Brake Fluid: Dot4 vs Dot5
 

Just bought some AP Dot5.1 brake fluid to replace the Motul Dot4 thats in at the mo.
I thought Dot5 was for track use only as it takes on moisture too rapidly and therefore needs changing more often.
The packaging on the AP stuff says "road and track" and that it should be changed at least every 2 years.
The Dot4 was ok when first bled but after a trackday the lever comes too far back for my liking before the pads bite.
Anything i need to know before i put the new stuff in?

Re: Brake Fluid: Dot4 vs Dot5
 

Dot 5.1 is not the same as Dot 5.

I'm pretty sure 5.1 is a similar forumulation to Dot 4. Dot 5 is not and can not be mixed with Dot 4.

I used some ultra-expensive dot 4 and it didn't make much difference (all they had at the time).
Would have thought you maybe just needed a general service on the brakes before the trackday - I presume you have braided lines?

I've not got braided lines but if it was the lines wouldn't brakes feel consistantly soft?
When i put the dot4 in i gave the calipers a good clean and news pads on. The brakes were great but the performance dropped after the trackday making me think i boiled the fluid.
Can the SV calipers generate enough heat to do this or am i barking up the wrong tree?
Don't really want to spend money on braids if the problem is caused by something else. I would have thought the stock lines would be ok for a couple of years.

As G says, DOT3, 4 (variants thereof like "super" etc) and DOT5.1 are of the same family and as such any higher spec can safely be used to replace a lower spec.

DOT5 is of a silicone base and is intended for competition use only. It doesn't absorb moisture (like the other types do), which sounds as though it ought to be a good idea, however because it doesn't absorb it, then any moisture which gets in the system can collect and cause problems like corrosion, boiling, or even freezing.

AFAIK no brake manufacturer will recommend the use of DOT5 for road use.

Brake fluids will quote "dry" and "wet" boiling temps, dry being brand new stuff, wet being with moisture absorbed.

I use DOT5.1 usually, not because I push brakes hard but the difference in price is trivial so why not use the higher spec anyway?

Put the new fluid in now.
Used the same the procedure as with the dot4 a few months ago but cant get the lever to feel as firm. Tried turning the bars (to move the calipers around) and tapping the lines.
Is the SV's system known for trapping air at a particular point?
Do i need braids after all?
The lever is firmer than it was but it's annoying cos i know the brakes arent working as well as they could. :evil: