"Soft" brake pedal when engine running

[new2yukon]

So hydraulic system has been opened up since you "swapped calipers". You got air trapped in your ABS manifold. It will take a very long time of locking up the brakes to activate the ABS pump and then bleeding to get it all out, if ever. You need a bidrectional scan tool and perform an auto bleed which actuates the solenoids in the ABS manifold. Is your Brake light on in the cluster????

After more testing today, you're probably right. But the caliper swap and hose swap etc were an effort in routine maintenance and didn't cause this issue but somehow I got this issue but don't know when or why. I've just decided this issue needs fixing. The new MC did help because the pedal holds really good now with engine off but unfortunately didnt solve the running softness.

 

[new2yukon]

After checking the booster with pedal tests and engine cycling it seems to test as it should.

Booster check valve only allows air one way so that's good. I get the big "whoosh" when I pull it after a run cycle. So it holds vacuum.

Vacuum hose has good suction when pulled from the booster with engine running so that seems fine.

Sooooo...the "only" thing left seems like the abs has air in it??? Or its bad in some manner. As you guys suggested I think that's my last issue....need a shop to do that for me and hope that fixes it.

 

[new2yukon]

If tou have tried everytging else, cap off outlets on master cylinder. Bleed and test for firm pedal.

I would do that if this issue arose after I put in the new MC but this issue was prior so I really feel most if not all of this issue is something else.

 

[new2yukon]

I'm going to make a shop appt and will update this after I know more.

 

[rockola1971]

After more testing today, you're probably right. But the caliper swap and hose swap etc were an effort in routine maintenance and didn't cause this issue but somehow I got this issue but don't know when or why. I've just decided this issue needs fixing. The new MC did help because the pedal holds really good now with engine off but unfortunately didnt solve the running softness.

If you opened up the hydraulic system which you most certainly did when you changed out calipers.....that caused the issue. And that issue is air trapped in the system that you will never get out without a bidirectional scanner using the auto bleed feature. Is your BRAKE light on in the instrument cluster when engine is running?

 

[new2yukon]

If you opened up the hydraulic system which you most certainly did when you changed out calipers.....that caused the issue. And that issue is air trapped in the system that you will never get out without a bidirectional scanner using the auto bleed feature. Is your BRAKE light on in the instrument cluster when engine is running?

No brake light is on. This issue was prior to my caliper swap, but even so, the calipers are downstream from abs so I dont follow how that would even cause an issue like mine.

 

[OR VietVet]

No brake light is on. This issue was prior to my caliper swap, but even so, the calipers are downstream from abs so I dont follow how that would even cause an issue like mine.

Because air in the system can travel. What @rockola1971 is saying about a bidirectional scanner is correct. Otherwise, you will over think the problem and say things like, "I don't follow how that would even cause an issue like mine". You have asked for help. You are being given help.

 

[new2yukon]

Because air in the system can travel. What @rockola1971 is saying about a bidirectional scanner is correct. otherwise, you will over think the problem and say things like, "I don't follow how that would even cause an issue like mine". You have asked for help. You are being given help.

I know what you are saying but also know that this issue was prior to my caliper swap so that in itself can't be blamed. Yes, air rises but its also opposed by gravity and the fluid.

This could also have been a bad booster but its not. It could actually be a bad modulator and not even air from what I've been reading. I'm trying to do a proper diagnosis prior to concluding air in the abs system.

 

[OR VietVet]

I am not saying the calipers caused the problem. I am saying the task of changing the calipers likely put air in the system and has traveled from the calipers to the ABS system.

 

[Matahoe]

From experience a spongy brake pedal is with out a doubt air in the system. Either in master cylinder, ABS module or lines/calipers. Air in ABS module accumulator section would require bleeding at the module itself (somewhat challenging) or using a scan tool to activate the automatic bleed procedure.