67 Brake Fluid help

[Ara G.]

Hi all,
I am replacing my master cylinder this weekend with a correct 509 redone by WhitePost. I removed the black paint from the machined areas by the brake lines, as well as removed the paint from the front DC pad.
However, is there a way to tell what kind of brake fluid my car has in it currently? I obviously want to fill the system when I bleed it with the same type of fluid that's in there now, but I do not know how to tell the difference between Dot 3,4,5..
I am not sure if one type is compatible with another type (meaning adding DOT 5 to my system that already has DOT 4 in it for example). I just don't want to screw it up (as I'm good at) so any advice is always appreciated.
Thanks in advance!!!
ARA

[Joe R.]

Re: 67 Brake Fluid help

Hi all,
I am replacing my master cylinder this weekend with a correct 509 redone by WhitePost. I removed the black paint from the machined areas by the brake lines, as well as removed the paint from the front DC pad.
However, is there a way to tell what kind of brake fluid my car has in it currently? I obviously want to fill the system when I bleed it with the same type of fluid that's in there now, but I do not know how to tell the difference between Dot 3,4,5..
I am not sure if one type is compatible with another type (meaning adding DOT 5 to my system that already has DOT 4 in it for example). I just don't want to screw it up (as I'm good at) so any advice is always appreciated.
Thanks in advance!!!
ARA

Ara,

I'm planning to go the Dot 5 (silicone) route since it doesn't absorb water and doesn't absorb paint. But you must flush all Dot 3 / Dot 4 fluid out of your system. Check out this thread:

https://www.forums.ncrs.org/showthre...=2667&uid=3500

Joe

[Michael J.]

Re: 67 Brake Fluid help

Here's a thread about IDing the brake fluid I started when I had the same question:
https://www.forums.ncrs.org/showthre...75461&uid=5640

[Larry M.]

Re: 67 Brake Fluid help

Ara:

This question has been asked many times before, so the answers are in the archives. Joe Lucia provided an excellent writeup on this subject about 6 months or so ago.

However, the short answer is this: drain a little of the fluid from one of the brake calipers. Mix it with new DOT 3 or DOT 4. If they do not mix, but remain separate phases, then you have DOT 5 Silicon. If the mix together, then you have DOT 3 or DOT 4. These are similar, and most folks use DOT 4 even though their Owners Manual says use DOT 3. DOT 4 is a better fluid with a higher boiling point than most DOT 3. There are a few high performance DOT 3 brake fluids that approach DOT 4 performance. FORD MOTORCRAFT DOT 3 is one of these high performance ones. I have used it in other cars for many years when DOT 3 or DOT 4 was specified.

My 1967 Corvette has DOT 5 Silicone fluid, and I recommend it. But it requires a clean system or a lot of flushing to remove the older fluid.

Larry

[Michael F.]

Re: 67 Brake Fluid help

why do you recommend it? I have heard that it does not work well at altitude and does not compress very well resulting in spongy brakes???

[Larry M.]

Re: 67 Brake Fluid help

why do you recommend it? I have heard that it does not work well at altitude and does not compress very well resulting in spongy brakes???

I have not experienced this. There was a very good thread on this a few months ago......very thorough and detailed. Do a SEARCH for this info. Terry M, Joe L, and myself were part of this discussion, so you can also search on our names.

I have had my DOT 5 installed for 15 years without problems or corrosion issues. I finally changed it out a few months ago when I redid the trailing arms and had to bleed the brake system.

Larry

[Jim L.]

Re: 67 Brake Fluid help

I have heard that it does not work well at altitude and does not compress very well resulting in spongy brakes???

Utter nonsense. Any system filled with DOT5 that behaves like this wasn't filled and bled properly.

I've had DOT 5 fluid in my collector cars for nearly 30 years with no problems at all, even at elevations approaching 10000'. Both of our track cars use DOT5 (for its outstanding boiling point) with no problems.

Success with DOT5 fluid is all about technique.

Jim

[Steven S.]

Re: 67 Brake Fluid help

I'm in the DOT 5 camp as well, I was sold on it years ago when everyone was switching because of the moisture issue, but let me just say this... I'm hearing that many of the brake system rebuilders are not recommending dot 5 and some will not warranty their items if used with it. I know for a fact Apple will not warrant their work if using silicone and I believe that White Post is also opposed to it. I've also had a discussion with Ken McCormick from Lonestar and while at the time of our conversation it wouldn't affect his warranties, he wouldn't recommend it for long term use. Most of the reasons I'm hearing are related to the silicone affecting the seals over the long term. On the flipside Jim just attested to the fact that he has been using it for 3 decades without issue, so hopefully I have the same sucess because I sure don't feel like switching all mine back to Dot 3/4 either .

Steve

[Jim L.]

The proof is in the puffing(?)

You want to know how DOT5 fluid affects brake parts? Take a look at this wheel cylinder which, from new, had nothing but DOT5 for 20+ years.



For the curious, this is a replacement 1-1/8 front cylinder from my '60. I removed it in order to put a correctly sized 1-3/16" wheel cylinder back on.

Jim