lee Posted April 8, 2023 Report Share Posted April 8, 2023 So I have new AP brake kit fitted but the pedal is scarily low. I’m told this is characteristic when the system now have more fluid to push around but also that it’ll get better when the pads bed in?? What we say? Quote Link to post Share on other sites
RobH Posted April 8, 2023 Report Share Posted April 8, 2023 (edited) Is the piston area in the new callipers now greater than the originals? If so the master has to shift more fluid - so it probably won't get much better, effectively you would have altered the 'gearing' of the system. To fix it you would need a larger diameter master cylinder. Edited April 8, 2023 by RobH Quote Link to post Share on other sites
BlueTR3A-5EKT Posted April 8, 2023 Report Share Posted April 8, 2023 45 minutes ago, RobH said: Is the piston area in the new callipers now greater than the originals? If so the master has to shift more fluid - so it probably won't get much better, effectively you would have altered the 'gearing' of the system. To fix it you would need a larger diameter master cylinder. What about rear cylinders? Quote Link to post Share on other sites
Motorsport Mickey Posted April 8, 2023 Report Share Posted April 8, 2023 46 minutes ago, RobH said: Is the piston area in the new callipers now greater than the originals? If so the master has to shift more fluid - so it probably won't get much better, effectively you would have altered the 'gearing' of the system. To fix it you would need a larger diameter master cylinder. Excellent description Rob. Mick Richards Quote Link to post Share on other sites
lee Posted April 8, 2023 Author Report Share Posted April 8, 2023 1 hour ago, RobH said: Is the piston area in the new callipers now greater than the originals? If so the master has to shift more fluid - so it probably won't get much better, effectively you would have altered the 'gearing' of the system. To fix it you would need a larger diameter master cylinder. Thanks Rob. makes sense. so now I need a bigger M/C is there a common part that fits straight on? Quote Link to post Share on other sites
RobH Posted April 8, 2023 Report Share Posted April 8, 2023 Can't help you there I'm afraid Lee. Perhaps the people who sold you the callipers might know? Quote Link to post Share on other sites
roy53 Posted April 9, 2023 Report Share Posted April 9, 2023 Lee i have the Willwood set up on mine but nothing special re the master cyl . Although i do have a tilton pedal box with seperate cyl's for front and back. Roy Quote Link to post Share on other sites
FatJon Posted April 9, 2023 Report Share Posted April 9, 2023 I have exactly those calipers on mine and the pedal is NOT low so it’s not a characteristic and you are correct to question this. Quote Link to post Share on other sites
FatJon Posted April 9, 2023 Report Share Posted April 9, 2023 and it’s a standard MC too. Quote Link to post Share on other sites
Andy Moltu Posted April 9, 2023 Report Share Posted April 9, 2023 2 hours ago, roy53 said: Lee i have the Willwood set up on mine but nothing special re the master cyl . Although i do have a tilton pedal box with seperate cyl's for front and back. Roy If you have a separate cylinder for front and back in a Tolton pedal box are you sure you have the std master cylinder? Quote Link to post Share on other sites
Andy Moltu Posted April 9, 2023 Report Share Posted April 9, 2023 You will always have a longer pedal if you increase the piston area of the caliper. All you can do is minimise other causes. Adjust the rears properly. Check there is no play in the pedal or the clevis pin. Bleed all air out of the system. Adjust your front wheel bearings to minimise pad knock off. Failing that, take th calipers off. Put the originals back and fit decent pads (Mintex 1144 or Hawk) if you need more cooling track down one of the old kits that use a spacer in the caliper as fitted to contemporary Fords and vented disks. Quote Link to post Share on other sites
Waldi Posted April 9, 2023 Report Share Posted April 9, 2023 Venting the brakes (again) and bedding in the new pads may do it. New brake pads soften the pedal a bit. Waldi Quote Link to post Share on other sites
roy53 Posted April 9, 2023 Report Share Posted April 9, 2023 4 hours ago, Andy Moltu said: If you have a separate cylinder for front and back in a Tolton pedal box are you sure you have the std master cylinder? Yes you are correct Andy. My mistake . i have 2 master cylinders in the Tilton pedal box , the TR3 ones with seperate reservoirs. Sorry for misleading Roy Quote Link to post Share on other sites
lee Posted April 9, 2023 Author Report Share Posted April 9, 2023 Thanks again chaps. Bit of conflicting responses since FatJon doesn’t have the issue and others say it’s normal. I’ll give it a good drive, bed everything in and go from there Quote Link to post Share on other sites
Mark V Posted April 9, 2023 Report Share Posted April 9, 2023 I fitted ap calipers,(racetorations supplied) and brake pedal travel was also fine, has a standard tr6 master cylinder. Been on car 10years or so. Mark. Quote Link to post Share on other sites
lee Posted April 10, 2023 Author Report Share Posted April 10, 2023 11 hours ago, Mark V said: I fitted ap calipers,(racetorations supplied) and brake pedal travel was also fine, has a standard tr6 master cylinder. Been on car 10years or so. Mark. That’s good to know. Quote Link to post Share on other sites
TRTOM2498PI Posted April 11, 2023 Report Share Posted April 11, 2023 On 4/9/2023 at 8:44 PM, lee said: Thanks again chaps. Bit of conflicting responses since FatJon doesn’t have the issue and others say it’s normal. I’ll give it a good drive, bed everything in and go from there Hi Lee, I run these AP 4 pot calipers on my 6, with the associated Ford Escort RS Cosworth vented discs, and Mintex 1144 pads. Standard M/C, & servo. Pedal should not be low at all, so not a characteristic of this brake set-up. I've had this set up since 2010. Quote Link to post Share on other sites
lee Posted April 18, 2023 Author Report Share Posted April 18, 2023 By way of update the brakes are still as useful as a handbrake on a canoe but it turbs out the Servo is t working. Strange though as it was refurbished by past parts a few yrs ago but the car hasn’t been used. Plenty of draw from the inlet and the one way valve is good. Bit puzzled really Quote Link to post Share on other sites
FatJon Posted April 18, 2023 Report Share Posted April 18, 2023 Not a lot to go wrong in a servo. If the diaphragm isn’t leaking it can’t really go wrong. I would be checking for the front piston in the master cylinder being stuck in the forward position. Not seen it personally but I hear it happens due to corrosion in the bore, likely after standing for some time. Also happens when bleeding as the piston moves further up the cylinder than it would during normal use, hits the wear ridge, sticks. Quote Link to post Share on other sites
roy53 Posted April 18, 2023 Report Share Posted April 18, 2023 I think with all the hastle you are having Lee i would try a replacement master cyl. £40 or £70 just to eliminate it. Roy Quote Link to post Share on other sites
John L Posted April 18, 2023 Report Share Posted April 18, 2023 (edited) I think you have to determine if the issue is actually in the front. Why not eliminate the rear brakes, clamp off the rubber hoses at the trailing arms, if the pedal is now good, the problem is in the rear brakes. Have you tried locking the brake pedal down overnight, this nearly always works to get rid of the last bubbles. Have you checked the brake pushrod to the servo clearance? John Edited April 19, 2023 by John L Quote Link to post Share on other sites
lee Posted April 18, 2023 Author Report Share Posted April 18, 2023 Thanks guys. I should add that the M/C was also refurbished with a stainless bore. rear brakes also new. Only thing bugging me it the shuttlecock valve (not sure it uk cars have this? It often locks off when bleeding brakes Quote Link to post Share on other sites
Malbaby Posted April 18, 2023 Report Share Posted April 18, 2023 As a matter of interest, are the UK MOT guys strict on brake calipers not having any dust seals on the aftermarket caliper pistons. Quote Link to post Share on other sites
Erik Posted April 19, 2023 Report Share Posted April 19, 2023 Hi Lee, It has already been mentioned but have you adjusted your rear brakes properly? If they are not adjusted up you will have exactly the symptoms that you describe. If the brake pads are new then there will be a process of bedding them in and re-adjusting. Erik Quote Link to post Share on other sites
stuart Posted April 19, 2023 Report Share Posted April 19, 2023 13 hours ago, Malbaby said: As a matter of interest, are the UK MOT guys strict on brake calipers not having any dust seals on the aftermarket caliper pistons. I wouldnt have said so if the calipers were never fitted with them though TBH Ive never seen any calipers without. Stuart. Quote Link to post Share on other sites
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