Idiots guide to bleeding brakes

[michael760]

I have just replaced my master cylinder and now have to try & get fluid to each wheel.
Please can you give me hints & tips to help me.
I know about leaving the rear wheels on the floor to prevent the brake balance valve from cutting off supply.
Any other tips would greatfully recived.

 

[angel]

If you have the master cylinder with four outlets and pressure drop indicator contact, you will find a bleed nipple next to it. Bleed all four wheels first and then bleed PDI circuit by the master cylinder nipple.
When filling from dry the traditional way - assistant pressing brake pedal - I have found that brake fluid gets easier to wheels if you follow this procedure: Open nipple - press pedal - close nipple - release pedal.

 

[jjames687]

The best thing to always do is bench bleed the master cylinder before you put it in the vehicle. This is standard practice on all vehicles.

Put the master in a vice, fill the reservoir with fluid and with a long screwdriver or something start actuating the cylinder.

The fluid should start coming out of the fittings.

They sell bench bleeding kits that are basically a hose that threads into each fitting and then you run the hoses back to the reservoir and bleed the air bubbles out that way, but if you can't find or fabricobble that setup: (wearing nitrile gloves) cover each hole with a finger, then press on the screwdriver or whatever you have in the master with your chest and the fluid and air will be forced out past your fingers. The key is that your fingers will keep the air from being sucked back into the master and it will instead draw from the reservoir.

It's pretty crucial to bench bleed the master before putting it in the vehicle. You will still have to bleed the lines of air from breaking them open for the replacement but its a much longer process to bleed if the master is dry when you put it in, and there can be problems getting all the air out that way. Not sure if the back pressure can keep all of the air from leaving the master sometimes or what.

Just for context, I'm saying this as a nationally certified master automotive technician in the USA.

 

[angel]

When I first had to remove and refit the master cylinder on my R4, at the age of 18, I tried to bench bleed it, having read about it in an American book - no web or forums back then!
A major mess, brake fluid all over the place, master cylinder emptying from the lower union etc. In the end I did the system bleeding the usual way without trouble.
25 years later and at least one hundred master cylinder replacements, I (and no one in Europe, I think) never bench bleed any of them, instead I have used three different techniques (pedal pumping, pressure, vacuum) of filling / bleeding without trouble, vacuum bleeding being the most effective one.
Glad to find an American automotive engineer here to solve the mystery, is there someone we are missing here in Europe, or are American marter cyliders built that way that bench bleeding them has an advantage?

 

[jjames687]

Not an automotive engineer by any means. Just a shop mechanic. In fact, I'm having some fun here as I've come to Colombia for 6 months an bought an R4 and I'm trying to do my own repairs without any of my tools or shop equipment.

I think it definitely can depend on the manufacture and design of the master cylinder. I've noticed that the bigger ones, like in full sized pickups and trucks (certainly less common over there) seem to have more problems holding air inside, maybe because of the size of the cylinder and/or the seals.

Another differing point is whether the valve is internal or external to the master.

Yet a third thing to consider is that some ABS units, especially some of the 90's ones, don't like to get very much air inside them and definitely don't like to bleed it out once they do. Bench bleeding the master minimizes the amount of air you have to send through the system to get it bled.

Also, in a professional shop environment, especially here, workers are paid by the job and not by the hour, so there is a monetary incentive to make the process more efficient, bleed the master then put it in and spend less time on the brake bleed later.

 

[jjames687]

Interesting that you've not had trouble with it. It does sound superstitious, but I've personally have anecdotes of myself and other people I've worked with putting a master brake or clutch cylinder in, bleeding the system extensively, having it still seem soft after all the efforts, and then taking the cylinder out again and bench bleeding it and then having everything work fine. This has only happened to me once, but I believe religiously in the bench bleed.

Seen other less competent techs have problems in the shops I've worked in that were blamed eventually on not performing a bench bleed.

Live by the bleed, die by the bleed.

 

[jjames687]

Also interesting that you've had the best luck with vacuum bleeds, are those with a hand pump or an air powered one? I've had problems doing bleeds with the air powered ones.

The partner-pump method or a pressure bleed are more effective in my experience.

If I'm just replacing a caliper or a wheel cylinder, I will usually just gravity bleed them. The key is that sometimes air is trapped in the walls of the caliper (they are cast so the surface is rough). So I'll gravity bleed them and then close the bleeder, tap the walls of the caliper a few times with a hammer, and sure enough a few more bubbles come out. My theory is that the vaccum bleeder just sucks fluid through and doesn't disturb the bubbles.

Also, my boss swears that excess or rapid pumping when bleeding brakes aerates the fluid with micro bubbles, which makes the system soft.

Not sure what your experience is, for me its been hundreds of cylinders on multiple vehicles, trying to fit things into a short time-frame, and trying to make things perfect, as in, the customer shouldn't have to come back and have us do it again.

 

[angel]

I use a vacuum pump, not pressure device. Still, there are systems that will not completely bleed that way and need an extra sequence of pedal pumping or combination of vacuum / pedal bleeding to get air fully out. Still I find it the most efficient way to fill a system from dry.

What do you do about all that brake fluid dripping from M/C outlet ports from the moment you remove the pipes used on bleeding until you tighten the last pipe union?

 

[michael760]

I use a vacuum pump, not pressure device. Still, there are systems that will not completely bleed that way and need an extra sequence of pedal pumping or combination of vacuum / pedal bleeding to get air fully out. Still I find it the most efficient way to fill a system from dry.

What do you do about all that brake fluid dripping from M/C outlet ports from the moment you remove the pipes used on bleeding until you tighten the last pipe union?

I’m going to try and bleed the master cylinder up first using an assistant (Dad) on the pedal then try bleeding the rear right drum using a pipe in a jar of fluid over the bleed nipple.
Then hopefully the rear left and then the fronts.
I was thinking of trying to put a compressor on the brake lines from the master cylinder and open the bleed nipples on each wheel to see if anything came out?
Not sure if that would work or weather it’s a bad idea?

 

[jjames687]

I’m going to try and bleed the master cylinder up first using an assistant (Dad) on the pedal then try bleeding the rear right drum using a pipe in a jar of fluid over the bleed nipple.
Then hopefully the rear left and then the fronts.
I was thinking of trying to put a compressor on the brake lines from the master cylinder and open the bleed nipples on each wheel to see if anything came out?
Not sure if that would work or weather it’s a bad idea?

Hey michael,

Don't hook the compressor up to the system, no need to push air through it. If you're worried about what's in the lines already then push a lot of fluid through.

 

[jjames687]

I use a vacuum pump, not pressure device. Still, there are systems that will not completely bleed that way and need an extra sequence of pedal pumping or combination of vacuum / pedal bleeding to get air fully out. Still I find it the most efficient way to fill a system from dry.

What do you do about all that brake fluid dripping from M/C outlet ports from the moment you remove the pipes used on bleeding until you tighten the last pipe union?

Bucket under the bench you bleed it on. Plugs that came with the cylinder go back in. In the car, fender cover always, rags under the the spot where the installed master goes, and if you spill a drop somewhere clean it quickly with a rag and brake kleen.

 

[michael760]

Got fluid to both rear brakes so they are both working well.
The fronts do not want to draw any fluid through though?
The handbrake (manual) operates fine so am I right in thinking that the front wheel cylinders are stuck?

 

[mojobaby]

A few years ago, I was having a huge problem bleeding my brakes. Angel suggested a vacuum pump, so I ordered one from Amazon and was surprised how easy my life became.

I used to use the brake pedal method but wasn't always able to find someone to pump the pedal for me.

One thing should be noted however. With a vacuum pump, there is a tendency for "false" air to be drawn in through the threads of the bleed nipple. I wondered why there was an endless stream of bubbles! I use PTFE tape (plumbers tape) to seal the thread before I start.

 

[jjames687]

Got fluid to both rear brakes so they are both working well.
The fronts do not want to draw any fluid through though?
The handbrake (manual) operates fine so am I right in thinking that the front wheel cylinders are stuck?

The hand brake is mechanical and doesn't rely on hydraulic pressure from the brake system. As long as the shoes are adjusted properly, the hand brake should work.

Have you checked the level of fluid in the master? Also have you tried just gravity bleeding the fronts? I would crack the right front and open the lid of the master and see if fluid will come through on its own. It could depend on the valves and the shape of the lines if it will gravity bleed or not.

When you had Dad helping, you were having him pressurize with the pedal (pump a few times and hold), and then opening the bleeder and letting the fluid and air release, and then closing it before he pumped again correct?

Sorry for asking so many questions, just trying to know what process you were using so we can know how to go forward.

 

[jjames687]

A few years ago, I was having a huge problem bleeding my brakes. Angel suggested a vacuum pump, so I ordered one from Amazon and was surprised how easy my life became.

I used to use the brake pedal method but wasn't always able to find someone to pump the pedal for me.

One thing should be noted however. With a vacuum pump, there is a tendency for "false" air to be drawn in through the threads of the bleed nipple. I wondered why there was an endless stream of bubbles! I use PTFE tape (plumbers tape) to seal the thread before I start.

Hey mojo, the false air thing has been my experience too, that's why I prefer the gravity bleed and then pressure/pedal to finish, if one can be patient.

 

[jjames687]

If you have the master cylinder with four outlets and pressure drop indicator contact, you will find a bleed nipple next to it. Bleed all four wheels first and then bleed PDI circuit by the master cylinder nipple.
When filling from dry the traditional way - assistant pressing brake pedal - I have found that brake fluid gets easier to wheels if you follow this procedure: Open nipple - press pedal - close nipple - release pedal.

Angel here briefly describes the bleed process, but in more depth.

1. With the reservoir on the master full:

2. Have your assistant press the pedal a few times slowly until it begins to get stiff so that you have some pressure in the system to work with. (pressing too fast can in theory cause bubbles in the fluid)

3. With the assistant holding the pedal down, open the bleed valve, air and/or fluid should exit with pressure. They should also feel the pedal go to the floor. The assistant should hold the pedal down until you:

4. Close the bleed valve completely.

5. Then the assistant can release the pedal and start pumping again slowly to build pressure. Once they feel pressure you can open it again.

6. Repeat on the same bleeder until only clear fluid comes out every time and there are no bubbles or air exiting. Check the master frequently to make sure it doesn't run out of fluid. If it runs out of fluid you have to start again from the beginning as there will be air in the system.

Notes: In theory you should start from the furthest one from the master and move to the closest. Also, make sure the pedal is held down until the bleeder is completely closed, this draws fluid from the master instead of drawing air back in from the bleeder.

 

[michael760]

Thanks so much for your advice.
I have tried using a vacuum pump but yeah I think air is leaking past the pipe on the bleed nipple so I reverted back to the standard assistant (dad on pedal) system.
The rears have come up great with putting a pipe in a jar of fluid and pumping the pedal (while the wheels are on the ground) lots of horrible discoloured fluid & air.
At least I feel I’ve got somewhere!

I know the handbrake is mechanical so I’m happy that the shoes are free and they stop the drum.

I’m just wondering if the front cylinders are seized up?
I have tried to get the drums off by undoing the 3 philips screws and pulling at the drum but I can’t budge either one!
I also backed off the square adjusters so they were spinning at the slackest (if that makes sense)
Any advice on how to get them off?
I will see if I can borrow my assistant again over the weekend and have another go at bleeding.
Thanks again for all your advice
Mike.

 

[laxeian]

Regarding removing drums, borrowed advice tip from another thread, have you tried refitting wheel to use as extra leverage to free drums?

 

[michael760]

Are the studs attached to the drum??

 

[laxeian]

Unsure, mines disc at front, can’t remember if advise was for front drum, just as good idea to remember incase needed