How can air disappear by itself from the

Brake Bleeding - V50 1979
In the official workshop manual, one can read: “Should the brake pedal for The dual brake system not be 100% firm - then drive for some time - and normally,the system will stiffen up by itself”

How can that be?
Does any of you have a good explanation about such “miracle”??

Presumably they are suggesting that trapped air may work it’s way back up the lines and into the master cylinder reservoir.

One technique for removing trapped air after bleeding is to leave the bike overnight with the brake lever pulled back against the bars.

I presume this is something similar.

It is kinda true that the air bubbles will travel UP the hoses to the master cyl…BUT if you put the fluid in by syringe (Or similar) from the caliper to the mast cyl it pushes the air up and out, cover the master cyl with a cloth as it does squirt out

After rebuilding the calipers, they can sometimes take a while to get the pistons sitting in just the right place. They can stop a distance from the disc and need a greater distance of push to get them to contact. This will ease of with a bit of use as they settle down. Tying an elastic band around the lever, or a brick on the pedal overnight will have the same effect

I’ve never worked out how pressure can remove air bubbles from a sealed system.It is also true that after rebuilding the braking system, you probably will have put in new pads. These take a little time to bed into the discs, and may feel a bit spongy while this is happening.

Guess your right…

What Don said it’s the pistons and pads settling. Especially true if new pads, they need to bed (wear down) onto disc properly, this can make bleeding especially difficult if you put new pads in first, this means you also disturbed the pistons so they’re slack as well, it’s often amazing how the feel hardens up after the first few miles thereafter. Incidentally can be the same for cars, when my old Ford had new discs and pads on the back it took a month for the brake pedal to go hard again. HTH Appendix (edit): remember the pistons are self adjusting and ‘otch’ up to the disc as the pads wear down, the seals sort of act like springs and pull the pistons back slightly when released so that the pads are free, BUT if have been disturbed then will have some extra slack to use up so won’t be quite there yet until have been used a bit. Hope that makes sense.

Mike H2014-01-13 16:47:15

Me neither. I’m not advocating it as a procedure. I’m just offering it as an explanation for the advice he was given.