DOT 5 Brake Fluid
Thread Starter
Safety Car
Joined: Oct 2004
Posts: 3,725
Likes: 5
From: Minnesota
DOT 5 Brake Fluid
It's time to flush my brakes and I would like to go with the DOT 5 silicone fluid since the vette will sit about 6 months of the year. How thoroughly do I have to flush out the DOT 3 to make this conversion? Are there any compatibility issues? Thanks. 
Burning Brakes
Joined: Jun 2002
Posts: 837
Likes: 3
From: Texas
I believe there may be some compatibity problems between the silicone and glycol fluids. Here is an interesting thread that may help.
http://theoildrop.server101.com/cgi/...;f=16;t=000232
http://theoildrop.server101.com/cgi/...;f=16;t=000232
Racer
Joined: Jul 2004
Posts: 492
Likes: 0
From: Burlington Ky
I can tell you my experience with it. My work decided to go with Dot 5 several years ago. We have a fleet of over 500 motorized equipment. So, at service checks or whenever something needed brake work, we flushed the system and put in Dot 5. I have never replaced so many master AND wheel cylinders/calipers in my life as a result. It was discovered that not only are the two fluids not compatible, but internal seals designed for Dot3 or that have been used with Dot3 swell and break down with Dot 5. So, after the failed experiment, we went back to Dot3. It also causes corrosion. I wouldn't recommend it.
Last edited by 79ls1; Nov 9, 2004 at 12:27 AM.
Burning Brakes
Joined: Oct 2001
Posts: 1,185
Likes: 0
From: New Wilmington PA
In the past few years I have seen many members try this conversion. To my knowledge, none have liked the result. The consensus had always been that our older system just works better with DOT 3.
I'm not the final word though. Not by a long shot. I've actually missed out on a lot of forum happenings for about the last 6 months.
I'm not the final word though. Not by a long shot. I've actually missed out on a lot of forum happenings for about the last 6 months.
Thread Starter
Safety Car
Joined: Oct 2004
Posts: 3,725
Likes: 5
From: Minnesota
Well you guys convinced me to stick with the DOT 3. Sounds like that Castrol LMA (low moisture absorption) stuff would be the way to go if I can find some. Now to crack those bleeders without nightmare results. If only I could put the acetylene torch to those things. 
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
I picked up some Valvoline DOT4 synthetic brake fluid at AutoZone. Good stuff -- compatible with DOT3 -- and cheap, too. 
Use penetrating oil on the bleeders. Start spraying 'em several days in advance!
Use penetrating oil on the bleeders. Start spraying 'em several days in advance!
Burning Brakes
Joined: Nov 2000
Posts: 948
Likes: 0
From: Johnston Iowa
When I did the frame off on my 69 I replaced everything in my brake system. New stainless solid brake lines, braided flex lines, calipers, and master cylinder. I have been running DOT 5 for over 2 years with no problems at all. Car will stop on a dime.
I went with DOT 5 for 2 reasons:
1. I had never ran DOT 3 in this system.
2. I don't drive the car year round.
I went with DOT 5 for 2 reasons:
1. I had never ran DOT 3 in this system.
2. I don't drive the car year round.
Pro
Joined: Mar 2001
Posts: 633
Likes: 1
From: Hamilton, ON, Canada
I switched to DOT5 sometime in the early '80's with no leaks, swelling, or other problems. Switched because of a leaking caliper with DOT3 and because the car sat idle for extended periods. In all honesty, I don't think I changed brake fluid since the car was new in '75 until first caliper leak in early '80's. Still running DOT5 and plan to continue. It's worked out well for me.
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Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by jdmick
It's time to flush my brakes and I would like to go with the DOT 5 silicone fluid since the vette will sit about 6 months of the year. How thoroughly do I have to flush out the DOT 3 to make this conversion? Are there any compatibility issues? Thanks.
Melting Slicks
Joined: Oct 2001
Posts: 2,064
Likes: 1,382
From: Halifax, Nova Scotia, Canada
Originally Posted by 75 Hot One
I switched to DOT5 sometime in the early '80's with no leaks, swelling, or other problems. Switched because of a leaking caliper with DOT3 and because the car sat idle for extended periods. In all honesty, I don't think I changed brake fluid since the car was new in '75 until first caliper leak in early '80's. Still running DOT5 and plan to continue. It's worked out well for me.
Best thing I ever did.
Be sure to flush the old system completely.
I'm sure there are lots of people that have had problems with DOT5, however, I'm convinced it has nothing to do with the DOT5 fluid.
Le Mans Master
Joined: Mar 2004
Posts: 7,465
Likes: 1,486
From: Little Rock AR
I have DOT 5 in a couple of cars. It is recomended that you do the swap when you are replacing the braking system. The old DOT 3 will leach out of the old rubber seals and old hoses over time and allow corrosion to occur. If you change out the calipers, master cylinder and rubber hoses you should be fine.
I used DOT 3 to flush the system first, then replaced all the rubber hoses and the calipers. Then I drained the system, bench bled the new master with DOT 5 and installed the new calipers. After the usual Corvette brake bleeding torture routine, all was fine.
If you do not like to purge the brake system frequently the DOT 5 is a good choice. It does not absorb water so your system will not need to be flushed periodicaly. I doubt I will ever have to mess with the system ever again.
-Mark.
I used DOT 3 to flush the system first, then replaced all the rubber hoses and the calipers. Then I drained the system, bench bled the new master with DOT 5 and installed the new calipers. After the usual Corvette brake bleeding torture routine, all was fine.
If you do not like to purge the brake system frequently the DOT 5 is a good choice. It does not absorb water so your system will not need to be flushed periodicaly. I doubt I will ever have to mess with the system ever again.
-Mark.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Just because silicon doesn't absorb water is not necessarily a good thing. Water can accumulate in a spot and corrode that spot out. While bleeding a system I got a large amount of water all in one spot. At least normal brake fluid mixes and holds it in suspension.
That said I run silicon because I am constantly splashing some of it on my paint somewhere and it doesn't eat paint.
That is the only reason I run it.
I believe FORD makes the best brake fluid.
That said I run silicon because I am constantly splashing some of it on my paint somewhere and it doesn't eat paint.
That is the only reason I run it.
I believe FORD makes the best brake fluid.
Le Mans Master
Joined: Oct 2000
Posts: 7,831
Likes: 5
From: Austin TX
Originally Posted by norvalwilhelm
That said I run silicon because I am constantly splashing some of it on my paint somewhere and it doesn't eat paint.
That is the only reason I run it.
That is the only reason I run it.
I run it in three cars and haven't had any problems.
