wherry Posted October 13, 2008 Report Share Posted October 13, 2008 Since I've had my Mont I've been a bit underwhelmed by the Grimeca single piston front brake's performance. It's always been less powerful than I'd like it to be and lacked bite. I've bled it repeatedly, changed the master cylinder seals and put new mounting bobbins on the disc. These have all helped and it's actually not been too bad for a while. However, we had an extremely wet, sandy and muddy trial the other day and towards the end of the day I started losing the front brake almost completely from time to time which really didn't help my score. I've cleaned it all up now and it's not too bad again but the bite point changes from one application to the next whilst you're riding which just isn't any good. You go for a dab of brake and the lever almost comes back to your fingers and you haven't actually slowed down. Other times it's where it normally is. It's no good. I'm going to strip it all down and rebuild the caliper and put some new pads in. Does anyone know which of the available pads work best with the solid disc and single piston caliper? The bigger question, however, is where the varying bite point is coming from? One of my theories is that the disc, which is very loose on it's mounting bobbins, wobbles about and pushes one of the pistons in, so your first squeeze of the lever just takes up the play generated by that, without putting any real pressure on the pads. Should the disc be really loose? I can experiment with reducing the play on the disc mounting and see what difference that makes but does anyone have any thoughts or experience they can share with this? Cheers. Quote Link to comment Share on other sites More sharing options...
motovintage Posted October 15, 2008 Report Share Posted October 15, 2008 I'm chasing the same problemb with my 315, I don't think it's the disk, I think its the master cyl seals, I have been very pleased with the pad life using dunlopads Quote Link to comment Share on other sites More sharing options...
wherry Posted October 16, 2008 Author Report Share Posted October 16, 2008 (edited) Thanks for replying MV, it's reassuring to know I'm not the only one with this problem. I have replaced the master cylinder seals on my bike and it definitely helped to make the brake feel more positive. Whilst, with the benefit of experience, I would never 100% rule anything out, I don't think that the varying bite point is down to the m/c seals. If they were faulty, or if there was a score on the m/c bore I think the performance of the brake would be repeatably poor wouldn't it? I have had a chance since my last post to have a look at the disc and caliper. I cut some little rings of thin card out and put them under the rims of the disc mounting bobbins to reduce the disc movement. This made no difference whatsoever to the brake bite point problem but did enable me to see that the disc was being pushed over from it's rest position by the inner caliper piston when the brake was applied. This led me to take the caliper off to have a look. With the caliper upside down in my hand and an old file between the pads, when the brake was applied the inner caliper piston pushed out nicely but the outer wasn't moving. I took the pads out and got the piston moving but it's definitely sticky compared to the inner one so I think this is probably the problem. I'll rebuild the caliper in the next week or so and see if that improves matters. Edited October 16, 2008 by Wherry Quote Link to comment Share on other sites More sharing options...
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