My brake system is all brand new minus the distribution block.
11.75" disks
E body front calipers
Willwood perportioning valve
B van lightweight master cylinder with MP firewall adapter
10" rear drums
Right Stuff lines everywhere

Which DOT fluid do I use?

there has been some real informative threads on this, you might see if you can retrieve em (I cant figure it out to save my a$$) & I would Google it, something will come up.

Dot 5 Silicone

X2

Dot five for me too.

Have only used DOT5 in all my Mopars for 20+ years now with no problems. Rockauto has the best price if you are ordering other stuff anyway.

Only way to go..

Dot 5 or face the possibility of damage to paint

Asked & answered (& unamimous!)

Perfect! That's what I was going to GUESS... But nothing like getting the dope from the Moparts faithful.
Thank you!

For what it's worth DOT 5 is not recommended for much of any racing application. It's boiling point is quite a bit lower than DOT 4...but for a classic car, avoiding the risk of substantial paint damage typically overcomes that recommendation.

I will likely use DOT 5, I doubt I'll have any issues with it while autocrossing.

If I may piggyback on this post, to change over to DOT 5 from DOT 3 would that just be a thorough bleed of the MC and lines? Another vote for 5, but 3 is in my car now.

Despite all the "OMG never mix them and any part that's ever had DOT X can never touch DOT Y fluid" that is sure to start now, they are fully compatible!

In fact if you're going from 5 (silicone) to 3 (glycol) fluid, any water that may have collected in the low spots (because it doesn't mix with the silicone fluid) will likely be absorbed and flushed out by the glycol (which is hygroscopic).

It's more important to get the system as dry as possible when going from 3/4 to 5, and for the opposite reason.

Edited for "compatible", not "miscible". The two fluids do not, in fact, mix except that the glycol fluid (or maybe the water suspended in it) leaches the purple dye out of the silicone fluid.

Since you are not using Willwood calipers DOT 5 is the way to go

Another word of caution: I have a Howe clutch pull-type slave cylinder and DOT 5 leaked past all the seals. I called Howe and they said "our seals are not compatible with it".

Would have been nice if the instruction sheet had said so! $19 for a rebuild kit, a cup and an o-ring. Then they had the nerve to charge me $14 shipping on something that fits in a $1 first class envelope. I flushed the master and line, put DOT 4 fluid in the clutch system and no problems since.

Still have DOT 5 in the brakes and no leaks anywhere.

My Willwood brakes are on their 2nd drag car. Same calipers I've used since the mid 80's. Always have had and still running Dot 5. Never an issue.
Doug

Dot 3 does a good job for me

Just me If you are sealed up now I would keep it as is. Charles thanks for the heads up on the slave cyl as I have one (not a Howe) but I will avoid dot 5. I likely would not have used it but now for sure I will avoid it (on that app for sure).

IMHO, if going to switch, change EVERYTHING. Just so nothing is contaminated, etc, etc,etc. Not to mention all of the headaches.

I switched to Dot 5 when I changed over to the 2-bolt MC.
As the guru (Ebooger), advised:

Flush with the Dot 5 till its only purple coming out and you're good to go, it's not overly critical, they can be mixed"

Mine has been solid for 3yrs now.

I use DOT 5 in my cars and even with Wilwood brakes on the front of my Demon. Never any problems.

Second that. I have dynalites on three cars with dot5 and they are excellent. We are switching to Cartel due to issues with the normal stuff we use getting lots of air.

Have had bad luck lately with the repop drum brake master cylinders and DOT 5 FYI.

Which brake fluid? One answer would be whichever you like. Seems like the all have their + and -.

DOT3 has great tolerance for water and is readily available and cost effective.

DOT4 has higher boiling point when it is dry but not so good wet.

DOT5 silicone does not attack paint if spilled and does not absorb water. The water just collects in the low spots. Heaven help if you do need to repaint where it has spilled however.

I drive mine "hot" time to time and run DOT4. I also change it pretty often to get the water out. I have also touched up the inner fender where the MC leaked and messed up the paint. No issues boiling the fluid.

They all work 99.9+% of the time.

I have been fighting with a new 15/16" disc brake master cylinder on our '67 300. I'm going to try a new master tomorrow after work. Very irritating lol.

Ding ding ding I do believe we have a winna.