Brake Fluid

[fixxervi6]

So in another thread I said I "upgraded" to DOT 5, a few of you mentioned that it wasn't a good idea, googled backed this up so I had an oh shit moment.

Ran an entire bottle of DOT3/4 through the system and pulled a vacuum on it until the fluid ran clear. I plan on doing it again just to be triple sure, I read a few horror stories about putting DOT5 into a DOT4 system, one was the front caliper locked up due to the DOT5 causing the seals to swell.

So I continue to read up on DOT5 and it appears most modern DOT5 fluids now contain anti-swelling agents so that people don't pull a smart idea like me and destroy stuffs. But the big no no is mixing them.

Like I said, I'm going to pull a vacuum on the system again tho, flush a bunch more DOT4 through there before she is done, but I think it'll be ok.

[fixxervi6]

Yep just confirmed it with the brand I bought, you can use DOT5 in a DOT4 system as long as the DOT5 has the anti-swelling shit (mine does, thank god) without any issues as long as you flush the system and you don't mix.

Still going to buy a bottle of DOT4 and flush it all through again with a vacuum to make mega sure all that purple shit is out.

[U-Turn]

Well, you had good intentions.

[fixxervi6]

I talked to the manufacture

They said, DOT5 will work fine in DOT4 systems that are not ABS as long as you flush all the of the DOT4 out, but if you have ABS stick with DOT4 due to its higher vescocity.

If you run DOT5 he said you need to make sure you flush the system real good every year because all moisture/water will settle to the bottom of the caliper as the DOT5 doesn't absorb water at all.

He then said you can switch back and forth without any issues so long as you do a flush, told him I did a ran a full bottle of DOT4 through there with a vacuum and he said then your fine, DOT5 won't hurt the seals or anything like that.

Also, while it is true that DOT5 has a higher boiling point it is also more compressable so the brakes may feel a little spongy compared to DOT4, but in terms of "damage to the system" there isn't a problem, it won't hurt seals or anything like that.

[Striple]

The brake fluid issue quickly gets confusing if you think of it in terms of the DOT ratings. Its actually not that complicated if you think of it in terms of their bases - glycol vs. silicone. DOT 3, DOT 4, and DOT 5.1 (but not DOT 5) are glycol-based and largely compatible with each other's systems. Only DOT 5 (but not DOT 5.1) is silicone-based, and suffers from the usual drawbacks of silicone (i.e., it does not disperse water, no discoloration when water content is high, etc.) - hence the need for smaller fluid change intervals when using DOT 5.

The real issue is to avoid mixing a silicone-based fluid with a glycol-based fluid. The chemical reaction between the two produces a sludge in your brake system, which is obviously something that you'd want to avoid. Considering that you flushed your system very quickly after figuring out the problem, it seems very unlikely that you are going to encounter any issues.