The Lotus Cars Community banner

1 - 20 of 22 Posts

·
Registered
Joined
·
139 Posts
Discussion Starter #1
Just want to throw out a brake question to all and hope someone may shed some light on a possible issue I had. Car is 2007 Exige. Brakes are stock rotors but with boe vented pistons and two piece rotors up front. Rear are stock calipers with ebc slotted rotors. I'm running Carbotech 10/12 pads. I have used this setup for over a year with great results. Fast forward to last weekend. I was at Palmer with NASA and the ambient temp was around 95. Track temp was 120-130 I'm sure. Anyway, first session no issues. Second session I was pushing pretty hard and just before entering turn 8 doing about 80 mph I hit brakes and pedal went nearly to the floor with virtually no braking. Spun out but luckily didn't hit anything?. I have had fade before but this didn't feel the same. Brakes came back and I ended up finishing the day with no more issues although I drove way mellow. I bleed after every track day and two days prior to this event I bled half a brand new bottle of Motul RBF600 through each caliper. When I was doing some mods over the winter I flipped the front calipers to bleed out any possible air as well. So i guessing due to high temps I may have boiled the fluid, but any other ideas???
 

·
Premium Member
Joined
·
11,687 Posts
How old was the b/f?

Last time bled?

Did pumping pedal help?
 

·
Registered
Joined
·
139 Posts
Discussion Starter #6
Fluid was flushed days prior to event and it was a brand new, unopened bottle. Didn't have time to pump them. Hard to explain but it was going into a tight , downhill corner and once I lost the pedal I was almost immediately in a spin. Hard to say because it happened so fast but I am guessing I had some braking because I stopped fairly quickly. It was just strange because the corner just before I went from about 100mph down to 40 and brakes were perfect. Came literally out of nowhere. I'll pull pads and report back
 

·
Registered
Joined
·
678 Posts
Did you disable your ABS (by pulling the fuse or a wheel speed sensor)? If not, I'm thinking ABS malfunction, because it sounds like "ice mode" but with a low pedal instead of a high pedal. The fact that the brakes were ok after it happened when you weren't pushing as hard is also consistent with an ABS malfunction (you stayed out of ABS), whereas boiled fluid would have stayed boiled (until bled out). You might try testing your ABS on the street (safely), but even if it tests ok, heat may have been a factor.

-Ed
 

·
Registered
Joined
·
4,869 Posts
Sounds like you just exceeded the temperature of the fluid, or had some residual moisture/contamination in the fluid. Like @jds62f asked, I'm wondering if you also overcooked the pads. If the pads don't look bad, then you probably had something contaminating the fluid.

Check your brake lines, and look for leaks as well, just to be safe!
 

·
Registered
Joined
·
86 Posts
I think you were right the first time - boiled brake fluid. "Ice mode" doesn't let the pedal go to the floor. I've experienced the same symptoms under high temps and hard braking, as well as it coming back after cooling down/going easier on the brakes in subsequent sessions. The fluid weeping around the bleeder screw is also an indication of this (I don't know how it gets out, but it does). And I'm pretty sure the act of boiling puts at least a little air back into your calipers, so bleed right after it happens. For next time, get one of the cheap IR pyrometers and check the caliper and rotor temperatures immediately after you come off the track.

Brake fluid ages by absorbing water from the atmosphere, and when it does, it's boiling point lowers. The best way to check water content is to get some of those test strips that you dip into the brake fluid reservoir. I know you've bled the brakes to the tune of half a bottle, but it wouldn't hurt to put the other half through. RBF600 turns from light yellowish to brown as it accumulates moisture, so when you flush the system, you want the fluid coming out of the bleeder to be just as light as the new fluid coming out of the bottle. Also, when you flip the caliper, you need to hold it as high as possible (ideally above the level of the ABS unit).

Beyond that, you've already put in SS pistons, which help slow the transfer of heat from the pads to the calipers, so the only other things you can do is put in brake ducting or brake less. I am the first to tell people that they are losing time by braking too early and too light at corner entry, but it's just as easy to brake too hard and scrub off too much speed. Only your data logger knows for sure...

Good luck.
 

·
He's on fire!
Joined
·
3,192 Posts
Agree it seems your problem is with the fluid not the pads.

We're all in different places when it comes to braking. I've moved from braking as hard and as late as possible to bringing my braking points back a little sooner, braking less and getting on the gas sooner. According to my logger, I'm losing time coming to the end of the straight braking sooner, but braking less and being able to get on the throttle earlier carries all the way through the next straight and often results in overall time gain, not to mention it feels like I'm upsetting the car less. I suppose eventually I will seesaw back the other way, but for now braking really late usually also means over braking (for me).
 

·
Registered
Joined
·
139 Posts
Discussion Starter #13
Yeah, boiled fluid was my guess too. I was talking to a track rat at Palmer that day and he also suggested venting as well. He was saying when it's that hot on track,even light cars will have issues without proper venting. Thanks for all the input. Guess it's time to bleed away?
 

·
Premium Member
Joined
·
11,687 Posts
This has solved lots of problems for ppl....

How to Bleed Brakes:


Note that many people disagree with my method, so judge for yourself.

Taught to me by semi-famous Toyota engineer, who built championship winning cars and bikes.

1. Get Sears brake bleed kit (canister, hoses, adaptors for bleed valves) and their hand vacuum pump. Kits there have both components. Inexpensive.

2. Pour a little b/f in canister, hook up hoses and use the tightest adaptor you can.

3. Pump vacuum to 20-25” with bleeder valve closed.

4. Tap caliper with small hammer or similar. This releases the air bubbles clinging to the caliper into the stream. WHATEVER method you use, DON’T skip this step.

5. Open bleed valve.

6. When vacuum is almost (but not completely) gone, close bleed valve.

7. Check level in master cylinder. Do this often.

8. Repeat as needed.

Benefits:

* I have never had to remove a caliper and turn it upside down, even after replacing all the brake lines.

*Never got a firmer pedal using any other method.

*Requires only one person. Your wife/so will thank us both.

*You will not be pushing the piston in m/c into the rough area normally unused, thereby not prematurely wearing that seal. (Clutch m/cs are always used to full range.)

Note: On my Elise, I needn’t even remove the wheels.

Yeah, yeah, people use pressure bleeders, but my racecar mechanic friends don’t like these.

Yeah, I know about speed bleeders.

The above is my opinion. No responsibility for screw ups, injuries, maiming or deaths.

Take it, leave it. OK with me.
---

Another pretty big benefit:

When changing brake fluid (annually for me, biannually for others), we want to get the fluid out quickly.

So, with the bleeder valve open, I just keep pumping the hand vacuum. All the old fluid comes out fast.

But, remember to check the m/c level often.
 

·
Registered
Joined
·
139 Posts
Discussion Starter #15
I think you were right the first time - boiled brake fluid. "Ice mode" doesn't let the pedal go to the floor. I've experienced the same symptoms under high temps and hard braking, as well as it coming back after cooling down/going easier on the brakes in subsequent sessions. The fluid weeping around the bleeder screw is also an indication of this (I don't know how it gets out, but it does). And I'm pretty sure the act of boiling puts at least a little air back into your calipers, so bleed right after it happens. For next time, get one of the cheap IR pyrometers and check the caliper and rotor temperatures immediately after you come off the track.

Brake fluid ages by absorbing water from the atmosphere, and when it does, it's boiling point lowers. The best way to check water content is to get some of those test strips that you dip into the brake fluid reservoir. I know you've bled the brakes to the tune of half a bottle, but it wouldn't hurt to put the other half through. RBF600 turns from light yellowish to brown as it accumulates moisture, so when you flush the system, you want the fluid coming out of the bleeder to be just as light as the new fluid coming out of the bottle. Also, when you flip the caliper, you need to hold it as high as possible (ideally above the level of the ABS unit).

Beyond that, you've already put in SS pistons, which help slow the transfer of heat from the pads to the calipers, so the only other things you can do is put in brake ducting or brake less. I am the first to tell people that they are losing time by braking too early and too light at corner entry, but it's just as easy to brake too hard and scrub off too much speed. Only your data logger knows for sure...

Good luck.
I appreciate the advice, and actually one thing you said reminded me of something I forgot to mention. As you noticed in the above pic of the rotor , it appears some brake fluid ran down the side of the caliper. The day that I bled them, I finished up and for whatever reason didn't put the wheels back on. Figured I do it the next day. So next day I go to put wheels back on, and on the same caliper pictured above, there was a small bead of brake fluid right on top of the bleed screw. I checked it and it was fully tightened and I know I cleaned the caliper of any residual fluid after I finished. So I read what you said about fluid escaping if I did boil the fluid on track, but is it possible the bleed screw isn't sealing properly??? Do these things wear out? I don't over torque them but considering how many times I've opened and closed them I wonder.
 

·
He's on fire!
Joined
·
3,192 Posts
Mine used to do that too. I've taken to tightening them with a torque wrench to be consistent. 160in/lb up front for me, no more leaks
 

·
Registered
Joined
·
86 Posts
We're all in different places when it comes to braking. I've moved from braking as hard and as late as possible to bringing my braking points back a little sooner, braking less and getting on the gas sooner. According to my logger, I'm losing time coming to the end of the straight braking sooner, but braking less and being able to get on the throttle earlier carries all the way through the next straight and often results in overall time gain, not to mention it feels like I'm upsetting the car less. I suppose eventually I will seesaw back the other way, but for now braking really late usually also means over braking (for me).
Sorry, all but the most committed are on summer break from driving out here in the Southwest as most of the race tracks are out in the desert (or near the desert); this time of year the brake fluid isn't the only thing that gets cooked. I need to take my mechanic's hat off and put my driver's hat (helmet?) back on:

As you correctly point out, you always want to optimize corner exit going onto a straight, especially the longer ones. This is what some call a "Type I" turn, and the launch out of the corner onto the straight is everything.

However, when coming into a tight turn at the end of a straight, especially one which does not immediately lead to another long straight, one of the options is to carry all that speed for just a little bit longer, turn the nose towards the apex, and then slam on the brakes (remembering to release them at turn-in).This is what some call a "Type II" turn.

As an example, one of the tracks we run in Southern California is the "roval" layout at AutoClub Speedway in Fontana, where you fun flat out down the front straight, carry as much speed as your right foot will let you through NASCAR Turns 1&2, floor it coming out of the banking down the back straight, and then slow way down (to around 40 mph) before diving left into the infield part of the course at Turn 3. You could easily be sailing down the back straight at over 130 mph, so for every tenth of a second you stay on the gas and don't coast or brake, you are closing huge amounts of distance and time on those who do coast and/or brake gradually before arcing into Turn 3.

As the left hand turn 3 is followed almost immediately by a right at Turn 4, the two make kind of a chicane, so even if you brake really deep before 3, as long as you gather it up through 3 and get the car pointed in the right direction for 4, you can make huge gains on those who enter slow and drive big lazy arcs through these two turns.



And yes, Turn 3 can be really hard on the brakes AND the oiling system. And it's where most all the carnage occurs in club races...

Anyway, back to the garage...:wink2:
 

·
Registered
Joined
·
570 Posts
I'm going to a track day in Fontana in 2 weeks, so this was very timely advice. Should be fun. It's the first time I'll have the Elise on track. I'm sure I'll come away with many things that need upgrading... Haha
 

·
Registered
Joined
·
86 Posts
If you're going to do the full roval (sometimes organizers just do the infield section), I would recommend installing a baffled oil pan (S111 GPan3 or BOE TOC) as not only cornering but also braking forces can cause oil starvation, usually with disastrous results (especially if you have sticky tires). Actually, you should do this no matter what track you go to. If you're going to go deep in the braking zones, you'll need track-oriented brake pads (I use Carbotech XP10s on the front and XP8s on the rear).

The big Fontana track will allow you to hit faster top speeds than most anywhere else in Southern California, and the highest cornering speeds through NASCAR 1 & 2 (if you are brave). A couple of tips particular to driving at high speeds on big banked ovals:

- If you have relatively low HP (say, below 240) and/or aero drag (starting with a splitter and wing roughly the size of an Exige), you will hit a pretty significant aero drag "wall" somewhere above 100 mph. There's nothing wrong with your car, that's just the way Lotus' are (with a fairly high Cd of around .45); only more hp or less drag will change that.

- You don't need to brake before NASCAR turn 1; many people lift just before turning in, and/or if you start in the middle lane, just turning down to a lower lane in the banking will scrub off speed. If you have some downforce and not that much hp, you should be able to get through without lifting much at all, but work your way up to it; if the car doesn't feel rock solid planted into and through the banked turns, don't push it (we're only doing this for fun, right?)

- Never suddenly lift on the banking unless someone is spinning/crashing right in front of you (but you knew that...). If you find yourself going through at a fairly high rpm, consider using the next higher gear -- this will reduce the amount of torque reaction at the rear wheels if you do need to lift. Smoothness is your friend.

- If you somehow find the tail coming around in the banking DON'T COUNTERSTEER. Keep the car pointed down the track towards the infield line and stay on the gas, and only back off on the throttle gently to regain rear grip if you broke traction by overcooking the gas to begin with. Countersteering on a high-speed banking is the surest way to hit the wall if your tires suddenly catch.

Here's an in-car video to help you visualize the track (not my best lines or fastest laps, but it shows a variety of "conditions"):

 
1 - 20 of 22 Posts
Top