Leung

Hey guys,
can anyone tell me what I would have to do if I wanted to switch from DOT 3 to silicone DOT 5 brake fluid? Is it only flushing out the existing system with denatured alcohol? Is there anything else involved? TIA

mrvette

I did it years ago with a complete system rebuild of all the wet parts, and blasted the lines with carb cleaner, then a air jet....been fine since...15 years now....

but to just do it without complete overhaul/replacing all the soft parts....

I wouldn't try it....

guaranteed trouble....

jordan89

Why not just go to DOT4 or DOT5.1?

glen242

I throughly flushed with denatured alcohol, flushed again with DOT 5, and was good to go. Did this 5-6 years ago.

For bleeding, I replaced the standard bleeders with the type that use a check ball. For the life of me, I cannot remember the brand name.

I also, at this time, replaced the seals with 'O' ring pistons and new flex lines, all from Precision Engineering.

jimvette999

As mrvette stated, you should disasemble every component and remove the glycol based DOT 3 IMO. Don't forget the distribution block. I switched to DOT 5 years ago and have no regrets.... no more hygroscopic brake fluid for me.

Bee Jay

Don't do it. Go to Dot 4 synthetic instead. My brake performance with Dot 5 sucked.
Bee Jay

babbah

I installed Stainless Sleeved Calipers all round on my 67 Vette and used DOT5 in 1982. To date, I have never touched the system since and the brakes work perfectly and the pedal is very firm. The car stops on a dime! DOT5 is the way to go!

mds3013

At least for me this worked also. The dot 5 fluid surrounded the old fluid and removed it from the system without flushing with some other procedure. I used about 1.5qt. total to remove the old fluid. This was in '83. I just rebuilt the rear calipers last week and the SS bores were in perfect shape. I did the Boss'es '69 LTD to power drum with dot5 and it stops better than ever. More due to power than dot5 but I like the dot5. mike...

Curby

With 2 bleeders on each caliper, the rear can be relatively well flushed, but the fronts really can't.

I would suggest disassembling the calipers and getting rid of the old DOT3 fluid.

I sucessfully flushed the system on my Infiniti by running clear DOT4 fluid through it then ATE Super Blue DOT4 fluid through it. I could tell when the system was flushed by the color fo the fluid. I bet there is still some of the DOT3 fluid in the calipers.

glen242

In what way did your performance 'suck'?

Bee Jay

I used to be stationed at LA Air Force Base. Me and some friends would get up at 0 dark thirty and head up to the Angeles Crest freeway, a very high speed mountain pass. We had to get out there before the Rice Crotch Rockets did. After four or five hard corners my brakes would get spongy. Dot 5 silicone when it gets hot is very compressable. My brakes would be spongy till I bled them again. I couldn't figure it out till someone explained it to me. Once I replaced the Dot 5, another pain in the ***, the problem went away. I use Dot 4 synthetic now. After rebuilding and sleeving my factory brakes numerous times, I tossed them for my Wilwoods. Wildwoods, Hydroboost,and Dot 4 sythetic. I'm done with my brakes. Stop on a dime, chip change. Dot 5 is great for concourse cars that aren't driven hard, in my humble opinion.
Bee Jay

yellow 72

I chased a soft pedal problem for years with DOT 5...bled them a bazillion times using every method known to man. Finally got fed up, switched back to the conventional stuff and VIOLA! problem solved

Bee Jay

Yellow cars need extra good brakes cause they are faster.
Bee Jay

glen242

Strange.

Here are the DOT specs for brake fluid:

Lets look at what the DOT ratings mean. The table below shows the MINIMUM wet and dry boiling points for DOT 2, 3, 4, and 5 brake fluid in degrees fahrenheit.
DOT 2 DOT 3 DOT 4 DOT 5
Dry Boiling point 374 401 446 500
Wet boiling point 284 311 356

Do you think your fluid was boiling? Having to bleed seems to indicate air in the system.

I'm really confused.

Bee Jay

I don't think it was boiling, but getting damn hot. Then it would get spongy. Ask the racers why they don't use Dot 5. I've been told compressability. Maybe I have it wrong, but going back to Dot 4 solved my problem.
Bee Jay

mrvette

I been DOT 5 for some 15? years now, since I bought the car, a SCCA buddy was using it in his race car....my '72 had stainless lined calipers on it already, so I rebuilt it all since they leaked....lip seals with no springs, and DOT 5 worked for about 2 years, then started leaking again...went O ring pistons/seals....lasted about 5 years or so with DOT 5, street driven daily...a few years ago I replaced the O rings but today with Hydroboost, the brakes are fine....if you have a soft pedal, the problem is in the booster....assuming you don't have air, and if you have O rings, you have no air problems...unless you are a idiot...

so DOT 5 don't suck up water naturally like the others do...

no rust...

can't say about boiling points since I don't race, but have done some goodly high speed stopping, and not so awful evil....ie, nothing noticed....

Leung

Thanks for the replies guys. I will probably be switching over to dot 5 silicone later this summer.

drwet

My '79 has had Dot 5 in it since I got it about 17 years ago. The guy I bought it off was a friend of mine and he tells me when he converted it he just flushed the system with alcohol and replaced the fluid eith Dot 5. I have replaced the calipers twice since, and most of the lines once, so there should be no trace of the Dot 3 left. My brakes have always been excellent. The experts tell me that the silicone fluid is more compressible and leads to a softer pedal, but I've never been able to tell. I also have a '66 with Dot 3 fluid and I can't tell any difference between the two cars. I would have no reservations about using the Dot 5 fluid again.

bruced267

I used Dot 5 on a Harley I used to have, It was next to impossible to bleed the system! Thats my only experience with Dot 5. Why would anyone want to switch?

straub18045

i went to dot 5, guaranteed last brake fluid change. did it when i had to replace calipers,master and flex lines. dont say my performance was effected, if anything it would be better, scientifically speaking