Front Brake Upgrade Makes Soft Pedal

[boywonder]

Originally Posted by carringb

One more thought.... Did you happen to see what fluid they put in?

Is there any chance somebody tried to do an upgrade to DOT 5.1 fluid, and accidentally put in 5? DOT-5 is very compressible unlike 5.1l which is really high-temp DOT-4.

I just don't buy the brake piston size mismatch could possibly cause this....

Yes DOT 5.1 and DOT 5 (silicone based fluid) are completely Immiscible.

You end up with a big mess......did this accidentally on MTB brakes a few years ago....now I have a quart of brake fluid that nobody will recycle other than county haz waste place.

I'm not buying the size mismatch either.....no way....

[TomsBeast]

Originally Posted by ShuttlePilot

... they bolted right up and looked correct but the bleed valve wasn't at the correct height to bleed all the air out...got a few more bubbles out and cured the mushy peddle.

Keep looking and you'll find it and your big brakes will be awesome.
-Eric

I was going to suggest the same. Like realestate, location, location, location... Sounds like you used all good parts, but retrofitted brake caliper blackets mis-located where the bleeder isn't the highest point, is a common issue with brake swaps in hot rods and race cars.

It's worth a look see.

So long as you have flexable lines, mislocated calipers aren't a huge issue. You simply remove the caliper bolts and bleed the system after temporarily repositioning the caliper, so the bleeder valve is the highest point. You have to make a spacer equal to caliper thickness, or temporarily rotate the caliper so the bleeder is highest, and the pads grip the rotor during bleeding (easy if you don't have a dust shield), or something that accomplishes the same thing. After bleeding, just bolt up the caliper in it's non-perfect position, and move on.

I'm not saying this is your problem, but it's something to look at, as ASE trained profession mechanics often can't "think out of the factory installed box", when it comes to modified/adapted systems.

[JoeH]

If they are 2008+ OEM brakes the brackets are exactly the same for both sides. So, are the calipers with the exception of the bleed screw location which should be toward the top. Hard to understand how a decent shop would have made the mistake of putting them on the wrong side but stranger things happen. Good luck with the trouble shooting.

Funny timing. I've got all the parts to do this swap as well as rebuild the front end with new ball joints, tie-rod ends, and drag links. Figured I would be into it for $2k in labor so going to give it a go myself. Any day now....

[JoeH]

Jage, didn't you just do ball joints? I recall a thread from last summer. Did you re-use them in the new knuckles?

[REF]

First off, how the hell are ya?!?
You had asked so I’ll add that I just had a FF rear axle built and installed, they swapped over rear brake assemblies from my SF without issue.


'03 Ford E350 7.3L Diesel
SMB RB50 w/CCV top
Quigley 4X4 w/Deavers & Agile RIP kit

[bet on black]

I would keep trying to bleed it before you throw parts at it. I had really good luck gravity bleeding my van after the 4 x 4 conversion. Pedal is nicely firm. Stock master cylinder, 2013 axles with the big brakes. Make sure the bleeder is on the top. Sometimes you have to tap the calipers a little bit to get all the bubbles out.

[bet on black]

Also make sure you don't have a leak.

[MadScience]

I have '08+ f-series axles front and back with the brakes that came with them. FWIW, they bleed much better by putting pressure on the reservoir side than by using a vacuum on the caliper end. But just using a vacuum on the caliper wouldn't leave you in the state you seem to be in.

I don't feel like I have enough data points yet, but I do vaguely feel like there may be some differences in fluids in terms of how hard I can get a pedal regardless of the vehicle. I'm using ATE 200 in the van now.

[arctictraveller]

Since fluid is non compressable, something is expanding or leaking. Once the calipers are expanded and the pads a few thousanths off the rotor, the amount of fluid needed to move the remaining distance is almost nothing. As RPA said, an out of round caliper will push the pads and pistons back a bit resulting in more travel needed to contact the rotor, but you should feel pulsing if that were the case. If the pedal will slowly sink to the floor with steady pressure, either there is a leak, or the master cyl is bypassing fluid past the piston seal. If you can pump up the brakes and then get a firm pedal, air in the system is the most likely cause, although an expanding brake line will will cause a soft pedal too. Since you had firm brakes with the current hoses, they are less suspect. Despite your repeated efforts at bleeding, (assuming all the new parts you installed are working correctly) I have to vote for trapped air somewhere.

[jage]

Update time. So my friendly local diesel shop replaced the master cylinder first and when that didn't work were like "we need to do the HCU". Now that was **** expensive and ... didn't solve the problem. They bled it a dozen times and gave it back with the whole "the rears are filling up that's your problem."

So since then the pedal has remained soft and I can pump it up and then push and it drops to the floor, pump it up from there, push and it drops to the floor. It's also slightly worse cold. That all just screams master cylinder right?

Anyway this week I finally made time to take it to a high end 4x4 shop here. By high end I mean the "shop car" they run you back in is a brand new Colorado pickup and a simple rear diff fluid exchange tops $250 (ask me how I know).

In any case I explained at length and the tech was like "master cylinder" about half way through. I'm like well you would think that but this other shop just did that and the HCU.

So of course the first thing he does is by-the-book cap all the brake line ports from the master cylinder and the pedal still creeps to the floor. Of course that's under warranty at the first shop so while I consider paying "dipped in gold" rates to just have it done, I instead take it back to my friendly local shop.

First thing he says is "well we already replaced that master cylinder twice." and I'm like "Twice? This is the first I'm hearing about twice."

Anyway they remained convinced there is no way it's the master cylinder but "they'll look at it again". I'm seriously wondering now if they ever replaced the master cylinder once, much less twice and if two units failed why are they still using that supplier?

Seriously I want to like this shop but when I took my van back for emissions recently the guy at the desk literally paled when he saw me. I have a really hard time believing that he doesn't know they botched it and was literally just waiting for me to come back on them.

AAAARRGGGGH! I just want the **** thing fixed right. If they can't pull it out this time I feel like I need to go to the new shop and pay AGAIN to have it redone.