Rear Brakes not working properly on 2012 Expedition

[dvdtms]

My rear brakes are not engaging far enough. With the rear wheels off SCR sitting on jack stands, the rear calipers engage just enough to stop the wheels at idle. Under a load they aren’t working at all. I drive 20 miles today in traffic and when I got home I was able to touch both rear calipers and there was not much heat in them at all so the calipers aren’t engaging with any pressure. The pads probably have 50-75% left on them. The brake pedal feels fine and doesn’t go down any farther than normal. The pedal isn’t spongy at all. I have removed the pads and rotors as weak as calipers and everything is installed correctly. I greased the caliper pins and everything is free. Does anyone have any ideas as to where to start? I feel like it’s a pressure issue but not sure if it would be master cylinder or ABS unit. There are no leaks and the master cylinder has plenty of fluid. Any ideas would be appreciated.

 

[S20Workstation4]

The only thing I could think of: maybe there is a buildup of rust within the calipers? I had some rust build up on my rear calipers in my 2010 Expedition, but it wasn't enough to cause problems.
If not checked already, I would try and re-bleed the rear brakes, to eliminate the possibility of having air in the rear lines.

Hope this helps,
-Joseph

 

[dvdtms]

Thanks for the reply. I took the calipers off and they were clean. I greased the pins and the slides and it didn’t make any difference. I think it’s a fluid flow issue. Maybe a restriction somewhere. I’m going to get under this weekend or next week and follow the brake line to make sure it hasn’t been dented or crimped. I’ll check all the lines and then start checking flow from the master cylinder and abs system.

 

[whtbronco]

If the caliper piston boot is in good shape, you can't see where the piston meets the bore in the caliper.

A good place to start I think would be to flush or at least bleed the brakes that'll show you if you have good fluid flow.

I questioned new calipers I installed recently so I removed the calipers and had my wife slowly press the bake pedal while I watched the piston to see if it moved smoothly and enough. You might want to put a piece of wood or something to prevent the caliper from popping if you let it go far. This is just another idea.

 

[dvdtms]

Thanks. That makes sense. I can try that to make sure they are moving. They are moving but it’s very possible they could be seized and not moving enough. I think it would be odd that both would be seized though. I will definitely look at that.

 

[whtbronco]

Agreed, it would be a bit unusual for both calipers to be seized or partially seized at the same time.

It may be that the piston in the master cylinder for the rear brakes is leaking a bit. That would effect both rear brakes. Having a helper push the pedal while you bleed the rear brakes will help identify that.

 

[dvdtms]

That’s one of the first things I plan to do. I’ll post back after I get a chance to pull it in my shop and work on it a bit. I’m off all next week so that is 2nd on my list after I fish a bit.

 

[GlennSullivan]

Unusual for both calipers to have the same issue at the same time. My guess is air in the circuit / lines feeding rear brakes.

Less likely but still a possibility is either the Anti-lock brake module or the flex hoses to the rear calipers are partially collapsed. I had a front brake problem that the solution turned out to be replacing the ABS module and the hoses.

 

[callwill]

Is there a brake balance valve in the system?

 

[dvdtms]

I’m not sure. Where would this be located.