Brake discs

[TimClarke]

I had a similar issue on the bike I bought last year. There was a dark print of the brake pad on the inside face of the disc and a consequent pulsing of the brake at low speed. Particularly annoying when trying to come to a smooth halt.
Colour me nasty but I introduced the brake disc to my random orbital sander with some 60 grit. The chrome on the disc is incredibly hard so no concerns about taking too much material off, but with a bit of effort I managed to remove the imprint making sure to address the whole surface to keep it consistent.
That's fixed it. Initially, the braking power wasn't as good as previous but as the disc surface polished up again and bedded in over just a few miles it's back to the same power as before minus the judder.

That's really interesting - i'll have a good look

I wonder if I just stick a couple of hundred miles on the bike the braking process will take off the rust/patchiness?

[Galligaskins]

Ah. Have to say yours looks a lot worse than mine did I'm not sure that looks recoverable at home. I don't think normal brake usage will rectify that. I did a few hundred miles on mine with nothing like the level of rust/patchiness and it didn't improve, hence resorting to the orbital sander as I reasoned I had nothing to lose. I hope you can get your discs sorted somehow. Maybe The Disc Doctor as others have said. I've no experience with them.

[TimClarke]

Ive just been looking through the parts catalogue and it looks as though the hydraulic pipe and the bleed nippl

P4050044.JPG (98.34 KiB) Viewed 150 times

e are the wrong way round on my bike?

[Morini Jen]

Hi Tim.

As far as I'm aware, it doesn't matter too much as the brake pipe and bleed nipple are connected. The bleed nipple on my bike became rusty and I was worried about removing it so Alex at NLM (who really knew his stuff) fitted a banjo with an incorporated bleed nipple on the brake line side. It works fine.

If you need more confirmation, Steve Browns 3½ Sport (which may still be for sale) has the same arrangement as yours.

[MickeyMoto]

The calipers are reversible for left and right, if you look at them, as Jen says, it does not matter as either 'port' can be used for hydraulic pipe and bleed nipple.

[TimClarke]

Than k you!

[TimClarke]

Well.

The only thing I really didn't like about the bike was the brakes.

Unpleasant pulsing on the front and gabbing/overheating on the back.

I thought it odd that an expensive renovation hadn't addressed either.

The rear disc was absolutely shot with deep grooves and the pads were in a shocking state. New pads and a skimmed disc have improved things very much cosmetically but it's not as powerful as it should be - I am wondering that they've taken so much metal off to get rid of the scroring the disc isn't thick enough now? It measures 5mm?

Front discs skimmed down to 6.3mm and they look great and the calipers are rebuilt too. BUT, having gone for a spin around the block the pulsing is EXACTLY the same as it was before so I'm at loss really. Any ideas?

[Galligaskins]

That is strange, given that the discs have been substantially skimmed.
One thought - are the discs sitting flat onto the hub, and is the hub of the wheel true? If you haven't already, it might be worth raising the front end and spinning the wheel and checking for run-out. It doesn't need much to make a difference.
In the motorsport world, I've known people with hubs that were poorly machined from new which made the disc wobble slightly as it went round, causing a pulsing brake pedal. Had a similar effect myself but from bent half-shaft ends from taking too much kerb on track. Used to squeak rythmically when I came into the pits. Had about 0.5mm run-out at the edge of the rear discs which I hadn't noticed until I put a dial test indicator on them.
If your discs have been off, is the mounting surface clean and free from paint/powder coat/ corrosion debris?