Dot 4 or Dot 5 ?
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
There is even more to this than the different DOT numbers for brake fluid - there are two types of DOT5 that are not compatible with each other!
I have owned my 1990 bike from new and for years used whatever DOT5 brand I could find - it was not commonly available during the early years and my nearest Harley dealer was a long way from home.
So to be safe, don't just use DOT5 fluid, use HARLEY DOT5 fluid.
Why? After about twelve years my brakes started playing up, so much that I dismantled the front and rear master cylinders. They were both full of a grey jelly-like stuff, that was not fluid! Worst still, the cylinder bores, which should be smooth and high-precision, were badly corroded, with a lot of pitting. The same corrosion was in the wheel cylinders.
It cost me a complete set of brake components - front and rear master and wheel cylinders and brake pipes. I couldn't face rebuilding the disgusting things I had dismantled. The fear of brake failure of a bike weighing over half a ton, with my precious wife on the back, was just too much to bear.
So read these words with horror! Do not mix or mess with brake fluids. If you have, be prepared to give your brakes a thorough check over. I don't use Harley fluid to line their pockets, or out of extreme brand loyalty, but because that is the only way I can be confident of getting the same stuff every time and saving my skin.
If your bike is recommended by Harley to use DOT5, use Harley DOT5! The only alternative to that is if all your brake components are after-market and have never seen DOT5.
I have owned my 1990 bike from new and for years used whatever DOT5 brand I could find - it was not commonly available during the early years and my nearest Harley dealer was a long way from home.
So to be safe, don't just use DOT5 fluid, use HARLEY DOT5 fluid.
Why? After about twelve years my brakes started playing up, so much that I dismantled the front and rear master cylinders. They were both full of a grey jelly-like stuff, that was not fluid! Worst still, the cylinder bores, which should be smooth and high-precision, were badly corroded, with a lot of pitting. The same corrosion was in the wheel cylinders.
It cost me a complete set of brake components - front and rear master and wheel cylinders and brake pipes. I couldn't face rebuilding the disgusting things I had dismantled. The fear of brake failure of a bike weighing over half a ton, with my precious wife on the back, was just too much to bear.
So read these words with horror! Do not mix or mess with brake fluids. If you have, be prepared to give your brakes a thorough check over. I don't use Harley fluid to line their pockets, or out of extreme brand loyalty, but because that is the only way I can be confident of getting the same stuff every time and saving my skin.
If your bike is recommended by Harley to use DOT5, use Harley DOT5! The only alternative to that is if all your brake components are after-market and have never seen DOT5.
Last edited by grbrown; Sep 4, 2008 at 06:29 AM. Reason: To make it make better sense!
Seasoned HDF Member
Joined: Dec 2004
Posts: 11,068
Likes: 1,478
From: Texas! Ya mean there's someplace else?
I've used DOT 5 from several sources over the last 25 or 30 years. Never had a problem as you described. I think what happened in your case is that you mixed DOT 5 with DOT 5.1. DOT 5 is silicon based, while DOT 5.1 is polyalkylene glycol ether based. They aren't compatible.
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
I've used DOT 5 from several sources over the last 25 or 30 years. Never had a problem as you described. I think what happened in your case is that you mixed DOT 5 with DOT 5.1. DOT 5 is silicon based, while DOT 5.1 is polyalkylene glycol ether based. They aren't compatible.
Seasoned HDF Member
Joined: Dec 2004
Posts: 11,068
Likes: 1,478
From: Texas! Ya mean there's someplace else?
I discovered that the hard way! What idiot in the DOT thought it was a good idea to give two completely different and incompatible fluids similar names and not ensure the difference was clear?! If they had been called, say, DOT5 and DOT6 it would be all too obvious! We can mix DOT3 and DOT4, but not DOT5 and DOT5.1 - Doh!
Ten scariest words ever uttered: I'm from the government, and I'm here to help you.
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
I live in the UK - those words are just too true! Two nations united by a common evil....
Thread
Thread Starter
Forum
Replies
Last Post
TOMMYBLAZIN
Frame/Suspension/Front End/Brakes
8
Apr 14, 2022 10:03 PM
sintax
Frame/Suspension/Front End/Brakes
3
Jan 23, 2015 08:13 AM
