worked again , hence the replacement all those years ago.

Steve

[rgh0]

The servo is user serviceable if you can get the kit of parts and have the needed skill to rebuild properly. Probably easiest to find a professional to do the rebuild if not confident you can do it or cant find a rebuild kit.

cheers
Rohan

[types26/36]

You could try these people for a kit although I have no experience with them.
http://www.powertrackbrakes.co.uk/brakes.html

[Europatc]

Hello Steve, I have used Powertrack over the past 3 years for all my brake parts. Their service is first class and so far they have always had the parts in stock. I don't recommend people or services readily but they are first rate. Im just a very satisfied customer and nothing more
all the best
Stuart

[AHM]

The air valve controls the amount of air that is let into the pressure side of the chamber.

When there is a positive pressure differential on the fluid side it lets air in and a negative pressure differential it opens to the Vaccum side and sucks air out - When the fluid pressure is at equilibrium both sides of the valve are closed - this is how it applies pressure in proportion to the pedal effort.

Try using it - It may improve.

Do the revs increase at lighter pedal pressures? Is the servo providing any assistance?

[john.p.clegg]

"could be pedals interfering...? "

Maybe the shaft is a little tight and pressing the brake moves the accelerator ??

John