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Anyone having disc brake vibration problems with big wheels?
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Midwest aircooled
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PostPosted: Thu Jun 24, 2010 5:06 pm    Post subject: Anyone having disc brake vibration problems with big wheels? Reply with quote

Hey everyong,
I'm working on a kit car at the shop, (its a Manta if anyone knows what they look like, its an exotic car wanna be) anyway the owner wanted to run Porsche 911 GT-2 wheels. I said whatever you want. He bought the wheels and had tires mounted, all new stuff, they are 18x9.5's in back and 17x8 in the front I beleive. We installed 5x112 pattern disc brakes all around, (e-brake kit in the rear). This is on a IRS pan. The brakes are just the standard ones that empi and everyone else sells. To get the rear wheels to work, he made spacers (he owns a machine shop) to get them out far enough becuase of the offset they have. They are about 4" thick, but very nicely made. They are on front and rear. The front is having no problems, but the rear has a vibration when you apply the brakes that I cant get to go away. It was even doing it just from the little bit of drag the pads have on the rotors while driving. Once the pads heat up a little, its even worse. We are talking MAJOR vibration, its like a loud drone that is deafening if you really push on the brakes hard. I have had the calipers off at least 10 times, sprayed the pads with CRC disc brake quite, checked and rechecked for anything rubbing or hitting, and even had the car up on jack stands with the engine running in gear to watch it. The caliper isn't in a bind, you can move it slightly (floating on the slide pins). I can't explain it at all. I have installed many disc brake kits and never had a problem like this. I was thinking it could just be bad pads, but all the kits come with the same pads and they are never a problem... I haven't ever done a setup like this with real big wheels though. I'm wondering if having the large dia/wide wheels could be amplifying a small vibration into something big and making it worse?? Like a harmonics type thing... I'm running out of options or things to try. Any suggestions would be great.

Thanks,
Jason
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tripicana
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PostPosted: Fri Jun 25, 2010 1:51 pm    Post subject: Reply with quote

probably the cheap empi disc brakes.
get a dial indicator and measure the runout on the discs.
or possibly the 4" spacers?! that does not sound very safe at all.
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Midwest aircooled
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PostPosted: Fri Jun 25, 2010 8:10 pm    Post subject: Reply with quote

There's no run out.. They aren't warped or anything like that. I ran it on jack stands and watched them. Its not like a pulse, its a vibration that sounds like a howl when your inside the car.

The spacers are hard coated billet, very thick, and the car is lightweight. I have installed many of those disc brake kits and never had a problem like this. Granted they aren't the best, but they usually work nicely.

Jason
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luckystiff
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PostPosted: Fri Jun 25, 2010 10:34 pm    Post subject: Reply with quote

check and see if you have a small knot/lump on one of the tires or possible tread seperation. if theres is a knot/bump it will eventually lead to tead seperation and ultimately blow out. might not have been there when the tires were mounted as i've heard of it happening after a good drive warming them up good.

oh and another thing to look at if they are directional tires make sure one or more didn't get mounted backwards. seems dumb but i have seen it done...ken....
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Bruce
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PostPosted: Fri Jun 25, 2010 11:16 pm    Post subject: Reply with quote

How about removing the big wheels and the thick spacers and bolting on some skinny stock tires to see if it still does it.
That would tell you where the problem lies.
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Midwest aircooled
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PostPosted: Sat Jun 26, 2010 5:15 am    Post subject: Reply with quote

Good suggestions... I'll look at the tires and such.

I just messed with it more yesterday. Just holding the pads with channel locks on the rotors I can get them to vibrate when turning the wheel slowly. I'm also noticing the rotors look kinda polished for only have a couple miles on them. I'm trying different pads, I think these have too much metal in them. The noise really sounds like a metal to metal type sound.

Jason
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Storkalator
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PostPosted: Mon Nov 15, 2010 7:37 pm    Post subject: Did you solve your vibration issue Reply with quote

Just put an EMPI rear disc kit with e-brake on a stock 74 beetle. Exactly the same symptoms. Did a 4 wheel drum to disc conversion. Fronts seem fine. The rear rotors both were off centered towards the engin. Both had .022 clearance between the inboard part of the caliper that is mounted to the bracket. Nothing for the first 200 yards then the noise started and got worse. Pulled the emergency break a couple of times and it quited down but as the parts heated the noise (you described perfectly) became unbelievable!!!!!!!!!! I was about to take the calipers out and inlarge the clearance by removing some material from the caliper. I was going to try some axel spacers but was warned off that approach. There is no way to shim the caliper inboard to increase the clearance because of the way the adaptor plate and caliper mount. At any rate it sounds like centering the rotor may be pointless based on your experiments with the pads / channel locks etc. Did you find a solution or is this $400 down the tube and back to rear drums?
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TonyC66
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PostPosted: Sun Feb 09, 2014 10:39 pm    Post subject: Reply with quote

I know this is a very old thread, but u am having the same issue with my rear empi disc brake kit. Has anyone ever encountered this and come up with a legitimate solution?

Thanks
Tony
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Timwest007
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PostPosted: Fri Jul 25, 2014 5:01 am    Post subject: Reply with quote

I also am having this issue any results yet
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Mike Fisher
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PostPosted: Fri Jul 25, 2014 8:32 am    Post subject: Reply with quote

That is at least 4 of you here with the same problem & no solution? My squareback stops good with it's stock disc/drum brakes. I would re-drill the stock drums to your favored bolt pattern or buy new drums & put drum brakes back on the rear.
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ps2375
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PostPosted: Mon Jul 28, 2014 8:15 am    Post subject: Reply with quote

Has nobody tried a different pad?
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Mangofish
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PostPosted: Fri Mar 06, 2015 2:48 am    Post subject: EMPI rear disc brakes vibration Reply with quote

I am working on a 1974 VW Superbeetle. and I'm having the same problem with loud harmonic vibration sounds that fill the entire car with tremendous noise. I installed the EMPI front discs in September, and they are still working great, but then the original mastercylinder began failing, so I installed the recommended EMPI large diameter master cylinder in preparation for installing rear disc brakes. This created an extremely abrupt and overly firm feel of the brake pedal, which is not recommended while still running drums in the rear, but everything worked OK. Now it is March and I just finished installing the EMPI rear disc brake kit. The pedal feels good now. The rear discs do exactly what others describe as with the loud harmonic vibration that fills the car with noise. Very Scary sound! It occurs at 5 mph or less with very light pedal pressure. This noise reminds me of the harmonic noise that occurs on a crystal wine glass by gently rubbing a moist finger around the top edge of the wine glass. With the wine glass analogy in mind, I can compare how the new disc rotor is similar to the wine glass, and the brake pads are like a finger rubbing around the top edge of the wine glass. Even with the wine glass you have to move your finger slowly to get it to go into a harmonic vibration. My brake pads rub at the edge of the rotor and still have not worn in enough to make full contact. I think it is the rotor itself that is vibrating, and making the noise. Maybe if I coat the inside of the rotor with "Disc Brake Quiet", this can subdue the vibration from happening.
I have already put Disc Brake Quiet on the pads yesterday, but the noise did not change. So maybe I'll pull the rotors off and coat them too. I am also thinking of buying the heavy duty forged mounting bracket to replace the stamped steel mounting bracket. On a bright note: the bug really stops quick!


Last edited by Mangofish on Sat Mar 21, 2015 1:47 am; edited 1 time in total
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subhuman
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PostPosted: Fri Mar 06, 2015 7:44 am    Post subject: Reply with quote

had the same problems with the harmonics with my aircooled disk brakes in the rear. what helped was to chafer or bevel the lead and tail edges of the pads, plus use the brake quite product on the back side of the pads. hope this helps!
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slalombuggy
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PostPosted: Sun Mar 08, 2015 9:40 pm    Post subject: Reply with quote

Make sure the calipers are perfectly parallel to the rotors, if you have the stamped brackets they may be slightly off and require a tweek. I had this problem on my buggy and it ended up being the caliper not sitting right. The forged brackets are much better. I didn't have this problem when I put them on my 57.

brad
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Mangofish
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PostPosted: Sat Mar 21, 2015 1:28 am    Post subject: Reply with quote

During installation I did notice that the pads were not making perfect parallel contact with the rotor and it was caused by the mounting brackets being slightly mis-aligned with the rotors. But I did not try and tweek the brackets since the mis-alignment was so miniscule.
The days have slipped by since I last wrote and I have not made any changes to the brakes. The bug has been driven daily around town and the vibration no longer occurs. I can see that the pads have worn in and now make a much more even contact with the rotors. So I believe the vibration is caused by pads not making parallel/even contact and especially if they rub on the outer edge of the rotor. Since the vibration issue is not happening now I will leave the brakes alone. I am wondering if they will vibrate again when it is time for new pads to be installed in the future. At that time I may coat the inside of the rotors with Disc-Brake-Quiet.
These brakes have already come in handy while my daughter was driving around, she was thankful for how well they worked!
As a side note, the wheels, tires and suspension are all stock.
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Zuesticle
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PostPosted: Tue Aug 25, 2015 8:23 pm    Post subject: Reply with quote

WOW! I thought I was the only one having this exact issue. Rolling around the streets the locals walking on the sidewalk were freaking out and getting scared of my car, kind of made me chuckle...

So it seems I need to look at the alignment of my brake pads in relation to my right-rear disc. Awesome thread, thanks!
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mallred
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PostPosted: Sat Oct 17, 2015 8:03 am    Post subject: Reply with quote

Had the exact same problem with horribly loud harmonic vibration with my Empi rear discs.
I did not have the problem, until I had over 1000 miles on them. It had nothing to do with applying the brakes.
It would only last a second or two, a mile down it would do it again.
It resonated through the body shell SO bad, it was impossible to tell where it was coming from! It sounded like the front firewall!
I had to have my wife roll the car down my long driveway a few times before it did it.
I could tell EXACTLY where it was coming from standing outside the car (left rear).
I had pulled the pads to look at them a week earlier, and they were fine.
This time one pad had a big chunk broken off, and the other one was cracked through in the middle.
As "Subhuman" posted above, I chamfered the leading and trailing edges of the pads, and applied CRC Disc Brake Quiet. PROBLEM SOLVED!
(I had applied a Disc compound the week before, and it didn't help.)

I think this issue may arise from using the stamped steel caliper brackets, I would imagine they have a bit of flex to them.
They are also anything but flat, I spent a LOT of time with a mill file on these, to get the axles to seal.
In retrospect, I should have shelled out the extra $60 for the forged caliper brackets. Smile
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