Mushy Brake Pedal After New Brake Lines

[Lord Snax]

Howdy,

My '05 Yukon XL recently suffered from the dreaded rusty brake lines. I replaced all the steel lines with new ones and filled and bleed the system, including the ABS pump. However, my brake pedal is still mushy and goes to the floor easily.

I have heard the master cylinder can wear out if air gets in it, but I am not sure if that is the case with mine.

Have anyone of you had this issue after replacing all the brake lines? If so, how did you fix it?

Also, my Yukon has StabliTrak if that info helps.

Thanks,
Lord Snax

 

[iamdub]

Gotta be a leak or air or you blew out the seals in the MC when bleeding. Did you push the pedal to the floor when bleeding? Might be worth your time to invest in a vacuum bleeder.

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

 

[Scottydoggs]

if the master went dry at any point, you need to bleed it.

i crack both lines off the master free then snug em back up, put a wrench on the nut wrap a rag around it then have a helper pump the brakes like you would a wheel caliper, pump em up, then you crack the line nut, you will hear air and fluid spit out, repeat till its just fluid, then do the other line nut. make sure the master stays full while re bleeding.

once done with the master you need to re bleed all 4 calipers.

 

[SnowDrifter]

How did you bleed abs?

 

[Lord Snax]

How did you bleed abs?

I used an OBD tool.

 

[Lord Snax]

if the master went dry at any point, you need to bleed it.

i crack both lines off the master free then snug em back up, put a wrench on the nut wrap a rag around it then have a helper pump the brakes like you would a wheel caliper, pump em up, then you crack the line nut, you will hear air and fluid spit out, repeat till its just fluid, then do the other line nut. make sure the master stays full while re bleeding.

once done with the master you need to re bleed all 4 calipers.

I did bleed it already. I will try again. As iamdub mentioned to go all the way to the floor when bleeding. I did not do that. I will when I bleed them again.

 

[corvette744]

More info when you pump the brakes and hold and open the bleeder what happens-air or all fluid.Im guessing air in your system if it worked fine before the line changes.I believe you need a scanner to purge the abs system to get all the air out.

 

[Lord Snax]

More info when you pump the brakes and hold and open the bleeder what happens-air or all fluid.Im guessing air in your system if it worked fine before the line changes.I believe you need a scanner to purge the abs system to get all the air out.

I already used an OBD tool to get the ABS to bleed the air out of it when I bleed the system. I have a feeling that there is still air in the master cylinder. I will bleed the master cylinder again when I have some time this week or next weekend, following iamdub's suggestion about pushing the pedal to the floor. I'll see if that makes a difference.

Thanks for the info.

Edit:
It was all fluid out of the bleeders by the time I was done bleeding it today.

 

[HiHoeSilver]

I already used an OBD tool to get the ABS to bleed the air out of it when I bleed the system. I have a feeling that there is still air in the master cylinder. I will bleed the master cylinder again when I have some time this week or next weekend, following iamdub's suggestion about pushing the pedal to the floor. I'll see if that makes a difference.

Thanks for the info.

Edit:
It was all fluid out of the bleeders by the time I was done bleeding it today.

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.

 

[iamdub]

I did bleed it already. I will try again. As iamdub mentioned to go all the way to the floor when bleeding. I did not do that. I will when I bleed them again.

I already used an OBD tool to get the ABS to bleed the air out of it when I bleed the system. I have a feeling that there is still air in the master cylinder. I will bleed the master cylinder again when I have some time this week or next weekend, following iamdub's suggestion about pushing the pedal to the floor. I'll see if that makes a difference.

Thanks for the info.

Edit:
It was all fluid out of the bleeders by the time I was done bleeding it today.

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.