Should I switch from DOT3 to DOT5??

[SLICKMAN]

I’m in the process of installing new calipers and I wanted to get some input regarding switching from DOT3 to DOT5? I was told that if you switch, you need to flush out the system first, is that true?…

 

[Vette/Berlina-coupe]

-dis or dot, --that is the question....

-the different grades may mix ok, but why not obtain max-advantage of the up-graded oil by purging the old, and in with the new; -you can go 345*f Synthetic (such as Valvoline-Synpower, which is definitely compatible with ordinary old-type 245*f brake-fluid), or 500*f/boiling-point Silicone (my preference, -NAPA always has in quarts, is popular with many gp-racers, --but ng for ABS-brakes owing to cavitation); --then opening one wheel-cyl. at a time, -just blast air through the lines, until only air comes out of each wheel-cyl. ... --then reconnect master-cyl. (having primed it with your new oil choice) and pump-in your new oil (caution: -pump slowly if using Silicone-oil as it has a higher viscousity-index, so will thus cavitate if agitated; ie: capture air-bubbles, which gives a soft-pedal); --however Silicone virtually eliminates future brake-cyl. corrosion (hence, no need for costly s/s cyl.-bores), and may be less prone to the C3's dreaded brake-cyl. air-pumping syndrome (check with C3 racing-experts on this). For the ultimate in hard-pedal feel, always install non-expanding s/s-braided brake/flex-lines. Moreover, if you have special stainless-steel rigid-lines, and s/s-bores in all five of the cylinders, then if you are not an aggressive driver, it wouldn't actually matter if your oil is hydroscopic (ie: water-absorbent, -like the old cheaper mineral-oil) type would it.... ~Bob vH
:TALK :dance

 

[JohnZ]

Re: -dis or dot, --that is the question....

-the different grades will mix ~Bob vH

No, DOT3 and DOT5 will NOT mix - they are totally non-miscible liquids (polyglycol and silicone). Some people get away with "blowing out the system", but the right way to do it is to disassemble the entire system (including the master cylinder and calipers), flush and clean everything with alcohol, lubricate the seals with DOT5, and put it all back together before (very gently) flushing and bleeding with DOT5.

Hardly worth all the hassle - polyglycol-based DOT3 and 4 fluid has been the industry standard for 75 years, and those systems will last forever if you flush/bleed them with fresh fluid once every two or three years.

 

[Cortez69er]

Do yourself a favor and don't do it. I did it 2 years ago and now I regret it, it is not worth the hassal. Silicone brake fluid is also 5 times as expensive and hard to find.
They also say that silicone is not recomended for high performance applications and gives the pedal a slightly less solid feel. My current thinking is that if none of the current new sports cars use it, why do I need it in mine?

 

[SLICKMAN]

Well, looks like I'm going to stick with the DOT3

 

[GW74]

I replaced the DOT 3 in my 74 last year. Here is my experience and my 2 cents.
Yes DOT 5 is more expensive and is now available from all the major supply houses as well as my local parts store. Because it is silicone based it does not absorb moisture. No moisture in the brake lines will ensure that they won't rot from the inside out. It will also keep the caliper sleeves in better condition which ensures a better seal and I have found that my pedal is firmer.
I pumped out the master cylinder and cleaned it with denatured alcohol. I refilled the master cylinder and bleed the lines following the Haynes Manual procedure. I used one of those vacuum pumps so it was a one man job. You will see the difference in the color of the fluid once the DOT 5 starts to come out the bleeders. I pumped plenty of new fluid through the lines to make sure all the DOT 3 was flushed out.
DOT 5 does have a lower boiling point so I wouldn't use it for racing but for helping preserve the brake system of my weekend joy ride I am very satisfied.

 

[offshore]

Ya there right dot 5 won't absorb water it just puddles in the calipers & lines and only ruines them in one spot much faster.

 

[offshore]

I replaced the DOT 3 in my 74 last year. Here is my experience and my 2 cents.
Yes DOT 5 is more expensive and is now available from all the major supply houses as well as my local parts store. Because it is silicone based it does not absorb moisture. No moisture in the brake lines will ensure that they won't rot from the inside out. It will also keep the caliper sleeves in better condition which ensures a better seal and I have found that my pedal is firmer.
I pumped out the master cylinder and cleaned it with denatured alcohol. I refilled the master cylinder and bleed the lines following the Haynes Manual procedure. I used one of those vacuum pumps so it was a one man job. You will see the difference in the color of the fluid once the DOT 5 starts to come out the bleeders. I pumped plenty of new fluid through the lines to make sure all the DOT 3 was flushed out.
DOT 5 does have a lower boiling point so I wouldn't use it for racing but for helping preserve the brake system of my weekend joy ride I am very satisfied.

dot5 has a higher boiling point and is great for racing.

 

[VETTEX2]

DOT 5.1 WILL work and won't hurt a thing.....DOT 5 WILL NOT MIX.....

 

[MaineShark]

Well, looks like I'm going to stick with the DOT3

Go with DOT4. It's fully compatible with any remaining DOT3 in your system, but with better properties.

Joe

 

[Gunther]

Hi Joe,


Pls clear you private msg box, it's full.
I would require your assistance for some private matter.

Thanks and rgds. Gunther

 

[Roy]

Do Not Use Dot 5 in Street Application

Dot 5 was developed for race track use where calipers get extremely hot. Racers chage the brake fluid after every race. The reason for the frequent DOT 5 brake fluid change is that it will not absorb moisture. That doesn't mean that moisture will not be drawn into the system with DOT 5 - it will. The same heating and cooling of the DOT 5 fluid will draw moisture in just like DOT 3 or DOT 4. The moisture that is drawn into the brake lines will settle at the lowest point - your calipers.

If you are willing to change your DOT 5 brake fluid every month - go for it! In street application you won't notice any difference except in your time and money. DOT 3 and DOT 4 brake fluid was designed to absorb moisture because it keeps the water loecules suspended so that you don't need to spend your weekends flusing your brake system.

 

[MaineShark]

Hi Joe,


Pls clear you private msg box, it's full.
I would require your assistance for some private matter.

Thanks and rgds. Gunther

Cleared...

Joe

 

[c4cruiser]

According to the GM Service manual for my 92, DOT5 fluid should not be used at all in ABS-equipped cars. Apparently the silicone fluid can cause cavitation in the ABS pump. I would think that the same warning would show up in C5 manuals.

There are a number of excellent DOT 3 and 4 fluids available for Vettes. I use the Ford HP Motorcraft fluid in my 87 autocross car and Castrol LMA for street use in my 92 Vert. Both are very reasonable priced and available.

I change the fluid in my 87 before each track day and after 4-5 autocross events.