89 Sportster1200 Brakes - DOT 5 or DOT 5.1 does it matter?

[stanleychung]

Here's a situation my friend is facing;

Runs a 89 Sportster 1200, recently acquired and methodically going through servicing every aspect of it, and he has come to the brake system.

Unsure of the current DOT grade of the brake fluid currently in the master cylinder. Color of current fluid doesnt match the manual specified brand new DOT 5 fluid. He knows DOT 5's color changes as it ages so flushing the system is most likely the next step.

Now question is that is there any harm in using DOT 5.1 (or any of the other DOT grade brake fluids) as opposed to specified DOT 5 (its quite a lot more expensive than the other grades). Can anyone shed any light on this? Thanks.

[F5 Dave]

On an old bike it's probably a better idea to pump the pistons out & clean out all the old muck that collects behind the piston being the lowest point. Then fill with 5.1 or 4.

5 is a silicon & not really that flash for roadbikes. There will be a heap of info on the net if you google it, (and a lot of mythology, try ignore that -you aren't racing) suffice to say I think the above action is safest for brake performance on old brakes that were never super when new.

Means you can clean up the piston, pop out the seals which get white powdery gunge buildup in their seats, none of which are good for performance. Seals are often ok but replace any that are worn or twisted. It's all quite simple of you are methodical. Keep clean, if using metal cleaner make sure all gone before putting seals back in.

[kwaka_crasher]

DOT 5 and DOT 5.1 are NOT COMPATIBLE. DOT 5 is silicone based and DOT 5.1 is glycol based like Super DOT 4, DOT 4, DOT 3 etc...

If it specifies DOT 5 that's what he'll have to use. The materials in a brake system designed for DOT 5 will be incompatible with a non-DOT 5 fluid.

[stanleychung]

Update: Just bled through the front brakes with harley specified DOT 5, yes that is very correct DOT 5 and DOT 5.1 are completely different and incompatible and if left to sit in a container for an extended period of time will separate.

[cruza]

Yeah harley runs dot 5 , got to be careful sometimes aye. Could have been a expensive fix.