Master cylinder
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Cruiser
Joined: Jun 2018
Posts: 168
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From: Rochester, NY
Master cylinder
So I just got a new chrome master cylinder that said it was a direct fit for my bike but when I got it it said only use dot 5 fluid. My stock system was dot 4. Since the master cylinder is new and has never been used with dot 5 fluid can I just run it with dot 4 fluid like the rest of my brake system has been using or is there a difference in the material of the seals and gaskets?
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Cruiser
Joined: Jun 2018
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From: Rochester, NY
Originally Posted by Madduc
Use the DOT4.
Road Master
Joined: Jun 2019
Posts: 952
Likes: 528
From: Richmond TX
HD has flopped back and forth on brake fluid usage. My '05 Springer was marked to 'use DOT 5 only'. When I went to replace the fluid it was clear that someone had moved over to DOT 4. The brakes were working fine but I opted to go ahead and flush it thoroughly and move back to DOT 5. Again, the brakes worked fine. I am very confident you will not have compatibility problems. I am assuming your new part was never used with DOT 5. If it is a used part that has seen DOT 5 it wouldn't hurt to flush it with alcohol just like what you've read on the web about converting.
Good luck with getting everything up and working.
Good luck with getting everything up and working.
Road Master
Joined: Nov 2019
Posts: 966
Likes: 665
From: Rhode Island
HD has flopped back and forth on brake fluid usage. My '05 Springer was marked to 'use DOT 5 only'. When I went to replace the fluid it was clear that someone had moved over to DOT 4. The brakes were working fine but I opted to go ahead and flush it thoroughly and move back to DOT 5. Again, the brakes worked fine. I am very confident you will not have compatibility problems. I am assuming your new part was never used with DOT 5. If it is a used part that has seen DOT 5 it wouldn't hurt to flush it with alcohol just like what you've read on the web about converting.
Good luck with getting everything up and working.
Good luck with getting everything up and working.
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From: Ft. Wayne IN
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Cruiser
Joined: Jun 2018
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From: Rochester, NY
Originally Posted by Since 1968
HD has flopped back and forth on brake fluid usage. My '05 Springer was marked to 'use DOT 5 only'. When I went to replace the fluid it was clear that someone had moved over to DOT 4. The brakes were working fine but I opted to go ahead and flush it thoroughly and move back to DOT 5. Again, the brakes worked fine. I am very confident you will not have compatibility problems. I am assuming your new part was never used with DOT 5. If it is a used part that has seen DOT 5 it wouldn't hurt to flush it with alcohol just like what you've read on the web about converting.
Good luck with getting everything up and working.
Good luck with getting everything up and working.
I also don't think it actually says on the master cylinder use only dot5, I think that was just on the packaging but it had big warning labels which is what spurred the question. If it didn't have that then I wouldn't have thought twice about filling it with dot4, which is already in the other parts and stock for the bike. The master cylinder, in case that matters is a Bikers Choice chopped master cylinder with the same as stock on the bike, 9/16 bore.
It also doesn't have ABS so no worries there.
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From: San Diego, CA
There are no requirements for different seals between the use of DOT 4 or DOT5... DOT 4 is glycol based and DOT 5 is silicone based. If you mix them, you can create sludge in your brake system.. I suspect your master cylinder says "DOT 5" because it was made for a bike model during the DOT 5 years...
DOT 5 was considered a progression from DOT 4. It's a better brake fluid in terms of higher wet/dry boiling points, it won't absorb moisture readily, and won't harm painted surfaces if spilled on them..... Many early HDs (I forget when they started using DOT 5), use DOT 5... my '01 & '03 Both use it.. my anti-lock brake '16 bagger uses DOT 4.
It was discovered that DOT 5 didn't play well with anti-lock brake systems... so around 2006ish, when Harley started using anti-lock brakes in a couple models, they switched all models back to DOT 4....
Don't use DOT 5 with anti-lock brakes, or mix the glycol based with silicone based, and you will have no problems. Some people switch from one to the other, and it's OK, as long as they properly and completely flush their brake systems of the "other" fluid...
If you want high performance brake fluid with anti-lock brakes, there is a high performance glycol based brake fluid called DOT 5.1. It rivals, or beats, the silicone based DOT 5 in wet/dry boiling points, but still absorbs moisture and damages painted surfaces....
DOT 5 was considered a progression from DOT 4. It's a better brake fluid in terms of higher wet/dry boiling points, it won't absorb moisture readily, and won't harm painted surfaces if spilled on them..... Many early HDs (I forget when they started using DOT 5), use DOT 5... my '01 & '03 Both use it.. my anti-lock brake '16 bagger uses DOT 4.
It was discovered that DOT 5 didn't play well with anti-lock brake systems... so around 2006ish, when Harley started using anti-lock brakes in a couple models, they switched all models back to DOT 4....
Don't use DOT 5 with anti-lock brakes, or mix the glycol based with silicone based, and you will have no problems. Some people switch from one to the other, and it's OK, as long as they properly and completely flush their brake systems of the "other" fluid...
If you want high performance brake fluid with anti-lock brakes, there is a high performance glycol based brake fluid called DOT 5.1. It rivals, or beats, the silicone based DOT 5 in wet/dry boiling points, but still absorbs moisture and damages painted surfaces....
Last edited by hattitude; Mar 9, 2020 at 09:03 AM.
Thread Starter
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Cruiser
Joined: Jun 2018
Posts: 168
Likes: 86
From: Rochester, NY
Originally Posted by hattitude
There are no requirements for different seals between the use of DOT 4 or DOT5... DOT 4 is glycol based and DOT 5 is silicone based. If you mix them, you can create sludge in your brake system.. I suspect your master cylinder says "DOT 5" because it was made for a bike model during the DOT 5 years...
DOT 5 was considered a progression from DOT 4. It's a better brake fluid in terms of higher wet/dry boiling points, it won't absorb moisture readily, and won't harm painted surfaces if spilled on them..... Many early HDs (I forget when they started using DOT 5), use DOT 5... my '01 & '03 Both use it.. my anti-lock brake '16 bagger uses DOT 4.
It was discovered that DOT 5 didn't play well with anti-lock brake systems... so around 2006ish, when Harley started using anti-lock brakes in a couple models, they switched all models back to DOT 4....
Don't use DOT 5 with anti-lock brakes, or mix the glycol based with silicone based, and you will have no problems. Some people switch from one to the other, and it's OK, as long as they properly and completely flush their brake systems of the "other" fluid...
If you want high performance brake fluid with anti-lock brakes, there is a high performance glycol based brake fluid called DOT 5.1. It rivals, or beats, the silicone based DOT 5 in wet/dry boiling points, but still absorbs moisture and damages painted surfaces....
DOT 5 was considered a progression from DOT 4. It's a better brake fluid in terms of higher wet/dry boiling points, it won't absorb moisture readily, and won't harm painted surfaces if spilled on them..... Many early HDs (I forget when they started using DOT 5), use DOT 5... my '01 & '03 Both use it.. my anti-lock brake '16 bagger uses DOT 4.
It was discovered that DOT 5 didn't play well with anti-lock brake systems... so around 2006ish, when Harley started using anti-lock brakes in a couple models, they switched all models back to DOT 4....
Don't use DOT 5 with anti-lock brakes, or mix the glycol based with silicone based, and you will have no problems. Some people switch from one to the other, and it's OK, as long as they properly and completely flush their brake systems of the "other" fluid...
If you want high performance brake fluid with anti-lock brakes, there is a high performance glycol based brake fluid called DOT 5.1. It rivals, or beats, the silicone based DOT 5 in wet/dry boiling points, but still absorbs moisture and damages painted surfaces....
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