Gravity bleeding brakes - more info please

[mattsplatt]

Hello,
(My first post here, after many a time over the years finding the answers I needed already here... thank you everyone)

I swapped a rear caliper the other day on my NA6 and let the master reservoir run dry. (how the heck do you block that rear brake hose properly anyway?)

I searched online for info about air bubbles, am I likely to have to bleed the whole system due to this, etc, etc and ended up here reading that it's possible to gravity bleed an MX5.

Tried it (just one rear corner) and it didn't work. I wasn't really expecting one corner to work, even though others here have said you can do one side or one end at a time. I am guessing this has to do with the brake proportioning/isolating system. Can someone please explain how that works, and would you normally expect to be able to bleed just one rear corner?

The corner was about 50mm above being level with the rest of the car, so I don't think that would have been a big problem.

Thank in advance!

P.S. So I bled it to that corner with the pedal, and it feels fine, but I want to do the other rear caliper and flush the whole system in the near future.

[ja9]

Hi Mattsplatt and welcome,

I'm wont be answering your question exactly but I do have the best way for one person to bleed their brakes. They're called Speedbleeders. They come from the US and are relatively cheap to buy. Google it to get all the info you require and Youtube so see how simply it is.

Regards - John

[deviant]

Speedbleeders need to be used with care. There are a few threads on here with people having problems with them weeping.

[hks_kansei]

Also if you've run the master cylinder dry it's likely that there's air in the lines up closer to the master as well (and maybe in the lines leading to the other calipers)

Best bet is to bleed the whole system, it's also a good opportunity to give it a flush since it's likely never had a fluid flush. (usual bleeding method, just pump a whole bottle through, then use another bottle for the actual bleed)

[project.r.racing]

If the master has been run dry, you need to bleed all four lines.

If you ever to do this sort of job again, either buy line clamps or caps from an auto stop, they are cheap as chips. or use a broom handle and just press the the cylinder slightly creating press and locking the fuild into the system.

What you did by dissconnecting the caliper and leeting the line drip dry is basicly gravity bleeding.

[mattsplatt]

What you did by dissconnecting the caliper and leeting the line drip dry is basicly gravity bleeding.

Yes, but it bled out, not in. :-) That line refused to refill by gravity alone. Even an attempt to get it started with a bit of suction failed.

So is there something about the proportioning/isolating valves that prevent a single corner from being flushed/bled by gravity?

[NitroDann]

Not in my experience but if you have big bubbles it wont happen, kind of like siphoning.

Get a length of clear hose and suck the fluid through.

Dann

[project.r.racing]

What you did by dissconnecting the caliper and leeting the line drip dry is basicly gravity bleeding.

Yes, but it bled out, not in. :-) That line refused to refill by gravity alone. Even an attempt to get it started with a bit of suction failed.

So is there something about the proportioning/isolating valves that prevent a single corner from being flushed/bled by gravity?

of course it bled out. dunno how it could go dry if the fluid went in/up.

doubt you get a line to refill by gravity alone, just not enough pressure vs air pockets ets. i'd use the brake pedal to refill the line.

and if doing the job by yourself. broom handle wedged between the pedal and seat backrest should hold the pedal down in place while you screw up the caliper nipple.

[mattsplatt]

What you did by dissconnecting the caliper and leeting the line drip dry is basicly gravity bleeding.

Yes, but it bled out, not in. :-) That line refused to refill by gravity alone. Even an attempt to get it started with a bit of suction failed.

of course it bled out. dunno how it could go dry if the fluid went in/up.

Yes, yes. I know. :-) I was only referring to your suggestion that it gravity-bled like I wanted. ;-) Never mind...

Of course a line that's sucking air will run down more easily than one which is sucking fluid.

Thanks for your replies, all. No one has suggested there's a designed system to prevent the thing flushing to one corner by gravity. There must simply be too much resistance and not enough weight of fluid unless as least a couple of corners are opened.

I'll flush the whole works when I get a sec.

Just to be clear about the references to using a broom handle to hold the pedal down; If I'm flushing all corners together by gravity, the broom handle is not needed - the pedal can stay up, yes?

[Zcootz]

Go to super cheap, spend $20 and get yourself one of the 'one man' brake flushing kits. Has a hose with a one way valve and accumulator and you just keep pumping fluid through till the bubbles stop

[Zcootz]

Or buy the bloke next door a stubbie and get him to press the brake pedal while he drinks the beer. Some jobs a just way easier with two of you there

[Racing Logic]

Go to super cheap, spend $20 and get yourself one of the 'one man' brake flushing kits. Has a hose with a one way valve and accumulator and you just keep pumping fluid through till the bubbles stop

I have just started using one on my MX5 project and its fantastic. Best of all I don't need to get the wife to pump the peddle and here her whinge about my stupid little car.