Bleeding Brakes

[jbcollier]

Bleed the master cylinder first.  Remove the brake lines and hold your fingers over the ports.  Have your assistant depress the pedal and hold it down.  Allow any pressure to release past your fingers.  Hold tight and have the assistant release the pedal.  Repeat until clear fluid flows out.  Reattach lines and bleed as normal.

[4129R]

I now have a hydraulic pump to pressurise the master cylinder. It took me ages to get it to seal on top of the MC, but I can get the pressure at the top of the MC up to 1 bar (16 PSI).

At last, I have no fluid leaks, but the system loses pressure from 1 bar after a few minutes, yet no fluid comes out anywhere when left pressurised.

I am getting FA at the 4 bleed nipples at each wheel.

I have bypassed the servo.

When pressurised, I release the 1 pipe connection on the single circuit brake MC which goes back to the servo, fluid comes out of that connection and I tighten the 7/16" fitting, but the pedal seems not to be pumping.

I have run out of ideas.

I will have to pressurise the system, and loosen every connection to see if fluid comes out.

Is 16 PSI enough to force fluid though all the empty pipes?

Could all the rubber flexible hoses have blocked up when sitting dry for about 4 years? 

The previous 5 cars I have done gave me no such problems. The pedal worked, it pumped easily, and I managed to bleed all 4 nipples without any major problem. Why is this one being so difficult?

[BDA]

Sorry for my misunderstanding. Here's what I'm not sure of:

Did you bench bleed the M/C?

Having done that, this question is moot, I guess but before you connect any tubing to the M/C, when you push the brake pedal, does fluid come out of the port?

I don't know what you mean by "FA."

Checking my pressure bleeder, it calls for 10 psi so 16psi should be plenty.

You can check for blockages by disconnecting the tube at the M/C and at the cylinders and calipers and blowing air through it. Where does air come out? If you get air at each wheel, do you get more at one than the others? You could connect all but one wheel and try it for each wheel independently. This is assuming no booster in the circuit so you probably have to make adjustments to this strategy (i.e. bypass the booster or test up to it and after it). I doubt the rubber hoses would be blocked just for sitting around but a small critter could have caused you a problem.

[4129R]

Sorry for my misunderstanding. Here's what I'm not sure of:

Did you bench bleed the M/C?

I have fluid coming out of the port when the reservoir is pressurised and the 7/16" fitting is loosened.

Having done that, this question is moot, I guess but before you connect any tubing to the M/C, when you push the brake pedal, does fluid come out of the port?

No idea, I cannot see


I don't know what you mean by "FA."

"Fuc* All"

Checking my pressure bleeder, it calls for 10 psi so 16psi should be plenty.

You can check for blockages by disconnecting the tube at the M/C and at the cylinders and calipers and blowing air through it. Where does air come out? If you get air at each wheel, do you get more at one than the others? You could connect all but one wheel and try it for each wheel independently. This is assuming no booster in the circuit so you probably have to make adjustments to this strategy (i.e. bypass the booster or test up to it and after it). I doubt the rubber hoses would be blocked just for sitting around but a small critter could have caused you a problem.

Not easy to blow air through the piping. Maybe I will have to make up a connection from my compressor to the hydraulic pipes, but that would blow brake fluid all around my garage, which would be corrosive and mess up the paintwork of all cars in the proximity.

[4129R]

When you pressurise the master cylinder reservoir by 10-16 PSI, how does the hydraulic fluid pass through the master cylinder so you can bleed the nipples at all 4 wheels?

Well ...........

I have connected another master cylinder and remote reservoir in my bench vice. I have filled the reservoir, and fluid comes out the port straight away. I have then connected a long clear hose to the port via a rubber flexible hose. As I pump the piston, fluid just bubbles up in the reservoir.

Tomorrow I will try sticking my finger over the open port to see if I can get it to pump out of the port, and not up into the reservoir.

I didn't have this problem on the previous 5 cars I bled successfully from dry.

[BDA]

How do pressure bleeders work? Similarly to vacuum bleeders but backwards!

I'm deconstructing this since I've pretty much just accepted that they work but I think what happens is the piston in the M/C when your foot is off the brake, is behind both the inlet and outlet ports of the M/C. So fluid is pushed from the reservoir into the cylinder and out the outlet port via the air pressure in the bleeder. You could crack open all four bleed screws if you wanted but I just do one at a time. I connect a plastic tube to the bleed screw that goes into a bottle and opens beneath the level of fluid in the bottle. We used to use a soda/pop/cock bottle but you can get nice plastic bottles for the same purpose. Vacuum bleeders work the same way only they suck the fluid from the bleed screws pulling it from the reservoir but they can draw air through the threads of the bleed screw, for example, so I prefer the pressure bleeder.

In the bench bleeding you describe, you directed the fluid from the output port of the M/C to the reservoir but you saw fluid bubbling up in the reservoir that did not come from the tube connected to the output port? I think I misunderstood your description. I don't see how that could happen in a single circuit M/C.

I have used mine several times and it's great! It is a one man operation and should produce fewer bubbles than pump or vacuum bleeding might.

[GavinT]

Did you bench bleed the M/C?

I have fluid coming out of the port when the reservoir is pressurised and the 7/16" fitting is loosened.

Having done that, this question is moot, I guess but before you connect any tubing to the M/C, when you push the brake pedal, does fluid come out of the port?

No idea, I cannot see

Errr . . . hold the bus, please.
1. Either fluid comes out of the port or it doesn't.
2. How do you know if you can't see it?

Or do you mean that you see 'evidence of fluid' when you go look after the fact? – the situation is not clear.
At a guess, I'd say 'evidence of fluid' is not the same as 'fluid flow'. The MC might dribble fluid but won't work if it's 90% full of air.

Follow JB's advice in Reply #30 and you'll quickly identify if a problem exists.
JB is essentially describing a bench bleed performed in the car to save pulling the MC. Perhaps it's time to literally do it on the bench so that you can see the fluid flowing properly from the outlet port.

Tomorrow I will try sticking my finger over the open port to see if I can get it to pump out of the port, and not up into the reservoir.

That's the important part . . and keep the finger in place while the piston retracts.
Good luck.

[4129R]

https://www.youtube.com/watch?v=7rImn6nJ4Dw&ab_channel=GarageGurus

So having bench bled the MC, how do you stop air entering the system when you disconnect the clear plastic hoses and fittings, and start installing the MC on the car?

Surely the hydraulic fluid will start leaking out as soon as you disconnect the pipes and fittings and let air back into the MC.

Hold the bus, please.
1. Either fluid comes out of the port or it doesn't.
2. How do you know if you can't see it?

As soon as I loosen the 7/16" out port pipe fitting, fluid leaks out of the MC.

In the bench bleeding you describe, you directed the fluid from the output port of the M/C to the reservoir but you saw fluid bubbling up in the reservoir that did not come from the tube connected to the output port? I think I misunderstood your description. I don't see how that could happen in a single circuit M/C.

I have connected to the single out port, a rubber flexible hose, like on the front calipers or where the rear trailing arm pivots on the Y of the chassis, with a clear plastic tube attached to the other end of the hose. All that happens when I push the extension rod in the vice  is air bubbles up into the reservoir, and FA comes out of the out port into the rubber hose and clear plastic tube.

[4129R]

I have this morning bench bled another new MC (as per the video in my post above) so no bubbles come out, then plugged both holes on the bench with 3/8" UNC and 7/16" UNC bolts, fitted the MC to the car, carefully attached the reservoir pipe and the outlet pipe, and tightened everything.

One bleed nipple open, 100 pumps on the pedal, and the fluid level does not go down at all.

I pressurised the system to 16 PSI and it slowly went down to 0 PSI over 3m30s, with the leak coming from the hydraulic pump, as fluid was going from the MC reservoir back into the pump as the pressure decreased.

No fluid leaks anywhere.

Current problems are 1)  the MC is not pumping fluid properly (2 different new MC tried, same problem) and 2) nothing comes out of any bleed nipple when the remote reservoir is pressurised to 16 PSI, even though there is fluid in the pipes as I found several leaks in the engine bay when I first pressurised the system.

[jbcollier]

Ok, you;'ve bench bleed the master (PS: I just fit rubber plugs to the ports when fitting).  Now disconnect the two lines from the master to the boosters at the boosters.  Hold you fingers over the lines as someone pumps the brake pedal.  Pedal pressure will overcome your fingers but still not allow air in.  Do you get flow?

[4129R]

I have pressurised the system, and systematically loosened the brake pipe unions one at a time, getting fluid coming out of the fittings.

It seems the rubber hoses have become blocked when sitting dry. This car is 4129R, which I drove successfully for about 1000 miles before stripping for a respray.

I replaced one of the hoses to the front caliper, and fluid is now coming out of the caliper bleed nipple when the system is pressurised.

I have ordered all 4 hoses for £28.00 on eBay.

Once all 4 have been replaced, I will address the MC problem again to see what will happen when pumping the pedal and the bleed nipples are actually working with new hoses.

[Bryan Boyle]

I have pressurised the system, and systematically loosened the brake pipe unions one at a time, getting fluid coming out of the fittings.

It seems the rubber hoses have become blocked when sitting dry. This car is 4129R, which I drove successfully for about 1000 miles before stripping for a respray.

I replaced one of the hoses to the front caliper, and fluid is now coming out of the caliper bleed nipple when the system is pressurised.

I have ordered all 4 hoses for £28.00 on eBay.

Once all 4 have been replaced, I will address the MC problem again to see what will happen when pumping the pedal and the bleed nipples are actually working with new hoses.

or...the fluid has congealed in the flex hoses from sitting for an indeterminate amount of time.  If I may make a suggestion?  Before replacing all the rubber hoses...disconnect all of the old ones and bin them.  Then FLUSH the remaining metal hoses out with fresh fluid (put bleed hoses on all the frame-mounted nipples and run to jelly jars to catch...).  THEN hook up the new flex hoses, reconnect, and bleed.  Just a suggestion (yeah, I know the 2 short and 2 rear arm mounted metal pipes aren't included, but they'll be caught up with when you go to bleed the system, since it will be essentially empty after this....)

[4129R]

The next episode in my master cylinder saga:-

I changed all 4 rubber brake hoses and one wheel cylinder, and now when I pressurise the reservoir tank on the brake master cylinder I can bleed all four corners at the bleed nipples.

BUT.

I disconnected the brake fluid pressuriser, and left a full reservoir of fluid to sort out the master cylinder not pumping properly problem.

I had bench bled the master cylinder, plugged the two holes, and fitted the MC to the car.

When I pumped the brake pedal a few times, the entire contents of the master cylinder remote reservoir emptied themselves over the front spare wheel area. It took much kitchen roll and a wash with soapy water quickly to stop the pristine paintwork on the wings and around the Lotus badge from being damaged.

It is a new MC. I have 2 more new MCs.

Why is the MC pumping back up to the reservoir? You cannot connect the pipes up backwards. The previous 5 cars I have done have all worked quickly using the same plumbing arrangements.

 

[jbcollier]

What master cylinder (brand and application) are you using?

[4129R]

What master cylinder (brand and application) are you using?

Girling 3/4" bought from Banks. Single circuit. Just the large connection to the remote reservoir and the normal connection to a male brake pipe fitting which takes a 7/16" spanner to undo.

My plan for tomorrow, unless anyone has a better plan, is to bench bleed another brand new MC, fit that, and see what happens.