I recently replaced the rear brakes and rotors, and now I’ve lost about 80% of my braking power. The brake pedal goes all the way down to the floor with very little resistance. I’ve double-checked all my work and everything appears to be installed correctly.

The only issue I noticed is that the brake pad wear sensor broke as soon as I touched it. I didn’t replace it because I don’t have one on hand. Could that be causing the loss of braking power?

Also, if you look at the first picture, you can see that the rubber dust boot on the caliper piston is torn. This happened when I was pushing the piston back in to install the new pads and rotor. Could this damage be related to the brake pedal going to the floor and the loss of braking performance?

Any help or insight would be greatly appreciated.

 

If you didn't open the bleeder than you should just have to pump up the pedal a few times. If you opened them there is a procedure on bleeding the brakes that I use a scan tool for, as for the dust boot just replace it it does not have anything to do with pressure.

 

The only way you can have a soft pedal/pedal going to the floor after a few pumps to take up the gap from pushing the pads back, would be a leak or air in the system.

Did you open the bleeder or lines at all?

Was your fluid level dramatically low at any point?

Did you bleed the brakes if you did open the system?

 

1 The wear sensor wire being disconnected will not affect the operation of the rear brake or braking system. I just bought a pair of wear sensor wires from Amazon for $26 for my 2014.They may have them for 2016 models
2. The damaged dust boot will not cause the loss of pedal and braking power you describe. You do need to install a new dust cover to protect the brake piston from all the crap and corruption faced on the road.
3 If you have lost the pedal start looking for brake fluid, if the level in the master cylinder reservoir is low star looking for leaks. If the level in the master cylinder is good then you likely have a problem with the Master Cylinder.
4.Do you have any DTCs showing?
5 I hope you removed all the rust from the hubs and coated them with copper grease before you installed the new rotors. If not you could have wobbly brakes.

 

How did you retract the pistons? Did you force them back in, or wind them back in with the correct tool?

wombat

 

Noticed you mentioned pushing the pistons - these calipers require the pistons be rotated back into the calipers. If you did not rotate them the mechanism may be damaged such that the piston is not pushing against the pads. But still not sure why the brake pedal would go to the floor.

 

I didn’t open the bleeders. I’ve pumped the pedal many times and even drove the car twice around the block at low speeds, but the pedal still goes very low.

As for the dust boot procedure do I just remove the old one and simply install the new boot in its place, or is there anything else involved? I just want to make sure I’m not missing a step.

Raybestos WK2038 Professional Grade Disc Brake Caliper Boot and Seal Kit

 

The pistons were wound back using the correct tool. I did have an issue on the passenger side where the piston wouldn’t retract fully at first, so I opened it a bit further (it almost popped out) and then closed it again. After that, it went back in with pressure applied.

I’m wondering if opening it that far may have allowed a small amount of air into the system. Other than that, there wasn’t any other point where air could’ve entered.

 

The brake fluid level is at MAX. After driving the car twice around the block, letting it idle, and pressing the brake pedal many times, the level hasn’t changed at all.

There are no DTCs showing.

 

Very possible if air got in at the caliper. Bleed the brakes, see if you get any air.

If not, you may have gotten unlucky and damaged the master cylinder when pressing it down further the first time. I have seen issues when there is buildup in the bore and during normal use it never touches, but with the system open/pads pushed back and it can travel further than normal, it damages the seal and now leaks internally.

 

I'm thinking out loud now.

I'm guessing that it's possible that when you retracted the pistons, crud got pushed back into the ABS valve block. If the valves are stuck, then full pressure won't reach the calipers.

I would do a complete flush (using a scan tool to open the ABS valves in turn). Hopefully, any crud will get flushed out,

wombat

 

Will any DOT 4 brake fluid work, or do I need to get the OEM fluid from the dealership?

 

Any DOT 4 will work, it doesn't have to be OEM.

wombat

 

You can use any low viscosity brake fluid meeting ISO 4925 or better. I use Bosch ES16-32N It is available from Parts Avatar about $25 /L.

 

Anyone used this?

• UNIVERSAL BLEEDING KIT: This Orion Motor Tech brake bleeding kit will let you bleed each wheel in under 5 minutes without needing an assistant constantly pumping the brakes; the vacuum pump includes a compression tester and an adapter set that lets you work with nearly any vehicle's system

 

Hi JaguarXJL15,

I haven't used that specific vacuum bleeding kit, but I've used a similar setup with a Mityvac vacuum pump and fluid jar and it sometimes, but not always, works OK. Some brake systems, especially rears, cannot be easily bled by vacuum alone (or with a pressure bleeder, which is generally a better option). The ABS modulator valves and solenoids also have to be exercised with a scan tool. i don't know off the top of my head if that is true of the X351.

I also do not recall if the rear calipers are supposed to be set to service position with a scan tool or diagnostic system prior to pad replacement. On the X350 supercharged cars they are.

According to the X351 workshop manual, after the rear pads are replaced, the parking brake must be recalibrated, so it may help you to follow the steps below from page 7,404 of the manual. This should thread the pistons back out to their correct operating positions.



Cheers,

Don

 

I bleed the ABS pump with the SDD campaign but bleed all the calipers the old-school way. I have never had much luck with the Mityvac or hand operated vacuum bleeders- air leaks past the bleeder screw threads and breaks the vacuum.

 

I gave up on vacuum bleeding and have used a pressure bleeder for the past two years. It maintains fluid level in the Master Cylinder and provides positive pressure at the bleeder valves so air cannot leak in..

 

I think I’m going to do it the old-school way open the bleeder valve, have someone press the brake pedal, close the valve before the pedal is released, and repeat the process a couple more times.

Does the ABS scan tool walk you through the procedure step by step?

Appreciate everyone taking the time to reply and share their advice.

 

Same, I have had a Motiv power bleeder for over a decade now and love it.