Bleeding the brakes

[A3car19tdi]

Following repair of my abs ecu block,and putting in new fluid  I'm having trouble getting a good brake pedal. I have bled 2 times this week and I have heard I need to cycle the abs pump as the pedal is still soft. 

Not having software to use computers etc I have read that I can activate the abs brakes  on Grass etc to get air out of the unit and bleed off again after that. Maybe a couple times.

Is this correct ?  Should it work?

 

Thanks 

 

Edited December 16, 2021 by A3car19tdi

[Steve Q]

Even if this is true, how close is the grassed area from your home? I'd be careful. 

[A3car19tdi]

Brakes are ok I just have to press the pedal a lot further down .  No trouble stopping as such like that. Car stops normally.

I've done it on a load of gravel now so I'll bleed and see what comes . Abs was working well for sure!

[Magnet]

Hello Dan, 

Have you bled these brakes by having the engine running and getting an assistant to rapidly pump the brake pedal until it is as hard as it can be? At that precise moment, you open the bleed nipple. Repeat on each wheel - starting with the furthest away from the master cylinder. 
Perhaps you could let us know if you have, and how you get on if you haven’t. 
Kind regards,

Gareth. 

[A3car19tdi]

Hi.

The engine was not running. 

We used a one way bleed pipe, I put pressure on the brake pedal then the nipple was opened so the pedal goes down. I slowly pumped up and down 7 or 8 times perhaps 10 or so. Then held down pedal then nipple locked off. All in all done each nipple 4 times now I think all the time keeping the tank topped up. 

A bit different to your method ??? What do you think ?

[cliffcoggin]

There is too much potential for sucking back air through a one way bleed pipe to convince me it is a reliable method. If the fit of the pipe on the nipple is poor, air will be drawn back. If the thread on the nipple is worn, air will be drawn back. If the check valve is sticky, air will be drawn back.

The only reliable manual bleed method I know of is a two man operation in which one presses the pedal while other wields a spanner on the nipple. In essence: fit a hose to the nipple with the lower end in a clear glass jar, loosen the nipple, press the pedal to the floor and hold it there, tighten the nipple, release the pedal, top up the reservoir. Repeat until air bubbles can no longer be seen emerging from the hose. The spanner man controls the process and commands the other when to raise and lower the pedal using clear orders like "up" and "down", which the pedal man repeats when he has carried out the order.

There are various pressure and suction systems available which can automate the process, but having never used any of them I can not comment on their effectiveness.

You are rightly concentrating on getting the air out, but have you considered that the spongy pedal may be caused by defective seals in one of the cylinders?

[A3car19tdi]

That is the method we essentially used. My dad is a mechanic of old. He was the spanner man issuing destructions. The only difference was the one way valve in the pipe dropping into the Jam jar full of fluid. The brakes were perfect before I removed the abs unit for repair so I'm guessing seals are still all ok. 

Popped it back on the other day and commenced bleeding and the only logical conclusion is air somewhere still.  Could be the one way pipe but he knows what he's doing down there. 

 

[Magnet]

Hello Dan, 

I too would forget about fancy one way valves, and indeed a procedure which is   essentially  what you have done. 
I would still follow my procedure (and apologies for repeating ) :- engine running to assist servo operation. 
Your Dad gets on the business end with the spanner, and a tube (with one way valve removed -to minimise restriction of flow) over the nipple and the other end in a jar. 
Your job is to pump the pedal until it is as hard as you can get and at this point, you shout HARD to your Dad. This is his queue to open the bleed nipple to force the pressuring fluid out. He then quickly retightens the nipple. Repeat this say four to  five times in a row at each wheel. 
Top up fluid, and repeat at other three wheels - ending up at N/s front. 
If this fails then a trip to a garage to get it vacuum bled. 
Let us know how you get on Dan. 
Kind regards,

Gareth.