Brake fluid coming out the top of the reservoir.

[amrbose14]

Today, I had to keep wiping off brake fluid from the top of my reservoir as it was leaking out. The brakes were unaffected by this. The problem disappeared once it started raining, which slowed my progress around Bedford Autodrome considerably. So it seems like it was a result of either enthusiastic braking or cornering.

Is this something other people have experienced? Is it fixed with a rubber new seal? I bled the brakes recently - which may have disturbed things a bit.

Other than that, a cracking day! Brought to a slightly untimely end by a Ginetta that managed to find a barrier to crash in to.

Chris

87 220T.

 

[robwright]

What brake fluid are you using mate? I have heard of DOT 3 or 4 boiling under race conditions. I imagine it would certainly expand somewhat if used lets say more than enthusiastically on the track[]

 

[amrbose14]

Dot 5.1. Halford's best!

Is is not possible that it's just swashing out round the bends? I didn't have any fade.

ORIGINAL: robwright

What brake fluid are you using mate? I have heard of DOT 3 or 4 boiling under race conditions. I imagine it would certainly expand somewhat if used lets say more than enthusiastically on the track[]

 

[robwright]

Hmm good stuff mate. You could be right with your theory lol.

 

[Riverside]

There should be a small plastic cup that sits under the reservoir cap to prevent surging - I guess yours is missing, they are easily forgotten when removed for topping up the brake fluid.

 

[Diver944]

The fuid does expand when it gets really hot so if you had the reservoir filled to the brim (or more) then it will squeeze out under pressure. It's certainly not normal on track though so you need to check out the cause

 

[amrbose14]

The cup is actually present. I'm sure this is just me being dumb... how does it work exactly?

The cup has little slots in the side about 2/3 of the way up - presumably to let fluid into the cup from the main reservoir. It also *looks* like there might be a very small hole right at the bottom. But no fluid drains out of this when I lift the cap up. Is there supposed to be a hole there? If so it may be blocked.

Currently the little cup rises slightly when I take the cap off, because there is a level difference between the reservoir and the cup (when the cup is pushed down). The fluid level in the main reservoir is just short of maximum, but not quite enough to dribble into the cup. Perhaps this level difference is causing some kind of problem?

I'm not sure any of this could cause the leak, but...

From memory I do not belive it looked like the fluid had expanded, and I was checking on numerous occassions immediately after coming in from a few laps. So my feeling is that was not the problem.

ORIGINAL: Riverside

There should be a small plastic cup that sits under the reservoir cap to prevent surging - I guess yours is missing, they are easily forgotten when removed for topping up the brake fluid.

 

[944Turbo]

ORIGINAL: amrbose14

Dot 5.1. Halford's best!

Is is not possible that it's just swashing out round the bends? I didn't have any fade.

ORIGINAL: robwright

What brake fluid are you using mate? I have heard of DOT 3 or 4 boiling under race conditions. I imagine it would certainly expand somewhat if used lets say more than enthusiastically on the track[]

At the ring with a fresh fill of 5.1 I had the fluid come out the cap as well, no fade on the pedal and put it down to the fluid expanding.

 

[robwright]

Don't forget mate there is only 200ml of fluid in the whole system. In a smal capacity expansion can account for quite a lot.

 

[amrbose14]

I thought there was litre? I think the Clarkes garage info says '1l for a full change'

ORIGINAL: robwright

Don't forget mate there is only 200ml of fluid in the whole system. In a smal capacity expansion can account for quite a lot.

 

[amrbose14]

Did you ever get it again (the leakage)?

If you're right then presumably the solution is simply to take a bit out. 1/2 way between max and min looks like plenty of margin. The fluid level looks unchanged as a result of the leakage, so I actually lost very little.

Admittedly I have become a recent covert to braking fairly late and hard (although I'm still a bit of a track pansy - I like to maximise the probabillity of driving home!). It seems to combat brake fade very effectively (as opposed to very gradual and drawn out braking). But maybe that's the cause of it.

ORIGINAL: 944Turbo

ORIGINAL: amrbose14

Dot 5.1. Halford's best!

Is is not possible that it's just swashing out round the bends? I didn't have any fade.

ORIGINAL: robwright

What brake fluid are you using mate? I have heard of DOT 3 or 4 boiling under race conditions. I imagine it would certainly expand somewhat if used lets say more than enthusiastically on the track[]

At the ring with a fresh fill of 5.1 I had the fluid come out the cap as well, no fade on the pedal and put it down to the fluid expanding.

 

[944Turbo]

Never had it again, but that was probably the last time I changed pads and fluid at the same time and went on track within few, mostly motorway miles. I don't tend to top it up between pad swaps as pad wear takes it from max to min approximately. It also coincided with my not too smart (for the brakes) how fast can I get before the gantry experiment.
Tony

 

[Hilux]

From memory I do not belive it looked like the fluid had expanded, and I was checking on numerous occassions immediately after coming in from a few laps. So my feeling is that was not the problem.

I personally have never ever encountered surge leaks but have experienced brake fade on track while using fresh ordinary fluid in a couple of cars but low boiling point fluid will expand with heat as will any water in it if its old so change it immediately and use a higher dry boiling point fluid such as ATE or SRF.

What was the fluid level when cold? What pads do you have on it? If they have a tendency to overheat (ie; are overstretched for their rating) or are on their limits then huge amounts of heat transfer to the piston and then to the fluid in the calipers.

 

[amrbose14]

Aha... so our common point is replacing the fluid recently (a month-ish for me), although I had not replaced the pads.

A couple of years ago I sacrificed what was to be (honest!) a monumental victory in a kart tournament (albeit just a stag do) experimenting (in my over-confidence at being a lap ahead) with late braking. I gather it was a moment of classic slapstick comedy to watch me bash my helmetted head against the steering wheel, as sat in the kart, itself atop the tyre barrier.

ORIGINAL: 944Turbo

Never had it again, but that was probably the last time I changed pads and fluid at the same time and went on track within few, mostly motorway miles. I don't tend to top it up between pad swaps as pad wear takes it from max to min approximately. It also coincided with my not too smart (for the brakes) how fast can I get before the gantry experiment.
Tony

 

[amrbose14]

The fluid is virtually new, and was almost at the max. The pads had not been recently changed. The fronts are about 1/2 way down (Green stuff) and the rears (standard pads) are almost on the wear indicators (which have not yet come on). From what you say the rears may be causing the problem - but then they don't really get very hot compared with the fronts. I didn't have any nasty brake smells all day, and was a good boy doing proper warm up and cool down laps.

I'm beginning to think that the fluid must have been lower before, given the partial and almost complete pad wear, and that I've caused the problem by topping up the reservoir after bleeding.

ORIGINAL: Hilux

From memory I do not belive it looked like the fluid had expanded, and I was checking on numerous occassions immediately after coming in from a few laps. So my feeling is that was not the problem.

I personally have never ever encountered surge leaks but have experienced brake fade on track while using fresh ordinary fluid in a couple of cars but low boiling point fluid will expand with heat as will any water in it if its old so change it immediately and use a higher dry boiling point fluid such as ATE or SRF.

What was the fluid level when cold? What pads do you have on it? If they have a tendency to overheat (ie; are overstretched for their rating) or are on their limits then huge amounts of heat transfer to the piston and then to the fluid in the calipers.

 

[944Turbo]

Being near the max with thinner pads will probably transfer more heat into the fluid increasing any expansion, seems from our experience dot 5.1 swells with heat. Still thats the only downside i have found. Thinking back mine went from max to being full and overflowing and the reservoir was full when hot. And I basically braked very hard for the gantry From around 150 iirc and got the brakes really hot and pulled into the parking area. Once it cooled - went for a drive around the area it dropped back down, so if you were doind a cooling down lap or two you might not have seen the level high.
Tony

 

[amrbose14]

What you suggest makes alot of sense. I'll syphon some off before the next event. In a way it's unfortunate that this year virtually all it will have done is drive to 3 tracks and back. It gives me very little time to assess any problems. Still... at least the sills will rust more slowly in the garage!

cheers,
Chris

ORIGINAL: 944Turbo

Being near the max with thinner pads will probably transfer more heat into the fluid increasing any expansion, seems from our experience dot 5.1 swells with heat. Still thats the only downside i have found. Thinking back mine went from max to being full and overflowing and the reservoir was full when hot. And I basically braked very hard for the gantry From around 150 iirc and got the brakes really hot and pulled into the parking area. Once it cooled - went for a drive around the area it dropped back down, so if you were doind a cooling down lap or two you might not have seen the level high.
Tony

 

[Hilux]

Green stuff...................

Theres your problem in my view.

I had fade with them on my 944T (not on the Westy or G27 Ginetta [lighter]) so went back to Textar for road and PF 97 on track with ATE fluid and no probs any more.

 

[edh]

+1 for PFC 97's [] you will be amazed at how late and hard you can brake ....

or Mintex 1155's for a slightly cheaper option.

 

[amrbose14]

Mmm... I gather PFC 97s are pretty expensive? I had Mintex pads (1144s??) in a previous life. They were pretty dire when cold.

I've not really had any fade. Otherwise I might agree. I know greenstuff are not highly thought of. I chose them as a fairly soft option. In my Ford history, hot pads=warped disks, which gets expensive. I thought... if you're getting fade, calm down boy! Maybe I should also apply that principle to overflowing fluid!

ATE fluid means compulsory regular changes right? What else? Doesn't it do nasty things to seals and stuff? I'm trying to avoid things becoming too serious!

ORIGINAL: edh

+1 for PFC 97's  []  you will be amazed at how late and hard you can brake ....

or Mintex 1155's for a slightly cheaper option.