Master cylinder bench bleeding?

[rcx132]

I'm reassembling my brake system now on my restoration project. All the pipes, calipers, slave cylinders and master cylinder had been drained.

Manual says that I need to bench bleed the master cylinder before reinstalling. But bench bleeding doesn't seem to be any different from regular bleeding .... hold finger over master cylinder outlets to let fluid out but not let air in, and keep pumping until all air gone.

I want to avoid bench bleeding because fitting a full master cylinder drips fluid on everything, and all the bits underneath start rusting.

And if I'm using a suction system to bleed the system there seems even less need to bench bleed.

Thoughts?

 

[Kayos]

Is it to prevent the seals turning? If so I’d say you would be ok with suction bleeding as you don’t pump the pedal

 

[frank horton]

rebuild the m/cylinder and fit as soon as ur ready to bleed.......waste of time bench bleeding.......all the new m/cylinders I've fitted in 50 years we're only bled on the car.......frank

 

[johnik]

fill with fluid, open the bleed niples, go have a cuppa

 

[frank horton]

Johnie,
Like ur idea but brake fluid will mess up the paint on me floor.....hahaha....
could use a drip tray but prefer to be there.....frank

 

[johnik]

Johnie,
Like ur idea but brake fluid will mess up the paint on me floor.....hahaha....
could use a drip tray but prefer to be there.....frank

drip tray or put some water / wet rag on the floor where it will land

 

[Ruffian]

Gravity bleed first as said above, fill up then go have a brew, fluid shoul flow to lowest points, do 3 or 4 times (dependant on how big the fluid capacity is) usually on bikes now I like to leave them overnight to gravity bleed before pumping the fluid through for that last bit.

 

[armalites]

I have some of these, no mess. Should be fairly easy to replicate. They also make bleeding easy.

 

[rcx132]

Just saw on a specialist site that the reason for bench bleeding a master cylinder is that if you don't then you introduce a lot of air into the system. So it's not essential.

Though I wonder if the whole system is full of air whether it will build enough pressure to bleed? Will see.

 

[RichardM]

might be because of the angle of the cylinder holding fluid, on my bikes they can be a real pain to get all of the air out, cracking open banjos, filling the caliper then pressing the pistons back in us helps as well.

 

[CompoSimmonite]

I use a Mityvac vacuum bleeder and have never had any trouble with any type of system.

 

[CKJDJK]

I bought a Gunson pressure bleeder, the type that uses a spare wheel for air pressure, 35+ years ago but it is still around, £7 then. Changed it to run through a regulator off the compressor. Collected or made reservoir caps to fit hose. Apply about 10 - 20 psi to the bottle then just go round opening the bleed nipple as required with a bit of hose into a jar to catch the old fluid. Some times even all four at once. On a stubborn system you can still pump the brakes. It works and have used it on trucks, busses, cars, bikes, plant and military equipment. I keep meaning to replace it with a more professional set up but it keeps working. Used on empty systems, pipe replacement, master cylinder the lot.

 

[knighty]

slave drips fluid on everything, and all the bits underneath start rusting.

it's not really much help to you but it's handy to know - modern break fluid doesn't make things rust like the old stuff did

doesn't even take the paint off :-o

 

[8ob]

I'm reassembling my brake system now on my restoration project. All the pipes, calipers, slave cylinders and master cylinder had been drained.

Manual says that I need to bench bleed the master cylinder before reinstalling. But bench bleeding doesn't seem to be any different from regular bleeding .... hold finger over master cylinder outlets to let fluid out but not let air in, and keep pumping until all air gone.

I want to avoid bench bleeding because fitting a full master cylinder drips fluid on everything, and all the bits underneath start rusting.

And if I'm using a suction system to bleed the system there seems even less need to bench bleed.

Thoughts?

The only thing I have against Vac bleeding is the constant stream of air bubbles drawn in from around the loosened bleed nipple, it can give the impression there is air in the system so you keep going. I prefer pressure units with a big reservoir for one man bleeding, its one hit and its done.

Bob

 

[rcx132]

it's not really much help to you but it's handy to know - modern break fluid doesn't make things rust like the old stuff did

doesn't even take the paint off :-o

I think it does cause rust. I had trouble bleeding my system last year and bench bled the master cylinder. The spilled fluid caused serious rust under the master cylinder.

I think DOT 5 is the only fluid that is harmless. But DOT 3, 4 and 5.1 all cause rust.

The only thing I have against Vac bleeding is the constant stream of air bubbles drawn in from around the loosened bleed nipple, it can give the impression there is air in the system so you keep going. I prefer pressure units with a big reservoir for one man bleeding, its one hit and its done.

Bob

Putting some teflon on the nipped stops bubbles being sucked in. I tried a pressure unit but I don't think it had a cap to suit my system. Tried making one but not sure what happened it was few years ago.