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Dragging brakes

Purplejchild

By Purplejchild
in Ask A GM Technician

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Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted
5 minutes ago, tlaw91 said:

Contaminated hydroboost systems aren’t common but they do happen.
I’ve also heard abs modules staying ‘on’ and holding brakes.
Also,
Double check pushrod length/adjustment, make sure there’s free play in the pedal, if the rod is too long, or adjusted too far in, it’ll hold the pistons inside the master beyond the compensator ports and never let pressure bleed off after applying brakes

I could understand the pushrod being the wrong length if this issue started after changing the master cylinder, but it didn't.  The rod can't change lengths on its own, and even if it could, it would get shorter, not longer.   It really is acting like a compensating port being covered or plugged.  Easy way to test is to remove the cap from master cylinder, and using a clean rag, make a funnel shape around the open cap and have someone tap the brake pedal.  The brake fluid should spurt out the opening as the brake pedal tapped.  If nothing comes out, try the other cap, assuming it has two caps.  

 

I went through a bunch of cars with oil in the master cylinder when I was working at Firestone in the 80s.  A local gas station attendant used oil to top off the master, this was back when they would actually open your hood to check oil and fluids.  Every rubber part that the oil hit swelled up.   

tlaw91 Enthusiast

tlaw91

Posted
Posted

You have to swap it over when you change the cylinder.
Unfortunately with the way this whole deal shook out, unclear if he
A. Needs ABS module
B. Left contaminated oil in system when changing parts (unknowingly) and a new part is bad
C. Did something incorrectly, or some combo of the three.
When you’ve replaced the entire brake system other then the abs and it’s doing the same thing ur options are limited. And yes abs modules can do this.

Purplejchild Enthusiast

Purplejchild

Posted
  • Author
Posted

I think I might have a breakthrough.  I drove it today and it started to drag to the point it was almost locking up.  I got out a d loosened the master cylinder from the hydro boost and that released  the pressure,  so I drove it home loose and put washers on and drove it the rest of the day and no dragging.  So I hope this did the trick. Thanks for your advice and help...

tlaw91 Enthusiast

tlaw91

Posted
Posted

Sounds like pushrod length issue. Glad we helped, that was a tough one. Hardest issues I’ve ever had is when you fix the issue but then cause another with the same symptoms. I hate cars.

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

It sort of defies logic.  The push rod getting longer would be going against physics.  If the jam nut came loose, I would expect it to get shorter since becoming longer means it has to overcome the static pressure in the master cylinder.  You will want to unbolt the master cylinder and slide it off the studs so you can take a look at the push rod.  Having never seen behind a master on a hydra boost system I am just assuming the push rod can be removed this way.  The push rod should have a lock or jam nut preventing the rod from turning on its threads.  Be careful to avoid losing the current installed length.  Using washer as you did is a good way to help diagnose it, but is not wise to leave it that way.  You sure this didn't start after the master was changed?

  • Like 1
Purplejchild Enthusiast

Purplejchild

Posted
  • Author
Posted

I know I'm scratching my head also. The dragging of brakes  is what got this all started. There was 2 stuck front calipers  that might have been the original problem, and after fixing that mybe the pushrod might have continued the problem.  I don't know...

  • 3 years later...
BrianBrianBrian Enthusiast

BrianBrianBrian

Posted
Posted (edited)
On 6/9/2020 at 9:47 PM, Purplejchild said:

I know I'm scratching my head also. The dragging of brakes  is what got this all started. There was 2 stuck front calipers  that might have been the original problem, and after fixing that maybe the pushrod might have continued the problem.  I don't know...

Man...
I am so happy to have found your post.  I've been trying to solve this exact problem for the past month.
This was my post <--- 

After replacing the Brake pedal sensor switch, Front: Wheel hub Assembly, Rotors, Brake Pads, Calipers, and I even replaced the trailer brake module for the cherry on top.   And just like you, the damn brake drag is still there.    I've been trying to explain this to everyone and it feels like I'm the only one with this problem until I read your post.  I've only been able to drive locally before it gets so bad that it almost seizes. Like you, no codes have been thrown that I can relate to the issue. The next step for me was to replace the brake hoses and then the MC.  But since you mentioned you performed these steps I'll skip it and put the $$ towards the GM technicians.   I just dropped her off yesterday and the guy said he doesn't seem to think its a brake problem, but more likely an electrical problem.  Said they'll need the truck for a few days to comb through the wires...(sounds cheap, gulp)

This is old post but hopefully you can share your memory of the final fix?

Edited by BrianBrianBrian
  • 3 months later...
  • 1 month later...
beachboi New Member

beachboi

Posted
Posted
On 6/7/2020 at 10:11 AM, tlaw91 said:

Contaminated hydroboost systems aren’t common but they do happen.
I’ve also heard abs modules staying ‘on’ and holding brakes.
Also,
Double check pushrod length/adjustment, make sure there’s free play in the pedal, if the rod is too long, or adjusted too far in, it’ll hold the pistons inside the master beyond the compensator ports and never let pressure bleed off after applying brakes

Would the pushrod come out of adjustment on its own?

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