Mushy Brake Pedal After New Brake Lines

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

OP
OP
Lord Snax

Lord Snax

TYF Newbie
Joined
Jun 15, 2017
Posts
23
Reaction score
9
Location
Maryland
Just to clarify, @iamdub is asking if you did push the pedal to the floor, not saying you should. He is wondering because you can shoot it by doing so. Put a 2x4 down there, so you don't inadvertently floor it.
Sorry for the late reply, but thanks for the advice. I had my younger brother pumping the pedal as I was going around and opening the bleeders. Hopefully, he did not go to the floor with it.
 
OP
OP
Lord Snax

Lord Snax

TYF Newbie
Joined
Jun 15, 2017
Posts
23
Reaction score
9
Location
Maryland
NO!!! DO NOT PUSH IT TO THE FLOOR!!! I was just asking because I learned this the hard way on my '08 when I bled the brakes a few years ago. The MC was always just fine until I killed it while bleeding the brakes after a standard brake job. As Nate mentioned, lay a 2x4, brick or whatever behind the pedal so that the pedal remains within the stroke it's been accustomed to for so long. Even if you didn't go to the floor but went close, the same could've happened. Of course, make sure the MC is bled. But, with what you've done already- using a scan tool to open the ABS solenoids and not going to the floor, it sounds like you know what you're doing so I don't think you would've let the reservoir go empty.

I'm pretty sharp with these basic items so it was nerve-racking when I couldn't figure out why my pedal suddenly went soft when I was on my last corner during the bleeding. Other than an air or fluid leak, a blown seal in the cylinder can't be seen. You kinda just have to rule out every other possibility. If the MC on your '05 is original, it may have been really worn already so just stroking it slightly beyond it's normal range of motion is all it took to finish it off. I was getting mine ready for a trip to Florida, so I looked at it's failure as a blessing in addition to the lesson. What if I had to make an emergency stop during that trip and jamming on the pedal finished off the MC? I'd much rather diagnose and repair stuff at home than on the highway, hundreds of miles from home.

Thanks for the reply. To my knowledge the MC is original. I've never replaced it. Unless the previous owner replaced the MC, than its the original one from the factory. It may be time to replace it. My Mom was driving when the brake lines gave out on a highway with traffic lights on it. She said she sent the pedal to the floor multiple times to get the car to stop. Yup! This is looking more and more like a bad MC.
 

argus

TYF Newbie
Joined
May 6, 2018
Posts
6
Reaction score
5
How did you bleed abs?
I used an OBD tool.

Just curious, which OBD tool did you use? There aren't many that I am aware of that can bleed ABS, and I've wanted one that can do this for a while.

NO!!! DO NOT PUSH IT TO THE FLOOR!!! I was just asking because I learned this the hard way on my '08 when I bled the brakes a few years ago.

Could you elaborate what about pushing the pedal to the floor kills the MC? I'm not saying I don't believe you, I just don't follow.

My brakes have been slightly squishy for... well, a long time now, and I've never been able to determine if this has been a tiny amount of air in the system or if it's master cylinder related. But, I think I'm due for a new master cylinder anyway because it looks like it's leaking into the brake booster...
 

SnowDrifter

Full Access Member
Joined
Sep 5, 2016
Posts
2,402
Reaction score
2,577
Location
Washington. The desert side not the Starbucks side
Could you elaborate what about pushing the pedal to the floor kills the MC? I'm not saying I don't believe you, I just don't follow.


Generally has to do more with a poorly maintained brake system. Accumulated schmoo in the cylinder and/or any corrosion(rough spots) can either embed themselves in the seal, or scrape up the seal enough that the m/c develops an internal leak.

Some times you can have tooling marks or flash that do the same thing when you push the seals to the end of travel. Either way: Same result.

I've always taken quite good care of my braking systems. I don't fear pushing mine to the floor, nor have I ever had an issue with doing so across dozens to hundreds of vehicles (this includes customer vehicle m/c replacements). The way I see it: If bottoming the thing out causes it to go bad, then I'm condemning it anyway and replacing or rebuilding it. I'd rather find out during maintenance in a controlled environment than during say.. A panic stop or a surprise leak in the system - really anything that will cause the thing to depress further than expected.

YMMV
 
OP
OP
Lord Snax

Lord Snax

TYF Newbie
Joined
Jun 15, 2017
Posts
23
Reaction score
9
Location
Maryland
Just curious, which OBD tool did you use? There aren't many that I am aware of that can bleed ABS, and I've wanted one that can do this for a while.



Could you elaborate what about pushing the pedal to the floor kills the MC? I'm not saying I don't believe you, I just don't follow.

My brakes have been slightly squishy for... well, a long time now, and I've never been able to determine if this has been a tiny amount of air in the system or if it's master cylinder related. But, I think I'm due for a new master cylinder anyway because it looks like it's leaking into the brake booster...

I’m using a Foxwell Scan tool.
Here is the Amazon link: https://www.amazon.com/dp/B072VGJ7S8/ref=cm_sw_r_cp_tai_IvtBCbMW2R6RQ

As for the slightly squishyness you are speaking of. GM SUVs and pickups have always had a slightly squishy brake pedal. As long as you are not sending the pedal to the floor to stop the car, like my brake pedal is doing at the moment, I think you are okay.

The way I understand how working the MC past it’s normal stroke can damage it. Is that when metal parts are made, they are never perfectly smooth, even if they look and feel like they are. There are still microscopic imperfections in the metal. So the rubber seals in the MC, trough normal use, break in to the metal and wear the metal to fit. Over the years the seals can get brittle, and become easier to break. So when you move a very old MC past it’s normal stroke, it puts the old brittle seals on to parts of the MC that we’re never broken in. Resaulting in the destruction of the seals. Hope this helps.

- Lord Snax
 
OP
OP
Lord Snax

Lord Snax

TYF Newbie
Joined
Jun 15, 2017
Posts
23
Reaction score
9
Location
Maryland
@argus Its a little tricky to find the setting that bleeds pump in the Foxwell Scan tool. Here is a video that uses a different scan tool, but it’s very similar. Look around a bit in the abs section and you will find it.

 

iamdub

Full Access Member
Joined
Apr 23, 2016
Posts
20,712
Reaction score
44,433
Location
Li'l Weezyana
Could you elaborate what about pushing the pedal to the floor kills the MC? I'm not saying I don't believe you, I just don't follow.

My brakes have been slightly squishy for... well, a long time now, and I've never been able to determine if this has been a tiny amount of air in the system or if it's master cylinder related. But, I think I'm due for a new master cylinder anyway because it looks like it's leaking into the brake booster...


It's wear from age/use and, as Chris @SnowDrifter mentioned, lack of maintenance. The core of the MC is basically a piston in a bore. Over the years of normal braking, this piston is cycled back and forth thousands of times, mostly within a relatively short range of stroke. The piston seal(s) and bore wear together and are "seated/bedded-in" together in this particular area. The rest of the bore is virtually untouched and is still "tight". The difference is extremely small, but the tolerances are tight. Years go by and all is fine until someone pushes the pedal to the floor repeatedly while bleeding the brakes. The aged and fragile seals are then forced into this tighter and even differently-shaped area of the bore and they can be torn, causing loss of pressure. Old, dirty and contaminated fluid (the lack of maintenance Chris mentioned) exacerbates this problem as it's more abrasive from the particulates it contains, so the parts are worn more. There are other factors that determine if flooring the pedal will be an issue or not- The quality of the MC's build when new, the maintenance throughout it's service life, the type of braking primarily performed, etc.
 

06JET

Full Access Member
Joined
Apr 18, 2018
Posts
169
Reaction score
179
Location
Wisconsin
I have also have an issue with the peddle now needing to be pushed further that before I changed my brake lines. I don't recall pushing the peddle further down when the brake line burst in my garage. I had it on jack stands with it running trying to find a slight vibration and when I hit the brakes the line blew. I knew they were getting bad I just couldn't see how bad until it happened and I jacked up the body off the frame to replace them. I have a vacuum bleeder that I use and I have had them bled at a Midas shop and they activated the ABS while doing it. I have read since then that you should have the engine running while bleeding but haven't tried it that way. Would that have any effects on getting all the air out? Maybe it is time to change it out. Seems weird though, the brakes work and I do not have peddle leak down while braking but it used to be at the top of the peddle and now it is close to the bottom. I usually give it 1 pump and the second push feels much better/firmer but it is still much lower than it used to be.
Thoughts???
 

iamdub

Full Access Member
Joined
Apr 23, 2016
Posts
20,712
Reaction score
44,433
Location
Li'l Weezyana
I have also have an issue with the peddle now needing to be pushed further that before I changed my brake lines. I don't recall pushing the peddle further down when the brake line burst in my garage. I had it on jack stands with it running trying to find a slight vibration and when I hit the brakes the line blew. I knew they were getting bad I just couldn't see how bad until it happened and I jacked up the body off the frame to replace them. I have a vacuum bleeder that I use and I have had them bled at a Midas shop and they activated the ABS while doing it. I have read since then that you should have the engine running while bleeding but haven't tried it that way. Would that have any effects on getting all the air out? Maybe it is time to change it out. Seems weird though, the brakes work and I do not have peddle leak down while braking but it used to be at the top of the peddle and now it is close to the bottom. I usually give it 1 pump and the second push feels much better/firmer but it is still much lower than it used to be.
Thoughts???

Definitely sounds like air. I don't like having the engine running because I can't get an accurate feel for any improvement in the pedal response. If you bleed them and they're better but then get progressively worse, then air is getting into the system somewhere.
 

06JET

Full Access Member
Joined
Apr 18, 2018
Posts
169
Reaction score
179
Location
Wisconsin
My brakes have gotten slightly better over time but no where close to what they were before the brake line replacement. It really sounds like I have air trapped in my MC. I would have thought that even if it did have air in it that all the bleeding I have done and have had done would have got it out.
 

Forum statistics

Threads
128,788
Posts
1,805,457
Members
91,768
Latest member
PascalBlues
Top