Discussion
Hi, I'm battling a brake issue on my Fiesta ST at the moment where the pedals soft and unresponsive in the first half, then half way down it gets firmer but still the brakes aren't sharp and cant produce the stopping power they used to.
I must've bled my brakes over 10 times this year trying to get rid of any potential air and after replacing items, and using multiple different methods including the traditional 2 man method, pressure bleeding and doing diagnostics ABS bleeds. The pedal doesn't pump which I believe it would usually do if it was just air in the system, and the pads, discs and braided lines are all healthy. I've replaced my ABS unit twice, admittedly with second hand items but both appeared to be in good condition from the outside at least, plus a brand new master cylinder, and the fault is still there. Strangely after changing the ABS unit for the first time it seemed to fix the issue for a few days, then I parked the car up with them still feeling fixed, and next time I got back in they were instantly terrible again.
I'm starting to run out of ideas. I've heard handbrake adjustment can have an effect on the pedal, or there could potentially be an unknown issue with the calipers, although the pistons all move freely and the slide pins are all free and well greased.
Has anyone experienced anything similar or have any other ideas about what could be causing the issue? TIA
I must've bled my brakes over 10 times this year trying to get rid of any potential air and after replacing items, and using multiple different methods including the traditional 2 man method, pressure bleeding and doing diagnostics ABS bleeds. The pedal doesn't pump which I believe it would usually do if it was just air in the system, and the pads, discs and braided lines are all healthy. I've replaced my ABS unit twice, admittedly with second hand items but both appeared to be in good condition from the outside at least, plus a brand new master cylinder, and the fault is still there. Strangely after changing the ABS unit for the first time it seemed to fix the issue for a few days, then I parked the car up with them still feeling fixed, and next time I got back in they were instantly terrible again.
I'm starting to run out of ideas. I've heard handbrake adjustment can have an effect on the pedal, or there could potentially be an unknown issue with the calipers, although the pistons all move freely and the slide pins are all free and well greased.
Has anyone experienced anything similar or have any other ideas about what could be causing the issue? TIA
Edited by Joshs96 on Monday 28th October 09:47
Try testing the diaphragm on the servo with a vacuum tester. https://pagid.com/wp-content/uploads/2017/06/Servo...
I had spongy brakes on a car having to apply on a lot of pressure to slow down so I changed out everything (pads,braided brake lines, multiple bleeds) and it still didn't help, it turned out there was a tear in the servo which wasn't enough to trigger a lean code on the ecu but was enough to make the brakes really spongy.
As soon as it was replaced the pedal became firm again and got it's initial brake boosted bite back.
I had spongy brakes on a car having to apply on a lot of pressure to slow down so I changed out everything (pads,braided brake lines, multiple bleeds) and it still didn't help, it turned out there was a tear in the servo which wasn't enough to trigger a lean code on the ecu but was enough to make the brakes really spongy.
As soon as it was replaced the pedal became firm again and got it's initial brake boosted bite back.
untakenname said:
Try testing the diaphragm on the servo with a vacuum tester. https://pagid.com/wp-content/uploads/2017/06/Servo...
I had spongy brakes on a car having to apply on a lot of pressure to slow down so I changed out everything (pads,braided brake lines, multiple bleeds) and it still didn't help, it turned out there was a tear in the servo which wasn't enough to trigger a lean code on the ecu but was enough to make the brakes really spongy.
As soon as it was replaced the pedal became firm again and got it's initial brake boosted bite back.
Ok thanks for that idea I'll have a look into it. I'd kind of dismissed the servo as I thought that issues with it usually result in a very hard pedal, but if it had that effect for you it'll be worth a check.I had spongy brakes on a car having to apply on a lot of pressure to slow down so I changed out everything (pads,braided brake lines, multiple bleeds) and it still didn't help, it turned out there was a tear in the servo which wasn't enough to trigger a lean code on the ecu but was enough to make the brakes really spongy.
As soon as it was replaced the pedal became firm again and got it's initial brake boosted bite back.
RLK500 said:
When you bleed them, do you still see bubbles in the bled fluid. If so, you have a leak somewhere. If you haven't touched the calipers my first port of call would be the braided hoses. The unions need to be super tight, so worth checking.
Well I don't have any normal bubbles coming out, but I do have a strange situation where when I perform an ABS bleed, lots of extremely small bubbles come out of both front calipers, small enough that they look like small specs of dust or something. This only happens when performing an ABS bleed, and if left to gravity bleed for a couple of minutes after they clear up again. I've bleed the ABS unit many times now so I don't believe its just residual air inside it, but I've checked the caliper banjo bolts are done up tight and all the brake lines going into and out of the ABS unit are done up tight, and the fluid level doesn't drop at all, so not sure where these could be getting in. I took a video of it one time which you can see in the link below.
One thing to note is that this has only started since changing the ABS unit, and the brake issue was there before there was any sign of this.
https://youtu.be/MljMeO9bIzA
Edited by Joshs96 on Monday 28th October 14:43
It sounds like you have a pinhole leak somewhere which is drawing air in. Counterintuitive I know, but when you release the brakes there is a small amount of negative pressure which will pull air into the circuit.
Check around the caliper inlet ports, the master cylinder and any other joins in the brake lines you can find to see if there is anywhere that looks a bit wet.
Failing that it could be a faulty master cylinder, it would make sense given that replacing the ABS block close to it cured it temporarily.
Check around the caliper inlet ports, the master cylinder and any other joins in the brake lines you can find to see if there is anywhere that looks a bit wet.
Failing that it could be a faulty master cylinder, it would make sense given that replacing the ABS block close to it cured it temporarily.
Sounds like master cylinder.
If pumping the pedal doesn't firm the pedal up, it sounds like every pedal press is allowing the air in rather than compressing the air that is in there.
Having said that abs pumps can be real pigs to bleed once disturbed. If you have changed that and bled repeatedly I would be looking for the source of the air, not continually trying to chase it out.
If pumping the pedal doesn't firm the pedal up, it sounds like every pedal press is allowing the air in rather than compressing the air that is in there.
Having said that abs pumps can be real pigs to bleed once disturbed. If you have changed that and bled repeatedly I would be looking for the source of the air, not continually trying to chase it out.
The Wookie said:
It sounds like you have a pinhole leak somewhere which is drawing air in. Counterintuitive I know, but when you release the brakes there is a small amount of negative pressure which will pull air into the circuit.
Check around the caliper inlet ports, the master cylinder and any other joins in the brake lines you can find to see if there is anywhere that looks a bit wet.
Failing that it could be a faulty master cylinder, it would make sense given that replacing the ABS block close to it cured it temporarily.
It seems that way yeah, although I've checked over all the joints from the master cylinder into the ABS and the lines out of the ABS multiple times and haven't found any sign of brake fluid, and have tried making sure the fittings are done up tight, so I'm struggling to understand where the air could actually be getting in. It does seem to only be the fronts that have these tiny bubbles though, which I think is strange as well.Check around the caliper inlet ports, the master cylinder and any other joins in the brake lines you can find to see if there is anywhere that looks a bit wet.
Failing that it could be a faulty master cylinder, it would make sense given that replacing the ABS block close to it cured it temporarily.
I've tried changing the master cylinder and it didn't make a difference unfortunately. Part of me wonders if its possible the ABS unit might be receiving a faulty signal from somewhere that is telling it to keep an internal valve open, as I think this could explain why after I changed the ABS unit the first time it went from being fixed to faulty again without any input. Not sure if this could be a feasible explaination?
I think you'd be able to tell if it was the ABS unit just by trying with it unplugged, there shouldn't be anything that allows a poor brake pedal when passive
If you're convinced that you've checked everything and done it all properly (e.g. new copper gaskets on any banjo joints, everything else torqued to correct numbers rather than just FT'd, etc) then it could be some sort of weird servo problem
The strange aspect is that it's both front calipers producing bubbles, you'd say that means the problem would have to be upstream of the point where the circuit splits but normally on these sort of cars it's a diagonal circuit, so the fronts aren't actually linked at any point, including within the ABS block, or certainly not in any way where you'd expect a repeat issue between two units.
Makes me think that the bubbles are either a shared component issue (faulty braided lines) or that it's a red herring (e.g. just drawing air in through the bleed nipples during bleeding creating the false impression that there's air ingress)
If you're convinced that you've checked everything and done it all properly (e.g. new copper gaskets on any banjo joints, everything else torqued to correct numbers rather than just FT'd, etc) then it could be some sort of weird servo problem
The strange aspect is that it's both front calipers producing bubbles, you'd say that means the problem would have to be upstream of the point where the circuit splits but normally on these sort of cars it's a diagonal circuit, so the fronts aren't actually linked at any point, including within the ABS block, or certainly not in any way where you'd expect a repeat issue between two units.
Makes me think that the bubbles are either a shared component issue (faulty braided lines) or that it's a red herring (e.g. just drawing air in through the bleed nipples during bleeding creating the false impression that there's air ingress)
Unless theres some sort of minor damage to a fitting thats able to let air in but either none or undetectable amounts of fluid out then I'm sure everythings done up tightly. As part of this I've replaced the front braided lines as well with brand new Goodridge items, which came with new banjo bolts and copper washers, that I did up to the recommended torque.
I had considered that one of the fittings on a brake line from the master cylinder into the ABS unit may potentially be slightly damaged and causing the bubbles, however as you say if there is a cross configuration that must rule the idea out.
Perhaps as you say it could be air passing around the bleed nipple during bleeding, but again that seems odd as there is surely only pressure being applied to the caliper when carrying out an ABS bleed, so I wouldn't have thought air could get sucked in?
I had considered that one of the fittings on a brake line from the master cylinder into the ABS unit may potentially be slightly damaged and causing the bubbles, however as you say if there is a cross configuration that must rule the idea out.
Perhaps as you say it could be air passing around the bleed nipple during bleeding, but again that seems odd as there is surely only pressure being applied to the caliper when carrying out an ABS bleed, so I wouldn't have thought air could get sucked in?
It's not that unusual to be fair, don't ask me why, either a flow characteristic (or cavitation?) or maybe rushing it and there still being a bit of negative pressure in the lines as the bleed is opened.
I would still fire the car up to get the servo working and stand on the pedal to generate some big pressure and see if there's any obvious weepage though. You might not find it in normal use.
Unfortunately beyond that I think you're into the territory of replacing parts and hoping to find something that fixes it.
I would still fire the car up to get the servo working and stand on the pedal to generate some big pressure and see if there's any obvious weepage though. You might not find it in normal use.
Unfortunately beyond that I think you're into the territory of replacing parts and hoping to find something that fixes it.
Joshs96 said:
Unless theres some sort of minor damage to a fitting thats able to let air in but either none or undetectable amounts of fluid out then I'm sure everythings done up tightly.
It's entirely possible for a leak to let air in without letting noticeable quantities of fluid out.Gassing Station | Suspension, Brakes & Tyres | Top of Page | What's New | My Stuff