Richard Anderson Posted June 11, 2003 Share Posted June 11, 2003 I'm having some troubles with the uprated 4-pot AP brakes (all-around) in my ex-race SLR. After going round a long right hander at speed or some agressive slaloming the pedal goes all spongey. This would initially point to the pads getting knocked out by loose bearings or stub axel but, this has been investigated on TWO occasions by different, very repuatable Caterham Specialists and, although the master cylinder and the front offside stub axel have been replaced, the problem is still occuring. Together with a friend I have recently rechecked for play in all the bearings and found nothing wrong. We are at a bit of a loss as to the next best things to investigate...and, also, this has taken on a bit more concern as I have a trackday coming up soon and we are running out of time to fix the problem. Anybody got any ideas or can point me at a specialist who could fix the problem? Link to comment Share on other sites More sharing options...
Jason Plato Posted June 11, 2003 Share Posted June 11, 2003 I suspect its simply pad knock off . would be wise just to check that the caliper pistons are in good order and not binding in any way . Even when the bearings etc are in tip top condition this will still occur . I was watching the Bathurst race on TV and they had a pedal box cam , even their cars suffer pad knoock off , and hence why the drivers left foot brake check when going down a straight prior to the next heavy braking area . Dave Link to comment Share on other sites More sharing options...
Richard Anderson Posted June 11, 2003 Author Share Posted June 11, 2003 Thanks Dave...sticky pistions is something I will check but, If the pistons were sticking would I not get swerving under braking? ....I have had sticky pistons on another car and this is what happened. As to the pad-knockoff (which is what it surely must be somehow?) : sorry, may have misinterpreted what u are saying : but are u saying that pad-kockoff is to some degree normal, and that I should expect some variation in pedal feel? I haven't heard anyone else complain about variation in pedal feel....indeed, it makes heel/toeing almost impossible as the pivot point (brake) has altered significantly? Perhaps I should have said that the brake is (in my opinion) dangerously spongey....ie it requires pumping before you can get enough braking force sometimes. Rich Edited by - Richard Anderson on 11 Jun 2003 10:59:31 Edited by - Richard Anderson on 11 Jun 2003 11:00:12 Link to comment Share on other sites More sharing options...
Jason Plato Posted June 11, 2003 Share Posted June 11, 2003 pad knock off is common , in that you may get a little more pedal travel when braking after completing a High G corner . Whilst the pedal will have more initial travel the bite will be just the same . If you are getting bad spongy pedal , then I cant help you . As i have never suffered this . Dave Link to comment Share on other sites More sharing options...
Sheds Moderator Posted June 11, 2003 Share Posted June 11, 2003 As has been said earlier, pad knockoff will give you a long pedal but it will be equally solid when the slack has been taken up. You seem to be describing a spongy pedal, which improves on pumping, usually indic. air in the system. This *should* have been removed by bleeding after the m/c was replaced. Is it possible it is entering via the reservoir under severe cornering? only a guess. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 11, 2003 Share Posted June 11, 2003 When was the fluid last changed? What fluid is being used? Link to comment Share on other sites More sharing options...
Richard Anderson Posted June 11, 2003 Author Share Posted June 11, 2003 I assume the fluid must have been changed when the master cylinder was changed....that was about a year ago. Racing brake fluid was being used...I'm not sure about now. How easy is it to change the brake fluid and bleed the brakes? ...and what fluid should I use? Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 11, 2003 Share Posted June 11, 2003 Some racing brake fluids pick up a lot of moisture, so need regular bleeding. Probably at this stage it will be worth purging the system and moving to a known fluid and observing all the maintenance advice for that fluid. My personal choice is AP600 which is not as hydrophilic as many. Fitting instructions involve flushing the old fluid out of the system, purging with AP600 before refilling with fresh fluid. The race rear brakes need very careful bleeding, detaching the calipers from the de dion ears to hold them vertically. The pad retaining pins in the rear brakes can also corrode which can result in the pads not moving as freely as possible and only partial contact with the disks. It sounds like a good general service of the brakes is in order. The main emphasis in all of this is that extra care taken pays dividends in the braking feel. Edited by - Peter Carmichael on 11 Jun 2003 15:45:32 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 11, 2003 Share Posted June 11, 2003 Just one other question. The fluid in question isn't a dodgy purple colour by any chance? Link to comment Share on other sites More sharing options...
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