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Discussion Starter #1
hello all.

I just started basic ground level maintenance on My ST4 I picked up at the end of last season this week. I swapped in a new Motobatt AGM battery earlier in the week. yesterday I finally reinstalled the full fairing which had been off all winter with for a crack repair, cleaning and waxing. I also swapped out the tarnished fairing fasteners for new matt finished gold aluminum bolts...doesn't appear nearly as tacky as i thought it might and looks great with the red paint me thinks.

after reassembling everything I decided to go for an unplanned first of the season ride around town where my bike is stored for 10 minutes tops, just a quick shakedown run. after checking tire psi, oil, coolant, brake fluids levels i headed out. 10 minutes turned into over an hour riding back and forth from one end of the peninsula to the other...maine is awesome this time of year before the summer crowds hit.

Anyway, the one thing I forgot to check pre-ride was the clutch fluid level which ran dry while out and about. I forget I noticed it was low last season and oh well. this left me stuck on the side on the road with zero clutch. luckily I had just stopped at an interstection and already knew something was up. thankfully I was able able to pop it into neutral before losing the clutching ability entirely.

I was able to easily purge the air from the aftermarket slave cylinder with nothing but two hands and a 8mm socket which was all I had at the moment. that was after my buddy roadside delivered some DOT 3 brake fluid to me. DOT 3 was the best I could do at 6pm on a saturday evening in maine during a partially lifted C19 lockdown.

My question, is DOT 3 okay to sit in there for a week till I can cycle in some DOT 4 next weekend? I have heard of seals turning into jelly from using the wrong fluid. My bike is stored an 1.5 hours north of me otherwise I'd be swapping it out today.


Thanks
CJ
 

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Leave it. Dot3 is fine in the clutch.

Silicone brake fluid is the one you want to stay away from. Dot5. (Not to be confused with Dot5.1 which fine also. )


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You are ok to leave it in, as stated above: silicone based is the one that will screw it all up mixed with the old style stuff. Replacing all components one day? - hose, master, slave - sure, consider silicone as it has some advantages, but one of them is not finding it at a remote convenience store in an emergency
 

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Discussion Starter #5
I flushed 3/4 of a fresh liter can of pentosin super DOT 4 thru both brakes and the slave cylinders this past friday. I felt less guilty for using so much fluid on such a small hydraulic circuits after I popped open the last one, the front brakes reservoir and found thick brown goo. I wonder how long it takes to do that to brake fluid? anyway the front brakes felt fine before and a touch better now. yep, that reservoir condition matches the state of the air filter...amazingly the bike starts and runs great otherwise.
986064


986066
 

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I popped open the last one, the front brakes reservoir and found thick brown goo.
Part of the regulated requirements for DOT 5 silicone-base hydraulic fluid is that it be purple colored so as to stand apart from the more commonly used DOT 3, 4 or 5.1 brake fluids which are glycol-base. Apparently, someone previously added some DOT 5 fluid to a DOT 3/DOT 4 filled system or vice versa. When you mix silicone and glycol hydraulic fluids they coagulate and form a thick gunk.

So, flush the brake system thoroughly. It's also recommended by Brembo to replace all the rubber seals

This is what Brembo has to say:

BREMBO TECHNICAL NOTES

All Brembo braking products use natural-rubber base seals, and therefore are incompatible with DOT 5 silicone-based brake fluids. DOT 5 silicone-based fluids react with natural-rubber seals to swell them which can cause severe piston retraction problems.

There is no cure for problems caused by DOT 5 use other than complete seal replacement. Use only DOT 3 or 4 non-silicone type fluids … in your Brembo components.

(Yes, we know the cap on the Ducati rectangular master cylinders specifies “DOT 3–5 Fluids”, but please note: silicone-based DOT 5 fluids are not generally in use in Europe, but glycol-based DOT 5.1 fluids are. Hence, the DOT 5 cap designation.)
 

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I would bet the color and Goo is simply antique brake fluid that has not been changed in too long. I often find this in customers bikes that have never had a fluid flush and worse case it crystallizes and the crystals plug up the hydraulic ports so the fluid may not return causing safety issues. Simply flush everything through and be sure to clean out any sludge in the reservoir . you should be fine but on a bike like that I will flush it once or twice with clean fresh fluid. Running Dot 3 through is fine as a flush (as is using it) , expect a shorter life span than Dot 4 but it is certainly safe in the short term . it will be good to re-flush later with Dot 4 or 5.1 to help remove any build up that shakes loose with use.

If you use Dot 5 by mistake you may be okay if you flush it out pretty quickly but you need to understand what the mix does to rubber.
Dot 3 , 4 , 5.1 will expand rubber
mixing in Dot 5 will cause rubber to harden which may lead failures of any seal at the calipers or master. I have seen it mixed in and in cases where caught quickly and switched the system proved fine. If in doubt you would change seals which means new calipers and master cylinder is likely as Brembo does not offer rebuild kits for most modern masters. used ebay is a possibility but you will not know if it too has had Dot 5 any more than with a used motorcycle. Simply put there is no way to know so pay attention to the system and if you suspect you are having multiple hydraulic failures you may be changing them all to be safe. I would worry less on the clutch as it usually will not kill you with a failure but brakes.....
 
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