DOT 3 vs. DOT 5

[Deleted User 72]

So, after four (4) pages, we just average the subject line? What did we learn? That brake fluid eats paint? If I had contributed anything I would feel used.

[Jean]

If we'd continued with "what makes things swell" we would have to go over to the Speakeasy.

[oldbmwmc]

So here's the plan. I will rebuild the master cylinder but first I will flush the system using a new can of DOT 3. After flushing the system really really well I will remove the MC then clean it with warm soapy water. After a thorough rinse and dry I'll repaint it with gloss black paint then hone the bore, blow it out with compressed air and reassemble, lubricating the new seal with DOT 3. After careful installation the reservoir will be filled with clean DOT 3 and the system will be bled with new DOT 3. An annual bleeding will then be part of the ritual...

[Zombie Master]

Edit, I thought it appropriate to point out that I can't see how things can be ruined, and swell at the same time.
Use Dot 4 and things will be swell.

I thought it was was DOT 5 that would make everything swell.

Incorrect Major:

[Zombie Master]

Am I wrong or could the mixing of dot 5 and "proper" stuff be catastrofical. Say if there's some leftovers of 5 in the system after a change and you fill up with 4 or 5.1..
Or is it the plain 5.0 that can ruin thiongs and make them swell?

I think Me109 would be the expert on this.

Ahem, thank you ZM.

I think the best way to resolve this issue is to look at it mathematically.
If we subtract Dot4 from Dot 5.1 we get 1.1. That's 1 (point)1. Not to be confused with Dot 1.1 because that was superseded by Dot 1.2 in 1922.
So with the resultant 1.1, we add that to Dot 3 because they are compatible, and we end up with Dot 4.1 which we can see is a full Dot below Dot 5.1 which could become very confusing.
So, we round down the Dot 4.1 to Dot 4 and keep an eye (or two) out for leaks.

Problem solved.

See what happens when you stay in school! Now everyone can understand

[ME 109]

Incorrect Major:

Incorrect ZM

Dorothy (Dot) is on the left.

[kutter]

Had a conversation with a HD rider (forgive me!)
He had added Dot 4 to his system (Dot 5)as he was unaware
of differences in brake fluids. He had to pull everything
apart and clean and flush as one fluid has coagulated
and jelled in the presence of the other. Otherwise
no damage done.

[Jean]

You get "jelly when you do THAT.
But if you put DOT 5 into the DOT 3-4 system, it can ruin the "rubber" parts.