WoodyFromBama

2006 Cts-V w/6 spd Man

My son was driving down a long hill. He came to his exit and just slightly applied the brakes and he said the car started making a rough growling/grinding noise and felt like the rear end was lifting up. The sound he thought was coming from the right rear and he was sure something was tearing itself up. He immediately pulled into a park & ride and called AAA to have it towed to my house.

I put it up on stands and inspected it but found nothing that appeared broken, bent, loose or missing in the rear suspension. The wheels are tight and exhibit no movement suggestive of a bad wheel bearing nor do they feel rough or make any sound when turned by hand. The backlash when turning the driveshaft or either of the wheels back and forth seems normal and doesn't make any unexpected sounds. The CVs are at least tight enough that I can't get any movement by hand.

I started it and put it in first gear. When the speed gets up to about 15 mph the display says it is engaging traction control and it started to make a sound (not sure whether the TC message and the sound/feel are absolutely in sync or not) that is either a high speed clunk or a low frequency growl -- describing this stuff is as hard as telling a doctor where it hurts and how much -- and it becomes rev-limited -- rpm won't come up any higher no matter how far you press the accelerator. If you are standing next to the rear wheel well when the sound starts you can see the rear suspension start to "pulse" and twist forward as if you were holding the brakes on and giving it the gas at the same time. I don't know if this is expected behavior when the rear end is up and the wheels are off the ground and hanging unloaded.

No matter, the brakes are not being pressed when this occurs so I wouldn't expect ABS to be activated. It seems to me that it is either the brakes being pulsed causing the forward torque/twist or one or both of the wheel bearings are grabbing. I think binding in the differential -- input or output -- would not cause the torquing effect. Same if it were one of the axle CVs.

Tomorrow I'm gonna put it back on the ground and take it for a test drive to see if the symptoms are the same but tonight I'm hoping some of you folks who have experience in this area can address the question of what behavior to expect when running it in gear while the rear end is up and the tires are hanging unloaded. Should the traction control engage? Should the brakes pulse hard and loud? Should it rev-limit? It would help me to have a better idea of what to expect.

Thanks in advance for taking the time to read this and for whatever help you can offer.

Woody
2006 Cadillac CTS-V (80k)
LQ9 cast-iron block, 6 spd MT, Lorenzo 18" black 5 spoke/6 bolt rims, H&R Sport lowering spring set, Cross-drilled/Slotted rotors, Corsa cat backs, Kooks stainless headers and mini-cat downpipes, FAST 102 intake manifold and Big Mouth ported throttle body, Creative steel bushing kit, Ligenfelter air intake, Creative adjustable short shifter

SE-R Spec

iTrader: (2)

From my experience when the rear wheels are turning and the front wheels are stationary (on the dyno or on jack stands) the ABS system usually turns off so it shouldn't be engaging.

Maybe a wheel sensor gone bad?

BaMaDuDe87

Make sure the bolts on the brake calipers are still in and tight

actrite80

iTrader: (2)

Does this happen when TC and SC are off

WoodyFromBama

I haven't tried it yet this morning -- neighbors don't appreciate it when I fire it up too early or too late .

BudRacing

iTrader: (3)

I actually put my car up on jack stands last week when it sounded like something was caught in a wheel about a mile from home. It wasn't like what you're describing, though. I took off from a light and the sound immediately started and sounded like something was caught in a wheel spoke and it was loud. I immediately pulled over and visually inspected all wheel wells and didn't see anything there or underneath the car, but it persisted until I got home.

I put it up on jack stands, inspected everything, started it, put it in gear both forward and reverse, raised the rear control arms up and down--nothing. Sound never came back and I didn't find anything in my driveway that would have fallen out.

While the car was up on the stands, there was never any interference from TC or Stability even though the front wheels were stationary.

Your situation sounds like traction control/stabilitrak is engaging. I'd clean up all the sensors and check for contamination or damage to the wires. Have any of the wheel bearings been replaced?

WoodyFromBama

Thanks BudRacing. I'll inspect and clean all of the connectors today. No, no hubs have been replaced. But a few weeks ago my son said he heard some low speed clunking/clicking noises and took it in to a repair shop that said the axle nut on the right rear was loose so they torqued it down. That in and of itself is strange to me. I'm pretty old and have never heard of an axle nut working loose.

BudRacing

iTrader: (3)

Yeah, I would also find that strange. My OE axle bolts I couldn't get off with a 4ft cheater bar. I would definitely check that, though.

WoodyFromBama

@actrite80: On this car there doesn't appear to be seperate controls for those things. The button the the glove box turns the "Stability System" on and off -- that's all.

With the stability system on I get the previously described symptoms -- traction control engaged message, rev limit and ABS pulsing at about 15-20 mph. If I turn stability system off there is none of those symptoms.

Is this just telling me that this is the way it is supposed to work when on stands?

WoodyFromBama

My son added a little more info this morning. He said that when he first hit the brakes and the racket started the car was not slowing down, much less stopping. He said that he also got the impression that the right front was actually raising -- he described it as "standing up". He then pushed the brake pedal lightly and got enough braking that in conjunction with gearing down he was able to get it stopped.

isis

iTrader: (1)

WoodyFromBama

Ha ha. It's Seattle man - wet.

BudRacing

iTrader: (3)

If you were to take it for a quick spin in a safe-ish area, would this immediately reproduce itself?

WoodyFromBama

Hi and thanks for your help on this. Either cleaning all of the wheel speed connectors "fixed" the problem or it is still there waiting to show itself at a less opportune time. I took it out and it performed flawlessly over about a half hour of testing -- TC on/off, SC on/off, Competition Mode on/off -- not even a hint of a problem.

I'm gonna see if I can lay hands on a scanner that will read the ABS codes and see if there's anything there. If I can get a GM Tech II Scanner I will also do some diagnostics on the related sensors.

I noticed that the rear brake pads were not wearing evenly though both wheels feel/sound the same when rotating by hand. The driver side is wearing faster than the passenger side. Since the passenger side is down to about 1/8" I ordered a new set of ceramic pads.

As soon as I can gain access to a GM Tech II SCANNER I’ll test all of the associated sensors and update this thread but, for now, everything appears to be working fine.

isis

iTrader: (1)

WoodyFromBama

That is great advice -- will do and thanks!

BudRacing

iTrader: (3)

That's a good thought. Maybe a brake flush and bleed could help, but rebuilding the rear calipers would definitely be a good idea.

WoodyFromBama

I see kits that consist of pressure seals and dust boots and I see complete calipers. Wouldn't uneven braking likely be piston related? Do you know of any kits than include the pistons? Or is it usually ok just to clean the pistons and their cylinders and replace the seals and boots.

isis

iTrader: (1)

WoodyFromBama

I saw one ad for a set of front calipers that included a "pin set" that looked like the pins that calipers slide back and forth on. Normally I just clean and lube these and put them back. Is there a history of these calipers needing the pins replaced?