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bad master

primem

primem

New member
2004 gtp comp g with 230 000kilometers. background info... the car is mint mechanically, no dtc and drove perfect until today. the caliper pins and brackets were cleaned and lubed last year. brake fluid flushed last year.

thinking its a bad master cylinder. here are my symptoms.
driving off from a stop it feels like the brakes are dragging... stopped, idling with foot off the brake the car will not roll forward without stepping into the throttle. the brake pedal has no freeplay and the pedal is hard. Not hard to apply, hard feel right as soon as you apply the pedal. the booster is working properly. after a short 2 kilometer trip all 4 brakes were hot. no pulls or burnt pad smell but I have not driven it far. This weekend I will raise it up on the hoist and inspect the master and spin all 4 wheels and measure rotor temp with a ir gun.

anything else to consider?
 


If one or more of the sensors in the hubs are bad, it could be setting the abs off, my gt had one wire from the driver front hub sensor that was damaged and I could feel the abs kick in every once in a while without showing anything on the dic or gauge cluster.

Just another possibility.
 
thanks for the reply. the abs pump is not activating other than its normal pump test that the enhanced stability control program performs. no abs or any dtc are set.
 
The only other thing I can think to check is the e brake cable, it could possibly be binding and dragging the rear brakes.
 
when a master goes bad you have no brakes. pedal to the floor. if they seem to be holding the brake hoses to the calipers are known to fail and become a one way valve sorta.
 
I will test for that. I will let you know what I find out this weekend.

on another note...the vacuum assist on the s/c cars....is there a vacuum pump to supplement the manifold vacuum? I have yet to fully inspect the system.
 


if you had no vacuum to the brake booster the pedal would be rock hard. like when the car is off, pump the brakes a few times, rock hard, that's no vacuum.
 
An easy way to check for a bad brake hose is to pump up the brakes, release the pedal, and see if you can spin the wheel by hand. If the wheel is hard to turn, open the bleeder on that caliper and see if the brakes free up. If they do, then the hose is most likely the issue. If not, then something is sticking.

What types of lube did you use on the pins and brackets? I've seen petroleum based grease dry up when used on the pins and cause sticking due to how it interacts with the rubber boots. Silicone on the pins, moly or anti seize on the brackets has always worked well for me. Remove the caliper from the bracket and make sure you can move the pads by hand. It couldn't hurt to check the caliper pistons too, they should push in easily with a C-clamp.
 
Scottydoggs said:
if you had no vacuum to the brake booster the pedal would be rock hard. like when the car is off, pump the brakes a few times, rock hard, that's no vacuum.
Click to expand...

I do have vacuum. with the car off, I depleted the vacuum booster reserve and held the brake pedal down...started the car and the pedal sank lower...indicating the booster is working. I was wondering if the booster return spring was damaged and the vacuum booster applying the master.
what I find unusual, with the car running, the pedal is rock hard with no free play travel. this and what seems like 4 hot rotors make me think its something effecting all 4 calipers.
 
nik12937 said:
What types of lube did you use on the pins and brackets? I've seen petroleum based grease dry up when used on the pins and cause sticking due to how it interacts with the rubber boots. Silicone on the pins, moly or anti seize on the brackets has always worked well for me. Remove the caliper from the bracket and make sure you can move the pads by hand. It couldn't hurt to check the caliper pistons too, they should push in easily with a C-clamp.
Click to expand...

a/c delco silicone brake lubricant.
checking the calipers piston is a good idea as I need to rule a few thing out. I have delt with seized calipers, but never have they caused the pedal feel I have now. Usually, power brakes are so strong they will apply any seized piston...the square cut seal just won't retract the piston. Something is going on here that is different than a seized caliper or internally damage flex hose.
 
When you have a chance, with the car off, pump the brake pedal until it is stiff and then with your foot pushing on the pedal, start the car and see what happens. If the pedal drops straight to the floor you have a bad master that is bypassing itself. A bad booster will not supply any vacuum and leave you with manual brakes. Never seen a booster leave anyone with dragging brakes.
 


the pedal is rock hard and does not sink to the floor. the booster test passed...see post 9. the pedal goes down as the booster applies assist but the pedal is firm after the assist is provided.

the car was fine...stopped and went inside for 15minutes...came back out and the problem was there instantly as I backed out of the driveway.

guess I gotta test something sometime...and rule some stuff out and report back.

test drive, measure rotor temp, raised and spin the wheels and inspect brake pedal linkage and maybe disconnect and see where that leads
 
Ok... let's rule out what we know so far. The booster is not the issue because if it fails, it will not cause brake drag. It passed your pedal test. It won't be a hub bearing because the bearings on our cars are sealed for life, not the pack and adjust variety on older cars, so there is no concern for over tightened hubs. If you have this problem at all 4 wheels, which you could probably identify by taking rotor temps with a temp gun, then we need to look at something common to all 4 corners. We don't have metering valves because we have 4 wheel disc brakes so that is one less thing to be concerned with. You mention no Freeplay in the brake pedal... there needs to be some so that the cylinder in the master can be fully released so as to not cause drag. You can inspect this if you have the tool to measure it. What I would do is this... check all 4 rubber brake hoses that go to each caliper for feel and see if any are deteriorating. This would not cause a problem at all 4 wheels, but you need to rule them out. The brake pedal linkage should not be out of adjustment because in all actuality, there is no reason to ever screw with it to begin with. With all of your testing of the booster and master by pressing the brake pedal, you have to be careful with how far you run the pedal to the floor. You can over do it and actually ruin a master by pushing the piston in it too far. My bet at this point would be the MC. You could try bleeding the brakes for the sake of fluid inspection. Deteriorating hoses will leave junk in the fluid. In all of the brake jobs I have done on various cars over the years in the shop and in my driveway, I have only had 1 for a drag problem and it was a caliper issue on a Nissan Murano. I'm interested in knowing what you come up with... please post when you do.
 
drove to the gym and back today; all normal. 2hs later went out and the brakes were dragging again and hot again...this time the abs and stability control lights came on. Will pull codes when I get to work Monday.

want to disconnect the ebcm and see what happens but will pull the dtc first.
 
Last edited:
ABS lights tell me it's either the abs module, abs sensors in the hubs, or something else setting if off.

Seems off topic, but I just saw it on another thread... Check all of the engine and battery grounds/cables, pay close attention to the negative battery cable where it attaches to the body, passenger fender well under the fuse box. Bad connection there can set off just about anything electronically controlled in the car. Easiest way to fix is taking the cable off, cleaning it down to bare metal, add some washers on either side and put it back together. Hit it with some paint or other coating to keep it from rusting as fast, and see if that works.

Either way it's going to prevent more problems cropping up later.
 
the dtc set in the ebcm was c0132 pressurized circuit range performance, At the moment the system is working normally and the dtc is stored in history.
As per usually module diagnostics, it wants the integrity of the wires and reference voltages checked, if all are good...replace ebcm. I will monitor the system this week and do some testing this weekend.

if it needs a ebcm...are all trim lines ebcm's the same. I thought gtp comp g versions had different programming for the esc system. Can anyone confirm this?

the brake build options appear to be:
-jl4 control active brake
-nw7 traction control power management only
-nw9electronic traction control

I have jl4. Is it safe to assume I can use any boneyard ebcm with the jl4 option regardless of trim level? I doubt i'll find a donor gtp in the boneyard but many na cars.
 


drove all week with all 3 fuses for the abs/ebcm removed. the problem still occurred. I decided to ignore the dtc diag and perform a mechanical inspection first.


so today, I drove for about 10 minutes until I could feel the problem occur and then went into the shop and raised the vehicle on the hoist.

the brake temps at each rotor where:
L/F 160*C R/F 113*C
L/R 73*C R/R 94*C

with the trans is neutral, tried to spin each tire by hand and the both front were not moveable, both rear could be moved but were dragging hard.

pull the check valve out of the booster and all wheels spun. plugged the hose back into the booster and attempted to perform the same test again. this time the l/f was the only tire that would not spin normally.

pulled the both front tires and unbolted the front calipers from the caliper brackets. the left caliper appears to have been replaced previously (all 4 calipers are not painted red...it should have red calipers from factory).


the right piston pushed back normally, the left would not push back. cracked the bleeder and the left pushed back normally. I have ordered a l/f flex hose for next week. I may have more than one problem but will start at the flex hose.
 
Good deal on your trouble shooting. Unfortunately some problems aren't so cut and dry and we have to go through tedious steps of trouble shooting to get an answer, unless you feel like throwing parts at it, but I don't recommend that to anyone.
 
yeah, shotgun method can get expensive. I'm trying to gather evidence that points to a failed part. I can get a cheap master and booster from the wrecker if more than the flex line is required.

I think I have ruled out the ebcm...at least in my mind. Although service info doesn't say it, I believe the ebcm dtc is set from the brake pressure sensor seeing pressure when the brake pedal position switch is not closed. That must be a logic check performed by the ebcm; so I believe the ebcm is working properly.
 
put the l/f flex line on and the l/f wheel is still dragging. I am not addressing the 4 wheel drag until I get the l/f fixed as this problem is there all the time.


sheesh, the car uses another flex hose before the one at the caliper. this 2 foot line has 1 rubber flex line and 1 steel braided line.
I decided to go right back to the ebcm and crack the brake line out of the ebcm. cracked the line...pressure spurt of fluid and the wheel spun freely.


...would have been a good thing to do the first time...ah well, the new flex line is nice and shiny and the $21 purchase is good for the economy.


a used ebcm/bpmv assembly is next.
 
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