Rear Brakes NO to Poor stopping power

[bg1988]

My Rear brakes  have very low stopping power

Chevy Tahoe GMT900  2008

the front are ok  and brake good nice and hot

 

I have verified   by stopping Hard as possible a few times then   check the rear rotors and they are cold  to the  touch...    ( checked a second time  tonight slightly warm )

 

 I retried it tonight and it seems it  warmed a little bit but not much compared to the front.. 

Was able to touch them without burning my self

 

the front were very hot i can feel the heat coming off of them. (obviously did not touch them)

 

 

 

 

also the  brake fluid reservoir empties  to about 50% when the engine is started then refills it self back up when turned off .  you can hear a creeping noise from the rear driver side(while parked with engine off  and stops when the reservoir refills it self ) and the rear  passenger side squeals while driving   the rotor stays cold

 

 

  the pads look new and appear to be dragging on the rotors  or with in a fraction of a Millimeter  (like I  said magic cold rotors, they are not heating up even after the very hard braking in which all 4 rotors should be activated  along with the  regeneration  .. )

 

this SUV has never seen the snow  and very little rain since 2008   aka California car

 

 

I suspect the brake lines could be bad and expanding and not doing the "braking" when it's pressed

 

or   just very very poorly designed brake pads???

  who the hell makes rectangle brakes pads    it's like trying to fit a square  peg in a round hole  TOTAL FAIL in design                           

as you can see in the photo  there is very little surface area touching the rotors

 

Honestly the GMT900 has wimpy limp noddle  brakes 

 

How the hell is this rated to 6,200 pounds     i think with the wimpy brakes it has i'm sure it's  real life rating is just a few light weight bicycles on the hitch.  

 

 

 

i know GM intention was to use the Regeneration  to slow it down but if i'm using the friction brakes  It means I NEED TO STOP NOW not in a extra 20 or 40 feet..

 

 

 

 

My W-body bit the rotors so hard it ..   It was like a car accident  every time you pressed the brakes .   ( surprised the air bags did not pop)

 

they stopped on a dime..

 

Funny story one time my friend was in the car and did not put on his seat belt  I stopped hard and made him fly into the dash  ... ahha    

 

[swathdiver]

57 minutes ago, bg1988 said:

My Rear brakes  have very low stopping power

Chevy Tahoe GMT900  2008

the front are ok  and brake good nice and hot

 

I have verified   by stopping Hard as possible a few times then   check the rear rotors and they are cold  to the  touch...    ( checked a second time  tonight slightly warm )

 

 I retried it tonight and it seems it  warmed a little bit but not much compared to the front.. 

Was able to touch them without burning my self

 

the front were very hot i can feel the heat coming off of them. (obviously did not touch them)

 

 

 

 

also the  brake fluid reservoir empties  to about 50% when the engine is started then refills it self back up when turned off .  you can hear a creeping noise from the rear driver side(while parked with engine off  and stops when the reservoir refills it self ) and the rear  passenger side squeals while driving   the rotor stays cold

 

 

  the pads look new and appear to be dragging on the rotors  or with in a fraction of a Millimeter  (like I  said magic cold rotors, they are not heating up even after the very hard braking in which all 4 rotors should be activated  along with the  regeneration  .. )

 

this SUV has never seen the snow  and very little rain since 2008   aka California car

 

 

I suspect the brake lines could be bad and expanding and not doing the "braking" when it's pressed

 

or   just very very poorly designed brake pads???

  who the hell makes rectangle brakes pads    it's like trying to fit a square  peg in a round hole  TOTAL FAIL in design                           

as you can see in the photo  there is very little surface area touching the rotors

 

Honestly the GMT900 has wimpy limp noddle  brakes 

 

How the hell is this rated to 6,200 pounds     i think with the wimpy brakes it has i'm sure it's  real life rating is just a few light weight bicycles on the hitch.  

 

 

 

i know GM intention was to use the Regeneration  to slow it down but if i'm using the friction brakes  It means I NEED TO STOP NOW not in a extra 20 or 40 feet..

 

 

 

 

My W-body bit the rotors so hard it ..   It was like a car accident  every time you pressed the brakes .   ( surprised the air bags did not pop)

 

they stopped on a dime..

 

Funny story one time my friend was in the car and did not put on his seat belt  I stopped hard and made him fly into the dash  ... ahha    

 

That you Brent?  Mine stops great, even while towing a 6,000 pound trailer without brakes.  You need a new master cylinder or your old one needs an overhaul.  Do check the brake lines but the cold rotors is most likely the MC.

[bg1988]

27 minutes ago, swathdiver said:

That you Brent?  Mine stops great, even while towing a 6,000 pound trailer without brakes.  You need a new master cylinder or your old one needs an overhaul.  Do check the brake lines but the cold rotors is most likely the MC.

yeah  I abandoned the other thread   

 

  the master cylinder looks new condition 

 

 

 so it could be the lines expanding  as that would  explain the fluid dropping  upon startup..  or  air in the system  (drops just below that white sticker  so about 40% loss or so)  TRW brand

 

 

[swathdiver]

Don't think the level would drop that much because of brake line expansion, they'd burst.  Still leaning towards the MC, unless the pads are on backwards or the caliper pistons are stuck and not moving.

 

The slides have a built in spreader that keeps the pads off the rotor but it is a flat spring and doesn't seem enduring.  ACDelco came out with wire drag reduction clips that help keep the pads off the rotors and they do work.  My truck coasts a lot more after putting them on and we've only done the front so far.

 

Your master is different than mine, likely because of your hybrid technology.

[bg1988]

it's the same part#

22936000  or Replaces:20759706

 

 

the booster part is not the same

 

 

[davester]

The only place for that much fluid to go is the calipers.  It's almost as if a caliper is fully retracting when the truck is off, then extends out again when you start up the truck and push on the brake pedal.  Maybe pop the rear wheels off and look at the caliper pistons to see if they are moving much after the truck has been sitting (for that much fluid, it should be readily visible).

[bg1988]

the pads are sitting on the rotor.. with in a fraction of a millimeter( does not seem to be dragging as the rotors are not heating up after a few miles) 

[davester]

I was suggesting looking at the caliper pistons, as they can retract into the caliper without the pad moving.

[bg1988]

10 minutes ago, davester said:

I was suggesting looking at the caliper pistons, as they can retract into the caliper without the pad moving.

 yeah I don't want to pour any money into it yet   as i'm in the process of making a bond claim on the dealership...  it might end up returned...

 

 

this sucks because the engine does not burn any oil that is pretty rare for a AFM/VVT engine 

I don't think i could afford  buying a quart or two of oil every 1,000  miles

[riverbanks]

The level drop at startup?take the serpentine belt off for a test,this way you are eliminating assist,try that,short time,don't want any overheating,I suspect you have a sensitive hydrobost issue

[riverbanks]

Or too,like mentioned,weak master cylinder,loosen master from Mount a 1/8 to 1/4 inch,see if level does not drop as much, process of elimination, sometimes the "easy" button is broken,or just plain bad luck,oh,I've had the bad luck days lately,wouldn't be great if all I had to do was change wiper blades,I'm dreaming, of course

[garagerog]

OP, before you overthink this, find a safe place where you can set up pylons and do a 60-0 mph stopping test and compare it to published norms. Then you will have a starting point to judge your perceived lack of braking power. With an unloaded bed, the typical p/u truck or SUV is in the neighborhood of about 70% front braking power during a hard stop.

[riverbanks]

Agree,but the lowering of fluid at startup?

[bg1988]

The pedal felt firm, and the GM engineers claim the Hybrid comes to a halt in a shorter distance than the conventional Tahoe.  as edmuns says..

 

 consumer reports has a video of the guy hard braking  with the tires squealing

 

mine one did that once

 

 I had a interment power loss that one time..    when the engine was running

as all 4 disc brakes locked up...  i went from 50MPH to a stop very fast stop...

 

 

[sefiroxx]

Air in the line?