Bought an '03 RK and I was rebuilding master cylinders and calipers and all had globules of gelatin like material from the silicone brake fluid.....looked like partially dried silicone caulk. Does this happen because of age or something else? Anyone else seen this?
Thanks

 

Has happened many times because someone puts DOT 4 in a DOT 5 system they are not compatible.

 

What you have is a system that has had mixed 4/5 fluid in it as Big Money said....Completely clean and rebuild the master and calipers, get a new brake line set and use DOT 4 as it is a better fluid IMO. IF your master res cap says DOT 5 on it remove the sticker and somehow note the system is now DOT 4 if you go that route.

 

There is no reason to change away from DOT5, if that is the fluid your bike should have, I've been using it for well over 20 years with no reason to swap over. However strip and clean your master cylinders and calipers as suggested, as there is a risk of corrosion and damage inside, due to that awful stuff you found! If it says DOT5 on your master cylinder covers and service manual that is what I recommend you use.

 

Thanks for your input, y'all. Yes, I am familiar with the difference between DOT 3&4 and DOT 5 . I did not know that the result of mixing them would be the "gelling" of the silicone. I've had an '02 since new ( DOT 5 ), changed brake pads, flushed it several times and never a problem. One big benefit of the DOT 5 is that it doesn't mar the paint if you get it on it......more expensive, though.

I guess the previous owner couldn't read the info RIGHT ON THE MASTER CYLINDER COVER about the DOT 5.

 

Gaskets and seals for the two fluids are typically different material as well. Always stick with OEM specified brake fluid to avoid future problems.

 

I run dot 5 in everything.
Bill

 

Not true ... No adverse effects from using either fluid in any system as far as seals are concerned ( except ABS DOT 5 aerates in repetitive cycles ) as long as you clean the system thoroughly and flush with ( recommended ) denatured alcohol. However it is a good idea to stay with recommended fluid to avoid contamination ( mixing )during service performed by someone other than yourself

 

The borate esters in DOT 4 fluids can react with some seal materials differently than the silicone oil in DOT 5 fluid. Not all brake system elastomers are the same, depending upon bike manufacturer. Seal swell and hardness (durometer) can be impacted, depending upon the exact type of elastomer used in the seals. Because seal material can vary, it is still best to use the type recommended by the OEM. Just because you may not see an immediate change doesn't mean that long term durability won't be negatively impacted by swapping fluid types. In addition, the moisture absorbing characteristics of the two fluid types is vastly different, the silicone DOT 5 being less susceptible to moisture absorption.

Changing fluid type is just too much of a risk for a critical application like brakes. Best to play it safe and stay with DOT 5 (or whatever is recommended on the reservoir label) in my opinion. Not worth risking your life over a couple bucks saved moving from DOT 5 to DOT 4.

Perhaps some other forum members may have some input on relative swell and hardness changes in the HD elastomers when using the two different fluid types?

 

"borate esters", "elastomers", a meter to test the duro (hardness)...Quit it...you're driving crazy...........................JK

Btw, in regards to "swell and hardness"...i won't need a durometer...OUCH!

All kidding a side, "I hear ya brother". Interesting point...same material, good for each fluid, but then you introduce the other after being subjected to the previous...hmm, interesting.
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