Shuddering brakes

**pka15** · 5th February 2019, 12:59 PM

G'day all,
My 94 Classic has had shuddering brakes now for months. I have replaced the front rotors and changed the rear twice, new bearings each time and making sure the mating surfaces, between rotor and hub, were clean.
I've also had an on car machining done which helped for a short time.
I have also checked the run-out of the rotors with a dial indicator getting a reading, at most, of 0.002mm (0.0007").
At high speed it shakes violently with the pedal bouncing under foot. At low speeds it gives a grab and release feel with the pedal slowly rising and falling.
Most of the vibration can be felt in the seat with only the slightest occasionally in the steering wheel.
The car does have ABS but it is not the rapid ABS pulsing feel.
Any ideas would be appreciated. I'm just about at the stage of trying another, more expensive set of front rotors.
Thanks

**DoubleChevron** · 5th February 2019, 01:34 PM

It doesn't have a disintegrating 'CV joint does it ? (though in theory the cv joint should be unloaded under braking) It could be worth checking the suspension bushes/ball joints/etc ... anything that gets loaded under braking.

**pka15** · 5th February 2019, 01:46 PM

Thanks, worth a check.
I have done the CVs many years ago, but back then I was getting chirping tyre noise on tight turns. None of that at the moment.
I also replaced the Viscous coupling a while back.

**LRJim** · 5th February 2019, 02:06 PM

If its shuddering when coming to a stop check your radius arm bushes, they are probably shagged (i have the same problem here)
If its shuddering while accelerating and its constant have a look at your uni joints, rubber donut on disco is the culprit for this.

Cheers Jim

**Bradtot** · 5th February 2019, 10:19 PM

Swivel preload?

**Mercguy** · 6th February 2019, 07:59 AM

Yeah I concur... Radius arm bushes and swivel preload.
Check all the balljoints and universals as well, Lube or replace as necessary.

**pka15** · 6th February 2019, 07:45 PM

Thanks for all the input guys.
I've checked uni joints and the donut is fairly new. Haven't checked bushes yet.
Do you think these would still be the case if I am feeling the pedal rise and fall slowly when crawling in traffic?
I should add that I had the car on stands, ABS isolated, and had it in gear with the wheels turning very slowly. With the pedal pushed lightly by hand the wheels would stop and release consistently in the same spot as if there was a high point on a rotor, but this isn't showing up checking with a dial indicator.

**Mercguy** · 6th February 2019, 09:51 PM

Sounds like you better re-check your wheel bearings are correctly tightened. did you check the rotor for shiny spots (warping)? Swivel preload can absolutely cause this wobble under braking as well as radius arm bushes. check the preload before you put it back on the ground. check the radius arms for play with a prybar.

**pka15** · 7th February 2019, 05:24 AM

Okay. Thanks Mercguy. I'll probably have it back on the jack stands on the weekend

Originally Posted by Mercguy

Sounds like you better re-check your wheel bearings are correctly tightened. did you check the rotor for shiny spots (warping)? Swivel preload can absolutely cause this wobble under braking as well as radius arm bushes. check the preload before you put it back on the ground. check the radius arms for play with a prybar.

**theelms66** · 7th February 2019, 07:08 AM

You say you have checked runout with dial indicator. I assume you checked both inner and outer faces.

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