Unable to bleed brakes - is this due to ABS?

[gekkoa]

I changed a rear Brake Cylinder on my Daewoo Nexia GLXi and then tried to bleed the brakes and was unsuccessful.

When I push the brake pedal down air is expelled but when i release the pedal the air is sucked back in. If I push the pedal down and clamp the brake-pipe and then release the pedal when I undo the clamp the air sucks back in.

Am I having this problem because I have ABS brakes? Please, someone, tell me what to do.

 

[Hitachimad]

Do the bleed nipple up before you release the pedal.

 

[noonespecial]

Or use one of the one man pressurised bleeding kits which connect to the spare type valve. They make the job very easy.

 

[gekkoa]

HITACHIMAD, if I do the bleed nipple up before releasing the pedal, when Inext undo the bleed nipple the air rushes back in - in other words, I am bleeding properly but the system is not behaving properly.

NOONSPECIAL, am interested in the 'pressurised bleeding kit' but would like to know what & where the 'spare type valve' is.

 

[noonespecial]

HITACHIMAD, if I do the bleed nipple up before releasing the pedal, when Inext undo the bleed nipple the air rushes back in - in other words, I am bleeding properly but the system is not behaving properly.

NOONSPECIAL, am interested in the 'pressurised bleeding kit' but would like to know what & where the 'spare type valve' is.

Have a look at:
http://www.mgocaccessories.co.uk/acatalog/Gunsons.html

or you can buy them at Halfords etc -sorry should have been spare tyre valve eg the valve on your spare tyre.

Alternatively - when you are using the manual push pedal down method, have you been fitting a length of tubing from the bleed nipple to below the level of some brake fluid in a container? If so I do not see how you are drawing air in??

 

[gekkoa]

Thanks for that Noonespecial - but am not too sure as to where (which bleed nipple) pressure should be applied. I wonder if it wouldnt be better to have a vacuum to draw the fluid thru to the rear cylinder. I wonder if you could clarify this.

A mechanic friend of mine has been doing the bleeding whilst i've been pushing, pumping and releasing the pedal. I have every reason to believe he is competent and is doing it properly although he admits he has never bled ABS before.(Is blleding ABS a fundamentally different process?) I assume the tube is low enough but i will double check on this.

 

[noonespecial]

The system is simple it comprises:

1. A special cap which is temporarily screwed onto the brake master cylinder in lieu of the normal cap.
2. A tube which goes from the cap into a special plastic bottle.
3. A tune which goes from the plastic bottle to the spare type valve.

You fill the plastic bottle with brake fluid. The air from the spare type pressurises the bottle / brake fluid contained inside and the complete brake pipework system. You open the bleed valve on the wheel cylinder and old fluid is forced out by the air pressure and is replenished automatically from the fluid in the plastic bottle. All without pressing the brake pedal. Therefore it is also a one man job.

If on the other hand you are bleeding the brakes manually by depressing the brake pedal, you must have a tube run from the nipple you are opening and into a container of brake fluid. Then if the brake system sucks back it will draw in bake fluid and not air. If you do not have the tube submersed in brake fluid then you will draw in air.

 

[gekkoa]

Hi Noonespecial,

1)Pressurised bleed does sound more simple now it's explained to.Thanks. But just wondering where the cap is on the Master Cylinder - there are 2 pipes exiting the master cylinder - are we talking about detaching one of these and attaching the pressurised bleeding device here? I notice on the other side of the engine there is a more sophisticated component which has brake pipes going into it (as well as some electronics) - this has 2 bleed nipples on it ( marked R(ear) R(ight) Fl and Rl Fr). Not sure how this relate to the system and if these should be bled or whether they should be left WELL ALONE.


2)You said earlier you do" not see how you are drawing air in??". Sequence is as follows -
depress pedal - air ejected - bleed screw tightened - pedal released - pressure applied to pedal but no (or very minimal) compression - bleed screw released - air wooshes back in.

My friend said there was no point in sucking brake fluid back in as it will just push out again when the pedal is pushed again and bleed screw is released (maybe we should have given this a go).

The quality of the old brake fluid in the top up chamber is slightly different from the new brake fluid -they are not mixing very well. We think there is a possibility of a small amount of a foreign fluid in there (engine oil? water?). We have comnsidered the possibility that this is causing a master cylinder blockage.

3)Finally I found this info on the Net - "Vehicles fitted with' rear bias brake valves' will not bleed properly when the rear wheels are hanging freely". Does my Nexia maybe have ' rear bias brake valves' and is this what is causing the problem?

 

[noonespecial]

cap on the master cylinder is the screw cap through which you poor the break fluid and check the level. The Easibleed unit comes with various caps to which the tubes are attached. It may be though that it will not include a suitable cap for your car as standard. If not you may be able to get one from Easibeed or if not you can get one from the manufacturer, drill it and attach the tubes.

It sounds as though your friend does not know what he is doing. If you don't have a tube from the nipple into brake fluid then you are bound to draw in air. Think about it.

I think you need to read up about brakes, bleeding and what all the components do a bit really before you try the things I have suggested to you and before you do anything else to the brakes.

 

[gekkoa]

Successfully bled brakes using Gunson EAZIBLEED as recommended. Many thanks Noonespecial. In the end it was a simple and straightforward process.

 

[special stage]

Hi Guys i used a one man bleeder that i got of ebay.

http://cgi.ebay.co.uk/Brake-Bleeder...25953QQcategoryZ30917QQtcZphotoQQcmdZViewItem

Cheers.

Chris...