E450 Brake Master Cylinder K.I.A. ? Noooooo!!!

[deprived]

Okay - I've been slowly making my way through a front-end-rebuild of my 2008 Fleetwood Jamboree 26J. I've upgraded the components to new 2014 parts.

Only recently was I able to bleed the new brakes with a Motive Power Bleeder. I've bled brakes before using the "two-man" method but this was my first time using a pressurized bleeder. I bled the system extensively until all fluids ran clear and bubble-free.

Imagine my shock when I tested the brakes only to find the brake pedal SINKING TO THE FLOOR!!

I'm no expert but doesn't this usually indicate the master cylinder is shot?

How is this possible? Could the power bleeder have somehow ruined the master cylinder? I was only pressurized to 12 PSI.

Any ideas, musings, or suggestions? I don't mind replacing the MC - it's not too hard, at least in the few cars I done the job. But I'd rather not.

Has anyone else experience this?

Also, if you have personally replaced the MC in a E450 - are there any tips/suggestions/warnings?

THANKS TO ALL!!

[deprived]

j-d wrote:
Got any more pix to post?

I'll be sharing new stuff soon! We are in the middle of remodeling the interior of our camper so I'm spread pretty thin.

[deprived]

j-d wrote:
I think I mentioned when we corresponded, don't let the master cylinder go DRY. Were you able to prevent that, before and during the brake bleeding process?

SRockwood wrote:
Did you let it sit long enough with the lines disconnected for air bubbles to get back up into the MC or let it run dry? If so, it still needs to be bench bled.

:oNow that I am reading these responses, I can say, yep, I let the MC go dry during the front-end install. Shame on me.:S

Well, I'm going to move on!

I looked at the service records for the vehicle and saw that this is the original MC, so I went ahead and ordered a new MC from RockAuto. I figure as long as I have brand-spanking new calipers, pads and rotors, I might as well go all-in at this point and get a new cylinder.

It's still likely that in the middle of all of this, the ABS needs to be cycled, bled and reset. I found a mobile brake service here in Austin that will do the deed here in my driveway for 75 bucks.

I would just do, as some suggest, drive the vehicle until the ABS regained its senses but unfortunately, my driveway is situated at the top of a hill on a very busy street. Not a good place to experiment with questionable brakes.

Anywhoozle, thanks for all the great, thoughtful questions and suggestions.

[SRockwood]

deprived wrote:

rcmiller32 wrote:
Did you bleed the master cylinder before installing it?.

I did not install a new Master Cylinder, just two new front calipers.

Did you let it sit long enough with the lines disconnected for air bubbles to get back up into the MC or let it run dry? If so, it still needs to be bench bled.

Dumb question to try first: have you pumped the brakes up after bleeding yet?

[deprived]

rcmiller32 wrote:
Did you bleed the master cylinder before installing it?.

I did not install a new Master Cylinder, just two new front calipers.

[j-d]

Been wondering about you and the project. For me, brake bleeding was one step short of putting the wheels back on and setting it down. Is that where you are? Including connecting the ABS Wheel Sensors?

I think I mentioned when we corresponded, don't let the master cylinder go DRY. Were you able to prevent that, before and during the brake bleeding process?

I ask because we kept our master "wet" by plugging the hard lines where they disconnected from the flex caliper hoses. The new calipers were pretty much "wet" because they'd been removed from a complete, operable chassis and Quigley had put plugs in their holes.

Still, when we bled the brakes, they were like "Steppin' on a Prune" in that C.W. McCall song. Wife was helping me, pumping the pedal a few times then I'd let it off, etc. etc. Engine off, Engine running, disappointing. So, I gingerly drove it. Brakes were Absolutely OK. Just fine. I don't know why that was. It's possible the new pads weren't seated to the rotors and there was some lost motion.

If you're somewhere that lets you drive around at low speed and get a feel for the thing when there's nobody around to run into, I'd say try it. You'll be able to feel the front brakes "bite in." The rears alone'll feel more like a trailer is dragging you down.

We've taken several trips since the front end upgrade, probably 1,000 miles total, and it's been great. The stopping doesn't feel any more aggressive, like "Oops this is too much," just more confident. And if shorter stopping distance is needed, it's available with only some more pedal pressure.

Got any more pix to post?

[rcmiller32]

Did you bleed the master cylinder before installing it? It must be free of any air or air pockets before installing it. The bleeder will purge the air out of the lines and brake cylinders.

[ron_dittmer]

I understand most later day ABS brake systems require a vacuum bleed at the caliper or the common brake-pumping bleed. Pressure bleeding at the master cylinder is not recommended. I suggest you try vacuum bleeding at each caliper and draw fluid from that direction. Doing so could reposition internal M.C. valves to correct your problem. I don't know for certain, but it is surely worth a try.

The best vacuum bleeding system I know of is the pneumatic kind that uses an air compressor. I own the pneumatic one on sale here for $31.99, a consumer grade vacuum pump from Harbor Freight. The ones at our church CARS ministry are commercial grade versions of the same thing. They offer a friendly one man operation for vacuum bleeding of brake lines.

Good luck!

[enblethen]

Is it equipped with ABS system?
Some ABS systems requires you to bleed the ABS first, then the lines.