Really struggling to bleed brakes - advice requested
Discussion
I have bled the brakes on countless vehicles over the last 40-plus years, but never struggled the way I am in this instance - I'd be grateful for any advice.
A few sentences to set the scene; earlier this year my son bought a 2016 Movano van. In the first week of his ownership we spotted that a rear caliper piston was sticking causing the brake to drag. We whipped off the caliper, stripped out the piston, cleaned it up, refitted the caliper, bled the brake - all was good. He then used the van for the rest of the year without issue. At the MoT a few weeks ago, it failed on the same caliper dragging slightly and a 'twist' in the front flexi hose, so this time we fitted a new rear caliper and loosened the front hose, it took seconds to remove the twist. The problem started when we tried to bleed the brakes.
Whatever we try we cannot get any resistance at the pedal. By which I mean there is no difference in feel at the pedal between the nipples being tight and completely removed! We have spent hours and hours on this and have put many litres of fluid through all four calipers.
Most of the bleeding has been 'old school' pumping of the pedal, while the nipples are opened on the down stroke and locked off during the upstroke. In desperation, we bought a vacuum pump-based bleeding kit, but have had no success with that (I have separate questions on that but don't want to divert this thread).
We tried clamping the four flexi hoses in case we had a simultaneous failure of the master cylinder - and indeed, there was still no pedal. But when we blanked off the two MC outlets with M12 x 1,0 blanking plugs we get a rock-solid pedal. This would suggest the problem is between the MC and the calipers. However, we also discovered that if we only blanked off one outlet we again had no pedal - and most surprisingly - it didn't matter which one we blanked off
I have run out of ideas.....
A few sentences to set the scene; earlier this year my son bought a 2016 Movano van. In the first week of his ownership we spotted that a rear caliper piston was sticking causing the brake to drag. We whipped off the caliper, stripped out the piston, cleaned it up, refitted the caliper, bled the brake - all was good. He then used the van for the rest of the year without issue. At the MoT a few weeks ago, it failed on the same caliper dragging slightly and a 'twist' in the front flexi hose, so this time we fitted a new rear caliper and loosened the front hose, it took seconds to remove the twist. The problem started when we tried to bleed the brakes.
Whatever we try we cannot get any resistance at the pedal. By which I mean there is no difference in feel at the pedal between the nipples being tight and completely removed! We have spent hours and hours on this and have put many litres of fluid through all four calipers.
Most of the bleeding has been 'old school' pumping of the pedal, while the nipples are opened on the down stroke and locked off during the upstroke. In desperation, we bought a vacuum pump-based bleeding kit, but have had no success with that (I have separate questions on that but don't want to divert this thread).
We tried clamping the four flexi hoses in case we had a simultaneous failure of the master cylinder - and indeed, there was still no pedal. But when we blanked off the two MC outlets with M12 x 1,0 blanking plugs we get a rock-solid pedal. This would suggest the problem is between the MC and the calipers. However, we also discovered that if we only blanked off one outlet we again had no pedal - and most surprisingly - it didn't matter which one we blanked off
I have run out of ideas.....
ArthurH said:
I have bled the brakes on countless vehicles over the last 40-plus years, but never struggled the way I am in this instance - I'd be grateful for any advice.
A few sentences to set the scene; earlier this year my son bought a 2016 Movano van. In the first week of his ownership we spotted that a rear caliper piston was sticking causing the brake to drag. We whipped off the caliper, stripped out the piston, cleaned it up, refitted the caliper, bled the brake - all was good. He then used the van for the rest of the year without issue. At the MoT a few weeks ago, it failed on the same caliper dragging slightly and a 'twist' in the front flexi hose, so this time we fitted a new rear caliper and loosened the front hose, it took seconds to remove the twist. The problem started when we tried to bleed the brakes.
Whatever we try we cannot get any resistance at the pedal. By which I mean there is no difference in feel at the pedal between the nipples being tight and completely removed! We have spent hours and hours on this and have put many litres of fluid through all four calipers.
Most of the bleeding has been 'old school' pumping of the pedal, while the nipples are opened on the down stroke and locked off during the upstroke. In desperation, we bought a vacuum pump-based bleeding kit, but have had no success with that (I have separate questions on that but don't want to divert this thread).
We tried clamping the four flexi hoses in case we had a simultaneous failure of the master cylinder - and indeed, there was still no pedal. But when we blanked off the two MC outlets with M12 x 1,0 blanking plugs we get a rock-solid pedal. This would suggest the problem is between the MC and the calipers. However, we also discovered that if we only blanked off one outlet we again had no pedal - and most surprisingly - it didn't matter which one we blanked off
I have run out of ideas.....
Why was the "twisted hose" not replaced ? It could be damaged internally.A few sentences to set the scene; earlier this year my son bought a 2016 Movano van. In the first week of his ownership we spotted that a rear caliper piston was sticking causing the brake to drag. We whipped off the caliper, stripped out the piston, cleaned it up, refitted the caliper, bled the brake - all was good. He then used the van for the rest of the year without issue. At the MoT a few weeks ago, it failed on the same caliper dragging slightly and a 'twist' in the front flexi hose, so this time we fitted a new rear caliper and loosened the front hose, it took seconds to remove the twist. The problem started when we tried to bleed the brakes.
Whatever we try we cannot get any resistance at the pedal. By which I mean there is no difference in feel at the pedal between the nipples being tight and completely removed! We have spent hours and hours on this and have put many litres of fluid through all four calipers.
Most of the bleeding has been 'old school' pumping of the pedal, while the nipples are opened on the down stroke and locked off during the upstroke. In desperation, we bought a vacuum pump-based bleeding kit, but have had no success with that (I have separate questions on that but don't want to divert this thread).
We tried clamping the four flexi hoses in case we had a simultaneous failure of the master cylinder - and indeed, there was still no pedal. But when we blanked off the two MC outlets with M12 x 1,0 blanking plugs we get a rock-solid pedal. This would suggest the problem is between the MC and the calipers. However, we also discovered that if we only blanked off one outlet we again had no pedal - and most surprisingly - it didn't matter which one we blanked off
I have run out of ideas.....
"old school" bleeding should see then nipple released during the down stroke, and also closed before completion of the downstroke to ensure air can never get back in.
But considering there should have been negligible fluid loss during the works if done correctly, the fact you say there is "no" pedal is odd.
Because when there are multiple circuits from the master, the untouched circuit should still be functional.
I would try and bleed better. Whilst the master test you done is semi valid, you've now introduced even more air into the system which is not a great idea when you're already struggling to bleed.
Either use vacuum to pull fluid through to each nipple, or a pressure system to pump from the master.
If the van has ABS, it seems highly likely you have now introduced air into the ABS unit, this may just pull/push through or the ABS unit may need to be cycled with a scantool to assist bleeding.
You're beyond the point now where simply using the pedal is likely to work.
You could leave it with the nipples open for a few hours and let gravity try, and you may get an xmas miracle.
With troublesome systems it can help to push each caliper/slave cylinder fully home then either clamp or wire them all fully closed, this was the only way i ever got a solid brake on series Landrovers but found it works for other troublesome bleeds too.
Sometimes you can be pressuring every caliper/slave cyl in the system which helps move air around and you end up chasing it as ity were, clampe or wire pistons pushed fully home and you've eliminated that problem.
When bleeding, i don't open and close the valve, i put a clear pipe over the nipple and feed it down into a tray or whatever you use to collect the waste fluid, then with a rubber glove on hand open the valve and hold finger gently over the end of the pipe, then get wifey (my best assistant) to pump the brakes fully not too fast probably half a dozen times till fluid comes through without air bubbles, then close the valve during the final downstroke.
Working from the furthest brake to the nearest, you might have to go round several times, topping up the fluid again after each corner.
note....worth wearing goggles during this as it takes a bit of practice getting the right pressure of finger over the bleed pipe end, brake fluid spray can travel a surprising distance and sods law dictates its going straight for your eyes, ask me how i know this.
Course this may be all moot, if you have an ABS unit in the system it may not bleed properly without the necessary software connected priming the ABS unit.
The good old Gunsons easibleed kit can work wonders but not all master cyls are suitable.
Sometimes you can be pressuring every caliper/slave cyl in the system which helps move air around and you end up chasing it as ity were, clampe or wire pistons pushed fully home and you've eliminated that problem.
When bleeding, i don't open and close the valve, i put a clear pipe over the nipple and feed it down into a tray or whatever you use to collect the waste fluid, then with a rubber glove on hand open the valve and hold finger gently over the end of the pipe, then get wifey (my best assistant) to pump the brakes fully not too fast probably half a dozen times till fluid comes through without air bubbles, then close the valve during the final downstroke.
Working from the furthest brake to the nearest, you might have to go round several times, topping up the fluid again after each corner.
note....worth wearing goggles during this as it takes a bit of practice getting the right pressure of finger over the bleed pipe end, brake fluid spray can travel a surprising distance and sods law dictates its going straight for your eyes, ask me how i know this.
Course this may be all moot, if you have an ABS unit in the system it may not bleed properly without the necessary software connected priming the ABS unit.
The good old Gunsons easibleed kit can work wonders but not all master cyls are suitable.
You may have to bleed the ABS Unit first; this is messy as it involves cracking open each of the four output unions in turn with no way of collecting the ejected fluid other than mopping up with eg kitchen paper. Treat each union as a bleed screw inasmuch as you only open it when the system is pressurised, and close it before the pressure is lost, easy with a pressure bleeder on the reservoir but not too tricky with an assistant pressing the pedal as long as you get the 'Down' 'Down' 'Up' 'Up' conversation going. You'll see the fluid emerge with/without bubbles, or not at all...
Old school way, but needs 2 people.
Get someone on the bleed nipple of the rear wheel furthest away from the driver.
Pump hell out of the brake pedal until the pedal becomes rock solid and hold it there. Now have the assistant open the nipple, and as the pedal goes to the floor it will flush all the trapped air out of the brake lines and anything else in the lines. Repeat one more time, then do the same to the other wheels with the other back one next then the front one furthest away from the driver.
Get someone on the bleed nipple of the rear wheel furthest away from the driver.
Pump hell out of the brake pedal until the pedal becomes rock solid and hold it there. Now have the assistant open the nipple, and as the pedal goes to the floor it will flush all the trapped air out of the brake lines and anything else in the lines. Repeat one more time, then do the same to the other wheels with the other back one next then the front one furthest away from the driver.
Smint said:
The good old Gunsons easibleed kit can work wonders but not all master cyls are suitable.
And be very careful to check that the pressure in the tyre you're using is at or below the recommended pressure first BEFORE connecting to the easibleed.Too much pressure and/or aging plastic m/cyl reservoirs can be spectacular!
Thank you for your advice, much appreciated.
Thank you again - I will let you know what happens
stevieturbo said:
Why was the "twisted hose" not replaced ? It could be damaged internally.
This was a 'minor' on the MoT, the total twist was about 45deg of rotation, barely noticeable, I only mentioned it as it was another potential source of air entry.stevieturbo said:
"old school" bleeding should see then nipple released during the down stroke, and also closed before completion of the downstroke to ensure air can never get back in.
Totally agree, also accompanied by the 'Down' 'Down' 'Up' 'Up' " conversation with the assistant at the pedal, I prefer this to a tube submerged at its end, as it eliminates the risk of air getting past the nipple threads. We also tried the furious pumping approach which I have found helpful in the past in clearing troublesome airlocks. It seems to work by pushing the bubbles faster than they can travel back upwards due to the viscosity of the fluid. But in this case, no joy.stevieturbo said:
If the van has ABS, it seems highly likely you have now introduced air into the ABS unit, this may just pull/push through or the ABS unit may need to be cycled with a scantool to assist bleeding.
It does have ABS. Looking at where the MC pipes connect to the pump, immediately below the four outlet pipes, it looks like it should pull through - but it is where I will attack next.pando99 said:
I then used a pressure kit to push it through and boom, tons of bubbles and sorted.
The vacuum kit we tried seemed to fail by pulling air past the nipple threads - a pressure kit may be a better bet. I remember a Gunson kit I owned decades ago has a selection of lids; do modern MCs have a 'standard' lid size?TwinKam said:
You may have to bleed the ABS Unit first; this is messy as it involves cracking open each of the four output unions in turn with no way of collecting the ejected fluid other than mopping up with eg kitchen paper. Treat each union as a bleed screw inasmuch as you only open it when the system is pressurised, and close it before the pressure is lost.
This is what I will try nextNMNeil said:
Pump hell out of the brake pedal until the pedal becomes rock solid and hold it there.
Even with the nipples fully locked off and the pedal pumped for ages, it never becomes even slightly firmThank you again - I will let you know what happens
Try letting gravity do the work first if you do not have any suitable tools to assist with the job.
But even a simple large syringe and clear tube can work wonders to let you move fluid both directions and costs very little and also requires only one person.
Messing with a hose and caliper, really there is no possible way air should have got into the ABS unit, however, removing pipes from the master, there is no question you will have introduced air everywhere.
I get why you did it, or thought you needed to, but it will not help the situation.
But even a simple large syringe and clear tube can work wonders to let you move fluid both directions and costs very little and also requires only one person.
Messing with a hose and caliper, really there is no possible way air should have got into the ABS unit, however, removing pipes from the master, there is no question you will have introduced air everywhere.
I get why you did it, or thought you needed to, but it will not help the situation.
Vacuum can work but it really needs to be constant, not hand pumped (eg Mitivac) in order to get sufficient flow esp through the ABS unit and leave you with both hands free. Importantly, you need to seal the nipple threads with a suitably sticky and brake compatible 'grease', for the record I would advise red rubber grease. You can do this by either removing each nipple and applying the grease directly to its thread (clamp the flexi so that it's not immediately washed off by escaping fluid), or by smearing it around the base of the nipple in place... you'll soon see and hear when you've sealed the air leak.
TwinKam said:
Vacuum can work but it really needs to be constant, not hand pumped (eg Mitivac) in order to get sufficient flow esp through the ABS unit and leave you with both hands free. Importantly, you need to seal the nipple threads with a suitably sticky and brake compatible 'grease', for the record I would advise red rubber grease. You can do this by either removing each nipple and applying the grease directly to its thread (clamp the flexi so that it's not immediately washed off by escaping fluid), or by smearing it around the base of the nipple in place... you'll soon see and hear when you've sealed the air leak.
I usually put some ptfe tape around the threads.But a big syringe works fine to pull vacuum, and dead easy. And if you need you can also push fluid back up through with the same tool without even disconnecting to bleed both directions if needed
NMNeil said:
This would tend to indicate bad master cylinder seals.
And this would suggest otherwise.[quote=ArthurH
But when we blanked off the two MC outlets with M12 x 1,0 blanking plugs we get a rock-solid pedal. This would suggest the problem is between the MC and the calipers.
I've also never seen a master cylinder just randomly fail in such a manner. Ever.
I've seen plenty replace masters thinking they are faulty, and then still be unable to bleed the brakes...because the master was never the problem. It was their ability to bleed.
Really....try gravity first, let it sit for a few hours with the nipples open and keep an eye on fluid movement.
Failing that, either a pressure or vacuum bleeder. Trying to use the pedal these days just makes life more difficult. And find out if your vehicle is a troublesome one in terms of the ABS unit and whether it must be cycled or not in order to bleed.
Once we had discovered that we still had no pedal with all four flexi hoses clamped, all of the advice on the interweb said this 'proved' it must be the MC that had failed. But that didn't sit well with me, which is why we invested in the MC blanking plugs. We knew that fitting them would let more air in - but it was a necessary step in the debug.
The research I had done prior to posting on this forum suggested that the Movano was not a vehicle that needed special cycling of the ABS - but of course, that could be wrong.
I am going to invest in a pressure bleeding kit - if it doesn't simply 'work' by expelling the trapped air through the caliper nipples, I would then try removing the outlets from the ABS pump one by one and bleeding there (while appreciating how messy that would be).
Perhaps a kit like this? https://www.ebay.co.uk/itm/293435727170
As per my question above, I am still unsure about getting the correct lid for the MC. The modern kits aren't advertised with a range of adaptors. Are the MC lids now some form of standard size/thread?
The research I had done prior to posting on this forum suggested that the Movano was not a vehicle that needed special cycling of the ABS - but of course, that could be wrong.
I am going to invest in a pressure bleeding kit - if it doesn't simply 'work' by expelling the trapped air through the caliper nipples, I would then try removing the outlets from the ABS pump one by one and bleeding there (while appreciating how messy that would be).
Perhaps a kit like this? https://www.ebay.co.uk/itm/293435727170
As per my question above, I am still unsure about getting the correct lid for the MC. The modern kits aren't advertised with a range of adaptors. Are the MC lids now some form of standard size/thread?
Your link is from China.
You could ask if it comes with several different caps for different sized m/cyls but returns might be a bit of an issue!
I've had my Gunson's Eezibleed for several decades. (Now sold as the G4602 & there is a 'fits anything' cap available either separately or with a different kit. I haven't got & never needed that cap so I've no idea how good it is)
Mine came with half a dozen different sized caps & it's always been fine.
I use it with a old Metro wheel that I kept for the purpose.
But bear in mind my earlier warning about pressure!
You could ask if it comes with several different caps for different sized m/cyls but returns might be a bit of an issue!
I've had my Gunson's Eezibleed for several decades. (Now sold as the G4602 & there is a 'fits anything' cap available either separately or with a different kit. I haven't got & never needed that cap so I've no idea how good it is)
Mine came with half a dozen different sized caps & it's always been fine.
I use it with a old Metro wheel that I kept for the purpose.
But bear in mind my earlier warning about pressure!
just buy a syringe.
Cheap and dead easy.
Suck fluid to each corner ( noting sealing nipple threads ) and if needed you can then reverse bleed back to the master again by pushing the fluid back up.
https://www.ebay.co.uk/itm/404040262500
And you get a good visual on the state of the fluid in the pipe as you do it.
But again, try gravity first. You've been posting for a few days now, it would probably have bled itself sitting like that with the nipples open, or at laast got a good way to it.
But a pressure tool like that will work well too, and has been said, cap seal is important if you do not want a huge mess everywhere.
Cheap and dead easy.
Suck fluid to each corner ( noting sealing nipple threads ) and if needed you can then reverse bleed back to the master again by pushing the fluid back up.
https://www.ebay.co.uk/itm/404040262500
And you get a good visual on the state of the fluid in the pipe as you do it.
But again, try gravity first. You've been posting for a few days now, it would probably have bled itself sitting like that with the nipples open, or at laast got a good way to it.
But a pressure tool like that will work well too, and has been said, cap seal is important if you do not want a huge mess everywhere.
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