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MG MGB Technical - Brake discs

Does anyone have a good rule of thumb for when front discs are "too heavily scored or worn" and thus need replacing? Is it any level of scoring, sufficient for your nail to catch on, say?
Richard Coombs

Worshop manual states the maximum reduction in thickness must not exceed 0.040". The original disc thickness must be ranging 0.350"/0.340". Another point to check after, run-out must not exceec 0.003". The disc pair price is not that expensive in UK for standard ones.
Regards.
Renou

Assuming the discs are still thick enough I think the rule of thumb is as you describe - light scoring is ok but if you can catch your fingernail on it it's no good. My B had pretty deeply scored discs when I bought it in 1999 (certainly more than enough to catch your fingernail on) but it still stopped ok and the friendly MOT man grumbled about it every year but never put an advisory down. I then took it to a different garage when I moved house a couple of years ago and they failed it for the discs being "excessively scored".

To be fair, when I took them off they were far worse than they appeared at first inspection. New discs and pads are dirt cheap; fitting is a bit of a pain but even I managed with help from this board so it can't be that tricky!

Cheers,
Tim
T Jenner

Light scoring, if it is in concentric rings, and not causing any pulsing at the pedal, should be OK, whether or not you can catch your fingernail. The new pads will wear to that pattern. The real problem is usually glazing, which has less friction than a new or reground surface.
Art Pearse

Thanks everyone. I measured the thickness and was amazed to find it was hovering around the minimum of 0.3". I've gone for the easy option of a new pair. Only £30!!
Richard Coombs

Now comes the fun of parting them from the hubs. The nuts are partially shrouded, and you really need a very thin-wall socket to get on them properly, or a jig to clamp sockets onto both bolt-head and nut and a lever on each. I changed mine a month or so ago and just about managed, see http://www.mgb-stuff.org.uk/wn_brakesframe.htm and click on 'Calipers'
Paul Hunt

This thread was discussed between 12/07/2009 and 16/07/2009

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