Brake fluid vaporisation

[nbracken]

Yesterday I enjoyed a great track day at the Suzuka southern race circuit (it is next to the F1 track but is smaller and much more twisty). Weather was perfect and there were about 30 cars there, mostly Elise/Exige/Super Seven but with a smattering of Honda S2000, Porsche, other.

My Cobra (Unique Autocraft Python) with SBC and Jag running gear did incredibly well - way better than my expectations in terms of cornering and braking and I was really pleased. My lap times were comparable with the 7's and the Elise/Exiges.

During the third 15 minute session however my brakes suddenly deteriorated to the point where I had to stop the session. Basically pedal pressure dramatically reduced, I believe because the fluid had boiled or vaporised. Some of the Exiges had similar probs. Up to that point I had been really impressed with my brakes - the track had a grippy surface and my tyres (Toyo Proxis TS1) had warmed up and were really gripping well.

I run with the standard Jag set (ventilated discs on the front with inboard discs rear) but upgraded to include cross drilled discs at the front with EBC green pads.
I use Dot 5.0 silicone fluid (and have without probs for the past ten years) and which was last completely renewed 3 years ago.

I overcame the problem by letting the brakes cool down and then bled them and reused the bled fluid to top up (even though I didn't have the right gear with me, there was a workshop next door and the guys here were so incredibly helpful in what I have come to learn is the typical Japanese way, especially with foreigners.) This was enough to get a solid pedal back and to get me home (no one at the track had Dot 5.0 silicone of course and I had a three hours drive to do!) and today I will completely bleed with fresh fluid.

Questions: has anyone else experienced this and if so what do you recommend to address? I don't do track days regularly but would really like to make sure this doesn't happen again. I don't want to go to the expense of upgrading to racing calipers.

One thought I had was to make up some cooling ducts to run from the front air vents (just covered with mesh at the moment) to channel air to the calipers. Has anyone done this and if so ideas on parts sourcing would be good.

Thanks in advance for any insights or tips guys.

[neil still building it]

hi did you get any air out?are you sure the fade was to do with fluid boiling as before this the pads give up their best...to be on the safe side you would be best adding ducts with some way of shuting off for purely road use as you 'll need to get 'heat in' for them to operate well in 'normal' use this 'adjustable feature' is what F1 teams would like to use but are banned from doing so. it makes brakes operate within their oprating range...
hope this helps maybe
all the best
NEIL

[nbracken]

Neil thanks and yes we did get some air out of both front ( mostly) and rear (a little).

Regarding your suggestion on ducts and some kind of flap to close the vent, this is a good idea and one I may pursue. I found on the web today that Gerry Hawkridge (Hawk 289/427 fame) does sell some glass fibre ducts for this purpose as fitted to the original Cobras. I've sent him a note to find out the cost and availability.

I also found on one of the Jag websites that overheating of the inboard rear discs is common under heavy use (they get very little air circulating there) and several companies sell a vented disc conversion kit. This would be major work to fit them but as I am also thinking of changing my limited slip diff to a lower ratio one (2.88 at present and would like to change to 3.31) this is probably a task I'll do at the same time. A winter project I think.

[neil still building it]

hi nigel
also i'd recommend removing the pads ,scuffing up the discs with 40 grit paper(or as course as you're able to source)and do the same with the pads ,just enough to remove the glazed surface on the pads.this will help remove the over heated (glazed)surface and bring the pads /discs back to 'normal' sooner as the shiny coating won't bite like it should till you've worn thri=ough it .
NEIL

[Pictus]

hi nigel
i know this is sort of off topic you say you are using a 2:88 at the moment what gear box do you have in the car
also i noticed you are using green pads i was under the impression they were the street pads or was there no problem with the pads only the fluid

warren

[Grease Monkey]

Greenstuff pads are supposed to be a good road going compromise, or 'fast road' use as they're sometimes called. Better stopping than normal, less dust, less heat fade, but don't need to be glowing hot to work.

They also do red and yellow, but since these need to be really hot before they work at all, might be dangerous to use on a road car, especially on short trips. I guess if you wanted to go nuts on a circuit then drive home, you could swap pads to red when you arrive and back to green for the drive home. Bit tricky on the Jag rear end though!

[Cobra289]

Hi Nigel,

The guys from Nascar use a very cheap solution “Electrical FAN’s” I am thinking also to mount those things first to cool down my feet’s and second to cool down the brakes.

Those fans are from the marine type and you can have also water resistance.

They are from the firma Attwood and it will cost you +/- $25

Here you get a link: http://www.boatersland.com/blowers.html


Go to www.ebay.com and do a search for Nascar and you will find those FAN’s that are used for multiple purposes.

1)http://cgi.ebay.com/ebaymotors/ws/eB...966722342&rd=1

2)http://cgi.ebay.com/ebaymotors/ws/eB...966596153&rd=1

3)http://cgi.ebay.com/ebaymotors/ws/eB...966166045&rd=1

4)http://cgi.ebay.com/ebaymotors/ws/eB...966594448&rd=1

5)http://cgi.ebay.com/ebaymotors/ws/eB...966611161&rd=1

6)http://cgi.ebay.com/ebaymotors/ws/eB...966834404&rd=1

7)http://cgi.ebay.com/ebaymotors/ws/eB...966718102&rd=1

http://cgi.ebay.com/ebaymotors/ws/eB...966718417&rd=1



I think that those are good example of the use of the FAN’s



Best regards,

Cobra289

[nbracken]

Warren, I use Tremec TR3550 gearbox in my car. The problem was not with the pads but with the fluid vaporisation.

Cobra289, thanks for that suggestion. I will see if it is possible to install these fans in conjunction with the ducts that Gerry Hawridge sells.

Thanks for the feedback guys.

[Pictus]

that ok then about the pads as i have fitted them to my car and i would like to use it for the odd track day

Warren