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Author Topic: High Pitched Squeal - RF
tom_hampton
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Region: SW
Year : 1992
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Ok, I'm stumped. I've searched here, and miata.net, as well as several google searches. I've seen a couple posts on other forums for similar problems...but, without resolution.

I have a high-pitched squeal coming from the RF area of the car. The sound is very similar to a belt-squeal in pitch and general timbre. But, it has a beat to it...at approximatly the rotation speed of the wheel.

1. Comes and goes with road speed: 45 mph is the first significant point. there seems to be a null between 55-60.

2. It decreases somewhat under braking...but, not completely. This could just be due to the change in road spead.

3. I've also tried trailing the brake with no noticeable impact (I'm going to retest this tonight on the way home..I'm questioning my memory).

4. Is NOT dependant on engine RPM, or even engine on/off. I've coasted in neutral with engine off, with no change in noise level.

5. Is NOT dependant on ACCEL or DECEL.

6. I had a passenger hunker down in the foot-well to determine source of noise. He grew up in a race-shop helping his dad build race cars...and he is confident it is coming from the passenger front wheel area.

6. The noise is not ALWAYS present. But, it usually is. We had a 10 mile stint where it made no noise at all...even at 45mph.

7. This squeal was not present when I bought the car back in July. It HAS been present since I rebuilt the calipers, put in the braided lines, replaced the pads, and rotors. I also adjusted the brake pedal free-play at the same time.

8. I just repacked both front hubs with zero impact. Neither hub showed any since of scoring, pitting, discoloration, or deterioration.

9. there is no change clutch/declutch or in gear/neutral, or gear selection at fixed speed.

10. I feel nothing through either the steering wheel, nor the brake pedal.

11. Hard cornering has no impact.

If anyone has any suggestions, or similar experiences...I'm all ears.

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Tom Hampton
Miata build: http://www.tomhampton.info

wheel Verified Driver Made Donation to Website
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Region: kc
Car #: 20
Year : 92
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Turn up the radio. I haven't been able to hear high squeals since I turned 60.

Scott Zetterstrom Verified Driver
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Car #: 13
Year : 1990
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Make sure your new brake lines are not rubbing on your wheels. It is possible to install these with the fitting touching the wheel if you're not careful.

Good Luck.

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#13 SSM
ME Solutions LLC
Windsor Customs Racing
PBC Automotive

tom_hampton
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Region: SW
Year : 1992
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Not to hijack my own thread, but seems like that's "her" problem. [Wink]

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Tom Hampton
Miata build: http://www.tomhampton.info

Keith in WA Verified Driver Made Donation to Website
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Year : 95
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As a former bike mechanic, one of the hardest things to do was to diagnose a noise problem. When someone came into the shop complaining about a whump whump noise, we knew it was going to be a long day.

You've ruled out an engine noise and hubs which would be my first thoughts.

The thing that caught my attention is the speeds it squeals at. I had a little toyota truck way back when with a blown shock that didn't squeal, but generated a horible vibration at about those same speeds. It's hard to explain without getting all geekish but it's the natural frequency the springs want to vibrate at.

It definately sounds like something is loose and vibrating at the certain speeds causing the squeel. Hard to say what though. It could be caused by road vibration, which could be lots of things, or it could be caused by air buffering which would be body panels, under tray, etc.

I'd go over everything in that corner carefully, nut and bolt it, and look for anything loose or shiny spots. You could also swap your left and right shocks and see if it changes.

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Keith Novak
(Will work for tires)

tom_hampton
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Year : 1992
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Thanks Keith.

Geekish is okay with me. I've been an EE for 17 years and now an avionics Systems Engineer for 6. Have had more than a passing romance with 2nd, 3rd, and 4th order resonant systems.

In rough numbers it comes in strong at 45, 55, and 70 +/- 3mph...with nulls in between. there are probably more harmonics, but I didn't take her past 80.

Its definately the sound of a rotating part....a wrrr-wrrr-wrrr-wrrr at about 2.5 KHz. The beat amplitude envelope is very sinusoidal @ 2-4 Hz...depending on road-speed. You're typical AM waveform.

The frustrating part is the intermittency. Just when you think you've nailed it, it comes back and just kills the latest theory. Weak correlations suck!

I'm leaning towards the brakes...maybe the pads are dragging and resonating the rotor. It started immediately after R&R all the brake parts.

Swapping parts L to R is a good idea. And I will nut and bolt the thing...again!

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Tom Hampton
Miata build: http://www.tomhampton.info

NER88 Verified Driver
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Remove the brake clips and take a ride.

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Jerry

tom_hampton
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Year : 1992
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Interesting. You are correct... the brake clips are installed. Does everyone run without them? Previous threads have seemed divided...

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Tom Hampton
Miata build: http://www.tomhampton.info

geneclev
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Region: wdc
Car #: ssm 24
Year : 95
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It may sound to simple but make sure your brake shield is not rubbing the rotor

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coolman A/C&heating
windsorcustoms.com

Keith in WA Verified Driver Made Donation to Website
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About half run with clips and half without. I have mangled a tab and it squealed turning the rotors by hand but I didn't notice it on the road.

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Keith Novak
(Will work for tires)

B Boutz
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Region: Rocky Mountain
Year : 1992
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How do the clips cause this intermittent squeeling? I have the same problem which I thought it was belts. The sound is that similar. I have narrowed it down to the front passenger side.

tom_hampton
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Year : 1992
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How is not as important as "if". Once the source has been identified, explaining can be done as an post-exercise.

But, in short...everything vibrates. At different frequencies things will vibrate at different amplitudes. If the clips are just close enough (but, not touching the rotor at standstill) then at other speeds as the amount of vibration changes the clips may touch the rotor and cause a metal-on-metal squeal...with a thin, small, spring steel clip the audible frequency could be quite high...as it is.

The same thing applies to the dust shields. And just about every other sound that appears "at speed" but not at rest. Temperature can have a similar impact. Things grow and shrink with heat, and their resonant frequencies change (the points of maximum amplitude), as well.

I haven't noticed a marked temperature dependance...it comes and goes, but not as a function of run time, as near as I can tell.

I tested dragging the brakes last night. There is clearly zero impact on the sound, if I hold a constant speed with throttle...even up to full throttle, and the comensurate level of braking.

I wouldn't think the clips would make this noise under those conditions...but, they'll come out anyway. Then I'll try the dust shields.

Dang it! I want to go get an alignment...but, don't want to do that until I know what the problem is...and that I won't have to disassemble the corner.

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Tom Hampton
Miata build: http://www.tomhampton.info

David Dewhurst
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***It HAS been present since I rebuilt the calipers, put in the braided lines, replaced the pads, and rotors.***

Similar deal when I changed rotors, pads, hardware on my Ranger truck. When I stepped on the brake there would be a HARD metalic clunk, clunk, clumk which matched the wheel speed. Shouldn't happen after new pads & rotors, correct. Took wheels off & insected everything. All was good. Had a couple knowledgeable garage friends ride/listen, they never heard this type noise. They also looked. After a couple weeks of [banghead] listening to this CLUNK,the noise went away. Assumption, the pads & rotors needed a little more forplay before they decided they could get along together.

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Have Fun [Wink]

David Dewhurst
CenDiv
Milwaukee Region
Spec Miata #14

Keith in WA Verified Driver Made Donation to Website
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The clips can also get bent when you install them, and the tips of the spring tabs can rub the rotors. They could catch more at certain speeds than other I suppose. 5 minute job to remove them. You should be able to see if the dust sheild is dragging. It would need to be pretty bent.

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Keith Novak
(Will work for tires)

Randy Thieme
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Following this thread with interest since I'm having a nearly identical problem and the same corner. Except mine is not speed dependent. Once it starts it continues at all speeds.

Could also be debris caught in the brakes. Recently found a piece of klag (sp?) caught in the left rear caliper and rubbing against the disk. Explained the funny burning smell. [Eek!]

Maybe just noisy, competition brake pads? But that does not explain why applying the brakes has no affect.

I'll know more when I clean my front brakes tomorrow.

Randy Thieme
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Did not find anything. Now not sure of location of mine - maybe driveshaft? If the ground wire attached to the PPF frame was loose and the end was rubbing against the driveshaft it would probably reproduce my sound exactly. (But it's not - I checked.)

Tom: yours starts at 45 mph and then harmonics in rough multiples of 1.22? So there should be one at 36-37 mph. Suggests what ever's doing it needs a minimum amount of centrifugal force.

tom_hampton
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Actually there is one at 21-22 also. But, it isn't is not as predictable as the faster speeds. Multiples of 1.0. Won't get to anything until the weekend.

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Tom Hampton
Miata build: http://www.tomhampton.info

Qik Nip Verified Driver Made Donation to Website Series Champ
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I'm betting on the dust shields. I've inadvertently bent a few (very easy to do) and they made some pretty intertesting noises.
Rick

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Fortune Cookie Racing SM 60
Directions for use: Race, Rumple, Repair ... Repeat!

tom_hampton
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Year : 1992
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Speedometer cable. Spray graphite lube...alls quiet.

The vibrations must carry through the chassis to make it sound like it is coming from the right front. Even with the car on jack stands...running in gear...I had to get our of the car to hear that it was coming from the transmission, not the wheel well.

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Tom Hampton
Miata build: http://www.tomhampton.info

Keith in WA Verified Driver Made Donation to Website
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Yup. Whenever someone came into the shop complaining about a whump whump noise, I knew it was going to be a long day.

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Keith Novak
(Will work for tires)

tom_hampton
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Amen to that! Nice bookend...

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Tom Hampton
Miata build: http://www.tomhampton.info

Randy Thieme
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quote:
Originally posted by tom_hampton:
Speedometer cable. Spray graphite lube...alls quiet.

The vibrations must carry through the chassis to make it sound like it is coming from the right front. Even with the car on jack stands...running in gear...I had to get our of the car to hear that it was coming from the transmission, not the wheel well.

Have not solved my noise yet. Interestingly someone on Miata.Net complained about a similar noise which only starts above 40 mph. That website also points to the speedo cable.

tom_hampton
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I put the car on jackstands, and ran it in-gear on the stands. Noise started up pretty much right away. I had the wife hold the throttle pedal while I walked around the car listening for the source. Once outside the car it was immediately obvious the noise was coming from the tranny area.

Shut off the car, pulled the speedo cable out of the trans, and refired. Bingo....no noise. Of course I had a small puddle of fluid.

If it DOES turn out to be the speedo cable, get some spray liquid graphite, and spray it down the cable. I ended up having to "fill" the cable end with the stuff and run the car in gear again. After about 5 minutes enough of the lube seeped down into the cable that the squeak stopped.

I've driven it about 6 hours since...without any squeak. Eventually I'll order a new cable.

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Tom Hampton
Miata build: http://www.tomhampton.info

Dave Lewis
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What I did was remove the cable from the gearbox carefully bbring it up to the engine bay and connect a drill motor to the cable. ran the drill SLOWLY in REVERSE as I dribbled some lube into the cable. Reconnected the cable and no noise. 3 years and no noise.

Randy Thieme
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Update: Since I had earlier done a partial hijack of this thread with my own high-pitch noise wanted to post the status. Mine was not the speedo cable. I disconnected it and drive about 15 miles. No noise until I started to leave a parking lot heading home. Then it made the noise briefly which ruled out the speedo in my case.

Double checked that a brake line was not rubbing on a wheel and confirmed that was not the case. Disassembled the front brakes to double check the clips and springs. Found a fair amount of brake dust on the pad surfaces towards the center. I'm assuming its possible for the pads to wear in a slightly cupped pattern since the center directly under the piston is under the highest pressure. Blew out all the dust between the pads and rotors with compressed air. Did that on all four corners. At the same time sprayed some dry graphite lube on the rear transmission seal. Noise seems to be fixed now. I'll know for sure with another test drive.

   

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