I did a track day at Snetterton this week and after about 5/6 laps the brakes were fading to the point where the lever was coming back to the bars, so each time I had to come in and wait for the brakes to cool and then they were fine for another 5/6 laps after that. I have never had this problem before and I can only think it is down to using P4/34 brake calipers as this was the first time I had used them on this circuit and they seem to be bigger and therefore retaining more heat I checked my fluid and it is DOT 4 and is quite new. I am going to change to DOT 5.1 a non Silicone version in the hope that this cures the problem, I have always used DOT 4 until now though. I have done plenty of track days at Snetterton before but never had this problem, but I have never used, up until now, anything more than the standard calipers on the bike, Goldlines 65mm. Any suggestions as to what this might be gratefully accepted and I wonder if anyone else has ever suffered the same problem. The pads I think are Goldfren but they came with the calipers and were brand new and they have not worn much at all. I just find it strange to have suffered the problem after so few laps, it seems to be a fluid boiling problem as the brakes would sometimes pick up a bit in between some corners when they had cooled a bit.
Raced with P4s and they were never anything other than great. Didnt matter how hard or long I was out there. But race pads fitted, £100+ a set, braided lines and 5.1 fluid. Have noticed n my 848 I get a little fade twoards the end of a session with pretty much the same set up other than radial monoblocks, but only if I have the lever set for feel rather than bite (ie closer to the bar) Reckon combination of pads and fluid
Fluid or air in the system would be my first guess, you're replacing the fluid so hopefully killing two birds with one stone. What's the M/C? Does that have a bleed nipple on it? Maybe some air getting trapped in there.
The master cylinder is the stock 748R item and the whole set up feels very positive with good feel normally, the brakes are very good and worth the upgrade but the fade took me a bit by surprise. I could feel the brakes fading after a few laps and then they would just go completely. I have full braided lines on the front with individual lines to each caliper.
If its all bled properly then it has to be the fluid . Dot 4 is probably the better long term oil Dot 5 , I am led to believe , will soak up moisture quicker and need replacing earlier . That is what I think is your problem now , contaminated oil , It sounds like it is getting hot very quickly and, once hot, oil contaminated with moisture will fade badly .
No that is all good, the fluid is quite new also but it may have soaked up air in the container. At the moment I seem to be looking at fluid that has gone "off" I reckon.
Once you have opened a container of brake fluid it becomes hydroscopic,meaning it will absorb moisture which is why it will go off after a good few weeks or thereabouts.
Michel.....You mean hygroscopic.......... ........you definitely cannot use brake fluid to look at underwater objects 'cos it bl**dy stings when you get it in your eye, as I found out when a plastic container squirted some at me :wink: AL
Word of warning,I did fail my English O level,mind you I failed everything else too,except French lol.
The rotors are alloy and the discs are stainless 996 Keyhole style. I feel, as I suspected, that it's a brake fluid problem. I just wondered as the calipers have more alloy in them, if you follow that, that they are retaining more heat somehow and causing the fluid to reach a higher temperature, hence boiling in this case. I have checked free run etc so there is no brake disc or caliper problem that I can see and no binding anywhere. In fact it all runs very smoothly.
One thing doesn't seem mentioned are the brake lines,how old are they?any bulges?could they be expanding when the system gets hot?
at the risk of getting shot down I would think it was more a mis-match between the pads and the brake discs (as Brian hinted at) and particularly the brake pads rather than a fluid problem as I imagine it's pretty new and you said is Dot 4. A clue might be that you said pads have hardly worn but after roughly how many track miles?. If they are a particularly hard compound and need lots of warming up even in this weather then it could be they would be better suited to cast iron discs. Do your discs now have a heavily glazed and/or a light 'golden' tint to them now?
Noticed my Evo fades a little last couple of track days, and wasn't before, so think dot 5 needs changing...my moneys on the fluid ;-)
could well be ^ and it's by far the easier of the two to cross off the list. How much money bradders?
The OP says he thinks the pads are Goldfren..........IMO, I think the most sensible thing to do is establish exactly what type of pads are fitted....... .............like other manufacturers, Goldfren have a variety of compounds and I wouldn't mind betting what the OP is experiencing is because the pads are sh*tty road-going compound or 'green' ones.......or even the carbon ones that need to get very hot to work properly, which can boil the ordinary fluid. My race experience with Ferodo and EBC threw up many surprises...........a Ferodo top race compound failed miserably........they wouldn't even get a half decent grip and standard EBC were loads better. Yet we put road going Ferodo in and they equalled the EBC performance.........In the end we went over to sintered EBC, because we needed serious grab (unlike solos)........at the start of a race, the grab was too much, but once they got hot the grab eased off, but never actually faded. AL
Fade is caused by gas given off by an overheating pad forming a friction free barrier between pad and disc requiring ever more pedal or lever effort. This will quickly overheat the system and boil the fluid. As said above, pad spec is probably wrong for your usage but you will need to renew fluid anyway after it has overheated and from a new container. Under normal conditions without, a spongy pedal / lever is either air in the system, soft lines that expand under braking effort or a combo of both. Personally, I would not change spec of fluid unless all else has been tried/rectified hope this helps
