What's diff between DOT 4 and DOT 5.1?

[soundbeltfarm]

the brakes on my bike are crap house.
i've tried everything i can think of and have looked online for help also.
i now have decided to try dot 5.1 but i read online where a guy put dot 5 into his brakes that used to have dot 4 and it all gummed up.
i know not to use dot 5 but what has been the improvement with dot 5.1?
cheers in advance.

[awayatc]

5.1 has a higher boiling point (270 c vs 230c for dot 4)
Since brakefluid absorbs moisture from the air it reduces its boiling point and therefore braking performance.
Less of an issue if you change fluid regularly....

DOT3 4 and 5.1 are polyethylene-glycol based
Dot 5 is silicone based.....
So only use Dot 5.1 when specified, it is not interchangeable with the other DOTs...
.have you put on braided brakelines? because the rubber ones will become spongy over time....

[Tony.OK]

You can use 5.1 with 4,but you can't use 5 with 4.
5.1 as stated in previous post has a higher boiling point and is more hygroscopic(absorbs water faster),it just means it needs changing more often.
5.1 isn't an improvement over 5,its a different fluid all together.
If you are going to use 5.1 just keep bleeding you brakes and topping up with 5.1 until you've flushed all the 4 out:niceone:

[Gubb]

About 1.1

Ba-doom-tischhh.

[imdying]

So only use Dot 5 when specified, it is not interchangeable with the other DOTs...Corrected.

[speedpro]

Fluids aren't compressible. Simply changing the fluid will not affect brake performance. It is extremely unlikely that the fluid will be getting so hot that there is a problem because of heat. Bleeding might help if you have a spongy lever and of course fluid will then be replaced. Going to braided lines might help the feel but will not increase brake power as that is dependant on the ratios between master and slave cylinder areas. Check that the pistons are free to move and if the caliper is a sliding pin type make sure it moves freely. Dirt bikes are famous for seizing up in these areas with all the dirt and sometimes cleaning that occurs. If everything seems good try different pads. The different compounds make a huge differance.

[soundbeltfarm]

yep i have pulled caliper apart and it all clean and running free

[Squiggles]

Defining craphouse would be a good start... do you have to pull the lever to the bar to stop? if you give the lever a squeeze, and it does little, then release and give another squeeze do you then feel it braking properly? what makes it craphouse?

how long since fluids changed? how many k's/hours on the bike? what condition are the pads in? (heaps of meat left? how long since they were changed?) any signs on oil muck on the disks or in the area of the pads?

[soundbeltfarm]

Defining craphouse would be a good start... do you have to pull the lever to the bar to stop? if you give the lever a squeeze, and it does little, then release and give another squeeze do you then feel it braking properly? what makes it craphouse?

how long since fluids changed? how many k's/hours on the bike? what condition are the pads in? (heaps of meat left? how long since they were changed?) any signs on oil muck on the disks or in the area of the pads?


no i dont have to pull to lever to stop.
but if im using one finger if i try to jam on the brakes i pull lever in till it hits other fingers and still not locking up brakes.
fluids changed about 5 days ago,
brand new pads,
70 hours on bike
no muck or anything on the pads or discs.

maybe i am just asking to much from my brakes but i have tried others and they are better than mine.

[Max Preload]

So just excessive lever travel?

Tie your brake lever hard back against the bar overnight. The travel will be reduced.

If the excessive travel returns over a day chances are the pistons in the caliper are gummed up. To clean them properly you have to completely strip the calipers and pop the pistons out - not a job for a novice because it can be tricky getting all four pots out as once one pops, the others won't have any pressure behind them to pop them out (I use low pressure compressed air). If you still have the old worn out pads they'll be very handy for assisting in doing this.