Brakes.......Where does the air hide?

[berni29]

Hi,

Does anyone know where the air hides in the braking system? I changed the master cylinder on my plus 2 recently, and cannot get it all out. I have left the car overnight with the pedal on the floor, bled the brakes to death and even pressurised the master cylinder to force fluid out (gently).

Also If the air is in the master cylinder do I have to bleed each corner each time I try to get a bit more air out, or is one corner (closest) ok?

Many thanks

Berni

[twincamman]

Im thinking you have a leak in the pipe system or at a fitting ----ed

[types26/36]

I have not seen it but I believe it is possible to fit the calipers to to the wrong side so the bleed nipple ends up at the bottom allowing air to remain in the system.Failing that if you have the the normal flexible brake hoses (not braided ones) try clamping each hose in turn to establish where in the system the air is trapped. I also believe some servo's need to be mounted at an angle to get all the air out.
Brian

[simon.mitchell]

Hi Bernie,

I'd suggest you get yourself an Eazibleed if you don't have one already. I had no luck at all trying to bleed my new braking systems the traditional way but after 5 minutes with the Eazibleed it was sorted.

Simon

[carrierdave]

Hi Berni,
I had great problems bleeding my brakes. The thing you need to have done was bench bleed the master cylinder before you put it in the car - easier said than done!!
Have you got a large sledge hammer? Is so take the lid off of the master cylinder and then push the hammer against the foot brake so that you have pressure on the pedal over night - Check the following day and hopefully most of it would have cleared.
Its all to do with the angle of the master cylinder as it lays in the car - air tends to get trapped at the back end.
Keeping pressure on it over night should help force the air out.

Dave

[berni29]

Hi All

Thank you for the tips. The calipers are on the right way up, and I did try leaving the pedal down overnight. Some air did come out after that, so maybe I need to do it again. I will get an Easibleed kit as well. I am not sure about the servo. I think that could well be a trap.

Thanks again

Berni

[Foxie]

Berni,

I too have been travelling this road.

Here are a few things you can ponder.

The fitting instructions for the Lockheed type servo specify the axis of the servo should be angled upwards at 25 to 45 deg. The air valve should sit at 4 o'clock and fluid inlet port at 8 o'clock.

The outlet of the servo is a high point in the system. Check this is bled by applying the brakes, and then cracking open the outlet union.

Check there is minimum run out/play in the discs, otherwise they knock back the pads too much, causing excessive pedal travel.

I measured 2mm of pull back on the front cylinders when the brakes were released. The pistons do not slide in the seals when the brakes are applied, they stretch out and back. I minimised this by fitting 4 lb anti knock back springs in the cylinders. (7 lbs gave a better result, put the pads made slight contact with the discs)

I find that up to three complete circuits of the bleed nipples are necessary to get a good bleed. For this reason I remove all the wheels and leave the car on stands.

The Eezi bleed is not so good by itself, it only uses a max of 20 psi. But in combination with the standard bleed technique it gives excellent results.
But be careful the cap does not blow off, you will have brake fluid everywhere.

Clamping the front brake flexibles give a great indication of whether there is air in the system or there is a problem in the calipers.

I have fitted a Tilton master cylinder, it has a horizontal outlet and a bleed nipple in the cylinder.

And I'm still not happy with my brakes.

Sean Murray

[patrics]

Hi Berni

You should have no problem bleeding the brakes on such a simple system ? unless something is wrong with one or more of the components. Also as long as you have someone to help you should need no special equipment other than a jar and a bit of hose.
Make sure that the brake pedal is returning fully allowing the master cylinder to recuperate.
The servo should be mounted at an angle.
Should have no leaks!
Starting nearest to the master cylinder open the bleed screw a ? of a turn only and get the helper to push the pedal fairly quickly to the floor and hold it down, lock off the bleed screw and let the pedal fully return. Repeat until you can see no more bubbles ? 4 or 5 apps
Do the next front then the rears.

Do not open bleed screw more than a ? of a turn and do not lift your foot off the pedal until the bleed screw is locked off other wise you will suck air back into the system via the threaded part of the bleed screw.

System should be fully bled but if you are not completely happy you could try the following but you will need a suitable tool to easily push the caliper piston back.

Remove the out board pad from one caliper (opposite side to bleed screw).
Gently push the piston out ? enough so that you can still get the piston return tool in.
Using the jar and hose open the bleed screw as before and push the piston fully back in to the housing and lock off the bleed screw.
Refit the pad and bleed that brake the standard way ? should only need one or two pumps.
Do this to all four calipers. If you have rebuilt the calipers wet you shouldn?t need to do this, actually if you have rebuilt them dry you shouldn?t have to do this but it?s an uncertain world!

The pedal should feel firm but on the second application it should feel shorter still, as the pistons will not have had time to recover. The amount the pistons moves back should be approximately 0.1mm.

Sean
I can not believe you have gone to such lengths. - Measures that weren?t needed when new aren?t needed now. Something is wrong ? Piston material, Piston diameter, fluid or build, but you have a problem which wasn?t there when new.

Hope this helps
Regards
Steve

[phatmendus]

I too am trying to bleed my breaking system. I read the posting just above this message, and it says to bleed the brakes starting nearest the master cylinder. Is this correct? I always thought you started furthest from the MS and worked your way back. Could somebody let me know what is the correct, or even the best way as I have got 'half' a pedal now but recon a few more attempts will be needed to sort it out.

Thanks

Simon

[types26/36]

I also read this and it is contrary to everything I have ever heard/read, I did a little more reading and from what I since read apparently there are different paterns for bleeding but it is usually associated with the the system used, ABS/anti-lock etc. Front wheel drive can be different to rear wheel drive (starting at the front) and I assume that as to do with brake bias with a FWD vehicle.
As Elans are RWD from what I understand/read bleeding should start at the furthest away from the master cyl.
Possible there is a reason so maybe Steve can explain why he recommends to start at the nearest.
Brian

[patrics]

Hello Simon and Brian,
I would start on the nearest or primary brake on any car as it makes the system stiffer which means you will push more fluid through when you do the other brakes. The reason why you might have read different ways to bleed is down to the system split.
Standard Elan has no split as primary feeds both front and back so you bleed the system nearest m/cyl then other front then any rear.
If you have dual system Elan then primary feeds both fronts so bleed both fronts then any rear.
If you have a modern front wheel drive car it will be X split so bleed the primary ? a front and diagonal rear. This would traditionally have been ?Primary feeds crown of the road? but now primary normally feeds left front and right rear.
Do not get to hung up on which to bleed first as the master cylinder has enough capacity to bleed a previously wet system no matter where.
If you bleed the system as I have said then you will get a good bleed but on a dry system that out board piston is important.
There is another but
I believe high piston roll backs are possibly responsible for the perception of air in the system and this is an issue with either: piston diameter / material / build or fluid used.
Best Regards
Steve