Flushing for Dot 3 to Dot 5, what to use?

[torredcuda]

I put Dot 5 in my Barracuda when I biult it so it was basically an all new system and it works fine with no issues. I`m working on my `73 Satellite brakes and want to put in Dot 5 but it currently has Dot 3 in it so I want to flush it out. I see some say to use denatured alcohol and others advise agaisnt it, what should I use?

[JH27N0B]

I used to work at an aftermarket brake manufacturer and at some point I seem to recall being told alcohol could damage the rubber seals, so I would never use it to flush a brake system.  The subject has come up before and some have said they used alcohol and haven't had any problems, but my opinion is why take a chance.
Really it's not that critical of a deal that every trace of the old Dot 3 needs to be gone before adding Dot 5 or your brake system will start boiling or blow up or something due to the mixing. 
I'd just flush with Dot 5 until the fluid in the jar starts looking purple.  Though I did notice something unusual when I was putting Dot 5 in the virgin brake system of my Challenger I was restoring a while back, that when the fluid was coming out of the bleeders and into the jar, it really didn't look very purple when it came out even though it was purple going in, I have no idea why going through the empty system made it more brownish looking just minutes later?
It took a lot of work to bleed but in the end the brakes are fine and not spongy.  It is hard to get air bubbles out of DOT 5 so one tip is to work slowly, pour the fluid in the master cylinder gently and don't pump the pedal aggressively when trying to bleed, or else you'll froth up the fluid and it takes a while for the little bubbles to settle back out.
The biggest risk to the rubber used in brake systems is anything petroleum based. 

[Filthy Filbert]

Why is "anything petroleum based" bad for rubber?   most rubber products today are MADE from petroleum products...


you could open the bleeders, remove the lid from the master, and let it drip dry.  Maybe use compressed air to blow out the old, but...be careful of the spray. 

Or, as said, just pump it all through until purple comes out

[dodj]

Why do you like DOT5?
I thought DOT 4 has better brake performance - lower compressibility.

[Filthy Filbert]

Why do you like DOT5?
I thought DOT 4 has better brake performance - lower compressibility.

I believe 5 is the one that won't eat your paint if you spill it.  Also, I believe it's silicone based, has much higher boiling temps, and will not absorb water from humidity in the air.

[Banana]

I used DOT5........I know the brake performance is a bit spongy, but the brakes work...........impossible to 100% avoid not getting fluid on the paint somewhere/sometime (at least in my case)

[JH27N0B]

Why is "anything petroleum based" bad for rubber?   most rubber products today are MADE from petroleum products...

Brake seals and grommets are typically made of EPDM rubber, sometimes SBR rubber.  EPDM and SBR are not compatible with petroleum products, when they are exposed to petroleum it swells up and gets destroyed.  Never use grease or penetrating oil anywhere where it might contaminate the internals of your braking system or you will be sorry!
https://askinglot.com/is-epdm-oil-resistant
https://www.lavelle.com/materials/styrene-butadiene-rubber-sbr

[dodj]

Why do you like DOT5?
I thought DOT 4 has better brake performance - lower compressibility.

I believe 5 is the one that won't eat your paint if you spill it.  Also, I believe it's silicone based, has much higher boiling temps, and will not absorb water from humidity in the air.

Yes,  But the downside,  is your brakes aren't as good.

[FSHTAIL]

Why do you like DOT5?
I thought DOT 4 has better brake performance - lower compressibility.

I believe 5 is the one that won't eat your paint if you spill it.  Also, I believe it's silicone based, has much higher boiling temps, and will not absorb water from humidity in the air.

Yes,  But the downside,  is your brakes aren't as good.

Incorrect, my brakes are just as good as before with dot4...

[mk]

[/quote]

Incorrect, my brakes are just as good as before with dot4...
[/quote]

Yes same here.......  even works very well in my race car with absolutely no sponge at all.

[torredcuda]

Why do you like DOT5?
I thought DOT 4 has better brake performance - lower compressibility.

I used Dot 5 mainly because it doesn`t eat paint, higher boiling point for performance braking and it doesn`t adsorb water which is good when the car sits a lot ecspecially over the winter. Back in `95 I didn`t know much about Dot 4 and Dot 5 was reccomended.


I was going to just bleed out till the Dot 5 came thru but was worried about compatability but it doesn`t sound like that`s a big issue if thee is a tinay bit of Dot 3 left in the system?

[dodj]

Why do you like DOT5?
I thought DOT 4 has better brake performance - lower compressibility.

I believe 5 is the one that won't eat your paint if you spill it.  Also, I believe it's silicone based, has much higher boiling temps, and will not absorb water from humidity in the air.

Yes,  But the downside,  is your brakes aren't as good.

Incorrect, my brakes are just as good as before with dot4...

OK, maybe my info is out of date now. But a couple years ago I looked at dot5, but dot 4 outperformed it because dot 5 silicone fluid compresses more even straight out of the bottle than glycol. At the time I couldn't find any racing/tracking sites that reviewed brake fluid even having dot 5 in the list of best brake fluids. So I stuck with dot4. That, and lots of people saying if I leave even a single drop of glycol in my system when I change my brake fluid to dot5 my brakes will be screwed....

[Filthy Filbert]

DOT5 is not recommended for ABS systems; I think it has something to do with how it can be easily aerated--absorb lots of very tiny air bubbles, which makes bleeding difficult.   The rapid solenoid action of ABS cycling can cause this agitation and will decrease brake line pressures.   

Might be part of why some have said that the brakes don't work as well and felt spongy.

[resq302]

You also might want to check with whoever rebuilt your brake stuff as I know I've seen warnings on certain rebuild companies that they will not warranty the rebuild if DOT 5 is used.  Maybe due to the rubber make up of the parts they use ?

[JH27N0B]

This subject just got beat to death again on Moparts.
https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2984493/dot-5-silicone.html#Post2984493
Liquids aren't compressible, so if ones brake pedal is soft using DOT5, that is because it is not fully bled.  It's more work to bleed your brakes with DOT 5, if you aerate it, it takes time to get the bubbles out.  Work slow, pour carefully out of the container, push the pedal slow when bleeding, not vigorously, it takes time but eventually you'll get a hard pedal.