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'03 Cadillac CTS
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Discussion Starter #1
Hi Folks;

We've got an '03 CTS with an interesting issue - intermittent front brake drag occurring on both front wheels (something, other then the driver, is applying hydraulic pressure to the front brakes ONLY).

Symptoms (when occurring) are severe vibration through the steering wheel and seat, lack of power (due to constant brake application) and increased noise (due to the drilled and slotted rotors).

In the past I experienced this issue once before for about 5 minutes when driving the car. Unfortunately it stopped doing it before I could determine the cause (it's intermittent and never happened again - that I'm aware of).

However, the issue came back and seems to be getting worse. This left us stuck on the side of the road today for several hours as we had to wait for the brakes to cool down. The wheels, tires and wheel wells were very hot and you could not touch the aluminum rim. We're fortunate there was no fire (I've seen that before from brakes overheating on other vehicles).

The rear brakes are 100% perfect - cool to the touch - this issue effects the front brakes only and both sides of the car equally. It's also intermittent and typically does not do this. Today it occurred on a long level piece of highway where the brakes are rarely used (they're not overheating due to intentional use or road conditions).

My thoughts are that there must be a valve (ABS?) or something like that which is keeping pressure on the front brakes under certain intermittent circumstances. When I returned to pick up the car today the issue was gone and the brakes were once again working perfectly (albeit, with a lot less pad!).

I used the car's internal scan 'tool' and found that there were zero codes. This causes me to again think of a mechanical/hydraulic issue - something like a stuck valve where pressure is being applied to the front brakes only.

Any Gm techs run into anything like that across the product lines?
 

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CTS 3.6L 2005 80,000 Miles
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probably have a sticking brake piston. try the following steps.

1.) use a suction device to suck all the old brake fluid from teh reservoir. Try to get as much of the black soot at the bottom out.

2.) pure new fluid into the reservoir, then bleed the system.

3.) repeat the process over the period of say a month to get as much residue out.

Now since your having a specific wheel that keeps giving the problem you may have to have the caliper rebuilt. I'm assuming that you aren't getting any CEL codes related to the break system.
 

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2004 Cadillac Cts
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162 Posts
probably have a sticking brake piston. try the following steps.

1.) use a suction device to suck all the old brake fluid from teh reservoir. Try to get as much of the black soot at the bottom out.

2.) pure new fluid into the reservoir, then bleed the system.

3.) repeat the process over the period of say a month to get as much residue out.

Now since your having a specific wheel that keeps giving the problem you may have to have the caliper rebuilt. I'm assuming that you aren't getting any CEL codes related to the break system.
couldn't agree more with this possible solution
 

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'03 Cadillac CTS
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Discussion Starter #4
Hi Briggy;

Thanks for the reply!

The symptoms are that both front brakes intermittently drag - as a pair. I probably wasn't clear on that in the original post. For that reason I tended to dismiss the calipers altogether as a potential cause as both would have to be intermittently sticky at the same time ;-)

There are no codes present for any module in the car.

That's kind of why I was considering an ABS issue. I'm not fluent with the ABS system but it seems to me that's about the only thing that could apply pressure to the front brakes when the brake pedal is not physically engaged?
 

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'03 Cadillac CTS
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Discussion Starter #5
couldn't agree more with this possible solution
Guys, BOTH front brakes are dragging at the SAME time. This happens intermittently. For example, when the issue occurs and you pull of to the side of the road you quickly find out that both front wheels are very, very hot (can't be touched). This is level driving with virtually zero brake application (to be more specific, up hill in a straight line after uninterrupted highway driving for 20 minutes - ie. NO brake application).

In order for a sticky caliper to cause these symptoms it would mean that both front calipers, as a set, would have to intermittently stick at the same time.

When this issue occurs the rear brakes remain at normal temperature. So the problem seems to be limited to the front brakes. The only thing that I can think of that could increase hydraulic pressure to the front brakes (only) when the brake pedal is not depressed would be the ABS system itself. Given that there are no codes present it causes me to wonder if there is a valve, or valves, in the ABS system that could be intermittently sticking causing these symptoms?

Are there any GM techs out there that have seen an issue present like this before?
 

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2006 3.6-Volant CAI, V-exhaust, LED swap, Clear DRL, 6000k
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Guys, BOTH front brakes are dragging at the SAME time.
he replied before you posted your response to briggy, so he couldnt have known what you were going to say and also your further explanation into the problem
 

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Discussion Starter #7
he replied before you posted your response to briggy, so he couldnt have known what you were going to say and also your further explanation into the problem
I understand, it's just a bit frustrating as I covered all of this in the my original post :)
 

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cts 3.6
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Could be the brake servo adjustment ( booster you call it ? ). Has the brake master cylinder ever been off ?

I had this problem on a Crown Vic.

The brake booster rod has an adjuster screw that is factory set, if it's too short then brake pedal travel is too long, if the rod is too long then the pads are too close to the discs, the discs warm up, then expand, and before you know it you have hot wheels.

Although this doesn't quite explain why the rear discs are unaffected.
 

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2004 Cadillac Cts
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Could be the brake servo adjustment ( booster you call it ? ). Has the brake master cylinder ever been off ?

I had this problem on a Crown Vic.

The brake booster rod has an adjuster screw that is factory set, if it's too short then brake pedal travel is too long, if the rod is too long then the pads are too close to the discs, the discs warm up, then expand, and before you know it you have hot wheels.

Although this doesn't quite explain why the rear discs are unaffected.
i apologize for my mistake it was late when i was reading the original post and didnt see that you said it was both wheels
now this is the post that i would agree with .... i'd check both the master cylinder and the lines coming off of it as well as the brake booster since they are connected
 

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Discussion Starter #10
No worries :)

I finally managed to get the car up and pull the front wheels off. I wanted to see firsthand how things looked in there. Both calipers are loose as a goose and all 4 pistons are free as can be. All 4 pads are evenly worn (almost to the milimeter). In other words, the front brakes themselves (mechanically) are fine. I suspected that from the outset but now we know 100% for certain.

I also grabbed a line wrench and drove around extensively hoping that it would do it again. The idea was that if I could get them to apply I could pull over and crack the lines to the master cylinder. If the brakes were then free I would know, for certain, that it was the master. If not, then it would pretty much have to be the ABS Pressure Modulator assembly.

Unfortunately, it wouldn't do it. It is intermittent and it is both front wheels. Back to square one, this time with the ability to completely rule out calipers/pistons etc. I always felt that was a long shot because it would mean both calipers or pistons on both sides would have to intermittently seize at the same time - something that would be extremely unlikely.

I did notice that there is also a brake pressure sensor screwed into the ABS modulator. I'm trying like mad to find out how that actually fits into the ABS system but the GM service manuals don't really explain much about it.
 

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Is there any free-play in the pedal at all? There should be a couple of mm. If there is no free play the pedal might be holding the pistons in the master cylinder just forward enough to prevent fluid from moving back up into the reservoir as the brakes heat up and expand, resulting in drag...

If you take the master cyl off the booster, the pushrod will be visible, there's going to be a factory measurement for how far it sticks out and it's usually adjustable as simple as a threaded bolt/locknut type of thing, usually easily visible with master cyl pulled forward, but double check in a workshop manual for both measurement and procedure before farking around.
 

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Cadillac CTS 2003, Pontiac Trans Am S.E. 1977
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I have a problem with my braking system. Sometimes the brakes will hum as if the ABS system is activating in a situation, but it does it randomly. The pedal will often move and the brakes do not completely work when this happens. Usually after the humming sounds happens it throws a code on the dash and says that ABS and TC have been disabled and they stay off, sometimes for days. I checked the F1-F6 Diagnostics and I got up to three EBC errors.

I had the car worked on a couple of months ago and the shop had to replaced one of the ABS sensors.

I do not know if this has anything to do with your problem, but I am aware that if the computer wanted to, it could activate the brakes without you pushing the pedal and stop the vehicle. Or it may just be mechanical.

All I know, you have a Cadillac!:yup:
 

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Discussion Starter #13
Is there any free-play in the pedal at all? There should be a couple of mm. If there is no free play the pedal might be holding the pistons in the master cylinder just forward enough to prevent fluid from moving back up into the reservoir as the brakes heat up and expand, resulting in drag...
There is some free-play in the pedal - in fact, the pedal has always felt very good. The car's a cream puff and I know the history very well. It's also a low mileage unit - about 90K. However, your thoughts on the master cylinder holding the brakes on was something I was considering but, the car would not exhibit the problem again no matter how long I drove it or how much I played with the brake pedal :-(

I ordered a new ABS Brake Modulator from Gm today (the ABS pump & valve assembly). When it comes in I'll install it, flush the system, put it back on the road and see what happens. It's an educated guess but at this point I think it's probably a good one. I'm hoping it also comes with a new brake fluid pressure sensor and kill two birds with one stone. It would be a lot nicer if the car coughed up a code but there's nothing there - it's almost always been a code-free car :)
 

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Discussion Starter #14
I do not know if this has anything to do with your problem, but I am aware that if the computer wanted to, it could activate the brakes without you pushing the pedal and stop the vehicle. Or it may just be mechanical.

All I know, you have a Cadillac!:yup:
Hahaha - you got that right :) In all truth though, we love the car and we want to support GM as they are a great company and support the North American economy in a BIG way. So, in a sense, we feel pretty good about bending over for the ole' General - hahaha :) We're just doing our part to eliminate their debt :)

You raised an interesting point - that the ABS can come on at will. The service manual states specifically that;

"The ABS cannot, however, increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking". I initially used that declaration to rule out the possibility that the ABS brake modulator could be applying the brakes (especially since it last occurred while I was going uphill in a straight line with my foot OFF the brake) until I realized that the statement isn't true. The traction control will apply the brakes even if the driver does not have his foot on the brake!

So I'm in agreement with you - it can do as it pleases :)
 

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No worries :)

I finally managed to get the car up and pull the front wheels off. I wanted to see firsthand how things looked in there. Both calipers are loose as a goose and all 4 pistons are free as can be. All 4 pads are evenly worn (almost to the milimeter). In other words, the front brakes themselves (mechanically) are fine. I suspected that from the outset but now we know 100% for certain.

I also grabbed a line wrench and drove around extensively hoping that it would do it again. The idea was that if I could get them to apply I could pull over and crack the lines to the master cylinder. If the brakes were then free I would know, for certain, that it was the master. If not, then it would pretty much have to be the ABS Pressure Modulator assembly.

Unfortunately, it wouldn't do it. It is intermittent and it is both front wheels. Back to square one, this time with the ability to completely rule out calipers/pistons etc. I always felt that was a long shot because it would mean both calipers or pistons on both sides would have to intermittently seize at the same time - something that would be extremely unlikely.

I did notice that there is also a brake pressure sensor screwed into the ABS modulator. I'm trying like mad to find out how that actually fits into the ABS system but the GM service manuals don't really explain much about it.

Don't be in such a rush to blame the ABS system. The ABS system is one of the most checked and double checked systems on the car. I'm pretty sure if you were experiencing ABS malfunction you would get some sort of a code. ABS is independently monitored through the traction control system, and visa versa.

The problem I've seen with many brake systems, is the break fluid break down builds up in the reservoir then travels down through the cylinder proportioning valve, then cylinders. In other words it's possible for it to effect the entire system, including the mechanical components of the ABS. This being said take the time to clean out the old fluid and soot. I was having a similar problem and upon doing this my entire braking system began to function better. Doesn't hurt to try. After eliminating fluid related problems then you go to other potential causes. This way you don't go out and purchase a new ABS system when yu don't have to.
 

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before you buy a new ABS unit, couldn't you try to pull the ABS fuse? or disconnecting the plug or something?

also, about another GM product (Holden VR Commodore) with a similar issue (brakes randomly locking/dragging) :
Theres a centre valve assembly built into the piston on the master cylinder for the benefit of abs
Try changing the master cylinder first... cause the seal may be swollen or malfunctioning
If that doesn't cure it... you need a new ABS unit
Which of course you can't buy...
 

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Discussion Starter #17
The issue (in this case) is that the client is more concerned with killing the issue off. They'd rather spend more money and ensure it never returns. However, I have been thinking of putting in a new master just to be sure (along with the brake modulator). You've got to remember, the issue is intermittent - it rarely happens. It's only recently that it really showed up again (this time in force). I've been driving the car for some time and can't get it to do it. If it was the master I would think I could have gotten it do it at some point.
 

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Discussion Starter #18
Good news - yesterday the car began to do it again and this time I was able to raise the front wheels and see just how hard it was to turn them manually. The drivers front required all my strength to move and the passenger wheel was about half that. I was also able to quickly crack the lines to the master cylinder to see if it was holding pressure to the fronts but there was nothing - the brakes were still held on.

So, we know for a fact it's not the master which means the pressure must be being held from lower in the brake system. The next thing down the chain is the ABS modulator and after that the brake hoses and calipers.

We've already eliminated the calipers from the equation and I have a really hard time believing that both front brake hoses are intermittently holding pressure - at the same time - so we're back to my original choice - the ABS modulator. Unfortunately the one I ordered showed up with shipping damage (it was packed very poorly by GM and two of the valves were bent). So, I'll re-order it and when it comes in I'll post back my findings.

The only other thing I can think of that could cause this issue would be a software/programming glitch in the ABS module itself. However, I kind of doubt that as this issue presents under pretty normal driving circumstances.
 

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Time to disable the ABS system ( if that's possible ) and run the car normally for a few days and see if the problem persists.
 
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