Support Team Shaun_E Posted April 22, 2014 Support Team Share Posted April 22, 2014 At Blyton this weekend I wasn't happy with the braking on my car. The brake pedal had longer travel than normal but it didn't "pump up" with repeated presses (so not pad knock off). It was "slightly spongy" but not everso. The car stopped OK but there wasn't much feel - it was hard to know when a lock up was imminent. I have Caterham AP big brakes, the standard master cylinder (never been a problem before), Pagid RS14 pads on the front and Pagid RS4-2 pads on the rear. I have flexible hoses on the rear calipers. The rear pads are pretty shot now so need replacing and I suspect the fronts have seen better days. So the questions are: 1. Any thoughts on the cause of the long, slightly spongy pedal? 2. Should I change the master cylinder to the AP item? What difference does it make to feel, travel, etc.? 3. What is the best combination of currently available pads front and rear? Is there a new leader? I never got on with Pagid RS15 fronts as they just glazed over with road use. My main use is sprint and hillclimb with some road use and the occasional track day/test day. I will be replacing the fluid with a good quality standard DOT4 fluid. I don't think there is any need for racing fluid but happy to be convinced otherwise. Off now to read all the other threads on this subject Link to comment Share on other sites More sharing options...
ECR Posted April 22, 2014 Share Posted April 22, 2014 I'm sure you probably already know this but just in case ..... The AP caliper has 2 bleed nipples and I have seen more than one person bleed the brakes using just one. Both need bleeding Link to comment Share on other sites More sharing options...
Kevsta Posted April 22, 2014 Share Posted April 22, 2014 I have a history spending silly amounts of time with the MC. I resealed it, was better, then went crap again. Fitted a good second hand one. Was great - for a year or two, then spongy peddle one year again. Fitted AP MC - gorgeous peddle feel! If this one goes then I might just try a Fred Flinstone! And yes, I have AP 4 pot fronts (standard rears - no change other than MC). Kev Link to comment Share on other sites More sharing options...
Support Team Shaun_E Posted April 22, 2014 Author Support Team Share Posted April 22, 2014 Roger - yes both nipples bled. 😶🌫️ Kev - others have also suggested that the standard master cylinder can be the cause of the problem and that the AP unit is better made. Of course Caterham are out of stock of the AP master cylinder - anyone know if it's an off the shelf part or a Caterham special? Link to comment Share on other sites More sharing options...
Area Representative Richard Price Posted April 22, 2014 Area Representative Share Posted April 22, 2014 Quoting Shaun_E: 2. Should I change the master cylinder to the AP item? What difference does it make to feel, travel, etc.? The standard master cylinder is 5/8" bore. From memory, I think the AP master cylinder is 11/16" bore. Therefore the piston area is something like 1.67 times greater. Thus the pedal pressure required will also be 1.67 times greater to achieve the same braking force. Likewise, all things being equal, the pedal travel will be reduced by a similar factor. However, the design of the AP cylinder is a little different, and its likely to actually start shifting fluid earlier than a stock master cylinder, so this will exaggerate the reduction in pedal travel further. Quoting Shaun_E: 3. What is the best combination of currently available pads front and rear? Is there a new leader? I never got on with Pagid RS15 fronts as they just glazed over with road use. My main use is sprint and hillclimb with some road use and the occasional track day/test day. I believe that one of the "selling" factors of most Pagid pads is "excellent bite". This could also be interpreted as "they lock up very easily......". My own feeling is that a more progressive pad may well be beneficial. However, getting the balance close to right is far trickier! If you were to use the same pad material front and rear, you're likely to end up with too much bias to the rear. I'm not a fan of any of the valves that limit or proportion pressure to either front or rear, which is why I modified my pedal box to incorporate dual master cylinders and an adjustable bias bar (like most proper race and rally cars..). I use Mintex 1144 pads front and rear, but have to wind the bias to the front to avoid locking rears. I generally find that my brakes work just as I expect them to each time I press the pedal cold, warm, or hot. Link to comment Share on other sites More sharing options...
ECR Posted April 22, 2014 Share Posted April 22, 2014 Like Richard, 144 front and rear but with a proportioning valve to limit the rears. This is with AP fronts and standard rears and a standard m/c. I find the longer brake pedal easier to modulate than with the AP master cylinder (just personal preference), but my brake pedal is always softer compared to a race cylinder brake setup. It is however, consistent. I fitted the race brake pedal last year (Brake pedal high effort 77198A - different pivot point) but can't honestly say I noticed the difference ... Oh, and Castrol SRF fluid Edited by - ECR on 22 Apr 2014 15:53:38 Edited by - ECR on 22 Apr 2014 16:30:45 Edited by - ECR on 22 Apr 2014 19:34:13 Link to comment Share on other sites More sharing options...
Budjuggler Posted April 22, 2014 Share Posted April 22, 2014 Shaun If you got FTD, I'm not sure I would wAt to improve the brakes Link to comment Share on other sites More sharing options...
A10ROX Posted April 22, 2014 Share Posted April 22, 2014 What brake fluid and how old? Link to comment Share on other sites More sharing options...
david nelson Posted April 22, 2014 Share Posted April 22, 2014 After pagid rs15 that locked up the fronts i now run performance friction 01 compound IIRC at the front and 1144 rears. This works for me with the AP master cylinder. David Link to comment Share on other sites More sharing options...
charlie_pank Posted April 23, 2014 Share Posted April 23, 2014 From your description it sounds as if something in your setup is not working as it should. Rather than upgrading items, I would concentrate on finding out what it is that is causing the problem first... Link to comment Share on other sites More sharing options...
Support Team Shaun_E Posted April 23, 2014 Author Support Team Share Posted April 23, 2014 Lots of good stuff - thanks. Brake fluid is off the shelf DOT 5.1 and the first thing I will do is replace it as it's been in the car for about 18 months. I've never been really happy with the brakes so I guess I am looking to change something rather than just refresh what is already there. I don't think I want to change the master cylinder (other than from a quality point of view) as I like some travel in the pedal and a progressive set-up. I don't want to increase the leg effort required either. Gill drives the car as well so this is important. I haven't got the time to fit a proper dual master cylinder set-up but understand this is the ultimate solution. I guess replacing or rebuilding the master cylinder might be one step and then choosing a front and rear pad combination that will get close to a decent balance (slightly front biased to be safe). Keep the ideas coming Link to comment Share on other sites More sharing options...
Wrightpayne Posted April 10, 2016 Share Posted April 10, 2016 ShaunDid you find a cause / fix for this?After winter lay up I've got a long pedal (longer than I remember) but brakes OK once they bite. Pumping the pedal doesnt make any difference.wondering if 18 year old master cyl needs replacing - next choice is standard or AP uprated. Std brakes all round with mintex pads up front.Ian Link to comment Share on other sites More sharing options...
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