420r Brake Reservoir leak

[CBuff]

Well after a year and 10 tracks days without incident it looks like I too have the brake reservoir issue.  On Sundays track day at nyst I noticed some fluid (brake) on the right rear wing.  The ppf did its job although it has left some evidence on that. The paint seemed to fair on.  There was about a 20% drop between the min and max line. 
 

seems like this is a common occurrence with hard track driving. Maybe I just wasn’t pushing hard enough thus far. 
 

in looking online.
https://www.caterhamlotus7.club/forums/topic/267797-leaking-brake-fluid-resovoir/

Seems like the ac race cape with bellows is the strong suggestion. But with this you lose the low level warning. I hate to lose this function but I check quite frequently and not sure I would even see a warning light in the middle of tracking it. The risk of paint damage is far greater than the warning light.  I have read about needing to remove the baffle and rubber seal as the bellows performs both functions 

https://caterhamparts.co.uk/master-cylinder/914-brake-master-cylinder-cap-race-no-float-switch.html

 

will likely get a brake reservoir sock for a belt and suspenders approach. 

question:  I assume the float switch is open unless the level drops thus closing the loop and triggering the light.  So leaving it disconnected (as the race cap doesn’t have the float). The light would remain off.  Might just shrink wrap it and zip tie it out of the way

Edited September 10 by CBuff

[MV8]

A brake master must allow air into the reservoir so fluid can flow out. Every master I have ever seen has a vented cap but a bellows has been added on most domestics since the sixties, extending service life of fluid by limiting exposure to air.

 

You can run a lower level or a bellows so it doesn't slosh out on hard cornering. Unplug the warning if you want.

Edited September 10 by MV8

[KnifeySpoony]

Fwiw i have the race cap and still dealing with leak issues on and off. 

[CBuff]

@MV8 I think the standard one is baffled but open to the outside. The race cap has an opening into the bellow chamber. I believe this keeps the inside and outside separated but can adjust for pressure with the bellows compressing. But I defer to smarter folks and once I get the race cap I can look.
 

@KnifeySpoonyThanks for the feedback.  Maybe race cap and motorcycle sock over.  This is the first time it’s happened. I was going pretty hard.  I saw your posts on blat chat regarding this.  Sorry to hear it’s still an issue.  Is it just a minor leak or do you have enough coming that it migrates to painted surfaces ?

[panamericano]

"Maybe I just wasn’t pushing hard enough thus far. "

 

Most part time drivers do not use the brakes nearly hard enough.  I was always easy no brakes, but with an excellent navigator decided to use the hell out of them.  Brakes are faster than engines.  So, I really used them hard on a down hill version of my favorite stage - Mil Cumbres (broken into 3 since down hill).  We totally busted out of our class but cracked a disc, so I figured that was hard enough.

[CBuff]

Josh at rmc just weighed in. He mentioned that the race caps can leak as well. @KnifeySpoony maybe that’s what you were alluding to.  
 

he said wrap and zip tie the standard cap.  

[slowdude]

Time for an upgrade to Wilwood? I look at opportunities like this for a tailored upgrade. 

Motorcycle sock over a master cylinder; I dont think i've seen that in use in practice. If the moto GP guys are doing it, I would. If not, idk what value other than catching the overflow.

[KnifeySpoony]

I keep a rag zip tied over the cap but intermittently still get some drips or misting in the engine bay. Never enough to get out onto paintwork. The brake fluid seems to have no affect on the black paint/powdercoat underhood. 

[sf4018]

Try bleeding the brakes and see if any bubbles come out, maybe the fluid is boiling. If so, check the specs for your brake fluid. The fluid I use has a boiling point of 310C for racing. If you have a handbrake check the rear pads for wear, that may be another reason for drop in fluid level, the standard rear pads wear super fast on track.

[CBuff]

@sf4018 copy. Will do.  I think this drop was definitely and a purge from the reservoir cap.  Which hasn’t happened this far.  But I was running hard which seems inline with others experience.  
 

I will likely zip tie a shop rag and maybe add the moto slave cover (basically a sweat wrist band). Might purchase the race cap which does still seem prone to this issue.  
 

I check it enough that I’m not worried about it dropping too much.  More worried about enough ejecting out freely that it mists out the bonnet and damages the paint.  I got lucky this time with the right rear wing taking the brunt of the hit and the ppf did its job. (Although the ppf now seems to have a spray pattern eaten into it).  Paint itself seems good. 

[CBuff]

So now I am perplexed.  I went to install the moto wrist band thing and planned on topping off the brake reservoir.  With the car now cold from sitting for a few days. The brake reservoir now shows full.  Like perfectly at the max line. 
 

this seems counter intuitive to me.  It was about half way between min and max at the track last weekend. I would think hot would be more full than cold. 
 

I am now questioning if I just kicked up some road yuck on the rear wing. And no brake fluid leaked.  

[11Budlite]

Could it be that brake fluid was sloshing around the reservoir/cap and drained down while it sat idle, or maybe it was overfilled a little to start? The reaction with the PPF seemed to indicate that it was brake fluid or similar. I'm not sure what road yuck was on track that day but I would think other cars would have been affected as well.

[CBuff]

The effect on the ppf def made me think it was brake fluid.  But when we checked that level was noticeable lower. Like mid way between min and max.  But when cold right at the max line. And that’s where it always has been.  Can’t imagine where that fluid went and then returned. Seems counterintuitive to be lower when hot. 
 

I put the wrist bad thing zip tied over the cap. Will keep an eye on it and see if that absorbs any fluid.