Fizzy Duck Posted March 15 Report Share Posted March 15 Hi all Recently had the opportunity to do some higher speeds in my Boxster than you can legally on the road, and noticed that when braking, the pedal is going soft very quickly. After a single brake from 120 I had no braking performance until they had cooled (15-30 seconds). This is when braking from 120 MPH firmly, but certainly not an emergency stop. At the time of braking, there was a metallic squealing sound coming from (seemingly) front left. Stopped when stopped braking. Front left squeals when braking softly as well from any speed. Braking from 70 seems fine. Pads and discs aren’t old and aren’t near replacement. Brake fluid due soon (next week). Wondering if anyone has any pointers as to what it could be? I.e. any common issues on the 981 which could cause these symptoms? Thanks in advance 🙂 Quote Link to comment Share on other sites More sharing options...
Carmine Posted March 15 Report Share Posted March 15 If the pedal went soft then you have a hydraulic issue - quite possibly boiling brake fluid due to water content. If the pedal stayed firm then you have a pad/disk issue. If you have a dragging caliper then the brake at that corner could well have started off hot and subsequently overheated. In normal driving is one wheel noticeably warmer than on the opposite side? Quote Link to comment Share on other sites More sharing options...
Tony Daniel Posted March 15 Report Share Posted March 15 I run Motul RBF600 and will be trying the RBF660 this year. I was invited to a OPC trackday at Anglesey last year and was slowing repeatedly from 120mph. Brake pedal pressure was fine but standard pads were toast after the day. Quote Link to comment Share on other sites More sharing options...
Fizzy Duck Posted March 15 Author Report Share Posted March 15 Thanks both for your input, very much appreciated Its going in to Philip Raby on Monday - I’ll take a look at the brakes and have a chat with them about it. Quote Link to comment Share on other sites More sharing options...
ATM Posted March 15 Report Share Posted March 15 I've had a sticky caliper on a rubbish car several years ago. I did find it by feeling the wheels after a run to see which is hotter. That car fell apart if you did a couple of firm stops and started to judder under braking. It was one of the fronts which do most of the braking. So [I think] it would get hot and then not have a chance to cool down. Generally shopping cars have more opportunities to bind as they only have 1 piston and so the whole brake caliper needs to slide on both sides. If any of this gets full of gunk and then add potential for corrosion it can become less than ideal. Where as our Porsche cars have a caliper which stays fixed and pistons on both sides push the pad into the disc. It should be less likely to bind or get stuck but anything is possible. So I'm less likely to consider binding as a potential problem even though its possible obviously. I believe squealing can be fixed by lubing anywhere that pad meets caliper. Basically anything that can move except where pad meets disc. I don't know if rhe squealing and poor performance are necessarily related. Generally aggressive track pad compounds squeal more than safer simpler road pad compounds. Another possibility is the pads are just cheap rubbish, discs too. Do you know when they were last changed and by who? Another possibility is the pads were badly bedded in after a change. New pads need to bed in. If you are not savage enough at the bedding in process they can get glazing on the surface. If you have say fronts glazed or rears glazed then maybe only half the car is braking properly. Sometimes by removing the pads you can see if they are glazed but you need to know what you're looking at, from experience. If you do remove you can try roughing up the surface, refitting and bedding in more firmly to try to fix this. Finally if pads have been cooked - and I mean properly cooked - by some over doing it - maybe on track previously - then they just won't work well and need changing. Generally the brake fluid schedule on our cars is very safe and fluid shouldn't just go off quickly. If just using on road it will be fine. If using the brakes in anger say a lot on track then it needs changing more often. If you cook the fluid - and again I mean properly cook it - then it's finished and needs changing. It won't fail but it will deteriorate. Hope that helps. 2 Quote Link to comment Share on other sites More sharing options...
Fizzy Duck Posted March 15 Author Report Share Posted March 15 35 minutes ago, ATM said: Another possibility is the pads are just cheap rubbish, discs too. Do you know when they were last changed and by who? Can’t remember when, off the top of my head, but everything has been done by Porsche. The car wasn’t driven on track, was just a high speed run. To the best of my knowledge, the car hasn’t ever been tracked before. I’ll report back any findings I have 🙂 Quote Link to comment Share on other sites More sharing options...
greenman986s Posted March 15 Report Share Posted March 15 That's some high speed run if not on track .... Quote Link to comment Share on other sites More sharing options...
½cwt Posted March 15 Report Share Posted March 15 First time you get real heat into the pads they release all sorts of gasses giving a soft pedal whilst this clears over a few stops. If it continues then this is not the problem but it gets your attention when it happens. The bedding in for Mintex M1155 fast road pads used to be do ten stops from about 40mph. Pedal goes to the floor for stops 6, 7 and 8 and then come back for 9 and 10. You need a clear quiet bit of road to do it on and not to lose your nerve.... Also remember 100 down to 70 is the same energy to dissipate as 70 to dead stop. 120 to 100 is not much less than 70 to stop either. 3 Quote Link to comment Share on other sites More sharing options...
Fizzy Duck Posted March 15 Author Report Share Posted March 15 Spoke to Philip Raby today about it. They’re going to take it out on Monday, do a few high speed stops and then check the brakes with an IR camera to see if there’s anything dodgy going on. Tuesday it’s going in for a brake fluid change anyway. Quote Link to comment Share on other sites More sharing options...
SRobins Posted March 27 Report Share Posted March 27 Any update on your brake issue? Quote Link to comment Share on other sites More sharing options...
andygo Posted March 27 Report Share Posted March 27 55 minutes ago, SRobins said: Any update on your brake issue? Op is taking a break at the moment. Quote Link to comment Share on other sites More sharing options...
Tony Daniel Posted March 27 Report Share Posted March 27 12 minutes ago, andygo said: Op is taking a brake at the moment. Corrected for you😄 1 Quote Link to comment Share on other sites More sharing options...
Fizzy Duck Posted April 3 Author Report Share Posted April 3 (edited) Fluid change has helped but I haven’t yet had the chance to test properly. On the road the pedal feels firmer under load. Will update once I get the chance to do a higher speed run 🙂 Philip raby didn’t spot anything out the ordinary and it passed the 111 check Edited April 3 by Fizzy Duck Quote Link to comment Share on other sites More sharing options...
Patt Posted April 4 Report Share Posted April 4 I've used the Performance Friction bedding in process for any new brakes: Whilst bedding, brake applications should be consistent and using constant pedal effort, which is progressively increased throughout the procedure. 5 light snubs*, light pedal application: 50mph – 30mph 5 medium snubs, medium pedal application: 70mph – 40mph 3 hard snubs, hard pedal application (no ABS activation): 100+mph – 30mph** Cool down period – 5 mile run with very little brake (Do not sit at side of road with foot resting on brakes when hot, this is likely to damage the disc). Stop and examine discs – discs should show evidence of heat cycle (coloration in flange) and possess an even transfer layer of pad material on surfaces. Quote Link to comment Share on other sites More sharing options...
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