FLYNAVY30

I know that DOT5 and DOT3 fluids dont mix. If I wanted to completely flush the DOT5 from one of my projects (not the Vette), in order to replace it with DOT3, what's the best way to go about doing that? I have a motive pressure bleeder, so I can push from the master down, just not sure what the best agent to use in order to ensure a clean system before refilling with DOT3.

Thanks,
Greg

roadster65

Hi Greg - Hope this helps you out - Best Regards GV


.

Gavin65

Greg, my understanding has been to go from DOT 5 to DOT 3 you need to flush the system with denatured alcohol as well as replace the rubber seals, if the seals are not replaced there is a very good chance the DOT 3 will degrade them.

roadster65

apparently it's the cross contaminant mixing that affects the seals and rubbers - interesting, if you can understand the Texas drawl - GV

.

roadster65

These are two very good vids that explain the technical aspects and uses for the various brake fluid types - GV

Brian VH McHale

I know a guy that is addicted to drinking brake fluid but claims he can stop any time he wants to.

SWCDuke

The only way I recommend is to disassemble all hydraulic components, clean in denatured alcohol and assemble with DOT 5. Also flush all pipes and hoses with alcohol and thorough dry with compressed air. As you are aware, DOT 3/4 is not miscible with DOT 5, so there is no way to get it all out by flushing. I've just heard too many horror stories about trying to flush out DOT 3 with DOT 5 to recommend anything other than the above.

Duke

SoCalErv

Many people including myself have bought cars, thus not sure of the types of fluids that are present.

So how does one determine which brake fluid is in your car?

Gavin65

Dot 5 is silicone and is a bluish/purple in color, will not eat at the paint . Dot 3/4 is somewhat clear to dark brown/black in color, black/dark brown when contaminated and needing replacement. it will also eat the paint if spilled on it. When I rebuilt the brakes on my 65 I used Dot 5, the master was rebuilt as well as the calipers ( SS sleeved and O ringed), and I replaced all the hard lines/rubber hoses. this was 5 years ago and I have had no issues, peddle feel is a bit different, you need to get every bit of air out of the system as it does not compress as well as Dot 3.

RatDog

draw some fluid out of the master cylinder, put it in a jar with water, and shake it up. Let it sit for a few minutes. If there is an obvious separation between the water and the brake fluid, it’s DOT 5

Typically, DOT 5 is purple and DOT 3 is yellowish in color. But not always. In the pictures below, the jar on the right has DOT 5 mixed with water. The jar on the left is DOT 3 mixed with water. These samples were drawn from both wells of my master cylinder that ended up with DOT 5 and 3 mixed in one well (not by me). The result was a mess. When the lines were flushed, there was a slurry of brake fluid and dissolved seals.



Steve

FLYNAVY30

This is exactly why I want to revert back to DOT3.....I absolutely hate the pedal feel in my '72 C20 Suburban....spongy and not nearly as crisp...feels like the braking equivalent of over boosted power steering.

Powershift

The way I see it you have two choices regarding changing the fluid:

1. Buy about 3 quarts of DOT 3/4. Use a suction bulb and empty out the MC. Fill with new fluid. Hookup pressure bleeder and flush about 1 pint thru each caliper. Start and stop flow a few times to agitate the fluid a bit. Hit calipers with rubber mallet as well to get rid of any air or prior fluid. Let sit overnight. Then do another bleeding of everything, but using less fluid. Then take a drive and check things out. Be aware of reduced brake performance over the next few months.........just in case.

2. Rebuild or replace all four calipers and the MC and any brake switch with new brake rubber parts. Blow and flush out the lines..........first with low air pressure and then denatured alcohol, and then again with low psi air. Button the system up and bleed with the pressure bleeder. Take for a drive and check things out. FINISHED.

Make your choice and move on.

Larry

RatDog

Larry - I chose door #2 when my brakes ended up with the DOT 3 and 5 mix. More expensive than #1 but it guarantees you get all the fluid out.

Steve

Gavin65

Agreed, this would be my only option, Greg the feeling you get in your suburban is directly related to the weight of the vehicle compared to a corvette, not sure if you have 4 wheel discs on it or not. yes it requires a bit more peddle effort but the ability to stop with confidence is there.

Gavin65

why don't you give the Suburban another shot with the power bleeder and get every bit of air out that you can, it may make a big difference in pedal feel, but still a bit different then DOT 3

C.T.

Regarding color, over time 5 will change from purple to amber, but will not lessen its effectiveness. It can be confusing however if you're trying to determine whether you have 3/4, or 5, in a system you're unfamiliar with. Then the mix-with-water and shake test is helpful.

FLYNAVY30

When I rebuilt the entire brake system on the Suburban, I used a Baer 1 1/16" master, along with Wilwood's D52 4-piston calipers front and rear. I've bench bled the master, and pressure bled the system at 10 psi 4 different times now. My last step before flushing the entire thing and going back to DOT 3 is to verify the pressure I'm seeing at each caliper, which Ill do once I'm back in the states. I appreciate all the input on flushing the system!

roadster65

Greg - as an extra precaution, recheck the integrity of any seals and rubber components too - GV

ejboyd5

Not knowing the age of the DOT 5 fluid or when it was introduced to the 1972 brake system, there is no way to assess the condition of the original rubber parts, The only practical and cost effective solution to this problem is complete flushing of the system and replacement of all rubber components prior to filling with new fluid. Anything else would constitute a band-aid fix. By the way, why DOT 3, why not use DOT 4?

John BX NY

I converted my 67 from DOT3 to DOT 5 more than 20 years ago by flushing the system through a few times with DOT 5 with absolutely no issues whatsoever. Disassembly and denatured alcohol cleaning neither recommended nor required.
The SAE paper below confirms...