Sinking Pedal after Break Work ...

[aigel]

On my 2015 Ram truck I did all 4 corners pads today and at the same time was gravity bleeding the brakes. It worked so well that I missed the right front caliper emptying out my master cylinder reservoir.

I refilled the MC, bled some more out of the front right with gravity then with pedal with a helper until there were no bubbles. Also pedal bled the front left, never saw any bubbles.

Brakes work very well, but with the engine running and with a lot of force, the pedal sinks to the floor, slowly, over about 10-15 seconds.

Cracked the lines at the master cyclinder and pedal bled that directly, but no improvement.

From all I know about brake systems, the MC is the culprit. There is no spongy feeling, truck brakes hard, so doesn't feel like air in the lines. Could it still have air in the MC it leading to this sinking pedal or are the MC seals shot (from being put through the wringer)?

What do I do next???

Thanks!

George

[A930Rocket]

I’d start by bleeding all calipers again.

Right rear. Left rear. Right front. Left front.

[Por_sha911]

Bleed all the calipers again from the farthest one first. Make sure you have gotten ALL of the old fluid out so that the entire system is fresh. Also, make sure you are using the right DOT fluid.

[island911]

Apply sinking brakes while parked and running - look for fluid puddle.

[Bill Douglas]

NOT criticizing your method. But maybe do the slowly pumping the pedal method. Just in case there is some air that is slipping past the gravity flow of fluid.

The SC was such a PITA I put speed bleeders on it. Life is so much easier now LOL

[aigel]

Thanks guys. I will do all four again. Do I gravity or pump? My intention is pump to more aggressively move any bubbles on. I have fresh fluid throughout already, so that's not a problem.

On the Porsches I always use the pressure bleeder with good results. This is the first time I gravity bled because of course the MC has different threads and my universal adapter didn't work on this MC.

No leaks, I am sure. I am trying again tomorrow. I'll keep you posted!

G

[Shifter]

If you have an air compressor, stop by your local harbor freight and pick up one of these.

https://www.harborfreight.com/brake-fluid-bleeder-92924.html

For a hf tool, it really works great for bleeding brakes on your own. I completely flushed the brake fluid on my jeep in about twenty minutes and had a perfect pedal.

[island911]

Originally Posted by aigel

..

No leaks, I am sure..

G

Then it's likely that the MC abraded some seals when traveling thru the extra range when pumping. Which suggests MC corrosion. :-/

[aigel]

Originally Posted by island911

Then it's likely that the MC abraded some seals when traveling thru the extra range when pumping. Which suggests MC corrosion. :-/

Yes, my worry exactly. I have seen that plenty of times and that's the reason I like to pressure bleed. But on 6 YO truck and 85k miles? (Factory fluid ...).

I think a round of thorough pedal bleeding is worth the 10 bucks in fluid and 20 minutes. Truck is back on the ground but I can get to the bleeders without jacking it up or removing wheels.

Thanks!

G

[Jeff Hail]

Need to get the bubbles out and past the ABS pump before and after the pump. If any air gets in the servo chamber/ accumulator you are not going to get it out by pumping the pedal.

The ABS section of the brake system cannot be bled without the use of the scan tool; there are no manual procedures for bleeding the HCU. Using the scan tool, select ECU VIEW, then select ABS MISCELLANEOUS FUNCTIONS to access the bleeding procedures. Follow the instructions displayed on the scan tool.

Think of it as two systems:

Bleed the calipers/ cylinders first.
Left rear wheel
Right front wheel
Right rear wheel
Left front wheel

Then bleed the abs system.

With the ABS bleeding completed, bleed the base brake system a second time using the same procedures that were outlined for bleeding the base brake system the first time. Once again, check the fluid level in the master cylinder and be sure that it is at the FULL level.

[unclebilly]

Just for fun, tell us about your pedal method.

I’m concerned you may not be doing this correctly and this is how you are getting air in.

[LEAKYSEALS951]

If you are in the market for a bleeder- Recently got this from HF:

https://www.harborfreight.com/pneumatic-air-operated-brake-bleeder-with-auto-refill-kit-57057.html?cid=paid_google|*PLA+-+All+Products|All+Products|57057&utm_source=google&utm_medium=cpc&utm_campaign=*PLA+-+All+Products&utm_content=All+Products&gclid=CjwKCAjww-CGBhALEiwAQzWxOqS1QbxLGRBi91_m8nilm7ZWNvmTRIblqmZv XSmNebDjyvK-rkGAcxoCvSIQAvD_BwE

I've used it to change all the fluids on everything here in the last month or so. Brake fluids/ Diff fluids/ AWD fluids/ Cerebrospinal Fluids. Specially' on the new fangled cars with no drain plugs on the differential cases. Works great.

[svandamme]

Originally Posted by unclebilly

Just for fun, tell us about your pedal method.

I’m concerned you may not be doing this correctly and this is how you are getting air in.

Pedal method really is easy and much more effective then vacuum pump nonsense.
And you can do it without any help, no need to have a second person with you at all !

The key ingredient is having a long, good fitting hose over the nipple.. and route it upwards...
Have at least 10 inches vertical tube, and all air will go up in the tube, and not get sucked back in the nipple.



Open the nipple.
Go sit in the car
pump till there's a good 5 inches of brake fluid in the hose and no more air comes out.
close the nipple

Repeat on the other 4 corners
DONE


No need to open/pump/close/open/pump/close/open/pump/close with a helper pumping for you...

Just open once
pump till you've flushed out enough oil and all air...
close.

All you have to worry about is making sure your brake reservoir isn't emptied when you pump out a lot.
fool proof. and all you have to buy is a bit of tube.. and fresh brake fluid.
no compressor needed, no vac pump needed (and those can do bad things with ABS in some cases, so another reason to avoid em)

[chrismorse]

When i was a service manager/writer at a dealership, (not porsche), i was frequently called on to supply the "leg" for pedal bleeding.

In a significant number of cases, we experienced a creeping pedal after bleeding that was not there before our work. I concluded that over the years, with normal use, and infrequent fluid flushing, that the MC seal had relatively limited travel and that any debris, rust flakes would get pushed to the end of normal travel - then with bleeding, if the debris was rough enough, the seal woulld get pushed beyond the prior distance, cutting, abrading the seal.

If you stomp the pedal and it is hard, initially, it is not likely air in the lines.

We then started using a pressure bleeder and recommending more frequent brake fluid changes to keep the MC as clean as possible. It takes time for rust and debris to develop and accumulate, so, one of the points of this is to flush every year or two - or more frequently if tracked.

If you decide to overhaul the MC, have a good look at the bore, to make sure it is pristine.

good luck,
chris

[LEAKYSEALS951]

^Interesting experience. I was mentally wondering the same thing this morning after seeing this thread.
Assuming the brakes get re-bled, assuming the ABS gets bled properly, and assuming it still doesn't work, I was thinking about the MC, and wondering if damage to these systems is more along the lines of a transmission flush, where the damage is already mostly done/setup for doom, and the flushing is the action that forces the issue, not the issue itself.

I did my neighbor's honda a week ago. We were redoing the brakes, so I suggested we flush it since we were in there. "They were done a year or two ago" he said. Reservoir fluid looked good, front caliper fluid looked okay. Rear- BROWN RUST CAME OUT BOTH!!!! His brake place was just changing the front. wtf!?!?!?!?

Fortunately I didn't know changing the fluid could potentially trash a MC. His car turned out okay. Now I know. I'm also a lot more careful spreading calipers on ABS cars compared to pre ABS to prevent backflow into the ABS. Glad my neighbors situation turned out okay. I'd feel just peachy explaining i'd trashed it.

[speeder]

You can also open a bleeder screw slightly while compressing caliper pistons to avoid back flow. If you do it carefully, a very slight bleed at the wheel will assure that no air went in.

Lots of good points on this thread. One thing that came to mind is that you do not have to move the MC piston through its entire range, (pedal to floor), in order to bleed brakes with a good MC. It’s usually a bad idea, for the reasons mentioned above.

The comment about dirty fluid in lines after a supposed fluid change at a shop is prime reason why I do my own brake work whenever possible. It’s absolutely true that shops will only change the fluid in the reservoir, which of course has exactly zero effect on brake performance and safety. The fluid in the reservoir almost never mixes with the fluid actually doing the hydraulic braking. At the very least, you need to flush fresh fluid through all of the lines and even then, you can wind up with dirty, old fluid trapped in calipers. None of this comes into play if you change it on time. Almost no one does.

[aigel]

A round of thorough pedal bleeding of all 4 corners in the right order produced zero air and pedal still does the same.

You guys are right, pedal bleeding does not require big strokes. But my helpers are not experts, so I am just glad they can do the procedure okay with me under the car. 1) put foot on pedal to build pressure 2) open bleeder 3) Pedal sinks towards floor and about half way down helper announces this 4) close bleeder 5) Pedal up - repeat. Key here, the way I learned it, is that the system needs to be under pressure whenever you crack the bleeder.

My money is on the MC, because an air pocket will give a springy pedal feel like an air shock. You compress the pedal but it can come back up. If it sinks, ever so slowly, that tells me the fluid is leaking past the MC piston seal.

Now what Jeff writes about the ABS unit is worrisome. On two fronts. Maybe I got air in it and that's causing my pedal effect but worse, if I replace the MC, I may get air in the ABS unit as well? I'd get a scan tool and do it all right, but very limited on time these days.

At this point it is either spending more time installing a new MC or throwing in the towel and just get some professional help this week.

What would you guys do next!?

G

[Rusty Heap]

switching between yellow and blue brake fluid assures you've totally purged the system too.

[LEAKYSEALS951]

Originally Posted by aigel

A

What would you guys do next!?

G

You've bled them again. It still sinks.

Assume both MC and ABS will be an issue. If time it tight, order the scan tool and the MC at the same time. Return the MC if not needed.

Test the ABS with the scan tool. Bleed as instructed.
If still sinks (probably will) change the MC
Use the scan tool to fix any ABS air bubbles changing the MC will cause, and you'll still have the scan tool to use for future stuff.


See if any google searches for your make and model can shed light on the hassle ABS bleeding/and or extra steps concerning the ABS unit changing out the MC to shed light on if you should punt.

Price this out time/$ wise versus biting the bullet and sending it in. My neighbor knows a good brake guy who won't even waste the rear brake fluid you just put in!

[island911]

pfft... /\ what do you know about leaky seals... oh wait.

I assume that the ABS system runs independent of the MC, but really don't know.

Does anyone have a hydraulic diagram for that system?