Bleeding brakes

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Richy Payne

Richy Payne

Member
Posts
13
Location
Harrogate
Hi folks, got a bit of a challenge that I’m hoping one of you fine people would be able to help with;
Replaces all brake lines, callipers and disks/pads on my 2002 D2 Td5.
I have bled the lines in correct order (FL / FR / RL /RR), then modulator bleed in order on each line with Nanocom, followed by a power bleed then a manual pump through just in case. No air bubbles visible.
When I fired her up and pushed on the brakes the pedal went to the floor. If I pump the pedal 3 times I get pressure up and the brakes hold. I take my foot off and it returns to the pedal going to the floor.
I have checked each line and there are no leaks.
The symptoms suggest to me that I have air in the system somewhere but I’ve pushed 2ltr of cloud through with no change. I’m stumped. Any ideas folks?
Cheers, Rich
 
Mastercylinder pressure seals are probably worn / being by-passed when you apply pedal slowly & seal OK when you jump on the pedal quick.
Like the old bicycle pumps that had leather seals and would only work well when operated quickly.
PS You'd need a lot of air in the system (ie a complete mastercylinder volume) to cause "foot to floor" - highly unlikely after the bleeding you've done
 
Pawl said:
Mastercylinder pressure seals are probably worn / being by-passed when you apply pedal slowly & seal OK when you jump on the pedal quick.
Like the old bicycle pumps that had leather seals and would only work well when operated quickly.
PS You'd need a lot of air in the system (ie a complete mastercylinder volume) to cause "foot to floor" - highly unlikely after the bleeding you've done
Click to expand...

Thanks Pawl. The only concern I have with that is that the máster cylinder was fine before I replaced the callipers.

I did have a conversation with a contact who owns a few Disco’s who suggested that it may be air in the brand new callipers that’s trapped and is notoriously difficult to extract, suggesting that I remove the callipers, pump the brakes so the pistons are close to their limit and then push the pistons back in whilst bleeding off. Does this sound like a possibility too?
 
Hi its common for master cylinders to fail after bleeding brakes as the sealing rubber travel much more in the cylinder during the bleeding operation the normal amount of travel is much less and this action damaged the sealing lip of the seal , you could try instaling a new seal kit maybe give the inside a hone with a breake honing tool, and a good clean out after honing,
 
Hi its common for master cylinders to fail after bleeding brakes as the sealing rubber travel much more in the cylinder during the bleeding operation the normal amount of travel is much less and this action damages the sealing lip of the seal , you could try installing a new seal kit maybe give the inside a hone with a brake honing tool, and a good clean out after honing,
 
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frostythor said:
Hi its common for master cylinders to fail after bleeding brakes as the sealing rubber travel much more in the cylinder during the bleeding operation the normal amount of travel is much less and this action damages the sealing lip of the seal ,
Click to expand...
+1 for that ^^^ , same thing used to happen with the clutch too
 
frostythor said:
Hi its common for master cylinders to fail after bleeding brakes as the sealing rubber travel much more in the cylinder during the bleeding operation the normal amount of travel is much less and this action damaged the sealing lip of the seal , you could try instaling a new seal kit maybe give the inside a hone with a breake honing tool, and a good clean out after honing,
Click to expand...

Does this mean that the problem could have been avoided if he only did power bleeding ? I'm asking because apart from the modulator, servo and the master cylinder, I did change all braking system components and never had this problem. But I always bled the system electronically.
 
NPG said:
Does this mean that the problem could have been avoided if he only did power bleeding ? I'm asking because apart from the modulator, servo and the master cylinder, I did change all braking system components and never had this problem. But I always bled the system electronically.
Click to expand...
Yes the problem could have been avoidable. It’s depending on the age of the vehicle of course but the issue is well known with older vehicles, so to avoid the issue don't press the pedal to the floor, half way works the same but the job could take twice as long.

Then there’s the Eezibleed kit which works sometimes, then with modern cars I expect that electronics will now do the job
Can’t help with modern cars, with my modern car it gets done on a service if required, but my disco and a classic car that’s tucked up in the garage has the brakes bled traditionally, with the foot pedal going half way to the floor only.
With the classic car I had the issue after 28 years of ownership and bleeding the brakes as necessary, the pedal went to the floor when I finished the job, but a new master cylinder fixed that, and so now use the Eezibleed.

With the disco I tried the Eezibleed once but the cap for the master cylinder didn't fit very well which made a bit of a mess, so now use the foot pedal halfway method.
 
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yes I have an Eezibleed, but none of the caps fit the brake reservoir, so I use a vacuum suction pump at each wheel, I clamp off the calliper remove the bleed nipple coat the thread in thick grease the reinstall it, remove the clamp, the vacuum it out, tighten up the bleed nipple,
after being in use for thousands of miles the edge of the seal gets very thin so any small rust or dirt area in the master cylinder will damage the seals sealing surface
 
I cut in half a clutch slave cylinder once to see how it is inside and i think the same happens withing the brake or any other cylinder after a long run: the inside along the normal travel of seals is "polished" in time and at the end there is a tiny edge where the seals stopped, then when the system gets empty and there is no pressure the piston will go a bit further than before and that edge hurts the old worn seals, IMO that's what happens
 
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frostythor said:
Hi its common for master cylinders to fail after bleeding brakes as the sealing rubber travel much more in the cylinder during the bleeding operation the normal amount of travel is much less and this action damaged the sealing lip of the seal , you could try instaling a new seal kit maybe give the inside a hone with a breake honing tool, and a good clean out after honing,
Click to expand...
Ok, so thanks for the help so far.
I have installed a new master cylinder and bled everything through again. Symptom’s basically remain the same.
With the engine off (no servo) I get pressure held on the pedal. Engine on and servo operative, pressure on the pedal and it slowly drops to the floor and I’m not pressing particularly hard either.
Stumped.
No fluid leaks either….
Any further suggestions would be greatly appreciated. Thanks in advance.
 
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