20 replies to this topic

[Sovereign01]

Having just rebuilt the brakes (new rear cylinders + shoes, new front calipers, discs and pads) and used the Gunson eezibleed kit (at the recommended 20psi) on each wheel in turn until the fluid ran bubble-free I've found that the brake pedal travels most of the way to the floor when the engine is running.

 

My mini is of the single circuit type (the master cylinder looks exactly like the diagram in the Haynes Manual for single). Is this normal when installing new parts or does it mean there's air trapped elsewhere in the system?

[nicklouse]

Sounds like you still have air in there. Or you did not keep the MC full and you have let air back in.

Remember the level has to be kept above half full or you will uncover the ports.

[Sovereign01]

I checked the brake fluid levels and the reservoir was completely full, I'm using the Dot4 Mobil brake fluid.

[mk1leg]

check all nipples are tight and hoses joints also the 2 person bleeding is still the best way to bleed the air out

[cal844]

check all nipples are tight and hoses joints also the 2 person bleeding is still the best way to bleed the air out

I agree, also follow the proper bleed sequence

[Spider]

Are the brakes adjusted up?

 

I've found usually after fitting a New Master Cylinder, the Gunsons kit good at getting the bleeding process started, but seldom actually get all the air out with that alone.

 

After getting it started, I've found the old fashioned pump and bleed method best.

[Sovereign01]

I adjusted the rears as best I could, and the handbrake is tight enough. I didn't touch the master cylinder, I just changed the calipers and rear cylinders.

[minimans]

Use a proper hose clamping devise and clamp up the four corners, then try the pedal again. If the pedal comes up release one clamp at a time until the pedal drops again, last clamp off is the problem corner. Probably the rears. If you really have trouble, sometimes jacking up the offending end as high as you can will help chase the air out. And bleed the rears will a nice slow pumping action as the pressure valve will sometimes cause problems bleeding air past.

[Spider]

 I just changed the calipers

 

Have you got the Calipers on the correct sides?  Bleed nipples to the top.

[russo]

Also their is no mention of master cylinder being overhauled. Maybe you are getting air into the system via faulty seals in master cylinder. Especially if seals are travelling over the full section of master cylinder bore due to bleeding.  

[Twincam]

Check to see if any fluid is leaking via the arm going from the pedal to the cylinder. Mine was leaking only a little.

Also, I've found pumping the brakes physically and leaving and block of wood holding the pedal down overnight has worked for me. Might help?

[AlexMozza]

I have found in the past that air was able to travel up the thread on the nipple.
Could be that.

[spiguy]

I have had a similar strange situation before, where no amount of bleeding at the corners got rid of it. In the end, cracking the unions at the master cylinder and bleeding there (press pedal a little, crack union, close union, let pedal up) got it out. Strange, but presumably some air trapped in their that wasn't for moving. Has happened a couple of times.

[tiger99]

AlexMozza, you are totally correct. I keep telling people that but no-one seems to believe me. The way around it is the two person technique, one presses the pedal, the other loosens and then nips up the nipple with the pedal held down. Do that on each stroke and the air can't come back in.

The better way used to be a product called ABV which stands for Automatic Bleed Valve. I used them successfully on various cars including Minis. They were like a normal nipple except that the conical sealing end was fixed to a thin shaft passing up the bleed passage to steady it, with a small spring to hold it down. When screwed in tight it was held against its seating like a normal nipple and made a good seal. When loosened about one turn, it became a one way valve, fluid and air could come out but nothing would go back in. Loosen first nipple, pump pedal a few times, tighten, top up reservoir, move on to second nipple... Job done in less than 5 minutes. Why are they not made any more?

There is a more complex product from the USA where the valve is internal in the body of the nipple and there is a seal for the thread. Should do the same job, but not so elegant.

spiguy, I have often wondered about plumbing in bleed nipples on both lines at the master cylinder. That should do what you describe, but would be less messy. What do you think?

[AlexMozza]

AlexMozza, you are totally correct. I keep telling people that but no-one seems to believe me. The way around it is the two person technique, one presses the pedal, the other loosens and then nips up the nipple with the pedal held down. Do that on each stroke and the air can't come back in.
 

 

I have found a good, fast way, again with two people is that one person loosens the nipple and then applies pressure on the top of the nipple.

This forces the nipple onto the thread. The person in the car can then just pump away!

The finger over the nipple stops air returning into the system, but the force of the fluid will go around the finger, allowing successful bleeding of the system!