OK - I bored some of you with my brake problem at Croft, actually had it since last year really.
Symptom - Pedal fine after bleeding, (but still spongy compared to when I first did hoses and RS14 etc ) t start of day, after some serious braking pedal starts to go softer and long.
OK - so thats fade, normally… but first I dont go fast enough or press hard enough to induce fade in RS14’s and when the pads are new they work just great ( still a soft pedal though )- no problems.
But thinking back to last year I suddenly had the problem when braking hard for the millionth time at Aintree at the end of the very long fast railways straight - thought my brakes had gone complete
Have come to the following conclusions:
Piston is extened further with worn pads - could be damage on a piston(s) allowing air in
I am braking harder than ever and some extra cooling is required
Geary disks ARE thinner at 22mm than standard 25mm and dont get rid of the heat ( prepares flame suit )
RS14 dont work so well when half worn ( have heard that somewhere but cant remember where )
So I’m gonna
Fit a new master cylinder ( i have it so why not )
It may be that you’re braking harder now, and yes, Geary’s disks are too thin and run too hot for my tastes.
That’s the main reason why I changed to the Mutsnuts (but those are not available anymore) but you can get others. like AP that are as thick as they should be.
The Lotus MS disks will not be able to be ducted, as they have the vents in the other side, you’d need alloy bells so the bell is straigh and on the outside.
So, if I were you, I would:
-change brake fluid for a fresh Super DOT 4 like Castrol Response or better
-new pads, you could also try SBS or Ferodo DS 2500 (which are also superb)
-the new master cyl, and refurbish if that doesn’t cure it.
-if it’s still not cured, then AP disks with closed alloy bells, so that if you need you can add ducting later.
I’d guess at this stage that you may have a wee air leak somewhere (although i’d probably also expect you to be losing fluid if that was true - an your not, are you?).
How recent is your fluid? and was it from freshly opened containers? (your on SRF aren’t you?) … however, when you put SRF in there did you flush out the old DOT4 stuff properly ? they ain’t miscible in each other and this will lead to water ‘pockets’ which could be your problem ? So i’d probably want to flush the whole lot out by poking more new SRF in to completely replce all that’s in there - you did replace the clutch fluid at the same time didn’t you ? This theoy is one of the reasons i’m happy to stick with DOT4 Castrol super RS at a tenner or so a pop…
I don’t think you are overheating your brakes - so don’t think ducting will cure it - i followed you for a wee while and am on very worn standard discs and cheapo (albeit new) mintex pads at the moment… no issues
Sounds like the caliper seals are on the way out to me, I would refurb them before doing anything else (no point in changing the master cylinder if you don’t have to).
Geary’s discs were just about up to the job on mine with slicks and 42s on although given the choice I would have a bigger, better quality, disc. No doubt I will upgrade next time I need to change them.
Thanks everyone - including Steve.E for pumping the pedal
I’m quite sure its caliper seals, Randy mentioned that on the day and as new pads solve it mostly it all adds up.
BG Developments are 5 mins from our UK office so I’ll sort it out with them.
Will also ask them about the 295mm AP rotors, and I can make up some bells to suit them ( if anyone has a drawing it would be handy ) and open up the air ducts, I mean what the heck I have a week at home
To check if it’s the MC if you press the pedal lightly it’ll start to sink, with force it wont…
If the seals go then you’ll also see the fluid level drop…
However having had a caliper apart recently it looks like the seals are VERY solid, just 2 solid rubber O rings… They’d have to be really perished to break I’d imagine…
Will also ask them about the 295mm AP rotors, and I can make up some bells to suit them ( if anyone has a drawing it would be handy ) and open up the air ducts, I mean what the heck I have a week at home
I was talking to somebody at Croft about making up bells for AP rotors (you can probably guess ).
I understand that Lotus Motorsport disks are AP CP5000s. They do a 295mm dia / 25.4mm thickness (see here, AP quoted me �115+VAT each for an 8 grooved (presumably) non-drilled rotor) and a 280mm for the rear (see here). Although is 280mm the right std disk dia?
There are drawing on the links. I’d be interested in how you get on.
Hmmm, maybe we’re talking about the Lotus MS disks being alloy-belled? if so, and if somebody has seen them, it must have been the S2’s motorsport ones then, because AFAIK the S1’s MS items didn’t have alloy bells, but were in the same configuration as the std ones, which meant they could not be vented properly.
Any pics of the disks you guys are talking about? basically they need to have the connection to the hub on its outside, leaving the vanes visible from the inside.
Thats whats stopped me changing seals before before - no leaks, but I did find some very fine air bubbles in the front offside when we bled them again …
Roxx - BG are a brake specialist in Bromsgrove and AP stockist
to correctly bleed front calipers u have to bleed both pistons. Normally on 4 pots u have 2 bleed screw. On our std fronts not. So to do a good job u have to unbolt them from the hub, turn them upside down, bleed. Then u have to turn the caliper on the correct position but be careful to turn in the right direction to avoid air from the outer cylinder to go to the inner cylinder through the pipe.
Then bleed again.
Doing this with patience u will never have air in the caliper. Without this procedure u will never get rid of the air from the inner cylinder.
I have ordered and just received the Lotus Motorsport brake kit. It consists of 4 x 295 vented rotors with ally bells. 2 x AP 4 pot callipers. 2 new ally front hubs. 2 new rear hubs. The rear hubs use the bigger motorsport bearings and have mountings for the 2 piston front callipers. You also get rose jointed lower ball joints and a bias valve and MC and a few other bits and bobs.
One thing I mentioned to Russell at Lotus was the way the fluid is fed to the standard front callipers and that I would like to change it. I’m sure people have noticed the round casting mark on the inside of the calliper in the middle where the fluid feed pipe “should” go. Russell said that the pipes in the kit will require modification to the callipers so that the feed goes to the middle. I can then have a bleed nipple at the top of both the inner and outer sides of the calliper.
Andy send me a PM so we can arrange to meet up as I’m sure I can lend you a disk and you can draw what ever you like mate.
Also when BG overhaul your callipers, wy don’t you get them to mod them so the fluid feed goes to the proper place in the middle of the calliper.
I’m sure you know, but you can’t use the handbrake on the rears with your new setup. Obviously not a problem, unless you need to MOT the car for road use.
I have ordered and just received the Lotus Motorsport brake kit. It consists of 4 x 295 vented rotors with ally bells. 2 x AP 4 pot callipers. 2 new ally front hubs. 2 new rear hubs. The rear hubs use the bigger motorsport bearings and have mountings for the 2 piston front callipers. You also get rose jointed lower ball joints and a bias valve and MC and a few other bits and bobs.
Sean…
Is it possible to order the Lotus Motorsport Master Cylinder?