R1100RT brake disc renewal

Replacing front brake disc rotors on the BMW R1100RT motorcycle

01/07/05

Trouble started with the front brake last year when the brake lever started to pulse gently under my hand while braking. As the year progressed it became slowly worse, at very low speed it was starting to grab, so, this spring I decided to sort it out.

This is the front L/H disc at 52,000 miles and, as you would expect, it does show some wear. First, I placed a clock gauge on the rim of the disc to check for warping and run-out, but found both were running quite true. I then put a micrometer on the discs and found they were worn down close to the 4.5 mm limit. Thickness did vary around the discs, hence the pulsing of the brake lever, but the thinnest point I measured was 4.51mm: pretty much worn out.

So, I needed replacement discs. Second hand discs didn't appeal because I didn't want to be back in this situation again soon. New BMW OE discs from Motobins were £395 (inc vat). I was really hoping to pay less than that. Motobins also sell Grimeca replacement Stainless Steel discs at £117 each including new mounting bobbins. a total of £275 (inc vat), so as that would save me over £100, that's what I ordered.

These are the Grimeca discs that arrived the next day, I have to say I was impressed with the finish, I put my micrometer on them and couldn't find any measurable difference in thickness on any part of the discs.

Fitting

I'll assume you can remove the front wheel okay, the only awkward bit is getting the callipers off the disc. Personally, I unbolt them, pull the calliper back toward the engine to clear the mounting lugs, then press the calliper lower mounting lug in toward the disc to spread the pads apart, usually, with a struggle, they will come off after that. After the discs have been removed from the wheel they need disassembling as the original carriers are reused, hear we're prising the e-clips out to release the bobbins.

Once the carrier is free, give it a good wash in hot soapy water, mine were in good condition, but you could always lightly re-spray them satin black. I suggest spraying them lightly because you don't want to spoil the fit of the bobbins.

Here we have the carrier, new bobbins, dished washers and e-clips. When fitting, the dished washers are placed domed side up. this is to place spring tension on to the disk and carrier to prevent rattle. The Motobins bobbins are made from steel, OE bobbins are alloy and wear causing the discs to rattle eventually. Time will tell how the steel ones fair.

This is how I refitted the e-clips, with a furniture dowel and light hammer to tap them in to place. Gently does it, but make sure they're fully seated.

The discs mounted on the carriers, almost too good for the bike!

Torquing the disc carrier to the wheel, 21N-m/15.5 ft.lbs

Before the jobs finished it's recommended to fit new pads or you risk imprinting the wear pattern from the old pads on to your new discs.

After trying EBC pads that rattled (no anti rattle clips) and Ferodo pads that squealed during low speed braking, I went for OE Textar pads, again from Motobins. I'll see how they go.

N.B. Tthe box says 'BMW R1200' but these pads fit a number of machines in the BMW range, including the R1100RT.

Pads and wheel replaced and after a brief bedding in period braking  was transformed, no rattles, no squeaks!

So what can go wrong?

Two easy mistakes, First is fitting the discs with the perforations going the wrong way, before you start refitting the new e-clips, just check you've got the disc the right way around on the carrier. Second is fitting the bobbins the wrong way around so the e-clips are on the outside, again check what you're doing before you fit the e-clips.

Take care before you ride off! The pads will need a brief bedding in period of moderate braking before they will stop you properly and check you have pumped the pads back on to the discs by slowly squeezing the brake lever a number of time before you go on the road for the first time.

Update:

My new discs and pads were fitted at 52,000 miles, The milometer is now showing 55,700 including a 1,900 mile trip across France, 400 miles of which was over the Alps, the brakes have worked faultlessly, no squeaks, no rattles.

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