Use of Dot 5 brake fluid

Started by martym00se72, May 06, 2019, 03:49:33 PM

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martym00se72

Hi All,
Just looking to see if there is anything stopping me from using Dot 5 high temp brake fluid in my 156 TS? At the track yesterday during the Peter Hall memorial 6 hour, towards the end of my 30 min stints, I found that I started to lose pedal as things got hot. I am running Hawk Black pads (and they are awesome on the track) on the front but I think they worked so well and got so hot that the fluid boiled eventually. It is/was fairly new fluid and I have every reason to think it was quality fluid, but I had to clean up the filler cap after the first couple of runs as it had overflowed...
'83 GTV6 - 3.0 is in! Ohhh yeah!
'99 156 T-spark - Formula 98 ready!

What do people do with their old 2.5...?

Citroënbender

That sounds pretty extreme. Sure there wasn't a little air trapped in the ABS bloc?

martym00se72

How do you diagnose that? The pedal was good to start with and stayed that way for the bulk of the time - Just progressively more travel as things got hotter. Should I just bleed the brakes with some Dot 4+ and see what happens?
'83 GTV6 - 3.0 is in! Ohhh yeah!
'99 156 T-spark - Formula 98 ready!

What do people do with their old 2.5...?

Citroënbender

#3
Glycol ester has a thermal expansion of well under 0.1%, if you take this as a main ingredient in your DOT4, you can work backwards, syringe-measuring the volume change between too full and where it was you started the race.

Say it's 20ml, if you take that as 0.1% of the system volume does it seem likely that you have 20/0.001 ml of fluid in your system?  :)


Edit for correctness of material specification and nomenclature.

bazzbazz

You can't use DOT 5 fluid as it is silicone based and not compatible with your system.

You can get RACING spec DOT 4 fluid with a much higher boiling point.
On The Spot Alfa
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Citroënbender

#5
5.1 is glycol based. 5.0 is silicone fluid.

martym00se72

Thanks guys. A fountain of knowledge as usual!
'83 GTV6 - 3.0 is in! Ohhh yeah!
'99 156 T-spark - Formula 98 ready!

What do people do with their old 2.5...?

Colin Edwards

#7
Motul 660, Martini RF700 or Castrol SRF brake fluid.  All Dot4 and compatible with the seals on your 156.  At more than $110 a bottle, the Castrol SRF isn't cheap!
Present
2023 Tonale Veloce
2018 Abarth 124 Spider
1987 75 3.0

Past
2020 Giulietta Veloce
2015 Giulietta QV
2009 159 3.2 Ti Q4
2012 Giulietta TCT Veloce
2006 147 Ti 2 door Selespeed
1979 Alfasud Ti 1.5

GTVeloce

I'm a fan of Penrite;
https://www.penriteoil.com.au/applications/motocycle/brake-clutch-fluids/racing-brake-fluid#/
It's very reasonably priced so I wouldn't hesitate to replace fluid before every event.
But make sure you aren't mixing silicone fluid (5.0) with non (5.1).

MD

I have experienced a crystalline deposition in components from using Penrite racing brake fluid. I raised this matter with the company as being a potential hazard from blockages but they dismissed my feedback. I have no such problems using Motul. Not cheap but it is the best.
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