Help!! front disc brake vibration

Hello, out there. I just got my first norton up and running, it's a 72 with the combat engine. The bike runs great, but I am having trouble with the front brake. I get a serious vibration when the front brake is applied. The vibration turns into a pulsating at lower speeds. It feels like once per wheel revolution. You can feel the pulsing in the brake lever. I had the disc re-surfaced at a local shop. They used their flywheel machine. I reinstalled the disc and found it made no difference. I put the wheel on my truing stand , using a dial indicator, I measured the runout to be .003". This seemes pretty good to me, but I could find no spec on this. Being the caliper is fixed rather than floating, I am sure runout is more critical. I had to rebuild the caliper and master cylinder when I first purchased the bike. (new caliper pistons, brake line and all seals). I have new pads ordered,The old ones have about 3/16" of lining left. I sanded the pads on a belt sander, before trying the resurfaced disc. I hate to spend 300.00 on a new rotor if it will not correct thr problem. Also are the 150.00 taiwan rotors any good. Any advice on this matter, would be greatly appreciated. Barry

I would not have tried the old pads on the resurfaced rotor.

I'd wait to see what the new pads do.

The caliper is fixed but has 2 moving plungers (unlike most Jap calipers of the same era with single plungers and the caliper sliding on rusty pins) so 3 thou should not cause problems. Have you checked the mounting surface on the hub, if this is damaged or corroded on one side the disc will not seat correctly and cause the same symptoms as a warped disc.

I think .003 is too much. This may be ok for a flywheel, but not a rotor. Try to have them get it dead on. More like .0003

Sorry Guys but what is a rotor in UK english? It is the brake disc?

This does not sound like a disc pad problem, so I don't expect you will see any improvement with new pads. I had the same type of problem as you describe in the past and corrected it by fitting a new Disc(rotor)

The symptoms are classic warped rotor but, as noted, could also be caused if the mounting surface is uneven or the rotor is not equally tight (torqued) all the way round. Make sure the mounting surface for the rotor is also true and that the rotor nuts are torqued to the correct spec. Note that if studs/bolts are/have been over-torqued, they can pull some of the surrounding metal and cause the surface to then be non-true, requiring re-surfacing of the mounting surface.

Have you noticed that it only shows up or gets worse when the disc is warmed up? I've been told that even if you were to true the disc now, the castiron can develop a memory so that when it gets up to temp it may take on the warp that isn't there when its cold. Current wisdom seems to be to avoid resurfacing discs.

Did you torque the fasteners?

You can "play" with the fastener torque to get the .003 reduced a bit.

The belt sanding may have introduced some of its own abrasive in to your braking equation, keep an eye on the disc.

RS

Thanks, for all the great advice. I did not torque the disc bolts I tightened them by hand , gradually in a star pattern. I'll go back, check the hub surface with the indicator, then torque the nuts. I think bpatton, may be onto the exact problem. I had previously removed the disc and cleaned it by hand with some fine emery. I was very happy with the results, as the vibration seemed to all but dissapear, However after a 5 minute ride the problem was back. The same thing happened after the disc resurfacing. The brakes felt much better. After the 5 minute ride the vibration was back. After a 20 minute ride the pulsating was at a dangerous level. In a hard stop the front tire would chirp with every pulse (dangerous and quite unnerving). I broke down and ordered a new UK disc from commando specialties. I sure hope it does the trick. Barry