Stingray Corvette Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
After not being satisfied with my dealer's service tactic for the pulsing brakes on my '17 Z51 with just 5k miles, as they just wanted turn rotors and charge me $120. With new GM rotors cost $120 each, I opted instead to own the problem and check everything out on myself. I had no problems checking the lateral runout of the rotors, even though the dealer said it can't be done because of the slots (I inspected aerospace parts for 20 years ;^). I found the front rotors at .004" runout. I didn't think that this was that bad, but continued my analysis. Upon removing the calipers and rotors, I found that BOTH front spindles has identical damage on the outer edge of the hub where the rotor and wheel mounts. There was a good sized dent on the corner of both and this displaced .020" material out on the machined faces. The fact that the rotors had matching dents into the backside proves this damage was done prior to the rotors being installed at Bowling Green or a sequencer feeding the line. Knowing what I know about automotive assembly (I work at a Tier 1 steering supplier), you can pretty much know that my car wasn't (isn't) the only one with this damage.

Once I stoned off the raised material, I installed new DBA 2-pc rotors and Hawk pads. The results was .001" runout and no brake pulsing. I sort of regret not remounting the original rotors and re-checking the runout, but I had already spent the money on the DBA rotors and pads for all 4 corners and just wanted to move on.

IMG_0573.jpg
IMG_0574.jpg
IMG_0575.jpg
 

·
Registered
Joined
·
947 Posts
After not being satisfied with my dealer's service tactic for the pulsing brakes on my '17 Z51 with just 5k miles, as they just wanted turn rotors and charge me $120. With new GM rotors cost $120 each, I opted instead to own the problem and check everything out on myself. I had no problems checking the lateral runout of the rotors, even though the dealer said it can't be done because of the slots (I inspected aerospace parts for 20 years ;^). I found the front rotors at .004" runout. I didn't think that this was that bad, but continued my analysis. Upon removing the calipers and rotors, I found that BOTH front spindles has identical damage on the outer edge of the hub where the rotor and wheel mounts. There was a good sized dent on the corner of both and this displaced .020" material out on the machined faces. The fact that the rotors had matching dents into the backside proves this damage was done prior to the rotors being installed at Bowling Green or a sequencer feeding the line. Knowing what I know about automotive assembly (I work at a Tier 1 steering supplier), you can pretty much know that my car wasn't (isn't) the only one with this damage.

Once I stoned off the raised material, I installed new DBA 2-pc rotors and Hawk pads. The results was .001" runout and no brake pulsing. I sort of regret not remounting the original rotors and re-checking the runout, but I had already spent the money on the DBA rotors and pads for all 4 corners and just wanted to move on.
Good sleuthing. While I suppose it would be a long shot, perhaps you could send this on to GM via customer service or somehow to the factory GM. I am sure the factory manager would like to know about this; not so sure that GM PR/Customer Relations/Service would though. Might bring up some unpleasant thoughts about warranty claims, lawsuits , etc. Imagine how many people have probably paid to have their rotors turned or bought new ones without fixing the problem. I wonder if anyone else has discovered this or if it was just a one off situation where someone dropped the rotors on their edges when installing them. --Bob
 

·
Registered
Joined
·
6 Posts
Discussion Starter #4
My experience is that this type of defect either wouldn't be caught at the dealership or if it did, they'd just repair and move on while charging the customer. My 36 years of buying new cars and being racer/fabricator/mechanic, I've grown to just want to avoid the dealer service experience whenever possible.

I'm not sure where in the vehicle assembly process the rotors get installed, but the Torx head retaining screws on the front rotors required no wrench to remove. They were most likely torqued at assembly, but once the wheels were mounted the torqueing of the lug nuts compressed a majority of the raised hub material into the backside of the rotor surface. Thus the screws were no longer bottomed out.

As for where the hubs got damaged, seeing as both sides were identical, my guess is there was some sort of fixture issue or possible an assembly person not following standard work (GM PAD). I deal a lot in root cause analysis at my job and not following work instructions is a big hitter, along with 4M Change (Man, Method, Machine, Material). The overall exposure is unknown, but it's almost certain to be many vehicles, not just mine.
 

·
Registered
Joined
·
997 Posts
Great work on problem solving your own issue. Unfortunately you are not the norm. Most of us wouldn't have your knowledge and abilities to handle this ourselves and just be at the mercy of the dealer or Mfg. And as you point out that doesn't always end well for the consumer. Having dealt with vehicle Mfg as a consumer for almost 50 years for me it rarely if at all goes easy without push back from the dealer or Mfg.
I'm always reminded of the statement made to me by a Service manager of a Manufacturer that will remain nameless of "Yep , motor doesn't sound right." .""Blank doesn't fix vehicles that are going to break ." "Bring it back when it breaks."
Got the feeling it was built to last for the warranty period no longer...
 

·
Registered
Joined
·
6 Posts
Discussion Starter #7
@15snow-ray...I can totally relate to your "it ain't broke, we don't fix" scenario. Back in 1988 I ordered a new Fiero GT right after Pontiac made the announcement that they would end production that year. The car came in about 2 weeks from the end of the run. I spent the next 2-years bitching about low oil pressure. GM changed transducers, gauges and I made them change the oil pump, but it still registered low with a mechanical gauge that I had T'ed into under the sending unit in the engine bay. GM finally stated. "The spec states that 6 psi at hot idle is sufficient, your engine has 7 psi...leave us alone." :rolleyes:

Well, 13 years later. with only 27k miles on the car, it spun the #5 rod bearing. Upon inspection at disassembly, I found one of the main bearing journals in the engine block was machined .030 oversized (and tapered .015 to boot). This meant that the oil pressure was escaping there and not sufficiently supplying the rod journals. This defect was done at the factory... possibly shoved thru due to lowering the bar as they got closer to the end of production.

For kicks & giggles, I contacted GM Service and asked for a consult over my old claim #. I wasn't looking for them to supply me a new engine, but would've been satisfied if they would listen to me and maybe help me out on the new GM Performance 3.1L crankshaft I was looking to buy. Sadly, the GM Regional Rep refused to meet with me. That pretty much sealed the deal and swayed my decision from Corvette over to a new Cobra Mustang that year. ;)
 

·
Registered
Joined
·
553 Posts
GMORPHAN, Great writeup! Sorry to hear the General was not responsive to anyone smarter then them.
 

·
Registered
Joined
·
150 Posts
Nice job finding the root cause.
 

·
Registered
Joined
·
7 Posts
Hmm...I don't know if my problem is the same but I've had pulsing in my brakes on my '14 Z51 for a long time,(feels like front). The dealer kept telling me they find no issue and it is probably my wheels are out of balance or tires have a defect blah blah even after new tires and balancing but now far past the warranty period. The front brakes occassionally squealed so they "lubricated" them and eventually replaced them but under moderate to hard braking I still get the pulsing.
I'm not mechanically inclined enough to check and measure as you did though I may print this out and bring it to them. I have gotten used to it but fo you think there is any possible saftey issue just living with it?
 

·
Registered
Joined
·
6 Posts
Discussion Starter #11
I believe 2014 thru 16 Z51's had a service bulletin on front brake rotors. GM launched with a 2 piece (cast over cast) rotor that ultimately didn't pan out well. They were replacing these with 1 piece rotors as the fix. Check out this link...
2014 - 2016 Corvette: Service Bulletin: #16-NA-170: Brake Pulsation and/or Vibration During Brake Apply
You should be able to visually look thru your wheels and tell if you still have the original 2 piece rotors, as they have the 9 legs going inside the actual rotor disk. That would be the first thing I would check. Good Luck!
 

·
Registered
Joined
·
7 Posts
Thanks! Just checked and yes I see the 9 legs indicating the original rotors. So what now? I am way past warranty. Are service bulletins something they have to do for free or only during warranty if the issue arises?
It mentions front and/or back rotors could cause the problem but I cannot tell for certain where the pulsing is originating..I think the front.
 

·
Registered
Joined
·
7 Posts
Could this be what is also causing my mysterious pull to the right? I have had it in 3 times for re-re-re alignment and they swear it is set right and maybe it is my tires or rims...no way.
 

·
Registered
Joined
·
1,462 Posts
Welcome to the forum gmorph. Great work in detecting the cause of the problem. Your knowledge is great to have as part of this forum. Also a nice job on the price you paid for your Z51.
 
  • Like
Reactions: jsvette
1 - 14 of 14 Posts
Top