Method(s) to check brake rotor runout without a dial gauge (1 Viewer)

[sunrk]

I need to check front brake rotor runout to see if one of them is warped too much. I don't have a dial gauge. My empirical mind tells me to take each rotor off in turn and put it on the stone kitchen benchtop which is measuribly 'flat' and check that way.

Reason I want to do it is that when I last changed brake pads, when I was test-driving to run them in I had two instances where the left side overheated and grabbed so hard I had to force the steering wheel almost 1/4 turn the other way to hold it straight enough to get off the road and let the pads cool off. Smoke, etc. from the brakes on that side. After two episodes of that they didn't grab like that anymore and I've been running on those pads for almost a year, but I get a pulsating brake pedal particularly when braking hard.

I'm going to investigate both the rotors and the calipers.

Am I being daft with the kitchen bench thing? I have no other guaranteed flat surface that I can use as a reference.

Craig.

 

[inkpot]

Just rotate each rotor inside of the caliper and see if the rotor alternates on which brake pad it touches?

 

[mudgudgeon]

Kitchen bench is not necessity going to give you a reliable indication of run out.

You'll get a bit of a visual indication as inkpot suggests.
Or rotate the rotor while holding a sharpie against the caliper so the tip just barely touches the rotor, if you get a consistent sharpie line around the rotor, you're probably good.

Bake shudder can be down to other things too. Wheel bearings can contribute, so can glazed brake pads.
I find the brake pads on my falcon sedan seem to glaze up and develop a shudder. A series of hard stops from 100km/hr in rapid succession (6-12 times) gets a load of heat into the pads and rotors and often eliminates it.

 

[Golgo13]

Just order a dial indicator from amazon or HF. It will be good enough to measure the runout and you won't have to disassemble anything.
Alternatively, push a steel scale against the rotor perpendicular to the face using the caliper for stability. Run the rotor around once so the high spot pushes the scale out and leaves a gap at the low spot. Then use feeler gauges to measure that gap.
Dial indicator is much easier/fool-proof though.

 

[inkpot]

You DO realize that SOME runout is Needed/ designed into disc brake systems? That ya what opens the pads back away from the rotor. Rotor thickness, not runout, is what can create problems.

 

[sunrk]

That may well be the case, but also true is that the run-out is meant to be limited to what the factory spec is so that brake operation is smooth and controllable. I'm not sure off the top of my head with the number is, or if it's different for pre-8/92 (smaller rotor) compared to post-7/92 (bigger rotor) front brakes.

One good thing is that genuine factory brake rotors for the bigger front brakes are plentiful as new product. I don't know that I want to go with slotted aftermarket rotors again as I really haven't determined that they've given me any perceivable benefit over std ones.