C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette

Switching from DOT 3 to DOT 5 Brake Fluid

 
Old 06-02-2010, 02:39 PM
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Leung
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Default Switching from DOT 3 to DOT 5 Brake Fluid

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
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Old 06-02-2010, 04:09 PM
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mrvette
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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....
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Old 06-02-2010, 04:12 PM
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jordan89
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Originally Posted by mrvette View Post
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....

Why not just go to DOT4 or DOT5.1?
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Old 06-02-2010, 04:16 PM
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Originally Posted by Leung View Post
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
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.
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Old 06-02-2010, 04:29 PM
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jimvette999
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Originally Posted by Leung View Post
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
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.
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Old 06-03-2010, 12:31 AM
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Bee Jay
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Don't do it. Go to Dot 4 synthetic instead. My brake performance with Dot 5 sucked.
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Old 06-03-2010, 12:41 AM
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babbah
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Originally Posted by Bee Jay View Post
Don't do it. Go to Dot 4 synthetic instead. My brake performance with Dot 5 sucked.
Bee Jay
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!

Last edited by babbah; 06-03-2010 at 12:44 AM.
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Old 06-03-2010, 05:31 AM
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mds3013
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Originally Posted by babbah View Post
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!
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...
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Old 06-03-2010, 01:44 PM
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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.
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Old 06-03-2010, 07:55 PM
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Originally Posted by Bee Jay View Post
Don't do it. Go to Dot 4 synthetic instead. My brake performance with Dot 5 sucked.
Bee Jay
In what way did your performance 'suck'?
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Old 06-03-2010, 11:16 PM
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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.
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Old 06-04-2010, 04:50 AM
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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
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Old 06-04-2010, 09:51 AM
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Originally Posted by yellow 72 View Post
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

Yellow cars need extra good brakes cause they are faster.
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Old 06-04-2010, 05:07 PM
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glen242
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Originally Posted by Bee Jay View Post
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.
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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.
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Old 06-04-2010, 06:09 PM
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Originally Posted by glen242 View Post
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.
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.
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Old 06-04-2010, 06:12 PM
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mrvette
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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....

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Old 06-05-2010, 12:09 AM
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Leung
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Thanks for the replies guys. I will probably be switching over to dot 5 silicone later this summer.
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Old 06-05-2010, 10:31 AM
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drwet
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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.
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Old 06-05-2010, 12:26 PM
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bruced267
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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?
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Old 06-05-2010, 01:18 PM
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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
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