How to check servo?

Post Tue Mar 08, 2005 6:57 pm

How can I check my servo is working correctly, i.e. no air leaks and is applying full pressure to pads?

I just want to check this out before I jump to conclusions and bin my EBC.

(OK I know Pagid come out tops anyway in the poll I did earlier, and so thats what I'll buy if my servo is working as it should. My thinking is that if the servo is dodgy then no manner of new parts would solve the problem.)

Post Tue Mar 08, 2005 7:31 pm

Once you switch the engine off, you should still be able to pump the pedal a good two times before the vacuum in the servo becomes depleated.

Once you've exhausted the vacuum, press the pedal down (it'll be quite hard by this point) and restart the engine. The pedal should drop by a noticeable amount.

All that's if the servo's working

Post Tue Mar 08, 2005 7:33 pm

engine off pump brake pedal until its harder to push( 6 pumps ish)

hold pressure on brake pedal and start engine, pedal should sink about 1/2 inch or so.

asuming you get as described above then the servo is working as intended.

whats the issue anyways ?

Post Tue Mar 08, 2005 7:34 pm

My way of checking is to pump up the brake pedal until it goes hard

Then start the engine, keeping your foot on the brake, if the servo is OK you will feel the brake pedal drop as the pressure drops away.

Can't comment if it's an accurate test or not, but seems to have worked for me in the past.

Post Tue Mar 08, 2005 7:58 pm

Good enough for the VOSA/VI and MOT, good enough for us :lol:

Its the only way to test these babies.

Post Tue Mar 08, 2005 9:34 pm

Cheers for the tip - I just did the test and it sort of passed with a C+.

Does the valve from the servo to the inlet ever need replacing?

Reason I'm asking is that I just can't believe that the "upgrade" pads I put on are no better than the worn OEM I took off and I want A+ braking performance!

Brake set up is: New BMW discs, EBC greenstuff pads, stainless braided brake lines, and new fluid.

Post Tue Mar 08, 2005 9:43 pm

There are a couple of valves from memory. Both shaped like little 3/4" dia cones in the servo line. However, if they fail, oily fumes from the engine can get up to the diaphragm and cause it to perish

TBH, I've heard mixed reviews of EBC pads from them being great, to the friction material falling off the backing within 1000 miles!

My opinion on the braking system in these cars is that there's too much car for the brakes. The front discs are designed to fit into 14" wheels which means they're pretty tiny out of necessity. Fitting bigger wheels doesn't necessarily impose any greater stresses on the system as long as the rolling rarius is kept pretty much the same as standard, but bigger wheels do provide the opportunity to fit bigger discs etc

Post Wed Mar 09, 2005 8:50 pm

I'll see if I can get new valve(s) then, and assuming that the servo isn't alreadty shot will see if that makes any different. Then I'll look at the pads and maybe try Pagid, and leave the servo till another attack of DIY diagnostics. My thinking is that any shot valves would make the system work inefficiently.

The valve(s) are a concern as I think the whole breather system (i.e. ICV / Servo/etc) may not have been breathing as freely as it could so that could have damaged the valves with carbon build up.

I cleaned the breather hoses out last summer, and they were completely blocked! Literally whole lumps of carbon came out, particularly from the pipe that runs from the rocker cover, and out under the manifold.

One other thing (starting to ramble now!) My pads/discs were changed on my day car today (320dES) and they have not yet bedded in, but as I drove home they felt just like the EBC on my E30 do... So I'm wondering if the EBC were not bedded in properly? My E30 is a second car and so dosn't get heavy use. Is there anything I can do to bed in or is it too late?

Thanks for everyones 2p! Gut feeling? Get some pagid.

Post Wed Mar 09, 2005 9:43 pm

anyone know how much a new servo is, cheers

Post Wed Mar 09, 2005 9:53 pm

remember that some pads need some heat in them to work at their most effective so they won't stop so well from cold.
"some heat" sometimes means that for the pads to be hot enough you should be able to smell the stench from inside the car whilst you're still driving
edit: for what its worth greenstuff didn't used to be any better than oem, just less dust.

Post Wed Mar 09, 2005 9:57 pm

Re: bedding in. If the pads have glazed over, you can pop them out and take the glaze off with some 80grit paper on a flat surface if that's any help?