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Rusty
Joined: 10 Feb 2009
Posts: 278
Location: Bunbury, Western Australia
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 Posted: Mon Jun 09, 2025 1:35 am Post subject: Re: Brake bleeding |
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| ukdave2002 wrote: | | If the M/C will pump up and hold pressure, then I don't think that's your problem, if it holds pressure then both the bore and main seals are good. |
This is not necessarily so !
Sometimes, the "primary" seal, the one that actually applies the pressure gets worn and will pass fluid back when in a resting position, but when you pump it up the internal pressure pushes the seal out onto the wall of the cylinder and allows you to get a pedal, often after one or two pumps, when you start pumping it will still allow some fluid past the seal until speed overcomes the fluid passing back and you build up a pedal, sometimes if it is bad enough when you have "pumped it up" if you release the pressure, but continue to hold the pedal in the down position you can actually "feel" the fluid start to pass back. If it's not to that point, then it is very hard to say for sure. Remedy?, if the cylinder on inspection is still in good nick, a seal kit, if badly worn, new cylinder.
This is not all that common, but does from time to time happen, and from the sound of it , may be what's happening to you.
Another thing you can do to check if this is the cause is just push the pedal "slowly" to the floor and see if it goes all the way to the floor, and if it "does", let the pedal rest for a few seconds and then push it "quickly" to the floor. If after the quick push you have a "low" pedal but not gone completely to the floor, then it has past some fluid back until the rising pressure seals it part way down the stroke and allows pressure to build up.
Why were you needing to bleed the brakes in the first place, had it run out of fluid or was it just the low pedal that pumps up right from the start?
Goodluck |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Wed Jun 11, 2025 4:29 pm Post subject: Brake bleeding |
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Today removed the cylinder and with the help of a 30mm socket and a three foot bar the end cap replaced both seals still no pedal pressure
Using the air pressure kit |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Wed Jun 11, 2025 4:30 pm Post subject: Brake bleeding |
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Today removed the cylinder and with the help of a 30mm socket and a three foot bar the end cap replaced both seals still no pedal pressure
Using the air pressure kit |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Wed Jun 11, 2025 4:55 pm Post subject: Brake bleeding |
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Today removed the cylinder and with the help of a large socket and a long bar removed the end cap replaced both seals
Bled with air pressure. Still no pedal pressure |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Thu Jun 12, 2025 4:41 pm Post subject: Brake bleeding |
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Today removed the cylinder and with the help of a large socket and a long bar removed the end cap replaced both seals
Bled with air pressure. Still no pedal pressure |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Mon Jun 23, 2025 7:41 pm Post subject: Brake bleeding |
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Now after purchasing a new master cylinder (?200) fitted it today connected to my pressure system bled all four wheels ran another litre of fluid through the system still no pedal pressure unless I leave the air pressure connected
I read something about backing off the adjusters before bleeding this I tried no improvement
So next will adjust the brakes and try again
Any other ideas. Thanks tom |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Mon Jun 23, 2025 7:42 pm Post subject: Brake bleeding |
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Now after purchasing a new master cylinder (?200) fitted it today connected to my pressure system bled all four wheels ran another litre of fluid through the system still no pedal pressure unless I leave the air pressure connected
I read something about backing off the adjusters before bleeding this I tried no improvement
So next will adjust the brakes and try again
Any other ideas. Thanks Tom |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Mon Jun 23, 2025 7:43 pm Post subject: Brake bleeding |
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Now after purchasing a new master cylinder (?200) fitted it today connected to my pressure system bled all four wheels ran another litre of fluid through the system still no pedal pressure unless I leave the air pressure connected
I read something about backing off the adjusters before bleeding this I tried no improvement
So next will adjust the brakes and try again
Any other ideas. Thanks Tom |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Mon Jun 23, 2025 7:53 pm Post subject: Brake bleeding |
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Must apologise for multiple posts when posting on iPad it tells me not posting when I view on my phone I see my error lol
I am using dot4 semi synthetic have now put 2litres through will this give me a problem |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Mon Jun 23, 2025 7:55 pm Post subject: Brake bleeding |
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Must apologise for multiple posts when posting on iPad it tells me not posting when I view on my phone I see my error lol
I am using dot4 semi synthetic have now put 2litres through will this give me a problem l |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4240
Location: South Cheshire
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| Posted: Mon Jun 23, 2025 8:16 pm Post subject: |
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| Although I have never found it made a difference on my own vehicles, is there a recommended bleeding order for your car? Or have you tried changing the order? |
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Miken
Joined: 24 Dec 2012
Posts: 577
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| Posted: Mon Jun 23, 2025 11:04 pm Post subject: |
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| Thinking back to when I fitted the new master cylinder to my A40 the other year, I started bleeding the wheels cylinders from the rear and went all round. The brakes were a bit spongy so I went round a couple more times, then once more for luck and they just sort of worked ever since then. As someone else mentioned, they felt even better the following morning. Because the reservoir is mounted remotely from the cylinder, high up on the bulkhead, any bubbles in that part of the system should just rise up and out. |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4240
Location: South Cheshire
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| Posted: Tue Jun 24, 2025 8:06 am Post subject: |
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Also when using the pressure bleeders, using a lower pressure can sometimes be better at driving out air than a higher pressure.
If you are still struggling to get the air out, jack the rear of the car up as high as you can, put it on stands leave over night, and then bleed the rear, if it still has air in follow the same procedure with the front, essentially you are encouraging the air to go to the highest point , which should now be around the wheel cylinders. |
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Southernscouse
Joined: 30 May 2024
Posts: 26
Location: Havant Hampshire
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| Posted: Tue Jun 24, 2025 6:06 pm Post subject: Brake bleeding |
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Spent another couple of hours today bleeding all four wheels with a tube fitted with a one way valve still no pressure
Will try raising the rear end next. Keep the ideas coming. Thanks. Tom |
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Miken
Joined: 24 Dec 2012
Posts: 577
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| Posted: Tue Jun 24, 2025 10:05 pm Post subject: |
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| So, if you slightly crack open the bleed nipple on one of the wheel cylinders and watch while someone else presses down on the brake pedal. What exactly happens? Does any fluid come out? |
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