Dot 5.1 Brake Fluid
Thread Starter
Instructor
Joined: Oct 2012
Posts: 222
Likes: 11
From: Johnston, Rhode Island
Dot 5.1 Brake Fluid
I am replacing my leaking front brake calipers with new CSSB SS sleeved o'ring calipers. I am also going to have the fluid flushed and the brakes bled. I know there has been a lot said about not using 5.0 dot brake fluid, but does anyone think it would be a good idea to use a good 5.1 dot fluid? This fluid was developed to fix some of the inherent weaknesses in dot 5 fluid and still be useable in systems that can't use silicon fluid. Anyone think using 5.1 would be a good idea?
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Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
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I think changing those cheap Orings out and running silicone DOT 5 is a great idea.
DOT 5.1 is just high grade DOT4
DOT 5.1 is just high grade DOT4
Melting Slicks
Joined: Dec 2009
Posts: 3,233
Likes: 657
From: Thunder Bay
DOT 5.1 is high performance (high temp) regular (glycol based) brake fluid. It is the best choice for our application.
Silicone can work, but you need to flush the whole system of the existing fluid if you want to switch to it. The bigger problem is a lot of components aren't compatible with silicone these days. Apparently the composition of silicone fluid changed some years ago and started eating seals and o-rings. Many suppliers of calipers will not honor the warranty if you use silicone.
The only advantage to silicone is it is not hygroscopic. In addition to the compatibility problem, it is also slightly compressible, and therefore not as effective as a hydraulic (brake) fluid.
FWIW I am running silicone (DOT5) in my car, but only because the previous owner went to the trouble of installing it. If I had my druthers, I would be running DOT5.1 and flush it every five or ten years.
Silicone can work, but you need to flush the whole system of the existing fluid if you want to switch to it. The bigger problem is a lot of components aren't compatible with silicone these days. Apparently the composition of silicone fluid changed some years ago and started eating seals and o-rings. Many suppliers of calipers will not honor the warranty if you use silicone.
The only advantage to silicone is it is not hygroscopic. In addition to the compatibility problem, it is also slightly compressible, and therefore not as effective as a hydraulic (brake) fluid.
FWIW I am running silicone (DOT5) in my car, but only because the previous owner went to the trouble of installing it. If I had my druthers, I would be running DOT5.1 and flush it every five or ten years.
Race Director
Joined: Mar 2017
Posts: 11,949
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From: Virginia
I think a choice was made to use different O-Rings, which are not compatible with silicone fluid, hence the warning label that comes with CSSB Inc brake kits. But their kits work great! I use their "high-heat" kits, which are likely Viton O-rings likely Silicone.
Anyway, 5.1 is fine. I started using Bosch ESI6-32N, because the old brake fluid naming convention was too simple, and it's a bit cheaper than the DOT 4 I had been using.
EDIT: These look like the CSSB kits I used. They are sold as Silicone high heat O-ring brake kits. I guess that's why they are incompatible with DOT 5.0 (silicone) brake fluid.
https://www.corvettecentral.com/c3-6...liper-o-192343
Anyway, 5.1 is fine. I started using Bosch ESI6-32N, because the old brake fluid naming convention was too simple, and it's a bit cheaper than the DOT 4 I had been using.
EDIT: These look like the CSSB kits I used. They are sold as Silicone high heat O-ring brake kits. I guess that's why they are incompatible with DOT 5.0 (silicone) brake fluid.
https://www.corvettecentral.com/c3-6...liper-o-192343
Last edited by Bikespace; Jun 4, 2025 at 10:25 PM.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,137
Likes: 4,247
From: US-PNW
DOT 5.1 is high performance (high temp) regular (glycol based) brake fluid. It is the best choice for our application.
Silicone can work, but you need to flush the whole system of the existing fluid if you want to switch to it. The bigger problem is a lot of components aren't compatible with silicone these days. Apparently the composition of silicone fluid changed some years ago and started eating seals and o-rings. Many suppliers of calipers will not honor the warranty if you use silicone.
The only advantage to silicone is it is not hygroscopic. In addition to the compatibility problem, it is also slightly compressible, and therefore not as effective as a hydraulic (brake) fluid.
FWIW I am running silicone (DOT5) in my car, but only because the previous owner went to the trouble of installing it. If I had my druthers, I would be running DOT5.1 and flush it every five or ten years.
Silicone can work, but you need to flush the whole system of the existing fluid if you want to switch to it. The bigger problem is a lot of components aren't compatible with silicone these days. Apparently the composition of silicone fluid changed some years ago and started eating seals and o-rings. Many suppliers of calipers will not honor the warranty if you use silicone.
The only advantage to silicone is it is not hygroscopic. In addition to the compatibility problem, it is also slightly compressible, and therefore not as effective as a hydraulic (brake) fluid.
FWIW I am running silicone (DOT5) in my car, but only because the previous owner went to the trouble of installing it. If I had my druthers, I would be running DOT5.1 and flush it every five or ten years.
If you really want to go back to E-G fluids, just flush out the silicone. The two fluids don't interact so won't form gel or sludge or anything of the sort. Buy a quantity of the cheapest DOT 3 you can find and flush with that, then put in whatever 3, 4, or 5.1 you desire.
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Verdad Gallardo
Team Owner
Joined: Jun 2001
Posts: 23,375
Likes: 1,067
From: Virginia USA
Been running DOT5 for years without problems. Years ago I replaced all my calipers with the o-ring style and nowhere in the instructions said to not use DOT5 and I asked the vendor (Van Steel I think, sucks getting old) if the o-rings were good with DOT 5 and the answer was yes. To this day my stock 4-piston caliper Vette stops better than any of my modern vehicles.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,137
Likes: 4,247
From: US-PNW
Been running DOT5 for years without problems. Years ago I replaced all my calipers with the o-ring style and nowhere in the instructions said to not use DOT5 and I asked the vendor (Van Steel I think, sucks getting old) if the o-rings were good with DOT 5 and the answer was yes. To this day my stock 4-piston caliper Vette stops better than any of my modern vehicles.