How do I bleed the master brake cylinder?
- Thread starter smashingguy
- Start date
First off, what makes you think you need to?
If you do, simply replacing the fluid will do this as new fluid placed in the reservoir and bleeding all the brakes (inlcuding the clutch too) will flush the fluid through the whole system. You cannot just bleed the master cylinder however.
One thing to bare in mind when bleeding brakes is to work from the furthest point from the reservoir. So if the reservoir is on the off side, work from the near side rear, o/s rear, n/s front, clutch, o/s front.
If you can get hold of a pressure bleeder, this will save you a lot of grief as you will only need to open the bleed nipples until the bubbles stop flowing and the fresh fluid comes through.
Manual bleeding is more time consuming and a pain in the proverbial, especially the clutch!
If you need info on how to manual bleed, let me know!
If you do, simply replacing the fluid will do this as new fluid placed in the reservoir and bleeding all the brakes (inlcuding the clutch too) will flush the fluid through the whole system. You cannot just bleed the master cylinder however.
One thing to bare in mind when bleeding brakes is to work from the furthest point from the reservoir. So if the reservoir is on the off side, work from the near side rear, o/s rear, n/s front, clutch, o/s front.
If you can get hold of a pressure bleeder, this will save you a lot of grief as you will only need to open the bleed nipples until the bubbles stop flowing and the fresh fluid comes through.
Manual bleeding is more time consuming and a pain in the proverbial, especially the clutch!
If you need info on how to manual bleed, let me know!
alias, I replaced the abs pump/ecu and then bleed all 4 corners using an eezibleed thingy. The brake pedal is going down to the floor, and I read on here that when other people had the same issue, bleeding the brake cylinder solved the problem. I will get it done properly by vagcom, but I need to get it safe to drive first.
On the positive side the replacement abs pump/sorted my other problems out. Any help you can offer is appreciated.
On the positive side the replacement abs pump/sorted my other problems out. Any help you can offer is appreciated.
The only way to bleed the system is to use the bleed nipples at each brake caliper.
If you can press the pedal to the floor you probably still have (lots) of air in the system. I know I fooked up once and dislodged a master cylinder seal by manual bleeding and pressing the pedal up/down too fast.
You didn't shake the bottle of fluid before you refilled? This makes thousands of air bubbles. (easy mistake to make)
you didn't let the fluid in the reservoir go too low? This lets air into the system.
You don't have fluid pissing out of a bleed nipple that is still open?
Bleed it again
If you can press the pedal to the floor you probably still have (lots) of air in the system. I know I fooked up once and dislodged a master cylinder seal by manual bleeding and pressing the pedal up/down too fast.
You didn't shake the bottle of fluid before you refilled? This makes thousands of air bubbles. (easy mistake to make)
you didn't let the fluid in the reservoir go too low? This lets air into the system.
You don't have fluid pissing out of a bleed nipple that is still open?
Bleed it again
I agree with Nath, sounds like you have a ton of air left in the system.
It is imperitive that the brakes are bled in the order I put above, as by doing it any other way will leave air in the lines. Plus you said you did the 4 corners, but didn't mention the clutch. The clutch uses brake fluid in the slave cylinder, and is essentially part of the brake system. If you didn't bleed the clutch too then its likely air in there is creating (or at least adding to) your problems.
When bleeding manually i.e. using the pedal, you must open the bleed nipple, get someone else to press the brake pedal all the way down to the floor and hold it there, close the bleed nipple then lift the pedal up. Rinse and repeat!
However, because the piston in the master cylinder isn't used to being moved across its full length (as you wouldn't normally be able to press the pedal to the floor) when doing it this way on an older car the seals in the master cylinder may leak and then you have the problems you have now!
The joys of bleeding brakes!
It is imperitive that the brakes are bled in the order I put above, as by doing it any other way will leave air in the lines. Plus you said you did the 4 corners, but didn't mention the clutch. The clutch uses brake fluid in the slave cylinder, and is essentially part of the brake system. If you didn't bleed the clutch too then its likely air in there is creating (or at least adding to) your problems.
When bleeding manually i.e. using the pedal, you must open the bleed nipple, get someone else to press the brake pedal all the way down to the floor and hold it there, close the bleed nipple then lift the pedal up. Rinse and repeat!
However, because the piston in the master cylinder isn't used to being moved across its full length (as you wouldn't normally be able to press the pedal to the floor) when doing it this way on an older car the seals in the master cylinder may leak and then you have the problems you have now!
The joys of bleeding brakes!
Thanks for the info. I didn't bleed the clutch, but I bleed the brakes in the order you described with the eezibleed and used about a litre of fluid (must of what came out wasn't very clean.
I am I right in thinking I need to remove the air filter and battery to get to the clutch bleed nipple (mk2 leon)?
I am I right in thinking I need to remove the air filter and battery to get to the clutch bleed nipple (mk2 leon)?
I have now bleed the clutch and brakes twice and there may be a slight improvement, but it's far from right.
I get a hissing noise when I initially press the brake pedal, but I can't remember if it was there before I started?
When i press the brake quickly it goes hard, but when I press it slow, it goes near to the floor. Any suggestions appreciated?
I get a hissing noise when I initially press the brake pedal, but I can't remember if it was there before I started?
When i press the brake quickly it goes hard, but when I press it slow, it goes near to the floor. Any suggestions appreciated?
get your car booked into a garage its clear your not a mechanic and dont know what you are doing, as per my previous reply in another thread to do this correctly am sure you need to open the abs valves with a diagnostic tool, the time it has taken you a garage would of had it done in a few hours.
I think this might be your problem.
If one of the brake fluid tank chambers empties completely (for example, due to a leak in the brake system), then an initial purge must be made on the hydraulic system.
Initial purge
– Connect the brake bleeder -SAT 1175B-.
– Open the air purge bolts in the order described and make an initial purge of the brake pads.
1 - Purge the front left and right brake callipers simultaneously
2 - Purge the rear left and right brake callipers simultaneously.
– While the hose of the collection bottle -SAT 1175B/1- is connected, leave the purge bolt open until clear brake fluid without bubbles comes out.
Purging
– Connect the Central diagnosis system -VAS 5051B- or central diagnosis -VAS 5052- to the vehicle adapter,“Selection function / component” → Chapter.
– Then:
– “Running gear”
– “Brake system”
– “01 - Self-diagnosis systems Mark 60/Mark 70”
– “03 - ABS/EDS/ASR/ESP Mark 60/Mark 70”
– “Functions”
– “Basic adjustment/brake purging”
– Once the purging process has finished, turn off the ignition and release the diagnostics connector.
Hope this helps.
If one of the brake fluid tank chambers empties completely (for example, due to a leak in the brake system), then an initial purge must be made on the hydraulic system.
Initial purge
– Connect the brake bleeder -SAT 1175B-.
– Open the air purge bolts in the order described and make an initial purge of the brake pads.
1 - Purge the front left and right brake callipers simultaneously
2 - Purge the rear left and right brake callipers simultaneously.
– While the hose of the collection bottle -SAT 1175B/1- is connected, leave the purge bolt open until clear brake fluid without bubbles comes out.
Purging
– Connect the Central diagnosis system -VAS 5051B- or central diagnosis -VAS 5052- to the vehicle adapter,“Selection function / component” → Chapter.
– Then:
– “Running gear”
– “Brake system”
– “01 - Self-diagnosis systems Mark 60/Mark 70”
– “03 - ABS/EDS/ASR/ESP Mark 60/Mark 70”
– “Functions”
– “Basic adjustment/brake purging”
– Once the purging process has finished, turn off the ignition and release the diagnostics connector.
Hope this helps.
I did have this problem in my MK1 Leon, did have to bleed both nipples on the master cylinder at the end to get it fully back.
On the MK1, the nipples were on the top and quite obvious to see. Was directly under the brake fluid reservoir.
When I go out later, Ill have a quick look under my bonnet and see if I can see them on the MK2.
On the MK1, the nipples were on the top and quite obvious to see. Was directly under the brake fluid reservoir.
When I go out later, Ill have a quick look under my bonnet and see if I can see them on the MK2.
Thanks for the above. I have just been out having another feel around but no joy. I have never had so much trouble trying to find a couple of nipples!
Heres the bleeding sequence.
1 - Rear right hand side brake calliper
2 - Rear left hand side brake calliper
3 - Front right hand side brake calliper
4 - Front left hand side brake calliper
– While the hose of the purge bottle is connected, leave the purge bolt open until clear brake fluid without bubbles comes out.
– Press the brake pedal 5 times to assist the air bleeding process.
– Tighten the air bleeder screw to 10 Nm, disconnect the bleeder hose and fit the protective cap onto the bleeder bolt.
– Repeat the bleeding process in the rest of the brake callipers following the indicated order.
– Fill the brake fluid reservoir to the “MAX” mark, taking into account the wear to the brake pads, and screw on the cap.
– Start the engine and check the movement and pressure of the brake pedal.
– If there is excessive brake pedal travel, check for leak faults in the brake system and / or repeat the air bleeding process.
– After purging the air from the system, test drive the vehicle. During this test run, at least one cycle of the ABS regulation must occur on each of the wheels.
In vehicles with the steering wheel on the left, first bleed the rear right side. In vehicles with the steering wheel on the right, first bleed the rear left side.
1 - Rear right hand side brake calliper
2 - Rear left hand side brake calliper
3 - Front right hand side brake calliper
4 - Front left hand side brake calliper
– While the hose of the purge bottle is connected, leave the purge bolt open until clear brake fluid without bubbles comes out.
– Press the brake pedal 5 times to assist the air bleeding process.
– Tighten the air bleeder screw to 10 Nm, disconnect the bleeder hose and fit the protective cap onto the bleeder bolt.
– Repeat the bleeding process in the rest of the brake callipers following the indicated order.
– Fill the brake fluid reservoir to the “MAX” mark, taking into account the wear to the brake pads, and screw on the cap.
– Start the engine and check the movement and pressure of the brake pedal.
– If there is excessive brake pedal travel, check for leak faults in the brake system and / or repeat the air bleeding process.
– After purging the air from the system, test drive the vehicle. During this test run, at least one cycle of the ABS regulation must occur on each of the wheels.
In vehicles with the steering wheel on the left, first bleed the rear right side. In vehicles with the steering wheel on the right, first bleed the rear left side.
Thanks hothatchsteve, I have a leak under the brake master cylinder. It is coming from one of the bolts attached to the servo. I guess i may have been a bit heavy footed when i was testing it. Is it likely to be a seal, and if so are these easy to get hold of?
As you say you've probably been heavy footed and folded a master cylinder seal inside out. This is letting fluid past the folded over seal and the fluid then escapes past the back of the cylinder where it bolts to the servo. You can replace the seals but it's really a falce economy, you're better off replacing the master cylinder.
Good luck.
Always remember to do manual bleeding very slowly.
Good luck.
Always remember to do manual bleeding very slowly.
Similar threads
