Explorer rear discs: not working at all! Thoughts???

[chuzie]

Installed and bled my explorer rear discs today and now my pedal goes all the way to the floor and I coast to a stop even after bleeding. Basically no brakes.

What am I missing here?

Duffs vac booster
50/50 master cylinder 69 el dorado
96 explorer rear discs

Strange thing is when we pump the system about 10 times, the MC seems to drain (rear most reservoir) about 2/3 and when we let off the pedal, fluid starts rushing back in and fills it up.

No lines are leaking or swelling.

I am stumped.

Thoughts?

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[66' bronco]

Are the calipers on the right sides? Bleeders on top, I know its a stupid question but it easy to overlook and has stumped people more than once.

 

[chuzie]

Re: Explorer rear discs: NO PEDAL!!! Thoughts???

Yes. That has bit me before in the past. Even removed caliper and bled it with bleeder vertical just in case.

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[chuzie]

Just talked to Matt Miner who suggested it may be my MC. Even though the 69 Eldorado MC is 50/50, it is valved to accommodate a front disc/rear drum.

He suggested I try a Corvette or 78 Lincoln MC.

 

[broncnaz]

MC is probably bad many times a seal goes bad when you bleed the brakes due to dirt/rust that was in the bore and since the pedal went down farther you got into that stuff and tore up a seal. Otherwise you should still have front braking.

 

[chuzie]

That makes sense. I bet that is part of the issue. Another thing I noticed was how much fluid volume bled from the rears vs the front. Significantly less volume from the front.

 

[chuzie]

I should also mention I am running T-bird fronts

 

[StnePny]

what is the bore size of the M/C ....

 

[chuzie]

The 69 eldorado MC bore is 1.125"

The MC bore sizes of my caliper donor vehicles are

78 t-bird 1.000"
97 explorer 1.062"

I was considering getting one of the two below but now I am thinking I need to step down to a smaller bore.

67 corvette 1.125"
78 mark v 1.125"

 

[Apogee]

It sounds like you have air in the system. Was the MC new when you added the discs or had you been using it previously with the disc/drum setup? The MC may have a residual pressure valve in the outlet port for drum brakes, however that should just maintain residual pressure on the rear discs causing excessive drag, not pedal issues.

Aside from swapping out the rear drums to disc, did you make any other changes with respect to the hydraulic system? Any leaky fittings, new hard lines, hoses, etc.?

Tobin

 

[chuzie]

The system ALWAYS sucked but at least I had pedal. The MC was installed in 2009. The ONLY thing changed was the discs and the rear hardline.

I have bled the ever-living piss out of the system. I agree is seems like air but don't see how it is possible. No leaks or swelling lines.

 

[Broncobowsher]

You have air in the system. When you pump and the master goes down, you are compressing air in the system. When the pedal is let up the air springs back and pushes the fluid back up. The hard part now is figuring where the air is at. Have you bleed the front as well?

 

[broncnaz]

Its the MC like I said you would still have front brakes or some kind of pedal due to the fronts if was only air.

 

[chuzie]

Re: Explorer rear discs: NO PEDAL!!! Thoughts???

I'm going to go with it is both. Don't want to go through the agony of chasing a ghost.

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[chuzie]

Okay, so here goes...

Installed 82 Corvette MC today. Spent an hour bench bleeding and there was ZERO air. Spend another hour bleeding the calipers and there is ZERO air. I am 100% confident there is ZERO air in the system

I STILL HAVE NO BRAKES.

I wonder if I am not getting enough actuation from the pedal and linkage. The adjustment screw on the MC end of the Duff's booster was made so no slop or over-engagement there. I measured the distance the booster rod travels, about 1.25".

Is this enough for this MC? The adjustment behind the booster, at the clevis, is maxed out.

It has been suggested maybe I have an issue with my pedal and linkage.

Who is running a Corvette MC with a Duff's booster?

What else can I do folks?

 

[Broncobowsher]

The more certain you are it isn't air in the system, the more I am it is.
Post pics of the calipers just as they are mounted on the truck. I just want to double check what you are so sure of.

 

[chuzie]

Re: Explorer rear discs: NO PEDAL!!! Thoughts???

Front or rear?

Here is a shot of rear driver side. Don't have anything stored of the fronts, but I can take a pic this weekend.

Went through 2 large bottles of fluid to ensure I got the air out of the lines. Only place for it to hide is in the calipers.

Thanks.

 

[Broncobowsher]

OK, I wasn't as clear as I should have been. Picture of the caliper but put the camera at the differential. Fronts too.

 

[broncnaz]

On the bad side even new MC's can be bad right out of the box. Air in one side should make little differance as you should still get some kind of pedal even with air you will just have spongey brakes.
As for travel issues can you do a quick double pump of the pedal? does it give you some pedal? if so then its either a volume or lenght of travel issue thats causin you not to get the volume. Although with disc brakes you should still get some type of pedal even without enough volume.

 

[DirtDonk]

Hey Chuzie, did you do anything to the front brakes at the same time?
New prop valve by any chance? Anything else changed?

I know you said you measured to verify the booster rod was the right length, but where did you compare? You did verify that the backside of the master cylinder's piston did not have that deep recess? Or if it does, that the rod is sticking out far enough to fully engage the piston?
It sounds like you did, but I just wanted to clarify that to be sure.

Are you seeing good strong fluid flow out of the bleeders when the pedal is pumped?
Are the pads hard up against the rotor, so you're not having to take up free-space each pump?
Are the caliper sliding surfaces clean and smooth?
And what about their condition? You say you just put them on, but frankly, the ones in the pic look like they've been installed for years! Is it just me?

Paul