Brake Pedal goes straight to the floor... Impossible to fix?
Discussion
Hi All,
I have posted this query before a few times and each time get recommended a different fix to try, which I've added to a list of what we've done below, so if the post feels familiar, that is why...
The track car a friend and I own has been off the road for a year now with a brakes issue we cannot resolve.
I was approaching Paddock Hill bend and hit the brakes and noticed they weren't "all there", it felt as if I only had half brakes, I took it easy and brought the car back in. The pedal was going fully to the floor with no resistance.
So far we, have:
-Replaced the master cylinder
-Manually bled the ABS and master cylinder from all connections to/from them (multiple times)
-Bled the brakes (multiple times)
-Used a pressurised brake bleeder to try and force the air out
-Tried emergency braking on gravel to try and activate the ABS to remove any trapped air
-Completely stripped the brakes down and refurbished the callipers with new seals, pistons, guide pins and grease
-Had the ABS Module professionally refurbished/rebuilt by a company that specialises in doing this
-Re-bled for over 3 hours after the module was reinstalled.
But despite all that, the pedal is still going to the floor with almost no pressure.
We’re stumped at what else we can do to fix the issue.
It seems like there is absolutely nothing left for us to try. We've seemingly looked at every part of the brakes system.
There is categorically 100% not any air in the system whatsoever, and all of the pipes and parts have either been replaced or refurbished.
Is there anything we may have missed?
I have posted this query before a few times and each time get recommended a different fix to try, which I've added to a list of what we've done below, so if the post feels familiar, that is why...
The track car a friend and I own has been off the road for a year now with a brakes issue we cannot resolve.
I was approaching Paddock Hill bend and hit the brakes and noticed they weren't "all there", it felt as if I only had half brakes, I took it easy and brought the car back in. The pedal was going fully to the floor with no resistance.
So far we, have:
-Replaced the master cylinder
-Manually bled the ABS and master cylinder from all connections to/from them (multiple times)
-Bled the brakes (multiple times)
-Used a pressurised brake bleeder to try and force the air out
-Tried emergency braking on gravel to try and activate the ABS to remove any trapped air
-Completely stripped the brakes down and refurbished the callipers with new seals, pistons, guide pins and grease
-Had the ABS Module professionally refurbished/rebuilt by a company that specialises in doing this
-Re-bled for over 3 hours after the module was reinstalled.
But despite all that, the pedal is still going to the floor with almost no pressure.
We’re stumped at what else we can do to fix the issue.
It seems like there is absolutely nothing left for us to try. We've seemingly looked at every part of the brakes system.
There is categorically 100% not any air in the system whatsoever, and all of the pipes and parts have either been replaced or refurbished.
Is there anything we may have missed?
TREMAiNE said:
Is there anything we may have missed?
You forgot to mention what kind of car it is, which is kind of important to be able to offer help. All we know is it has ABS. Given its been in a state of disassembly/reassembly what with replacing the master cylinder, it may need a diagnostic computer plugged in and the ABS module put into a service mode to allow it to be bled properly.Also in your list, you've not mentioned if you've thoroughly checked the brake lines including flexis, but given it would show an obvious fluid puddle if it has a leak, I'll assume you don't have a leak there. Unless the lines are enclosed by underfloor trim and its pooling there.
I'm not familiar with your ABS system and I don't know the recommended way to test it. Given everything else you've already done, I'd try to separate the different parts of the brake system and prove they each work as expected.
Does the master cylinder displace fluid at all ports when you press the pedal?
Does it resist pedal movement when all the ports are blocked?
If you connect the port directly to a caliper, does it apply that brake and resist pedal movement? Same for the other calipers.
Similar tests at the outputs from the ABS unit. The ABS unit is the most complex part and is the place I'd suspect first, but you should be able to prove everything else is OK.
Does the master cylinder displace fluid at all ports when you press the pedal?
Does it resist pedal movement when all the ports are blocked?
If you connect the port directly to a caliper, does it apply that brake and resist pedal movement? Same for the other calipers.
Similar tests at the outputs from the ABS unit. The ABS unit is the most complex part and is the place I'd suspect first, but you should be able to prove everything else is OK.
Did you prime the new master? Some will not bleed up if you don't.
Run pipes from the outlet ports and loop them back into the reservoir then very slowly press and release the pedal until absolutely no bubbles exit the pipes.
You have to do this as the master will sometimes shuttle the air back and forth in the cylinders if there is any back pressure .
edit to say the pipe end must be submerged in the fluid in the res (in case that was not clear..)
Run pipes from the outlet ports and loop them back into the reservoir then very slowly press and release the pedal until absolutely no bubbles exit the pipes.
You have to do this as the master will sometimes shuttle the air back and forth in the cylinders if there is any back pressure .
edit to say the pipe end must be submerged in the fluid in the res (in case that was not clear..)
Don't be annoyed, all the bleed valves are at the top of each caliper?
Going back a long time now i could not get the all drum brakes to bleed on my ex wd Landrover, went through pints of fluid bu always a soft pedal.
Eventually i clamped the slave cylinders shut with G Clamps, that worked a treat, could probably have wired them shut instead.
No reason why you couldn't do similar with calipers and pistons, using G clamps or whatever you have to hand to hold the pistons fully home, then try bleeding.
Going back a long time now i could not get the all drum brakes to bleed on my ex wd Landrover, went through pints of fluid bu always a soft pedal.
Eventually i clamped the slave cylinders shut with G Clamps, that worked a treat, could probably have wired them shut instead.
No reason why you couldn't do similar with calipers and pistons, using G clamps or whatever you have to hand to hold the pistons fully home, then try bleeding.
You need to re-check the master cylinder.
Either way it is not impossible to fix, it is just that you have yet to find the problem.
Basically it sounds to me that if you aren't losing fluid the only reasonable explanation for the symptoms you describe is the master cylinder seals.
Unless something is not how you describe it.
Either way it is not impossible to fix, it is just that you have yet to find the problem.
Basically it sounds to me that if you aren't losing fluid the only reasonable explanation for the symptoms you describe is the master cylinder seals.
Unless something is not how you describe it.
If you're at a loss, keep it simple and follow a process.
Plug the outlet ports on the master, and bleed/test like that. Master proven or disproven.
Likewise at the ABS unit. Block off either inlets of outlets, whatever is more convenient, whatever the case may be, and bleed to that point. And carry on as needed.
Isolate where any issues may be
But saying the pedal goes straight to the floor, with no resistance at all, either nothing is anywhere near bled at all, or it is a master issue. Even with gravity alone and nipples open to bleed ( although that can be a slow process ), it should be very easy to get some pedal to start with.
Or even a pressure bleeder, syringe and hose at each caliper, whatever. Getting some pedal to start with, should be easy.
Plug the outlet ports on the master, and bleed/test like that. Master proven or disproven.
Likewise at the ABS unit. Block off either inlets of outlets, whatever is more convenient, whatever the case may be, and bleed to that point. And carry on as needed.
Isolate where any issues may be
But saying the pedal goes straight to the floor, with no resistance at all, either nothing is anywhere near bled at all, or it is a master issue. Even with gravity alone and nipples open to bleed ( although that can be a slow process ), it should be very easy to get some pedal to start with.
Or even a pressure bleeder, syringe and hose at each caliper, whatever. Getting some pedal to start with, should be easy.
E-bmw said:
Unless something is not how you describe it.
Somtimes you get vehicles with such bad brake designs that they need to be bled off the vehicle to chase the air pockets out. I wouldn't expect to find that on a modern production vehicle, but you never know until you check. It wouldn't take a big volume of air to completely knacker the brakes.Hi All,
I've gone back to my friend with all of your comments (thank you, by the way) and he's made a point that I've described the issue incorrectly (sorry - it's been over a year since I've last seen the car in the flesh, he does all the work on it). The pedal doesn't go right to the floor. It goes about halfway and does have a solid resistance at that point. Granted, it is spongy, but there is some resistance, although not much.
I'm not sure if that makes a difference to the possible diagnosis, but we will go down the route of checking the master cylinder again.
Sorry for the novice question, but where Athlon has suggested to run pipes from the outlet ports and loop them back into the reservoir, then very slowly press and release the pedal until absolutely no bubbles exit the pipes, what parts and tools do we need to actually do this? Or is it re-routing existing pipes? Do we actually need a specific pipe in order to do this?
I've gone back to my friend with all of your comments (thank you, by the way) and he's made a point that I've described the issue incorrectly (sorry - it's been over a year since I've last seen the car in the flesh, he does all the work on it). The pedal doesn't go right to the floor. It goes about halfway and does have a solid resistance at that point. Granted, it is spongy, but there is some resistance, although not much.
I'm not sure if that makes a difference to the possible diagnosis, but we will go down the route of checking the master cylinder again.
Sorry for the novice question, but where Athlon has suggested to run pipes from the outlet ports and loop them back into the reservoir, then very slowly press and release the pedal until absolutely no bubbles exit the pipes, what parts and tools do we need to actually do this? Or is it re-routing existing pipes? Do we actually need a specific pipe in order to do this?
TREMAiNE said:
Hi All,
Sorry for the novice question, but where Athlon has suggested to run pipes from the outlet ports and loop them back into the reservoir, then very slowly press and release the pedal until absolutely no bubbles exit the pipes, what parts and tools do we need to actually do this? Or is it re-routing existing pipes? Do we actually need a specific pipe in order to do this?
You can make short pipes up or you can get plastic fittings with tube online, at least you could, any decent garage will be able to make short runs up. When you are doing this there is no pressure in the pipes at all so they only have to be just air tight enough when fitted to not pull air in to the joints on the return stroke. Sorry for the novice question, but where Athlon has suggested to run pipes from the outlet ports and loop them back into the reservoir, then very slowly press and release the pedal until absolutely no bubbles exit the pipes, what parts and tools do we need to actually do this? Or is it re-routing existing pipes? Do we actually need a specific pipe in order to do this?
So to summarise, remove the two pipes from the master, replace with two that loop back into the masters res, nip them up then slowly pump the pedal until no bubbles show up, there can be a surprising amount of air in the master. Once no bubbles, remove the pipes, replace the originals then just as you are about to nip them up have someone very gently press the pedal to push any air from the joints out, nip up, check the fluid level and try to bleed again.
TREMAiNE said:
It goes about halfway and does have a solid resistance at that point. Granted, it is spongy, but there is some resistance, although not much.
Sounds like you have a conventional dual circuit master cylinder and one of the circuits is producing some resistance.I'd still follow the approach I mentioned earlier.
TREMAiNE said:
Hi All,
I've gone back to my friend with all of your comments (thank you, by the way) and he's made a point that I've described the issue incorrectly (sorry - it's been over a year since I've last seen the car in the flesh, he does all the work on it). The pedal doesn't go right to the floor. It goes about halfway and does have a solid resistance at that point. Granted, it is spongy, but there is some resistance, although not much.
I'm not sure if that makes a difference to the possible diagnosis, but we will go down the route of checking the master cylinder again.
It makes a huge difference IMHO.I've gone back to my friend with all of your comments (thank you, by the way) and he's made a point that I've described the issue incorrectly (sorry - it's been over a year since I've last seen the car in the flesh, he does all the work on it). The pedal doesn't go right to the floor. It goes about halfway and does have a solid resistance at that point. Granted, it is spongy, but there is some resistance, although not much.
I'm not sure if that makes a difference to the possible diagnosis, but we will go down the route of checking the master cylinder again.
First thing to do from your new description is to do the foot to the floor very slowly & tell us what happens. When you are doing this try to have someone with a FOB bar across the wheel nuts or something at various points to see if ONLY certain wheels are being braked.
If the pedal resistance slowly builds up and the braking is consistent it is likely air in the system. If it just leaves one corner behind then that could point to the culprit if is just one corner.
If it stays very low to no resistance & then the resistance rises part way down it is likely still a master cylinder as above with 1 seal gone & 1 OK.
Edited by E-bmw on Friday 6th June 06:21
GreenV8S said:
E-bmw said:
Unless something is not how you describe it.
Somtimes you get vehicles with such bad brake designs that they need to be bled off the vehicle to chase the air pockets out. I wouldn't expect to find that on a modern production vehicle, but you never know until you check. It wouldn't take a big volume of air to completely knacker the brakes.You can buy gauges like these which will help show if you are getting any pressure at each wheel.
https://ebay.us/m/WppqTy
Another thing easier and cheaper to try is block off the front or rear brakes by fitting a small piece of pipe with the end sealed by bending over and isolate whether you have a problem with all brakes or just front/rears.
https://ebay.us/m/WppqTy
Another thing easier and cheaper to try is block off the front or rear brakes by fitting a small piece of pipe with the end sealed by bending over and isolate whether you have a problem with all brakes or just front/rears.
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