When I installed new OEM rotors with R4-S pads, I wanted happy with the braking until I did the ‘bedding in’ procedure. And I remember finding something on their website about it. Hmmm.

 

After much deliberation, I've decided on a path forward:
- Local shop quoted $50/disc for cutting, practically the cost of new rotors so skipping this
- I purchased the porterfield R4-S pads

1) I bought a flex-hone brake rotor hone and am going to use this in my drill tor refinish the existing discs, hopefully removing any existing pad transfer and roughing up any glazed areas
2) Install and bed in the new pads
3) Cross my fingers and hope the pulsation doesn't return
4) If the pulsation returns, I'm going to get new rotors and install them with the same Porterfield pads I have already used.

Thoughts?

 

Depending upon your tools and abilities, you can put a indicator dial on the disc and rotate it to see what's going on. It'll answer whether it's just one spot that's high, or if the entire disc is warped. Or just buy new ones...

 

Yes I considered this. I am going to mike the discs to make sure the thickness is still in spec. I'm confident the front ones are, maybe the back aren't. I don't have a dial gauge but the vibes come and go and aren't very intense so I am hoping I can get away without measuring the runout and just see how it goes. I think that worst case scenario I have to replace the discs after all. Do you think the new pads could be affected by the old discs? Seems unlikely to me but I'm a noob with brakes.

 

I used to track my car (not my F-Type) quite frequently (pre pandemic) and found that high braking temps are inevitable and this always resulted in glazed rotors for me.
As I run two piece rotors, they cannot be re-honed (they have an aluminium hat and are grooved rotors - this what I have been told by brake shops).
The usual answer is to replace the rotors and pads but I could not see the sense in throwing away relatively new rotors that are not warped ( and otherwise well above min thickness) and pads that are not worn - its a huge waste of money.
No amount of back of pad grease, silicone would quieten the brakes and I could feel that the glazed surface did not make for good frictional braking performance.
So I had enough, I could not accept the proposed waste - I took my rotors off the car and grabbed my sanding block (pictured) that I use for sanding plaster drywall and just sanded off the glaze with light straight line movements across the rotor while working my way around the rotor on both sides.
Given the back of the sanding block has a rubber backing and the 800 grit paper is not too coarse, I found that this was enough to just rough up the glazed surface without altering the rotors surface, and I did the same to the pads (changing the paper).
It works perfectly. Performance is restored, squealing is gone and since the rotors are large and can absorb the heat (380mm) they do not warp so I am really dealing with superficial glazing.
If the rotors were warped, that is a different story. They need changing.
I found the simple approach of light hand sanding using a rubber backed block to work perfectly - using light hand sanding in straight lines, just enough to remove the glazing.
I know this approach is very 'agricultural', but it has worked perfectly for me and has extended the life of perfectly good rotors and pads.
I have included a picture of my last rotor change, but you get the idea of sanding in straight lines across the rotor surface. If I did not do this, I could not justify tracking my car and changing pads and rotors after every track day.

 

Yup! A light sanding works just fine for removing any glaze, but can't correct warped rotors,

 

Yes definitely agree, if you’re getting vibration during braking , a light sand will do nothing. Otherwise I think the official / industry answer of binning perfectly usable rotors and pads is unnecessary and wasteful. Sometimes you have to step back a think about the reasoning offered by the experts and use your own judgement carefully without putting yourself at risk.

 

Get a It works great!! Ive used one for years and it takes away the shimmy and shake and makes the brakes work like new. Best if you can turn the rotor as you use the hone. Ive also just gone around in circles with the rotor on a bench.

 

Didn't I just link you a white paper on the myth of warped rotors?

 

It was an interesting read. Warned against using regular sand paper on the rotors too. Said to use garnet paper.

 

I watch a range of mechanic based YouTubers such as Car Wizard, Rainman Ray, South Main Auto etc and they ALL continue to use the expression "warped brake rotors".
The better ones then explain that does not mean the rotors warp (ie bend or twist) but instead it means uneven pad material deposition on the brake rotors.
I think we are stuck forever with the misleading expression "warped rotors" and we just have to learn to live with it and grin and bear it.

 

Like nails on a chalk board...