Reply
 
Thread Tools Display Modes
 
Old 02-16-2018, 05:50 PM   #1
Senior Member
 
jage's Avatar
 
Join Date: Apr 2007
Location: Franktown, CO
Posts: 7,591
Front Brake Upgrade Makes Soft Pedal

OK so I went with Paul (oldbonesclimber)'s brake upgrade. The pieces are built by dynatrac and made for the ProRock 60 that is on my van. I know other people have done this.

The upgrade requires 17s and replaces everything from the knuckles out, except the hub locks. Like I said it came from dynatrac and everything went on smooth as butter except the axle seals, but my originals were good so no real issue.

Now the brakes I upgraded were also good, with 4mm on the pads and even the dealership wasn't making a stink since they wait for 3mm. It stopped fine, nice firm pedal, rear brakes in excellent shape. The only issue I've had that might even be tertiarly related is I had to relocate (bypass) the vacuum cylinder a few years ago to get the cabin vents to change. There is a delay after starting due to leaks, but nothing that was ever evident in the brakes.

The real problem was the pedal. Once the brakes were bled the pedal was mushy. The increase in braking power made this not a problem but it was hugely evident when emergency stopping or when standing on the pedal.

The van would also creep in low range or when on a really steep hill.

Basically, with the van running, I could pump up the brakes then with one foot press hard on the pedal and feel it sink to the floor. Machine bleeding didn't improve anything over hand bleeding.

So the diesel shop replaced the master cylinder partially based on the idea that during the bleeding I'd dumped the pedal to the floor, which has never been an issue, but according to internet rumor can tear up the master cylinder seals.

When that didn't help they did the HCU. Kids don't really need college these days, right?

In any case with the HCU and the master cylinder, having the system bled more than a dozen times by everyone in the shop I took it out on the ice and played lock up the brakes for 15 minutes. Again from the internet, it's supposed to clear the ABS of pockets of air. I had the shop bleed it once more then paid the piper.

The HCU and master cylinder definitely improved things. Now when I pump the pedal up and stand on it, it only goes MOST of the way to the floor. It's almost driveble. The braking improvement of the new rotors and calipers is greater than what performance was lost in the pedal.

It's still not "right" though and that bugs the heck out of me. Even if the original SMB brakes hadn't literally saved my life once, even if I didn't have the twins package to cart around, even so this would still bother me.

The "final word" from the diesel shop is the size of the brake piston on the front is so much bigger than the rear, the rears are filling up and I'm feeling the difference in the pedal. I argued that this didn't happen to anyone else on the forum who did this, and they said it's all over the internet "I didn't expect this to happen", racing forums, basically everywhere except here, according to them (I'm sure if you google the right thing you can find anything you want, but it still remains the active theory).

They offered me two "fixes": go with an e450 hydroboost and never feel anything in the pedal again, or upgrade the size of the rear pistons to the "correct size" but we have no idea what that is or what the correct parts are.

Two additional things. My rear is still a semi-float spacer job, SMB OEM. It's possible everyone else upgraded to a full float rear before moving to the front brakes. I don't even know if upgrading to a full float would change anything about the brakes though.

The second and last thing, also according to the same internet I got the "trigger the ABS to clear air from the HCU" idea from: otherwise or always, depending on who is making the claim; the dealership must use a special bleed machine/computer that opens all the HCU ports, in order to properly bleed. The one thing I haven't done is take it to the dealership, and I don't know if this is actually true or if big shops have the tools to do this after 13+ years.

If I didn't know better (I don't) I'd swear there was a leak an I should have brake fluid dripping after some time, or the shop should have. A bulging line might feel like this too but I can't imagine a good diesel shop would miss this either. It's just how it feels.

So, with all that- any ideas? Is the mismatched piston size legit? Is there a good way to test (i.e. block/pinch the rear line should fix the issue)?

Mostly, what the heck do I do now?
__________________

__________________
and then
everything changed
jage is offline   Reply With Quote
Old 02-16-2018, 06:05 PM   #2
Senior Member
 
carringb's Avatar
 
Join Date: Jan 2009
Location: Corvallis, OR
Posts: 3,828
Have your hoses been replaced yet? This could easily be caused by a bad hose. The liner splits, and the fluid bleeds into the outer layer, and instead of leaking it just inflates the hose. The relation to the new brakes could simply be that somebody let a caliper hang from a hose during the job. They can be enough to damage it if it was already weak/old.

The HCU bleed procedure can be done with AutoEngenuity or most shop computers. I've only heard this being an issue for the rear brakes however, because the front brake circuit is short enough regular bleeding should get the air out. (FWIW - my workaround for the rears was to bleed the brakes with the nose pointed down a steep loading dock ramp).

Beware the larger caliper pistons will result in more pedal travel than stock, but it should not cause a soft or mushy feeling. I'd done the 2009+ front upgrade AND swapped in an E450 rear axle with its monster rear brakes, and the stock MC works fine.
__________________

__________________
2000 E350 extended wagon dually
V10 w/ Banks Powerpack, Diablo Predator
Buckstop Outback bumper/grill guard
Reunel rear bumper
carringb is offline   Reply With Quote
Old 02-16-2018, 08:06 PM   #3
Senior Member
 
jage's Avatar
 
Join Date: Apr 2007
Location: Franktown, CO
Posts: 7,591
Quote:
Originally Posted by carringb View Post
I'd done the 2009+ front upgrade AND swapped in an E450 rear axle with its monster rear brakes, and the stock MC works fine.
Their point was not that the cylinder is too big for the MC, it was that a much larger front piston with a smaller rear piston will cause the rear piston to fill first, resulting in the pedal feeling soft. Your monster rear axle with monster brakes would have solved that problem. The hydroboost swap is basically so much overkill it wouldn't matter (not something I want to do for several reasons).

As far as caliper hang the front lines were replaced with braided stainless with the brakes, the rear lines weren't touched. If the rear lines were bulging, I wouldn't expect an entire shop to miss this as an issue (apparently everyone from both sides auto and diesel got involved in my brakes). Is there any way to diagnose brake line bulge?
__________________
and then
everything changed
jage is offline   Reply With Quote
Old 02-16-2018, 08:27 PM   #4
Senior Member
 
mikracer's Avatar
 
Join Date: Sep 2013
Location: San Luis Obispo, CA
Posts: 2,020
Is the HCU the abs control module? I had an issue where the brake pedal would go to the floor when I was at a stop light. I changed the master cylinder and it didn't do anything. I didn't see any fluid leaks so I along with a couple shops were stumped.

I finally had a friend who is a mechanic at a Ford dealership take a look and his Ford software gave him instructions on how to check the ABS control module. Turns out one of the seals in the module failed which let fluid bypass. He replaced the module with a new one from Ford and it fixed the issue. Only downside is the module is expensive at about $900.
__________________
2005 E350 Chateau - V10 - Agile Offroad 4x4
2012 CTS-V Wagon - For the baby...
mikracer is offline   Reply With Quote
Old 02-16-2018, 09:06 PM   #5
Senior Member
 
boywonder's Avatar
 
Join Date: Jul 2013
Location: So Cal
Posts: 2,855
Quote:
Originally Posted by jage View Post
Their point was not that the cylinder is too big for the MC, it was that a much larger front piston with a smaller rear piston will cause the rear piston to fill first, resulting in the pedal feeling soft.
Fill? This sounds like nonsense......all of the pistons are always "filled" with brake fluid.......if they are not, you ain't done bleeding.......

....and the pistons are more or less extended out to the rotor surface even without the brake pedal depressed....when they are fully retracted after doing the pads, the pedal goes to the floor once or twice while the pistons extend.

..as CarringB mentioned, larger pistons moving the tiny amount they need to move to get to the rotors will need more fluid, causing the pedal to travel more for a given MC.
__________________
2008 E350 RB passenger 4WD SMB penthouse
2013 KTM 350 EXC
2008 KTM 250 XCF-W
2000 KTM 200 EXC
2003 Honda Element
boywonder is offline   Reply With Quote
Old 02-16-2018, 09:45 PM   #6
Senior Member
 
rallypanam's Avatar
 
Join Date: Feb 2013
Location: San Francisco/Nevada City
Posts: 3,548
Garage
Warped disc? Can cause the pads/pistons to be pushed out - which cause a soft pedal as the pistons extend and you push more fluid.
rallypanam is offline   Reply With Quote
Old 02-16-2018, 10:25 PM   #7
Senior Member
 
carringb's Avatar
 
Join Date: Jan 2009
Location: Corvallis, OR
Posts: 3,828
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.

HCU/ABS module failures are rare, although possible. But I don't see why a front brake upgrade would induce that, and the think the probability it randomly failed when the brakes were upgraded are probably lower than winning PowerBall and getting struck by lightning the same day.

I just don't buy the brake piston size mismatch could possibly cause this....
__________________
2000 E350 extended wagon dually
V10 w/ Banks Powerpack, Diablo Predator
Buckstop Outback bumper/grill guard
Reunel rear bumper
carringb is offline   Reply With Quote
Old 02-16-2018, 10:38 PM   #8
Senior Member
 
carringb's Avatar
 
Join Date: Jan 2009
Location: Corvallis, OR
Posts: 3,828
Also, was the upgrade the 6-piston SSBC kit? The difference in brake piston area between the SSBC kit with pre-'08 rear brakes, is less than the difference between front piston area and rear piston area on a van with 2009+ OEM brakes front and rear.
__________________
2000 E350 extended wagon dually
V10 w/ Banks Powerpack, Diablo Predator
Buckstop Outback bumper/grill guard
Reunel rear bumper
carringb is offline   Reply With Quote
Old 02-17-2018, 12:34 AM   #9
Senior Member
 
MadScience's Avatar
 
Join Date: Jul 2011
Location: SF Peninsula
Posts: 685
I'd be hunting for air in the system or a leak.

If these calipers have never been non-squishy, I'd also take a look at the piston to pad contacts.

But really, I'd be pressure bleeding this system a couple times before spending much time on anything else. If you swapped the ABS pump block, yeah, cycle it a bunch and bleed in between cycling it. In theory this can be done with a computer, or with these vans by braking on a poor traction surface.

If you have good fluid in there, you can just recycle the fluid you bleed out back into the reservoir a couple of times.

I'm also skeptical of the argument about size differential.

Leaks don't need to be large at all to result in a soft pedal. They are also an early indicator of line failures, so look into that carefully. If the fluid level drops at all, there's a leak somewhere.
__________________

'99 EB ex ENG KSWB news van, low rent 4x4 conversion (mostly fixed by now), home built interior.
MadScience is offline   Reply With Quote
Old 02-17-2018, 08:34 AM   #10
Senior Member
 
ShuttlePilot's Avatar
 
Join Date: Aug 2012
Location: Colorado Springs, CO
Posts: 373
Hi Jage, I agree with others that the piston size theory causing a soft pedal is bupkis. I could see that a dramatic difference in caliper piston area causing an imbalance in stopping power front to rear but you would be complaining of the van trying to swap ends on the race track for that. And that could be fixed with a brake bias adjustment. Sorry I digress.

You've got a nice list of what could be causing this here and I'll add two more experiences I've had. Replacing brake hoses. I have installed new fancy brake hoses that were what the cool kids were using only to find out they were expanding under braking. It was so obvious that when I held the brake line in my hand I could feel the hose expand when the peddle was pressed. Just to verify I put the old factory style hoses back on, only to test as they were to short to drive with, and rock solid pedal. Had to seek out different longer hoses that wouldn't expand. You mentioned replacing front hoses I would be suspicious of those since you've checked everything else.

Another, albeit slightly embarrassing one was replacing a set of calipers and swapping them right to left. That particular set was so symmetrical that they bolted right up and looked correct but the bleed valve wasn't at the correct height to bleed all the air out. The bleed valve was kind of in the middle and not real obvious as to be on the top of the caliper/cylinder. Realized Brembo had a tiny R and L cast into the caliper. Flipped them, 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
__________________

__________________
2005 SMB RB 4x4 6.0 PSD
A rocket on the pad is safe,
but it's not what rockets are built for.
ShuttlePilot is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

» Sportsmobile Registry

(No name yet)

Orv

ClifFord

EliMakes
Add your Sportsmobile
Powered by vBadvanced CMPS v3.2.3
Disclaimer:

This website is not affiliated with or endorsed by Sportsmobile SIP or any of its affiliates. This is an independent, unofficial site.


All times are GMT -6. The time now is 11:02 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2018, vBulletin Solutions, Inc.