Dot 5 Warning

L

laverdakeith

Hero member
  Got a nice old Jota on the bench just now the owner had rebuilt the brake systems with new seal kits, lines etc. and filled with Dot 5 Silicone fluid, I noticed that the master cylinders were slow to return so I stripped one for a look and the fluid has swelled the seals. So if you are rebuilding your brakes and are tempted by the benign niceties of Dot 5 I would advise against it as it seems the Brembo seals are incompatable with the fluid.

  Keith.
 
DOT5.1 synthetic is fine though and doesn't wreck your paint.
 
Isn't there a considerable price difference between DOT4 and DOT5? (the frugal Laverdisti will understand this ;))
 
Isn't there a considerable price difference between DOT4 and DOT5?
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Maybe, can't remember. The reason people may be tempted to use silicone is that it doesn't absorb moisture from the air and therefore can be left in the brake/clutch system for a very long time without deteriorating.  It's used a lot by the military who may have vehicles sitting around for months or years but then may be needed at short notice.

DOT5.1 is probably more expensive too, but as I said, doesn't wreck paint if you spill it.

Reggie
 
hi
i don't think there is anything wrong with dot4 fluid,we all know to be carefull with it as regards paint work,and its not really that much of a chore to replace it every two years is it?you don't get problems of air getting in if you are carefull and if you do it regularly you also get advance warning of impending internal rubber seal/hose deterioration,some thing you might not notice if you left the newer spec fluids in for longer which would inevitable happen,as is now happening in the newer diesels with longlife oil and 20,000 mile oil changes.which customers tend to ignore the bit that says 20,000 miles or annually which ever is sooner.Ive seen cars where the oil has not been changed for 4 years and the paper filter has been like brittle charcoal.you cant beat regular maintenance and inspection to catch problems before they become major faults
neale
 
I've using Valvoline "SynPower" synthetic Dot3+4 brake fluid, low moistener formula with a high boiling point.

Works well in the old machines. Here in the USA its on the self a most auto parts stores. Not very expensive too.
 
I use Castrol LMA, looks pretty similar to the Valvoline, DOT 3 & 4, high "wet" boiling point. It's vegetable based so you can have bunny-hugging "green" brake fluid (it's yellow, actually), also cheap, readily available (in US, anyway), and has the big advantage that it's actually blessed by Brembo. I was put onto it by a mate who has raced Ducatis with P08s, just like ours, for many years in BOTT/AHRMA successfully. He swears by it.
And it won't hurt paintwork.

Ken
 
Thanks Keith,

I've had some fun in the past with brake fluid. Front master cylinders stating only use DOT 4 and rears DOT5 etc.  :D They have to be joking, right?  :P

I normally use DOT 4 for everything. I don't mind changing it every year or two but I had one situation on my 500 Morini. The piston in the rear Grimeca master cylinder would stick and not release the full pressure on the caliper causing the brake to bind. I did a little research and found DOT 3 is glycol based. It needs to be changed more often as it is more hydroscopic but it is more slippery. I use DOT 3 in that brake now and problem solved.

If all else fails go backward in technology.  ;)

Rod
 
Yeh, had the same with my old SF2, Keith.  DOT 5 worked fine for a while; and then within 20 miles, the front master cylinder went from working to totally stuck. (The back was still ok).

Btw, this is a 'much argued about' topic amongst certain Ducrappi owners.  Some people seem to be able to use DOT 5 ok, others not;  but I'm pretty sure Brembo say don't use it, giving as reason the fact that their seals are natural rubber.  Curiously, however, it appears that the lubrication grease they provide is ... silicon-based.

But whatever  :).  Like you say: best to stick with DOT 4.  I'd rather have the minor chore of changing it every now and then than risk having no brakes.

Ciao

Craig

 
Just to add to the weight of evidence.... Yep, my front M/Cyl became stiff with DOT5 too. I say avoid, if using standard Brembo brake equipment. Hag.
 
It's my understanding that while Dot 5 doesn't absorb moisture it also doesn't exclude it. So anything drawn it from the atmosphere doesn't mix but settles in the low spots and causes corrosion. Dot 5 might be fine for garage queens that never get ridden and race stuff that gets frequent flushes but for use on the street,in weather, the Dot3,4 is best.
Rod, The info about the lubricity of Dot 3 is interesting. I beat on Honda cars for a living and there is a recall on some of the Oddysseys for a seal in the master cylinders wearing and leaking. The cause according to Honda is use of non Honda brake fluid which lacks the lubricity of the specified Dot 3 fliud. There are all sorts of ultra hi temp hi boiling point fluids out there but when you get down to it, most riders and many racers don't need any thing more than Dot 3.   
 
wdietz186 said:
Rod, The info about the lubricity of Dot 3 is interesting. I beat on Honda cars for a living and there is a recall on some of the Oddysseys for a seal in the master cylinders wearing and leaking. The cause according to Honda is use of non Honda brake fluid which lacks the lubricity of the specified Dot 3 fliud. There are all sorts of ultra hi temp hi boiling point fluids out there but when you get down to it, most riders and many racers don't need any thing more than Dot 3.    
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Thanks for the info on Honda using DOT 3. It seems to support what I read.

I noticed on the bench that the piston would bind in the M/C when I was assembling it with DOT 4. The return spring just wasn't strong enough to push the piston back when covered in the fluid but it would work when dry  ??? so I got on the net and did a bit of a Google and found some Tech Data Sheets.

From memory the DOT 4 was recommended to be changed every 2 years where DOT 3 was annually. Boiling point for DOT 3 was less too but I agree with you that a normal rider won't even get close to that in a normal road situation. There was no data on viscosity or friction ratings given but I did note that DOT 3 was Glycol based where DOT 4 isn't. I know that glycol is fairly slippery and as that is what I needed I bought a bottle to give it a try. The difference was immediate.  8)

Just my findings.

cheers

Rod
 
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