Brake reservice

Hawk Joined: Jul 14, 2012 Posts: 420 Location: New Zealand

Hi Folks.
Decided to check front brakes on the cb that I restored a long time ago as they were not up to my standard.
Stripped calipers and found piston rubbers a little hard and pads worn.
Condition inside calipers were very clean so a quick clean new seals and lube up good to go.
I have been running DOT 5.0 brake fluid all these yrs and all the other rebuilds with no problems, I do recommend it

Posted: Fri Jul 03, 2026 1:21 pm

I've been using DOT5 for many years on all of my restorations. I've never had an issue and would never go back to DOT3 or DOT4.

Posted: Fri Jul 03, 2026 2:44 pm

Do you start with all new seals, rubber parts and lines? Or in an old(er) system, what do you flush the system with?

Steve

Posted: Fri Jul 03, 2026 9:04 pm

My experience is starting brand new if you are switching to Dot 5. If it isn't spotless it will eventually booger up. How do you completely clean it?...dont know?

Posted: Fri Jul 03, 2026 10:21 pm

SteveG wrote:

Do you start with all new seals, rubber parts and lines? Or in an old(er) system, what do you flush the system with?

Steve

Steve - you're better off to tear down, clean, rebuild with new seals, (calipers and masters) and replace the lines.

Hawk Joined: Jul 14, 2012 Posts: 420 Location: New Zealand

Full strip down and replace all rubber components.
DOT 5 was used in the military for reasons that it sits around a lot which suits me.
Non corrosive and will not absorb water but if water gets in it will not breakdown,could cause a rust cavity in a section.
I have found a lot of mechanical parts personal and aligned staff cannot get their heads around this.

Peter.

Posted: Sat Jul 04, 2026 7:04 am

You can also completely bleed and replace Dot 3 or 4 every year or two. That works also.

MB-5 Joined: May 24, 2025 Posts: 20 Location: Seattle, Wa

This to me would be a great time to actually explain what the differences are and that there are actually 2 DOT 5's. The other is DOT5.1 and it isn't a silicone based like DOT5. And if the 2 are mixed it causes a lot of issues like having your seals break done and then no brakes. I for one would look at the 2 products and assume that they could be mixed as a lot of people would. Another issue is that DOT5 is not hydrophilic as DOT 3/4 are.

Just my seven cents...

Grant

Posted: Sun Jul 05, 2026 11:47 pm

Escape2012 wrote:

This to me would be a great time to actually explain what the differences are and that there are actually 2 DOT 5's. The other is DOT5.1 and it isn't a silicone based like DOT5. And if the 2 are mixed it causes a lot of issues like having your seals break done and then no brakes. I for one would look at the 2 products and assume that they could be mixed as a lot of people would. Another issue is that DOT5 is not hydrophilic as DOT 3/4 are.

Just my seven cents...

Grant

I would hope that anyone who pays attention to what they buy notices the different markings, i.e. 5 vs. 5.1. And just because they share the same first digit, common sense would suggest to NOT mix them. None of the bike builders I know would ever do that, just because they know better. As I have mentioned here over the years, and at this point, ad nauseam, I have been using it exclusively with all of my builds and restorations for at least a dozen years. I have NEVER seen an issue, and on at least one occasion during brake line upgrades, I tore into the calipers that had DOT5 running through them and the seals were still like new. I did that just to prove to myself and others that it doesn't eat into the seals like the conspiracy theorists would have you believe.

I have found that the DOT5 naysayers usually have zero experience with it, have never used it, and only base their unsubstantiated opinions on rumors and nonsense they've heard from other like-minded individuals with the same non-experience.

Use what you're comfortable using. I know that DOT5 works well for me and have tens of thousands of miles to show for it.

Hawk Joined: Jul 14, 2012 Posts: 420 Location: New Zealand

Very well put.
I have had the same discussions with these idiots

Thanks Tom.

Peter

Posted: Tue Jul 07, 2026 1:39 am

I am running Dot 5 in my build bike brakes. Everything was brand new, thats why I used it. In my Blackbird I did a major rebuild on Calipers and Brakelines. There are a couple things in that brake system that cannot be adequately cleaned nor bought brand new. Namely the Proportioning valve and another type of pressure balance very small unit on the right front fork. Therefore I went with DOT 4. I switched my 900F to Dot 5 back in the 80's and after about 10 years things look really crystalized. I had to redo the entire system. Did not want to go through that again. I will keep up with the Bleeding on the DOT 4. It's not hard really. By the way. 4 and 5 seem equally good to me. The brakes are awesome both bikes.

Posted: Tue Jul 07, 2026 12:57 pm

Hondo57 wrote:

I am running Dot 5 in my build bike brakes. Everything was brand new, thats why I used it. In my Blackbird I did a major rebuild on Calipers and Brakelines. There are a couple things in that brake system that cannot be adequately cleaned nor bought brand new. Namely the Proportioning valve and another type of pressure balance very small unit on the right front fork. Therefore I went with DOT 4. I switched my 900F to Dot 5 back in the 80's and after about 10 years things look really crystalized. I had to redo the entire system. Did not want to go through that again. I will keep up with the Bleeding on the DOT 4. It's not hard really. By the way. 4 and 5 seem equally good to me. The brakes are awesome both bikes.

10 years between brake flushes is a VERY long time. DOT3 or DOt4 would also be trash after such a long time. DOT5 isn't indestructible or permanent - it needs to be flushed periodically as well. And I agree that flushing isn't difficult, but many bike owners never do it. I suggest either flushing periodically or trade the bike in for a new one when it's time to flush. I like that idea. Cool

Posted: Wed Jul 08, 2026 2:15 am

Call it young, busy and thinking things will just last forever. Did I mention young?

Posted: Wed Jul 08, 2026 10:56 pm

I'm a huge fan of Dot 5 for our classic DOHC bikes. This is the best description of the pros/cons I've read:

https://www.v8register.net/articles/Brake%20fluids%20article%20R5%20Bob%20Owen%20230109.pdf

Hawk Joined: Jul 14, 2012 Posts: 420 Location: New Zealand

Great read on such a issue that has created good conversation.

Peter.

Posted: Fri Jul 10, 2026 5:00 pm

In everyday life, we've come to expect decimal numbers to work like software updates, where version 5.0 is just a newer, better version of 4.0, and 5.1 is a tiny tweak on top of that.

Brake fluid does not work this way. The numbers represent completely different chemical formulas, not a timeline of upgrades. For example, DOT 3, 4, and 5.1 are glycol-based fluids that can safely mix. However, DOT 5 is silicone-based and will ruin a system containing the others. Never assume a higher DOT number is just a 'newer version' of a lower one.

I think it's quite unfortunate that the regulatory deep state foisted that unconventional DOT 5.1 numbering of brake fluid on the public back in the 90s. Many people were already aware of the semantic versioning model of the x.y.z convention, and nowadays that schema is ubiquitous. This has resulted in much confusion and even damage to people who try to DIY their brake issues.

By the way, silicone fluid (DOT 5) holds onto microscopic air bubbles like soapy water, so bleeding becomes even more critical. If a rider puts it into a modern sportbike (or anything) with an ABS pump, the rapid pulsing foams the fluid instantly, leaving them with zero brakes in some situations. Glycol-based brake fluids (3, 4, 5.1) have low viscosity and surface tension, so the rapid mechanical hammering of the ABS pump passes through the liquid cleanly.

edit- I now see that the .pdf link that X7eater posted covers the abs dot5 issue, I hadn't looked at it yet when I posted. I am particularly amused by the issue presented starting at the top right column of page 4 regarding the mixing of glycol and silicone based brake fluids.