strange brake pad wear

[RobinSF1]

I heard a grating noise from my front brake yesterday so rode home slowly and just using the rear brake. Upon examination today, the pads on the left caliper have worn very unevenly and are very thin and below the limit in some corners. I have ordered new pads.

A previous owner has rebuilt the brakes and there are receipts for seal kits (but not pads). My first thought is that they have omitted shims when re-mounting the caliper.

I measured the thickness of each corner of both pads thinking this would help to calculate the thickness of required shims, but this has thrown up some contradictions!

The inner pad is toe out/positive camber; the outer pad is toe in/negative camber and the differences in thickness between corresponding pairs of edges on both pads vary by 0.14mm camber and 0.75mm toe

It seems that I will have to split the differences to get the least worst shim thickness but that won't make new pad faces parallel to the disc and there will be a much reduced contact area requiring both excessive bedding in and premature replacement.

Does anyone have a procedure for measuring and calculating brake caliper shim thickness? The approach of measuing the worn pads must be flawed.

Thanks Robin

[George 350]

Hi Robin.
It would be good to know whether the gap between disc and caliper is identical front and back or not. Wear as you describe suggests that the caliper isn't in line for some reason. As you have posted in the 500 section, I take it we are referring to the original type calipers that rigidly mount to the forks?
Is the pad wear similar on both sides? (Assuming you have twin discs on it).
An easy thing to check is whether the caliper top mounting bolts haven't deformed, on the long shank of the bolt.
Let us know how you get on.
Regards.
,George

[Steve Brown]

What George says plus are the calipers correctly fitted with the thick spacer on the larger top bolt? No shims ever fitted to these pads as far as I know.
Or even just loose calipers?

[RobinSF1]

Thanks for input. There was no spacer between the caliper and fork. This is what I was thinking of shimming. Back in the workshop tomorrow and will check further.

[Steve Brown]

Thanks for input. There was no spacer between the caliper and fork. This is what I was thinking of shimming. Back in the workshop tomorrow and will check further.

Then I think you've found the problem. From memory the spacer is 3mm thick approx. I think too, that the thick washers on the engine mounting bolts are the same. Bolt it up with the bottom fixing then measure the gap where the spacer goes.

[norbert]

Thanks for input. There was no spacer between the caliper and fork. This is what I was thinking of shimming. Back in the workshop tomorrow and will check further.

Then I think you've found the problem. From memory the spacer is 3mm thick approx. I think too, that the thick washers on the engine mounting bolts are the same. Bolt it up with the bottom fixing then measure the gap where the spacer goes.

I guess there are three thick washers on the V2s: on the mounting engine bolts, under the cilinderhead screw nuts and the spacer for the upper mounting bolt of the calipers. I do think to remember that the last ones thickness is diferent to the others.

[RobinSF1]

Yes, this is the original twin disk 500 SEI with Grimeca calipers mounted rigidly to the forks. It seems I have a combination of issues from those suggested.

The top stepped bolt on that caliper is bent, I hadn't noticed on disassembly, but checked by rotating in a drill. Will post a seperate request for 'wanted', I know where I can borrow one for Cadwell. The bolt on the other caliper is OK.

The pads on the other caliper are worn in a similar way, but with smaller variance in thickness.

There were washers rather than spacers on the top bolt between the caliper and the fork. With the the bottom of the caliper bolted up, placing steel rule + feeler gauges in the gap at the top between caliper and fork the gap is 4.8mm. My calipers appear to be powder coated gloss black. I vaguely recall from my first Morini in the 1980's that the calipers were a different finish. I'm wondering if the DPO powder coated them and as the faces of the bolt holes are powder coated rather than a machined surface, if this may also be a contribtary factor and the powder coating needs removing on those surfaces before getting suitable spacers turned.

[Steve Brown]

4.8mm sounds huge! Yes, I would also remove the powder coat from the mounting face.

[RobinSF1]

To close this off.

I have cleaned the calipers with brake cleaner and rags, poking into nooks and crannies (I havent stripped them). Cleaned the powder coating off the caliper contact areas which bolt to the fork. Fitted EBC Double-H Sintered Sportbike Pad Set FA076HH. Packed the space between fork and caliper top mounting with 4mm thick washers. Measured front and rear, top and bottom outside edge of the caliper pad slot using a template cut from a loyalty card with a steel rule. This looks OK. Went on a 200 mile ride around mid Wales over the Cambrian mountains and old Welsh TT circuit to bed the pads in. Brilliant result! Two fingered braking very powerful, emergency stop had me sliding into the tank. I don't normally brake like this, it was just to test things where there was no traffic.

How much improvement is from the new pads and how much through having a perpendicular force from the caliper rather than the skewed force before is unknown, but result is great.