Strange Brake Problem

[Mikeachrist]

Hi I’m hoping someone can point me in the right direction.

I have a 2016 fist, 93k miles. The other day I noticed a pull the left under braking, and a bit of a dive to the front right. I figured out that the front right caliper was not actuating.
I pulled it and renewed the guide pins, but they were fine.
I retracted the piston, no problem. Step on the brake, nothing piston doesn’t budge. I figured I need a new caliper, I disconnected the brake line, and applied the brakes, no fluid comes out of the line. Disconnect the hose from the hard line, apply brakes and no fluid comes out.

I attempted to pull fluid through via vacuum with a brake bleeder, nothing.
The three other brakes work fine, and I’m able to bleed them.

the pedal is not soft, if anything it’s occasionally a little hard (hard pedal happened at the same time as the inop caliper, no MIL, wouldn’t I get one with a vacuum leak?)

to be clear this didn’t happen after some work I did, the pads rotors and soft lines are stop tech and they have been installed about 40k miles ago. I flushed the fluid myself about 25k miles ago.

is it the ABS pump? Proportioning valve? No warning lights… I figured I’d get an ABS warning light or something.

thanks!

 

[jhullin]

Any updates on this? I'm having the same issue with the left rear.

 

[the duke]

My guess is either FOD in the line or maybe you need a new master cylinder? I think we have 2-way systems for safety and run a separate circuit front and rear, at least to allow some braking while the pressure bleeds off in the even one end of the car has a leak.

 

[jhullin]

In my case, the rear right bleeds but the rear left does not. Would a bad master cylinder allow one to work properly? I'm wondering if the abs valve is stuck for the right left. Thanks for the help....

 

[the duke]

In my case, the rear right bleeds but the rear left does not. Would a bad master cylinder allow one to work properly? I'm wondering if the abs valve is stuck for the right left. Thanks for the help....

The dual circuit should be proportioning front and rear, not left to right. Either it's blocked (FOD) or the ABS pump like you mentioned is stuck/dead.

If you get a connector and FORSCAN you can cycle the ABS pump and see if that fixes it. There might be a diagnostic cycle you can run. I would imagine for a safety system, there'd be internal codes the ECU is throwing that FORSCAN can view.

 

[jhullin]

Yeah, tried that with forscan, didn't help....No codes either. Can the abs valve be stuck in a closed postion resulting in zero brake function at all to that particular wheel?

 

[Jabbit]

Yeah, tried that with forscan, didn't help....No codes either. Can the abs valve be stuck in a closed postion resulting in zero brake function at all to that particular wheel?

Activating the abs pump at the specific wheel with the bleeder open didn't produce fluid?

 

[jhullin]

Activating the abs pump at the specific wheel with the bleeder open didn't produce fluid?

None with the abs bleed function on forscan, and none when having someone push down the pedal with the bleeder open. I even disconnected the line before the caliper with the same results.

 

[Dialcaliper]

The dual circuit should be proportioning front and rear, not left to right. Either it's blocked (FOD) or the ABS pump like you mentioned is stuck/dead.

If you get a connector and FORSCAN you can cycle the ABS pump and see if that fixes it. There might be a diagnostic cycle you can run. I would imagine for a safety system, there'd be internal codes the ECU is throwing that FORSCAN can view.

Front/Rear is not correct for passenger cars. Race cars do that for brake balance, but these days passenger cars are usually set up to pair diagonal pairs (FR+LR and FL+RR) on two parallel circuits. There’s no separate prop valve on modern ABS cars - proportioning is handled electronically by the ABS system.

If it’s one channel of the master cylinder going, it might cause a pull, but you’d probably start noticing some increased pedal travel. Have you also inspected the left rear caliper and the other pair for good measure? If the other three calipers actuate fine, from your description it sounds ABS related.

Have you tried a full system flush in order starting from the right rear, ending with left front and then the ABS bleed?

Also, not sure if its at all related but I just noticed in the service manual it says “due to the complexity of the fluid path in the rear calipers, it is necessary to engage and release the parking brake during the bleeding procedure.” Huh.

 

[jhullin]

Front/Rear is not correct for passenger cars. Race cars do that for brake balance, but these days passenger cars are usually set up to pair diagonal pairs (FR+LR and FL+RR) on two parallel circuits. There’s no separate prop valve on modern ABS cars - proportioning is handled electronically by the ABS system.

If it’s one channel of the master cylinder going, it might cause a pull, but you’d probably start noticing some increased pedal travel. Have you also inspected the left rear caliper and the other pair for good measure? If the other three calipers actuate fine, from your description it sounds ABS related.

Have you tried a full system flush in order starting from the right rear, ending with left front and then the ABS bleed?

Also, not sure if its at all related but I just noticed in the service manual it says “due to the complexity of the fluid path in the rear calipers, it is necessary to engage and release the parking brake during the bleeding procedure.” Huh.

Test drove yesterday with some hard stops and there was zero pull, and pedal felt fine. Using forscan I did abs bleed, selecting master cylinder first, which pumps fluid out both fronts at the same time. then the rears together but nothing came out the rear left ever. Tried several times. I have not tried the full system flush in the usual order although I did try bleeding the rear left by itself by selecting caliper on the bleed menu. Not a drop. Appreciate the help.....

 

[Dialcaliper]

Test drove yesterday with some hard stops and there was zero pull, and pedal felt fine. Using forscan I did abs bleed, selecting master cylinder first, which pumps fluid out both fronts at the same time. then the rears together but nothing came out the rear left ever. Tried several times. I have not tried the full system flush in the usual order although I did try bleeding the rear left by itself by selecting caliper on the bleed menu. Not a drop. Appreciate the help.....

Just out of curiosity, did you try the parking brake thing (engage/disengage) while bleeding the rear?

 

[jhullin]

Just out of curiosity, did you try the parking brake thing (engage/disengage) while bleeding the rear?

No I didn't, going to try again at some point.

 

[FiestaSTdude]

Just out of curiosity, did you try the parking brake thing (engage/disengage) while bleeding the rear?

Isn’t the parking brake cable operated? I don’t understand how that would affect the fluid, but I also know far less about it than the ford engineers so I’d definitely do it like they recommend.

 

[jhullin]

**Update**
My problem was the valve stuck closed on the HCU. I bought a used ABS module/HCU on ebay for 90 bucks and that fixed it. I ended up using my original ABS Module on the ebay HCU. I did have to use forscan to bleed and to do a Inlet Valve Calibration routine and then the Master Cylinder Isolation Calibration to clear the codes. Back to normal now. Thanks all for the help!