Adding DOT 3&4 to DOT 4

Closed Thread Subscribe

Thread Tools

Search this Thread

Mar 1, 2008 | 08:49 AM

Potato

Thread Starter

Intermediate

Joined: Feb 2008

Posts: 29

Likes: 0

From:

Adding DOT 3&4 to DOT 4

I am replacing my front master cylinder. Just paint damage from a bad seal. I have DOT 4 in the lines now. I don't want to replace all the fluid and have to bleed the system.
I have a fresh bottle of DOT 3&4. Can I use it to top off the DOT 4?

Mar 1, 2008 | 09:36 AM

ratcat

Tourer

Joined: Feb 2008

Posts: 295

Likes: 0

From:

RE: Adding DOT 3&4 to DOT 4

Sure, it will work, but why don't you just get a fresh bottle of dot 4, and flush all the lines, front and rear. You will be surprised at the crap that comes out after a few years of use. And document this in your manual.
I have one bike with dot 4, and one with dot 5, and if I was to mix the two...it would turn to jello!! So play it safe,

Mar 1, 2008 | 11:01 AM

Da Gumpmeister

Ultimate HDF Member

Joined: Dec 2007

Posts: 8,642

Likes: 6

From: Forest Lake, Mn

RE: Adding DOT 3&4 to DOT 4

Quote:

ORIGINAL: ratcat

Sure, it will work, but why don't you just get a fresh bottle of dot 4, and flush all the lines, front and rear. You will be surprised at the crap that comes out after a few years of use. And document this in your manual.
I have one bike with dot 4, and one with dot 5, and if I was to mix the two...it would turn to jello!! So play it safe,

+1 +2 +3 If it has been more than 3 yrs since you flushed and changed your brake fliud, then go ahead and do it now. 2 issues. Both related to moisture absorbtion. Will cause corrosion in the system and it will lower the boiling point of the fluid. Once a bottle of 3 or 4 has been opened, it begins absorbing moisture, closed or not (seal is broken on top of bottle/can) Store it UPSIDE DOWN. Another thing to do is put saran wrap over the top B4 you screw the lid on, thne store upside down.They recommend changing every 2 yrs. Ditto on the 4 with 5. JELLO and ugly to clean up. Seen it more than once.

Mar 2, 2008 | 12:12 AM

bagman1

Grand HDF Member

Joined: Dec 2007

Posts: 4,999

Likes: 55

From: Bay Area

RE: Adding DOT 3&4 to DOT 4

First I ever heard of DOT 3 & 4 being compatible. 4 is silicone based and 3 is not.

Mar 2, 2008 | 12:54 AM

ratcat

Tourer

Joined: Feb 2008

Posts: 295

Likes: 0

From:

RE: Adding DOT 3&4 to DOT 4

Dot 5 is silicon based and will not hurt your paint, dot 5 will not obsorb water, but it has poor hydraulic abilitys, that is why 08's with ABS have dot 4.
Dot 4 is standerd in most hi-end cars with ABS.

A brake fluid that is 3 and 4 compatible is not a factory (HD) fluid.
Use at your own risk.