I have just fitted new brake pads all round. 10 km. drive without using the brakes and stopped to check for dragging to find all four at about body temp. Gentle brake application on way back then allowed them to cool for the rest of the trip home. Checked for temp again and at about body temp so definitely not dragging. Great.
Fluid level in reservoir about 4mm below full mark as normal but I noticed a small amount of fluid had been expelled from the vent onto the top of the cap. Not enough to run down the side but a bit unusual as I've never seen this before.
I then removed the rubber cap to clean it and check the vent. The level was now UP by about 6 mm.
Has anyone had any experience with something like this ? What can be happening to cause this ?

G'day Falcon, I've been reading your other thread about reversing the lines out of the master. I am just about to go from Rev1 brakes to Rev2 and braided lines. May have some questions for you on that.
  Re the observation of rising fluid level in the reservoir.  It has to be heat. Google has hits for this but usually with dragging brakes, which you've eliminated. So guessing now...perhaps the fluid does not cool at the same rate as the disk and caliper ??  Only other thing I can think of is that if the brake lines are touching the coolant hard pipes under the cabin ??

Also I assume you didn't arrive back home and stop by using the handbrake only ? Some other google hits were discussing fluid leaks at the track out the top of the reservoir due to piston knock back (worn wheel bearings, disc expansion,) but applying the pedal would push the pistons out again, so unlikely to be your cause.
 A friend mentioned the other day that a cause for warped discs is track days (high heat) and leaving the handbrake on when back in the pits. Sounds plausible, better to leave it in gear or chocked I guess...
 
 
 
 
 
 
 
 
 

I'm of the opinion that the fluid level rise had nothing to do with heat as there was bugger all heat generated. That little drive was very gentle with absolute minimal braking to check for binding/dragging brake.
There are no coolant hoses close to hydraulic lines.
Wheel bearings are all new and all discs are brand new. I 've had a dial indicator on both sides of each disc. There is no runout detectable.
At the track I always try to do several cool down laps and after I come into the pits the car gets rolled along to let the disc cool out evenly for ten minutes or so. I've never used the handbrake at track.
Because of the "G" loadings on track I never fill the reservoir to the full mark but instead leave it about 4mm below to prevent spillage. Has always worked fine.
I am pleased to report that after a couple of track days at Morgan Park to bed in some new pads and then the drive to Canberra of about 1600km. the brakes feel great and I've not detected any variation in fluid level.
At Wakefield Park I gave the brakes a bloody good workout straight up to get rid of any build up from the road trip.
With quite good rubber on the ground I drove harder than I have ever done before. Would often here a tyre chirp but not sure where but suspect it was from a front. So I think the bias is very close for my level of ability.
Did over 300km on track and then about 1700km back home and fluid level went down about 3mm. Just as I would expect. On track it was generating a significant amount of brake dust on all four just as I would expect.

Good news then, and another problem that will remain unexplained. 
300 Kms is a lot of track time !!  

Yeah I have lots of problems that remain unexplained.
I love track time. Not near as quick as the other blokes but I get to go farther. More bang for bucks ??
That was over the two days on track.
Were you at the Nationals or Wakefield ?

G'day Doug.
I remember at the Hobart Nationals at Baskerville, as I recollect you did 200 km on the one day without stopping for lunch.
 
Anyway, yesterday I was a bit bored with nothing to do, so did your test to check balanced braking F/R that you had described in the previous post on reversing brake lines. My car has the stock NA ABS brake lines and prop valve.
After disconnecting my ABS, I went to a deserted gravel road, chose a section with just the right amount of loose gravel for the test, and braked hard to a stop with careful pedal modulation. 
I was pleased to note an exactly equal mound pushed up in front of all 4 wheels, with the same result after repeating the test, so all good. It seems like a very practical way to verify F/R balance, so thanks for the idea.
 
 

Falcon, no I wasn't at Wakefield or Tassie.  I took my son to Wakefield a few months ago, for his first track experience.
Brakes are weak and wooden, hate the ABS (1990 SW20T import).
 & Redd,
that discussion about gravel piling up in front of the tyres...never heard of it before , wondering if it is a valid test of equal braking ? Seems like it could be....

Hi Ian.
The gravel surface test was to establish which brakes were biting first. Originally the fronts were hardly working at all. Now they all bite equally with minimal pedal effort. Very similar to my 1998 Bathurst but it has ABS so that has to be taken into account too.
This test does NOT prove anything to do with high speed or heavy braking.
Brake bias front to rear (Proportioning) under those conditions would be very different. Hence the built in pressure differential of the different proportioning valves used in different models of these cars.
I noticed that high speed heavy braking pulls the speed right down but it would finally lock the rears. But this was with AD08 tyres on the rear. They are not near as grippy as the Kumho V70A that was used at Wakefield Park.
I don't think I locked up the rears with the Kumho so spot on with the present brake bias.
Definitely had some tyres chirping under heavy braking but pretty sure it was the fronts.
Your brakes appear to be working just as they should. I would expect nothing other than that from you!!
And I thank you for all your helpful advice over the years.
I really did enjoy that day at Baskerville track. Bloody near ran out of fuel and just about buggered the rear tyres too.
Great track and anti clockwise to boot. Good company and lots of laps.

Slightly more than one dog.
Gravel piled up in front of tyres was thunk up an patented by me 50 odd years ago. Initially perfected on English motorcycles which tended to either not brake much at all or lock either or both at different pressures on different days. You could gauge the success or otherwise by the degree of bark knocked off hands, yellbows. knees etc.
They then invented twin self energising leading shoe fronts. New experience. More bits of skin torn off.
Learnt a lot. Sold motorbike.
Happy to discuss your upgrade to the later model brakes. As you can see I have lots of experience. Just not all of it that wonderful. Part of the adventure.