Brake hose replacement questions

[nick_the_fish]

I think this was answered above but because it's the braking system I want to be really sure I am doing the correct thing.

As you can see below one side of the reservoir has emptied and the system has drained. Can I just refill the reservoir with fluid then bleed as normal with a vacuum bleeder (topping it up as I go)? Or do I need to bleed the master cylinder in some special way?

There is no abs, and it's a vacuum booster, if that makes any difference.

Sorry to ask a question thats already been answered but id rather be safe than sorry.

 

[Chris]

Nick, sometimes you can be lucky, but technically speaking you need to expel air that is sitting between the seals in the MC. Personally, I'd fill it up, use the vacuum bleeder and see if you've been lucky first.

 

[nick_the_fish]

Ok thanks Chris. How will I know if I have (or haven't) been lucky?

 

[Chris]

Is it steep where you live Nick? You'll know.

 

[nick_the_fish]

Ok, had a change of plan. Think i'm going to bleed the master cylinder anyway, its a good excuse to learn how to do it in the comfort of my own drive rather than in the middle of the desert somewhere where there is no youtube.

As I understand it there are 2 methods for bleeding the master cylinder while it is in the car - first running a short length of clear tube from the MC outlets back around into the reservoir, then filling the reservoir with fluid and pumping the peddle until no bubbles come out. Or second, running a long length of clear tube from the nearest calliper up to the reservoir and pumping the brake peddle.

Is this correct? and any thoughts on the best method.

Also, as I understand it you need to bleed the MC first, then bleed the brake system?

 

[Chris]

You can also take the output pipe off, put your finger over the hole, lightly, pump the pedal so that fluid squirts out then press hard whilst the pedal is let up again. This forces a draw on the reservoir rather then from up the pipe. If you use a pressure bleeder rather than a vacuum bleeder you can typically eliminate this issue. However, getting a pressure cap for a Cruiser is a bit like finding a Unicorn holding the Holy Grail. Some people have, I know, but I've never suceeded.

 

[nick_the_fish]

OK, Thanks Chris. Presumably I would need to do it on both output pipes if I used that method?

And as I won't be able to watch for the air to stop coming out as I would with a clear tube back into the reservoir, how many times would this need to be done to ensure all the air was dispelled from the MC?

 

[Chris]

Sorry Nick I can't answer that. My system was different I guess, but I only pumped it about twice iirc. There's not much volume in there to begin with. I didn't look for air bubbles as the fluid was just spurting out into the engine bay. If you can shove some tube in and put the end in a jar of fluid, I'd think it would work quite well.

 

[nick_the_fish]

OK, Bled the master cylinder which seems to go well. Then bleed the rear brakes which, again, seemed to go well.

However i've come to do the front brakes and its taking a LONG time. Bear in mind i have put new callipers on so presumably I need to fill up the cylinder in there, but when I am pulling through with the vacuum bleeder there is this foamy looking mix of brake fluid and air and I must have pulled through 300ml of it so far and it doesn't seem to be getting better.

Am I missing something?

ps. I am sure i'm getting a good seal because i can close the bleed nipple and depressurise the vacuum bleeder.

 

[Chris]

Suck don't blow...
Sounds odd Nick. If you start your new pistons pushed back into the caliper then there's only a teaspoon of fluid in them. Sounds like air getting in somehow. I wouldn't use 300ml to fill and drain the whole system from scratch. Well not much more.

 

[nick_the_fish]

Yeah thats what i thought. The fluid is coming out cloudy, but quickly goes to normal fluid so it seems like there is a tiny gap somewhere letting in tiny bubbles which is making the fluid cloudy. It's the same on both sides, so i'm guessing its upstream of the fork. Either at the master cylinder or at the new braided axle to chassis line. I'll have another look in the morning.