It's that time again, and poor Suzi has been failed on a 'binding front brake'. TBH, I'd not noticed, and I certainly would have if it made paddling in and out of parking spaces difficult. It's a single big disc and certain to drag a little, IMO, which it does if you turn the wheel by hand, but it doesn't require much effort to turn - it just doesn't keep spinning. I've taken the caliper to bits, greased the sliders, cleaned the pistons and renewed all the fluid, but with no real change in behaviour.
The MOT manual is pretty vague on the subject, saying only that "The assessment of bind, grab and judder in sub-sections 3.3C and 3.3D can be performed at any appropriate point during the test", in other words, it's up to the tester. Any thoughts on convincing him that it's not abnormal?
Last edited by: VxFan on Wed 4 Jul 12 at 00:33
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ive heard greasing the sliders on the calipres can make things worse, the experts on here can probably explain why
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A wee bit of disk runout can help here, pushes the pads away.
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Indeed. It's dead true, unfortunately!
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Might depend on the grease. Moly-based ones are common, as it has to last! Doesn't seem to be sticking, anyway...
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> if it made paddling in and out of parking spaces difficult.
A slightly binding disc brake wouldn't do that. What it may do is boil the fluid in the caliper while blasting down the dual carriageway at speed, leaving you somewhat discomfitted on arriving at the next roundabout.......:-O
What's the disc like? Worn crinkly ones create more drag than nice flat ones.
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It's worth temporarily slackening the bleed screw to make sure there's no residual pressure holding the brakes on. If there is residual pressure, this can be caused by twisted or internally collapsing flexi pipes.
As mentioned, taking the lip off the disc edge can help.
Also, the pads themselves can be a bit tight within the caliper. More often its spurious pads which aren't quite the right size which cause the problem. 5 minutes with a file on the edge of the backing plate can fix this problem.
As for the MOT regulation, yes, it is subjective - but, if it is just one side, there is some difference between the 2 brakes, and there is a problem to be sorted out.
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I thought you might be onto something there, NC, as the pads were a bit scruffy, with a bit of rust around, but I have now cleaned off all the rust and some blistery paint, with no effect at all. There is no air in the system (completely flushed) and the pistons even retract very slightly when letting the lever go. I could buy some new pads, I guess...
BTW, the bike only has one disc. It's over 12" across, and works very well - much better in fact than the twin discs on my old BMW!
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It's not binding that hard, fortunately. That's really my beef - it's just that the pads aren't pulling away completely, so you can't spin the wheel freely. It doesn't rub enough to heat up, and I think it's the same as it always was, TBH, but my MOT man has perhaps been told to focus on the point, hence the fail.
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I wasn't thinking of air being trapped, just residual fluid pressure - either from collapsing flexis, from sticking ABS valves (if fitted), or from the master cylinder not retracting fully. Depending upon the layout, the two front brakes will most likely be on different hydraulc circuits - so, its possible the hydraulic pressure may differ - hence my suggestion to open a bleeder to see if it makes a difference.
Some rubber brake parts can swell and bind up if you use the wrong lubricant - older GM calipers were very bad for this, and reacted allergically to copperslip!
However, as you say that you can see the piston withdrawing a bit, it's either the caliper slides, or the fit between pad and caliper which is causing the problem.
With the piston retracted, how freely does the moving pad move in the caliper? How freely does the caliper slide on its pins?
It's a fine line - the pad needs to have enough clearance to the caliper / abutments to move, but not too much so that it makes a knock when you change direction. Particularly with cheap pads, I find they need a bit of filing or grinding to get the fit right.
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The Triumph Sprint has a minor issue with the front caliper pistons in that they regularly need the pistons 'exercising'. This requires pad removal and then pushing the pistons out out under hydraulic pressure and then pushing them right back in using physical pressure a few times. The symptoms are a slightly woolly feel on the front brake lever.
The reason is the coating on the pistons combined with a bit of dirt for some reasons seems to cause resistance to the pistons and upsets the feel.
This can be cured by the 'exercising' process or rebuilding with an alternative piston from another model which has a different coating.
This is not particularly dangerous but the feel of the lever does suffer.
Last edited by: Fullchat on Tue 3 Jul 12 at 20:40
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Ah, just realised - we're talking about a motorcycle rather than a motor car. It's therefore best to ignore all I've written above!
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To be fair NC I hadn't twigged that either until you mentioned it. I was just throwing in another possibility into the equation.
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Should have made it clear - sorry! The site asks what you're writing about (for search purposes, presumably) but doesn't then show it in the post!
For the record, it's a Suzuki GS500. As NC says, something must be keeping the pads from moving, so will have another go with a file tomorrow :-(
It's very much like a floating caliper car brake, but on a smaller scale, and with two pistons. They, at least, are stainless, unlike most car ones that I've serviced, which have been fine apart from the rusting chrome surface that wrecks the seals. Why oh why, etc...
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Sidetracking myself now. What I really want to know is what criteria do testers use to determine what is or isn't 'binding'. A bit of drag on the pads seems pretty harmless to me, and from what I have read, whether it passes or fails seems to be entirely subjective.
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I would suggest that the wheel could be spun by hand and will rotate with only the slightest resistance from the pads on the disc which will be audible. The pistons/pads will totally release their grip on the disc. Any more of a resistance to the point where the wheel stops quickly indicates that not all is well and that the brakes are not releasing their grip.
Issue is that if the brake is constantly on to a lesser or greater degree then heat is generated which could effect the performance of the pads - they are manufactured to run from lowish temps (unlike competitions ones). The fluid could also boil rendering it useless. Either way brake fade or hydraulic failure could result.
Last edited by: Fullchat on Wed 4 Jul 12 at 00:46
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>> Should have made it clear - sorry! The site asks what you're writing about (for
>> search purposes, presumably) but doesn't then show it in the post!
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>> For the record, it's a Suzuki GS500.
Now added to header.
I've just done a test post and selected Suzuki from the drop down menu, and manually put GS500 into the subject header. Worked fine. By the looks of it all you selected from the drop down menus was "Miscellaneous" which is why the make didn't show in your post.
Vx.
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Thanks, Vx - I thought I'd selected 'motorcycle' but didn't add any detail. Mea Culpa!
You did, but for some reason it's not showing
Last edited by: VxFan on Wed 4 Jul 12 at 18:44
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>> but my MOT man has perhaps been told to focus on the point, hence the fail.
Get a second opinion, it may well pass somewhere else. I've had this before, where MOT place A fails something you think is all right, but place B passes it.
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A sticking front brake might be a common problem on the GS500(?) - it certainly happened on mine, although I have to admit that it was doing a pathetically low mileage per annum.
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Is it a single piston caliper?I had a similar problem on a GT500-it was cured by removing the mounting bolts,cleaning the holes in the caliper that they go thro',cleaning the "O" rings and re-assembling dry ie.no grease or other lubricant.
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The seals were the problem. MOT man* suggested they were worth taking out, and although everything looked OK from above, the channels were full of crap. Scooped that out with a blunt screwdriver and a cut-down lolly stick, wash out and reassemble, and the pads pull off completely, leaving a free-spinning wheel - perfect.
Many thanks to all for your help.
*A proper biker, with two sprint bikes, one ridden by his wife!
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"a similar problem on a GT500"
Nice. I always wanted one of those...
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Mine gets used in bursts, and not used when it's raining, if I can help it, but it lives outside and the problem turned out to be related, in that the channels for the piston seals had corroded and made them too tight. All sorted now!
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Your bike lives outside Mr Bagworth?
You need to prioritise and build a shed....for the wife!
Pat
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She's survived quite well so far (now 11 years old) but a shed would be good. Mrs JBJ thinks I spend enough time on her already, though...
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Full marks to Suzuki for at least making caliper pistons that don't rot so spectacularly on their exposed surface that you don't have a hope in hell of ever pushing them back in at a pad change. Are you listening, Kawasaki?? :-)
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Suzuki - MOT point - zookeeper
