My local track is Very Very Very hard on the brakes and creates brake fade on almost every car during the day.
It was my own fault for not bleeding the brakes after the last session (3x20 min sessions) but this last lapping day I could feel my brakes started to go spongy on the 14th lap of the 3rd session... I did slow the pace down but even so the 15th lap I lost front brakes... Rears musta slightly locked and the back end came around. Luckily no harm no foul and I drove away after the spin but I got me to thinking.... Would it be unreasonable to bleed the brakes 1/2 way though the day? I'm using rbf600 brake fluid.
Wow, I never had any issues like that. Do you have the floating rotors in the front?
@meatman - G'day Josh. Like Charley - I've never heard of anyone having issues like that, and certainly not to the extent that requires any bleeding to be done in the middle of a race event. These things are raced pretty hard all over the world, and in huge numbers too, so surely if this were common we would have heard....?
Another question to try and help understand what's going on - when you bleed the brakes in between events, do you mean to completely change the fluid in the circuits, or are you just talking about making sure there is no entrained air, etc?
I completely change my brake fluids after every second or third event (I only do 4 per year, so it's more based on time, about 6 months in the car), and while I'm at it I change the clutch fluid once a year. (every second brake fluid change)
I don't bleed my brakes at all in between that, unless I feel they have got a bit soft under my foot...
Hope this helps.
I'm using rbf600 brake fluid.
The spec from the owner's manual is Motul RBF 660. I would use that, starting with a full flush. The lifing schedule on master cylinder is 8000 km.
If your foot is sinking to the floor, I would replace components that have reached end of life and carefully inspect the whole system. There is no component lifing for brake lines, but they can and do fail. If your components are older than 8k km, I would probably just replace the front brake lines and master cylinders all around.
Wow, I never had any issues like that. Do you have the floating rotors in the front?
No, I have the fixed smaller brakes.
@meatman - G'day Josh. Like Charley - I've never heard of anyone having issues like that, and certainly not to the extent that requires any bleeding to be done in the middle of a race event. These things are raced pretty hard all over the world, and in huge numbers too, so surely if this were common we would have heard....?
Another question to try and help understand what's going on - when you bleed the brakes in between events, do you mean to completely change the fluid in the circuits, or are you just talking about making sure there is no entrained air, etc?
I completely change my brake fluids after every second or third event (I only do 4 per year, so it's more based on time, about 6 months in the car), and while I'm at it I change the clutch fluid once a year. (every second brake fluid change)
I don't bleed my brakes at all in between that, unless I feel they have got a bit soft under my foot...
Hope this helps.
To be clear, I have not actyually bled my brakes during sessions, only in between events. My local track, I cannot express how hard on the braking system this track is. Every car whether its a converted road car or full on race car (Stohr, radical etc) you will experiance degrading braking performance. Its that hard.... 200km/h ---> 40... 150 --->40 145 ---> 30 150 ---> 60 all on a 2.25 km (1.32 mile) long track.
If your foot is sinking to the floor, I would replace components that have reached end of life and carefully inspect the whole system. There is no component lifing for brake lines, but they can and do fail. If your components are older than 8k km, I would probably just replace the front brake lines and master cylinders all around.
I only let it happen the once so IIRC the pedal went soft, not to the floor...
Another question to try and help understand what's going on - when you bleed the brakes in between events, do you mean to completely change the fluid in the circuits, or are you just talking about making sure there is no entrained air, etc?
Only bleeding out the fluid in the caliper.
I would replace components that have reached end of life and carefully inspect the whole system. There is no component lifing for brake lines, but they can and do fail. If your components are older than 8k km, I would probably just replace the front brake lines and master cylinders all around.
I have replaced both brake master cylinders since owning the car.
Another question to try and help understand what's going on - when you bleed the brakes in between events, do you mean to completely change the fluid in the circuits, or are you just talking about making sure there is no entrained air, etc?
Only bleeding out the fluid in the caliper.
I think it would definitely be worth doing a full replacement then. I'm normally able to do it with a standard 500ml container of fluid (I use Motul RBF660) as long as you don't "overbleed" any one caliper. It's easier with 2 of these containers, and you'll need 2 if you are also doing the clutch slave cylinder at the same time.
As you know the front and rear brake circuits are completely separate, but with a longer feed line to the rear before it tees off to reach each caliper...
The first thing to do is to suck out as much of the old fluid as you can from the master cylinder reservoirs with a syringe. This makes sure you are minimising the chance of any contamination with old/new fluid. I then use a vacuum bleeder (mainly because I'm normally on my own) and aim to use about 100ml per side on the fronts and 150ml on the first rear caliper (to replace all the fluid in the long line plus bleed that caliper) and use another 100ml on the final rear caliper.
That should leave a small amount (~50ml) for a final 'pressure bleed' (with someone in the car) on all the calipers.
I only let it happen the once so IIRC the pedal went soft, not to the floor...
That is what I meant. I mispoke. If the pedal went all the way to the floor you would have little or no braking.
I was at the track last weekend with my spec racer ford. I had a similar experience as you; on the test day, second session, my brakes began to fade late in the session to the extent that I tried to slow for a corner behind another SRF3, and I unintentially passed him in the brake zone. It surprised me and the other driver.
After allowing the car to cool for about an hour, I hopped back in and depressed the brake pedal and it sunk down further than normal and had a spongy feeling. The crew bled the brakes, and then the pedal was stiff again and did not sink down as far. After that, the car was good for the rest of the day and for the next two race days.
So to answer your original question -- should you bleed your brakes between sessions? In my experience, yes if and when they begin to feel soft. I have had to do this with my Radical as well, mostly after neglecting to bleed the brakes before an event.
I use Castrol SRF and typically only bleed brakes when I change pads (2-3 times a year) and/or rotors.
It must be good stuff. When you do bleed, do you notice any tiny bubbles? For Radical, I have always used the Motul RBF 660. I always see two to four tiny bubbles when I bleed the brakes which is between events and at events if needed.
I have thought about using RBF 600 and bleeding more frequently because I hate using half a bottle of the 660 and letting it sit.
Wow, I never had any issues like that. Do you have the floating rotors in the front?
No, I have the fixed smaller brakes.
If you spend a lot of time on tracks that are very hard on brakes you might want to consider changing the front brakes (or F & B) to the 280mm floating rotors. To do this requires new, calipers, disks, ells, and hardware to Mount the disks to the bells. If you are not racing in the Radical cup I can get you after-market floating disks for ~50% of the cost of the Radical disks.
@davidf I rarely bleed just to pull air out of the calipers, so I don't really know. When I do bleed, I drain the master cylinders, and put in all new fresh fluid. I use a Motive Power pressure bleeder, and do it without pumping pedals. SRF has a higher wet boiling point than most racing fluid's dry boiling point, which is why you don't need to bleed as often. It's expensive though.
I have thought about using RBF 600 and bleeding more frequently because I hate using half a bottle of the 660 and letting it sit.
That is also my main reason. Dont use it you lose it.
Since we are on the subject of brakes.... Pads.... What's a good source for pads that is not a dealer?
