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Disk brake front knock and pulse

Ecomike

NAXJA# 2091
NAXJA Member
Location
MilkyWay Galaxy
Trying to sort out a caliper-rotor front brake knock sound on mine that has gotten worse after it broke the 4th anti rattle clip on the top side in 4-6 months and I decided to not install a new one this time. It was quitter with out the broken rattle clip at first but now is very noisy during a slow stop, knock, knock, knock.

No noise on fast stops,.

No noise when not braking, and no noise when braking at higher speeds, like on the freeway.

Rotor, caliper bolts, and pads are all new, and the calipers are factory rebuilt. I do get some brake peddle feedback pulse feel when I first brake at freeway speeds. Front axle shaft bearings feel and act good.

Any thoughts???

This is the same jeep that has given me a soft peddle unsolved issue for 4 years now that has stumped us all. The pulse and knock issue is new this year, and may have shown up when I replaced the rotors and caplipers, but not sure, just do not remember exactly when it started.
 
Are your pads shifting up when you brake? and did they wear a groove where they ride at?

Shifting up???

There is no sign of wear where the pads ride that I could see. I was a bit surprized with 290,000 miles. But I do not think I had this problem until I replaced the rotor, pads and calipers. And just on one side, drivers side. We see no obvious signs of bad parts on visual inspections.
 
Odd, I have slight grooves where my pads ride, eventually im gonna fix it, and what im meaning is when you hit the brakes thhe pads may be loose in the bracket and are coming up hard against the top of the bracket
 
Odd, I have slight grooves where my pads ride, eventually im gonna fix it, and what I'm meaning is when you hit the brakes the pads may be loose in the bracket and are coming up hard against the top of the bracket

Would that be due to the lack of an upper anti rattle clip that keeps breaking? What puzzles me is every new anti rattle clip I install on the top side breaks in about 200 miles. I know I am installing the clips correctly, I have 4 of these jeeps and been doing these brakes for 15 years.

The pads do no seem to be loose in the bracket. I am thinking either a bad (new) rotor that is not perfectly flat 360 degrees around, or something odd with the newly rebuilt factory caliper. But how to determine which if I am right or the question of what I am missing.

Is anyone using any other kind of anti rattle clip on these brakes????
 
I'd check again for wear where the pads ride. Most xj knuckles I see have a good groove etched in the back even on supposedly low mileage xj. Of course those are 90 up knuckles not sure about how my old 85 look and it's very high mileage


Sent from my iPhone using Tapatalk
 
Rotor, caliper bolts, and pads are all new, and the calipers are factory rebuilt. I do get some brake peddle feedback pulse feel when I first brake at freeway speeds. Front axle shaft bearings feel and act good.

Any thoughts???
Did you check the rotor to see if it is true?
 
Are the ears your pads are riding on notched and keeping them from engaging the rotor? May be why the clips keep breaking too.

We inspected them and as odd as it sounds, even with 290,000 miles on the beast I could not find any wear on what you called ears (the brake pad slide guides on the steering knuckle) that the pads ride on. In fact, except for flash rust they look new. I was shocked not to see any wear.

Also this braking tap-knock sound I get when gently applying the brakes, the sound is only once per 360 degree rotation of the axle shaft (which suggests a bad new rotor, only makes the sound when the top side anti-rattle spring has broken or been removed), that is making no sound on hard braking and no sound when driving at any speed, and was not making any noise till we replaced the caliper and rotor. The first time it made the noise one of the bolts was loose, Tighening the bolt and replacing the spring clip fixed it for about 200 miles, and the bolt never came loose again (the 2 bolts that the caliper slides on), but it did damage the new pads, so I replaced the pads that day. Since then it is the rattle clip that breaks every 200 miles and then the tap-knock sound returns.

I wonder if having just one rattle clip is making the noise more pronounced? But removing the other clip would not answer why the top clip (only the top clip) keeps breaking the 3/4 ends off.

Why would only the top clip keep breaking on the driver's side????

I will do a hard core inspection next time I take it apart but so far I am suspecting a caliper issue at this point unless the symptoms change, but the fact the sound is cyclic with once per 360 degree rotation makes it seem the rotor is bad, and is out of round. But if it was a bad rotor, why is it quiet the rest of the time, and why doesn't it affect steering, the steering wheel (no feedback I can feel) or cause rapid tire wear?

Why do I always have the problems no one else has ever had LOL.
 
Did you check the rotor to see if it is true?


Visual only when mounted.

To my knowledge I would need a run out gauge and lathe to test that, and I do not have one anymore. But I am thinking about the old style hubs with the built in bearing race, and this 4x4 is the cheaper rotor only style, so maybe I was over thinking this????

Just lay it flat on a glass table top and use a spark plug film gauge to look for warp-age???? Then I could mic it for thickness and see if it is the same thickness all the way around, outer to inner right???

I may just try that. Let me know if there are easier tricks for doing that please.
 
Easy might be having a reputable brake shop check them.
 
Easy might be having a reputable brake shop check them.


That is not what I call easy, LOL, I call that extremely painful, costly, time consuming, and impossible to find where I live. But thanks anyway.

And in my 45 years I found the phrase "reputable shop" to be an oxymoron.
 
In that case I would look for a way to set up a dial indicator and tighten the rotor to the hub.

EDIT: I would concentrate on the driver side. :)
 
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made a fair number of short trips and two long trips in this beast the last 7 days with the knock-tap sound unchanged and maybe getting worse, and the last 2-3 miles at 0-35 in the neighborhoods (after a 35 mile freeway run in some traffic at times) and suddenly the noise is gone. Go figure, but I know it will return, just not sure why and how it can seem vanish at times, to add to the puzzle. Seriously thinking of replacing the rotor as it dawned on me today that they way they are made, the inner part could be flat and keep the tire running true, while the out part the brake pads ride on could be warped. I am right on this???? I was thinking before the entire assy would be warped and that had wondering if the rotor could really be the problem.

I would suspect the pads, except the last set of new pads made the same noise and broke the rattle clips too....

There was no rattle until I replaced all parts trying to solve a mussy brake pedal issue that was never solved. So it must be a bad new part I think.
 
Any loose bolts?

When I first started battling the noise, one new caliper bolt had come loose, and one brake pad was damaged. Replaced the bolts, pads, an rattle clips and no bolts have come loose since. Replaced the top rattle clip about 4 times now, about once every 200 miles since that work was done. the Caliper and rotor were already new.

I also have one bad bolt on the clamp that holds the anti sway bar to the frame on the drivers side, but it would not / does not make a cyclic braking noise tap-knock.

I hear the sway bar when I go over a bump or ramp when the rubber bushing slides down the bar and makes metal to metal contact, but it sounds different and is quiet when braking. Also pulled the stabilizer shock a few weeks ago when I found the other rattle noise to be the missing bushings in it. Have not ordered the new one yet.

I picked up a new(rebuilt) caliper with new rubber and bolts, and rotor today. Hope to swap them in the morning. Plan to do a serious visual inspection of the pad guides, new and old rotor and caliper....
 
How about the unit bearing bolts?

Mystery solved for now. It did have notches or deep wear spots in a few places on the slide rails. I took a flat file and about 60 minutes of hand work to round off and smooth out the transitions on the rails so the pads can slide easily again, and on the new pads that already had some wear/nick/high spot issues in just 5-800 miles, used a nickel anti-seize to lube the slides, cleaned the hub plate surface of some dirt/rust/high spot crap where the hub and the rotor bottom onto each other that might have caused a little miss alignment issue (my helper is not very good at cleaning parts/stuff), and put all back together with new anti-rattle clips. The pulsing pedal feel and rap-knock-tap sound is gone for now. Looks like the slide knuckle part is just two star bolts away from being removable with out touching the ball joints and the rest of the knuckle assy? Is that right? Are these still available new for an 87 4x4 XJ???
 
Easy Fix for the Upper Rattle Clip Breakage:
1) Is there a Rusty Crust or Heavy/Rough/Uneven Casting Edge on the Outer Edge of the Disc?
2) If So, Put it Up on a Jack Stand, Get Under there w/ a Mill File & have a Friend Spin the Tire/Wheel as Fast as they can & File the Edge Back, until it's as Smooth & Even as you can get it.
(Round it a little too)

This Worked on My 7yr. Old Discs that had seen a Lot of Water Crossings. (Heavy Rusty Crusty Uneven Edge)
Keeps the Rough Disc Edge from Sanding Off the Middle of the Upper Rattle Clip, when Braking Hard or Slow & Steady.

I Know This Sounds JackLeg, (I'm a Machinist) But, It Works.
A Lathe Would Be the Best Solution, But, Ya Gotta Do what Ya Gotta Do, to Make Things Work in a Pinch!
UncleSarge58
 
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