Recently replaced the front brakes on my '94 with Hawk HP Plus pads paired with Hawk Talon rotors. I decided to go with Hawk because this is what the previous owner had installed on the car and I liked the way the pads engaged-- however, after installing and following the bed-in procedure detailed on the packaging, I am noticing a vibration coming from my front brakes; specifically seems to be coming from left front but it's difficult to gauge. This isn't the first time I've had this problem with these pads, and originally thought it was because I made the mistake of installing the new pads with old rotors which soon after started to crack along the edges (these were Baer drilled/slotted rotors). However I ended up with an extra set of the HPS pads (tried to order rears and they sent me fronts) so I figured I would take another stab at it with new rotors this time around. I had talked with my mechanic about this issue who is fairly knowledgeable with C4's and performance parts and he suggested the pads might also have been too aggressive for the rotors, so I went with Hawk's Talon model rotors as I knew these should pair well together with the HP Plus pads. However, the issue persists, albeit less severely. The vibration happens even with my foot off of the brake pedal, which made me think a sticking caliper could be at fault, but I drove the car and heated up the brakes and after immediately jacking the car up both wheels turned fine at the same rate so I'm not sure that this is the issue; there is also no noticeable pulling to either side or deceleration when the issue occurs. I don't want to keep dumping money into my brake system without a proper diagnosis, has anyone else run into this issue?

 

"The vibration happens even with my foot off of the brake pedal,..."

Maybe a wheel is out of balance...a weight could have come loose? Could try having the wheels re-balanced, or maybe try rotating the wheels/tires.

What about brake lines? I have heard of them rotting from the inside, causing a flap of line material inside of the line to impede fluid flow...making caliper release slow.

 

I ordered a name brand set of Rotors for my daughters 2011 Camaro and was very disappointed to learn that one of them had a high spot on it. I broke them in the right way and within 5 miles they had a bad high spot. I contacted the sales people who sold me the rotors and they just sent me a new set of front rotors without any questions. I had to pay to have the defective ones removed and the new set installed. Then I had to break them in properly all over again. I have noticed with drilled and slotted rotors that it takes a while longer for some brake pads to adjust to the rotor and for the first 50 miles or so.

Your choice of Brake Pads makes a huge difference in feel as you obviously know. I tried a set of Hawk Pads on stock rotors and it was a terrible feel. I don't race or Auto Cross so I don't think I need the Hawk Pads or the cryogenic treated rotors on my C3 or C4.

The worse thing I have done was try Silicone Brake Fluid, it is not the best for street driven Corvettes.

The best thing I have done to my brake system is to install the SS braided rubber lines from the chassis to the Calipers. That one part really makes a difference with the feel of the brakes, huge improvement over the original rubber lines. Just be sure that your new lines are D.O.T. Approved for use on our Highways.

Remember to FLUSH that Brake Fluid after Five years to prevent rusted out brake lines. Find a system that works for you and use it every five years. I use a Phoenix Reverse Bleeder to push the fluid up from the bleeder back to the Master Cylinder. Air likes to go UP so I help it along...

 

X2. I'd be looking at other things, besides the brakes.

 

You might pull the wheels off and spin the rotors to see if you can detect any wobble; even quality new can have a defect.

 

A few other details I should mention:

-The vibration usually starts after hard acceleration; it is an intermittent problem which I would think would not be the case for an off balance wheel?
-Once it starts, it worsens significantly when applying the brakes. But there is no noticeable degradation in brake performance.

Brake lines are something I hadn't thought about. Might look into the stainless steel lines as ctmccloskey mentioned.

 

I guess it's a possibility, but it seems unlikely considering the same problem has occurred on two separate sets of rotors of different brand/model. May try this the next time I have the car on jack stands though, thanks.

 

Strange. I would hope the new rotors aren't defective as I've had this issue with two different sets now, but it's possible. I chose Hawk pads at the beginning of this year as I was planning on autocrossing the car, but thanks to COVID I haven't had a chance to do so yet. I don't mind a rougher engagement as the car has a couple other modifications that make it drive more 'aggressively' (SPEC Stage 3+ clutch, aluminum flywheel, and looking at polyurethane bushings in the near future). But this vibration is fairly violent and intermittent so something is definitely not working as intended.

I may have to check out SS brake lines, have heard good things about them in the past and as far as I know the car still has the factory ones. I did not flush the brake fluid when I did the job so once this issue is diagnosed I will be doing that along with fixing whatever is causing this vibration.

 

Can you mount a GoPro (or some facsimile thereof) near the suspension to watch what the knuckle/arms etc are doing when the vibration occurs? Could you go to a 4wd dyno and hammer the brakes on that thing w/the hood open? Watch what happens?

 

It doesn't sound like brakes if the brakes aren't binding on jackstands. Check your wheel bearings, tie rods, etc.

 

What tires do you have? Does the vibration start after 55 MPH and get worse as you approach 80? Does the vibration eventually subside with driving, or does it remain completely constant?

 

Wheel bearings were replaced March of last year (20k miles ago) and inner/outer tie rods about 8 months (5-7k miles) ago, would be surprised if that was the issue especially considering it first appeared almost immediately after replacing the brakes.

I talked with one of the of the folks at Hawk today and he said the pads may be creating deposits on the rotors and to re-bed the brakes and see if that helps, so I will be doing that this weekend.

 

The car has Nitto NT555's. The vibration is more likely to occur at highway speeds but I've had it happen at 30mph and below. But sometimes I'll take the car out and it won't happen for the whole drive. Seems also to happen more often after hard acceleration.

 

Welcome to the club. I have Nitto 555 G2s and have the same symptom. And so did many others with C4s. Check this post: https://www.corvetteforum.com/forums...post1602394054

Needless to say I'll be moving to a different tire once I wear these out.

 

Huh, interesting! Your description with the vibration is very similar to what I have experienced, but I'm not sure that all of the symptoms match. Does it usually happen to you as soon as you get up to those speeds? I don't usually experience any vibration until I have been on the highway or been driving the car hard for a little while, I would think flat spotting would be immediately apparent once you get up to speed. I've also had it occur in the middle of 100+ mile drives, and I rarely go 3 days without driving the car, it's too much fun ! would be surprised if they flat spotted that bad overnight.

 

I usually drive my car every day to work and back and tend to notice it on the freeway--but it doesn't always happen. It's random. I could never quite pin it down until I heard from other Corvette owners who had the same "vibrates so badly at 80 MPH I was sure the car would break" symptom linked to the exact same tire. My car never did that on the old tires. If you have another set of wheels with other tires handy, or these tires are new enough that you can warranty them for a different brand, try it.

 

Hmm. Seems very odd considering this only started occurring after the brakes were replaced, but this does match up with what I have been experiencing. The tires were installed in March of this year so hopefully they will still be under warranty, I'll talk with my mechanic and see if he can confirm that flat spotting is the cause of the issue and let you know what happens. Thanks for the insight!

 

Another thought for you Sigma1!

How is the angle of your half shafts? Many years ago I had a problem with the wrong length bolt used on my rear springs outer mounts. This in turn caused my half shaft U-Joints go bad very quickly (less than 1500 miles) and they made a lot of vibration and noise. The half shafts should be as straight as possible to work their best and last a while. On my C3 it was a Chevrolet Dealer that changed the length of the bolt to a shorter one. The shorter the bolt the higher the rear end sits. Mine looked a bit jacked up after the dealer re-built my Differential for me.

After changing the bolts the shafts went back to a straight level position.