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Suggested brake fluid
#22358 Sun Feb 15 2004 03:55 PM
Joined: Jan 2002
Posts: 2,088
cmayna Offline OP
Shop Shark
Getting ready to install my new brake system (new SS lines and cylinders). What is the suggested brake fluid? Whats the difference between Dot 3, 4 and 5?

Craig's '50 Chevy 3100 5 window
My truck
If I'm not working on my truck or VW camper, I'm fishing with the wife or smoking Salmon.
Re: Suggested brake fluid
#22359 Sun Feb 15 2004 04:26 PM
Joined: May 2001
Posts: 9
Junior Member
DOT3 (&4) are glycol-based, while DOT5 is silicone-based.

In theory, DOT5 is superior to anything else as it has a higher boiling point and doesn't attract moisture, but for the life of me I have never had luck with the stuff. It seems to hold air which leads to spongy brakes and your system has to be totally rid of the old fluid as the two aren't compatible.

Valvoline Synpower makes a DOT4 that I can recommend. I wasn't satisfied with the brake performance in my '51, so I flushed out the DOT5 and replaced it with the Synpower DOT4 and all my problems went away.

Re: Suggested brake fluid
#22360 Sun Feb 15 2004 07:14 PM
Joined: Jun 2000
Posts: 2,773
Shop Shark
If it's a daily driver, go with dot4. If it's only driven to church (I know how often most of us go) use dot5.

52 3600
69 C-10
Re: Suggested brake fluid
#22361 Sun Feb 15 2004 08:31 PM
Joined: Sep 2003
Posts: 1,827
Shop Shark
smile Because of the high quality of restoration you are doing to your truck, Craig, I highly recommend DOT 5 Silicone. If you use regular Dot 3 or 4, you will put all of your paint restoration work at risk. Dot 3 or 4 will destroy your paint work no matter how careful you try to be. Dot 5 Silicone will not phase your paint work and be your best choice for all the other reasons. The only thing about Dot 5 that I have found to be a problem is leakage. It is so thin and slick that if your are going to have a leak in your system, it will show up with Dot 5 Silicone. Since you are totally rebuilding your system, that may not be a problem for you. I would take that chance.
As far as bleeding the air pockets out of it - yes, it does take longer to do that, but you can get them out. Patcience is the key! I know you have patience by what I see you are doing to your truck!
I have had it in my 37 since 1980 and have enjoyed all of the positive aspects of Dot 5 Silicone.
One last comment - it is expensive with a quart going for about $30.00.

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Re: Suggested brake fluid
#22362 Wed Feb 18 2004 05:34 AM
Joined: Jun 2001
Posts: 11
Junior Member
If you are starting out with clean lines and cylinders, use Dot 5.

I use it in my '54 3100, works fine.

Re: Suggested brake fluid
#22363 Wed Feb 18 2004 07:52 AM
Joined: May 2000
Posts: 235
Shop Shark
For those with original (vintage) master cylinders, DOT3. The newer stuff can harm the older rubber seals and cause leaks.


'48 Willys CJ-2A / '55.1 Chevy 3600 / '66 Austin-Healey 3000 / '04 Volvo wagon (parenthood!?)
Re: Suggested brake fluid
#22364 Wed Feb 18 2004 10:05 AM
Joined: Oct 2001
Posts: 3,459
Extreme Gabster
I use DOT3 or DOT4. Dot 4 is more hydroscopic than Dot3 (attracts water easier) but has a higher boiling point. Both Dot3 and dot 4 have a significantly lower boiling point when they are saturated with water, and should be changed annually since the stovebolt system is an open system. A system with a more modern master cylinder with a bellows breather can handle changes every two years. I change my fluid every 3 times I adjust the Hucks. Always change fluid anytime you open the system. I change it by cracking the far bleeder and topping it off as it bleeds down, and then re-bleed all four corners until it runs clear. That gets 99% of the water and crud out.

Paint & Body Shop moderator
A lone amateur built the Ark. A large group of professionals built the Titanic.
Re: Suggested brake fluid
#22365 Wed Feb 18 2004 02:03 PM
Joined: Feb 2000
Posts: 50
rat Offline
When I rebuilt my brake system I used Dot 5 and had trbl with leaks. I flushed out the Dot 5 and replaced it with Dot 3 and had no trbl. with leaks since. smile

'52 Chevy 5 window, it ran when I parked it
'53 Chevy 5 window, running the streets with me.
'55 Massey-Ferguson, tearing up the dirt
'89 Harley FXSTS, suicide clutch
'92 Harley FLSTC, equal time with the '89

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