Morning fellas,

I'm having a bit of an issue finishing a brake replacement job, never had this issue doing brakes before, was wondering what everyone's thoughts were.

I just replaced my rear rotors, calipers, and pads. (both sides on everything) and have bled the system via the bleeder with the truck on. The method being open the bleeder, depress pedal, close it as the pedal nears the floor, open it again once the pedal is back up, repeat. Closing it for good mid stream on the final push. I did this to all 4 calipers, and have done it 4 times now. There is plenty of fluid in the reservoir, and always has been, the person on the pedal checking all the while.

My issue is, no matter what I do, I cannot get any pressure to build behind my brake pedal. Technically I can stop, the brakes work, although I can't which ones for certain. When stopping I never fully lose pressure or my brakes. I just have to push the pedal damn near to the floor to actually stop the truck.

I can't find any air in the system but even if there were I should think I would still build pressure. I have functional power steering, fluid level good. I have inspected all 4 brakes during a brake test and checked for leaks, there are none. I am at a dead end here as I know next to nothing about the master cylinder which is what seems to be next on the list. Though I can't imagine how as everything worked fine before I began this replacement job.

Any help would be great! Thanks,
Andy

 

You didn't forget to put the cap back on the master cylinder did you?

Since you did most of the work on the rear brakes, I'd suggest you jack up the rear end, remove the wheels, and watch to see if the pads are grabbing the rotor when the pedal is pressed.

 

The bleed fittings are at the top with the calipers installed, right?

 

Yes, the bleeders are both on the top of the caliper.

As far as a cap goes, I put the cap back on the brake fluid reservoir. But that is the only cap that was removed in the engine bay. I know not of any other cap on the master cylinder?

 

I have ALWAYS bled brakes with vehicle off. Pump 4-5 times til pedal firm and crack bleeder

Never bled a Superduty, do they require engine to be on?

 

No, engine doesn't need to be running. Pump the brakes slowly until the pedal is as firm as it can get and hold it while someone else opens the bleeder fitting. When the pedal gets to the floor, the other person closes the bleeder. Start with the wheel furthest from the master cylinder. Repeat until the air is purged.

 

Aye, I should've specified, we did do with the engine off, using this method, the very first time we bled them. The other two times, I simply wanted wanted the key turned over, but my batteries were dead so I'd had to jump it, hence why I'd left it running for the following bleeds. After the first one didn't seem to work quite right I thought maybe the system needed to be under pressure.

Thinking about it though, even if I had air in the line, I should still have pressure behind the pedal, it should just effect the braking ability, no? Because the bleeds are good, I'm not getting any air, I'm just also not getting any back pressure at the pedal. Could this be something related to the master cylinder? As I know nothing about it, I don't know what to even look at or what to look for.

 

I know that you said that you didn't mess with anything else but I wonder if something in the hydroboost system could be giving you some grief somehow.

 

Aye, though I didn't touch anything else, I've done enough brake jobs in my time to know I haven't done this incorrectly. Be that as it is, this is my first ownership of both a truck and a diesel, so I am relatively unfamiliar with many of it's proprietary systems. So I suspect it has to be something else, despite not having touched it, at this point. Pray tell, what is this hydroboost system exactly? and what about it specifically do you think is suspect? So I can look into it.

Thanks.

 

I would go with rebuilt caliper bad....why were you replacing the calipers??

 

I would go through the bleed procedure again without the engine running since that seems to be the only variable from the other brake jobs you have done and different from the bleed procedure we all seem to use. Maybe with the engine running it changes something on the way the master cylinder pumps up. I have had stranger things happen to me. It may save you time and aggravation chasing a non-existent problem. I know it has helped me re-doing something that I thought couldn't make a difference.

 

There are several threads on this site about this system that can explain far better than I can. Basically the hydro boost is the power assist system for the brakes. As diesels do not generate vacuum like a gasser this system is used instead. It runs off of the power steering pump for hydrolic pressure to provide power to the brakes. Two independent hydrolic systems that are mechanically connected. BTW if you get into the power steering/hydro boost system at all it uses MerconV trans fluid not power steering fluid.