Pulsating brakes/new pad bed-in procedure

[sfdownhill]

My brakes pulse badly after installing new OEM pads. I probably hit the new pads too hard, too soon in the bedding-in process. Any input/insight would be greatly appreciated.

 

Preamble:

I did a delink with 5/8" front master cylinder and RC51 SP2 calipers [32mm/30mm pistons] on my 5th gen. These brakes were operating smoothly, running Galfer street/track pads with 80% pad left. Then I rode member RVFR's 5th gen. His full CBR600F4i front brake system [5/8" master cylinder and F4i calipers with 32mm/34mm pistons] running OEM pads STOPPED LIKE WOW with full control, great modulation.

 

The actions I took:

[1] Installed OEM pads in my SP2 front calipers. I carefully scuffed the existing stock rotors with emery paper, starting with coarse, then medium, then fine, to remove material the Galfer pads had deposited on the rotors' surface. Cleaned the rotors with brake cleaning fluid until rag came away clean.

[1A] Noted that the brakes with new OEM pads were working normally on surface streets and freeway on the way out to the country road where I would bed the pads.

[2] Bedded the pads in to transfer pad material from the new OEM pads to the just-scuffed rotors. All brake applications were made smoothly, starting with light lever pressure then increasing quickly to high lever pressure, then releasing steadily, never 'snapping' the lever pressure off.  Made 6 hard decelerations from 70mph to 30mph, with no cooling time between brake applications and never slowing to less than 25mph [Never coming to a complete stop].

[3] After the 6 decelerations from 70mph to 30mph, was careful not to come to complete stop and rode with no brakes for several minutes to allow full cooling of the brake components.

 

The result:

Front brakes pulsed intensely from high speeds [80-100mph] or mid speeds [50-70mph] all the way down to 20mph or less before they smoothed out. Even at 20-30mph, strong application of the brakes caused pulsing.

 

Hypothesis:

I believe I started too hard on the bedding in process; I probably should have done 4-6 decelerations from 40mph to 20 mph with modest lever pressure before moving on to repeated heavy braking from higher speeds. In the bedding process I applied too much brake force too suddenly and deposited pad material unevenly.

 

Attempted solution:

I went back to the emery paper and scuffed the rotors again, doing three rounds on each side of each rotor with coarse, medium, then fine emery paper. The pulsing smoothed out somewhat, and now, 1200 miles later, has smoothed further, but is not gone.

 

Research indicates uneven deposits of pad material may be a major cause of pulsing brakes:

 

https://forums.bmwmoa.org/showthread.php?21352-Not-warped-discs-but-pulsating-brakes!

 

Post #16 here has some pointers:

https://www.pnwriders.com/threads/cure-for-pulsing-brakes.194058/

 

Next steps:

[1] Definitely purchase dial indicator and check rotors for warping/runout

[2] Possibly have rotors bead blasted.

[3] Possibly send rotors to truedisk [truedisk.net] to have them ground flat.

[4] Possibly install new OEM pads after bead blasting or flat grinding.

[VFROZ]

I'm not sure on the use of so much emery paper. 

You might have gone too hard with it. 

My 01 has exactly the same set up as yours, and I clean rotors lightly with very fine emery paper and that is it. 

110,000km on it now and brakes are still fantastic. 

I'm now using Vesrah sintered HH pads, not because I like them but because they were on special at 50% off. 

I think EBC have a much better initial bite, after that there's not much difference.

Last weekend fooling around with my riding group I came up to a set of lights and noticed the tail end of the group wouldn't make it across, so after looking at the empty road and the clean surface I went for a panic stop practice/show off and braked hard enough with two fingers until the rear end came up slightly, then had enough feel at the lever to maintain it there until it stopped. 

It put a smile on my face.

Did you centre the calipers on the disk with spacers?

Also did you torque the disk bolts and add Loctite?

 

 

 

[sfdownhill]

Hi OZ - thanks for sharing your experience. Based on your light cleaning of discs with very fine emery paper, it does sound like I went overboard on the coarseness of emery paper and intensity of scuffing.

 

Do you do your light cleaning with the discs on the bike, or do you remove them?

How often do you clean them with emery paper?

 

I can relate to your near-stoppie-induced grin...I've had bikes that would do that, and that's what I'm after. I know I've got the raw materials, just have to figure out where to refine and where to re-do. The brakes did not pulse with the near-new Galfer pads, then I

[1] scuffed the discs [too hard with too coarse a grit?]

[2] installed new OEM pads

[3] Bedded the new pads in [too hard, too hot, too soon?].

This implies the pulsing is caused by something I did to the discs or something I did to the new OEM pads, or a combination of the two.

 

Yep, calipers are centered on the discs. Actually didn't have to use any spacers because they bolted right up to the F4i forks with the left caliper centered and the right caliper off only 0.5mm. Sounds like it will be worth finding a 0.25mm shim to be precise about the right caliper.

 

Torqued the disk bolts in a star pattern, but did not use Loctite. I will apply blue Loctite after I have the discs off. I plan on setting the discs on a very flat surface to lightly re-scuff with very fine emery paper.

[VFROZ]

If you have F4i forks, then you're one up on me. 

Its what I should have done instead of the VTR.  

Its worth checking that the pistons are nice and clean and that the pads spring clips are in correctly. 

When I bought me SP2 calipers, the previous owner had installed brand new EBC pads in them but the clips weren't in straight so the pads were not moving parallel to the disk. This caused them to wear at an angle, one pad was not making contact at all. Maybe that's why the bike ended up at the wreckers. 

I clean my disks every second service or so, disks on bike but calipers removed. 

Just water and a light paper. 

[VFROZ]

I also remove the pads, place some wet emery 400 grade on a flat surface and give the pads a very light clean up keeping them very flat.  

On the disks I only use 800 or 1200. 

Ive also never bothered to bed in pads. I just ride knowing the they will not work at their best for a few miles, and I try to not use the brakes too heavily. 

[Mohawk]

Pulsing is usually caused by warped discs. Get a dial gauge & raise the front wheel off the ground. Either remove the calipers or push the pads & pistons back so there is NO contact with the discs, the wheel should spin smoothly. Use the dial gauge to measure lateral & circumference runout.  There should be next to none. If the discs are bent they can be straightened, if they are heat warped then its simpler to replace them. Ensure the bobbins turn freely, with some tension/resistance.

 

YMMV

[sfdownhill]

Thanks again OZ. I really appreciate the numbers on emery paper grit and details about flattening out the pads, removing calipers to clean discs, and using only water. I rebuilt the calipers with all new seals and installed the pad spring clips carefully - I'm like a lot of folks on here in that I like to have things lined up, symmetrical, balanced, etc.

 

FYI - I had collected both VTR and F4i forks, and was going to go VTR based on Jamie Daugherty's input, then Duc2V4 developed a need for the VTR fork guts and I didn't need too valid a reason to shift my focus to F4i 43mm forks. Side note - I went with 8th gen triples and bars for the bling and don't like them. The handlebars are fixed too far forward to be what I consider comfortable and with their bolt-on method of fixing, there is no position adjustability at all. 5th and 6th gen bars - even with their locator tabs - have enough play to get better placement, IMO.

 

Mohawk, thanks for identifying the difference between bent and heat warped. Hope I didn't cause the latter. I put about 1200 miles on these brakes with the earlier Galfer pads working smoothly after the discs were straightened by Jim at Dr. John's Straightening in Anaheim CA. I'm on a job out of town for a couple days, but will stop off on my way home to purchase a dial gauge and use it to clear up the warped-or-not-warped variable. I had never considered circumference/outside edge runout, but you've got me curious, and I will check that too.

 

Findings to follow in a couple days.

[sfdownhill]

Pulsing brake issue resolved. If you like turning to the back of a book to read the ending first, the pulsing was caused by me leaving the new steering bearings too loose.

 

I typed Harbor Freight into my self-driving car's nav and it took me there to pick up a digital dial gauge and magnetic mounting arm. Thank you Duc2V4 for recommending the digital dial gauge over the analog. The digital's biggest advantage is that it can be zeroed. Set the gauge's feeler against the point on the rotor with greatest deflection away from the gauge, then zero it, and all readings will be in positive deflections. Saves all that pesky addition/subtraction of negative numbers. Also for around $12, the magnetic base was a godsend - it has an on/off switch for the magnet that made sticking it to my front stand simple and positioning even easier.

 

Measurement details and photos below. Rotors not warped and they had consistent thickness. After measuring the rotors, I followed VFROZ's procedure and lightly scuffed the rotors with 800 grit wet-or-dry sandpaper, spraying the work with water. Test ride revealed severe vibration still present under hard braking. Vibration was significantly more severe from 50-40mph in decelerations from 70-30mph and vibrated worst from 100-80mph in decelerations from 120-60mph. The two ranges of vibration being a factor of 2x of each other made me think in terms of frequency, so I checked everything again and rediscovered a slight click/clunk that I had previously written off to slight brake pad movement. The movement and click/clunk was actually play in the steering bearings. I had installed tapered roller steering bearings 3200 miles ago. In researching the installation and tightening of roller steering bearings, it was repeatedly recommended to be careful not to overtighten them - roller steering bearings require much less tension/torque than stock ball steering bearings. I left my steering bearings too loose. So I disassembled bars and top triple, tightened steering bearings 1/4 turn and reassembled/torqued everything. Steering was then way too tight, so disassembled, loosened 1/8 turn, reassembled, and the dreaded free play was gone from the steering.

 

Another test ride demonstrated complete lack of braking vibration and the very powerful, controllable brakes with great feel that I was shooting for when I went with RC51 SP2 front calipers.

 

Here's the setup and the on/off switch on the magnetic base.

If you've ever found yourself cussing a blue streak at an inanimate object because multiple threaded setscrews refused to allow you to properly place a measurement tool, you can see why I waste so much virtual ink praising the magnetic base:

 

 

I took readings at the outer and inner edges of the swept area of both rotors.

The left rotor varied only from 0.00-0.07mm at the outer measurement and 0.00-0.05mm at the inner measurement, thickness was 4.33-4.35mm around the disc. Right rotor was 0.00-0.06mm at the outside edge and 0.00-0.08mm at the inside measurement, thickness was 4.35-4.52mm around the disc. The service manual's max allowable rotor deflection is 0.30mm, so neither disc was warped:

 

Changed a couple things while I was in there.

Before:

 

After: