[Closed] Dot 4 Disc brakes

Use dot 5.1 just don't use Dot 5 as it's not compatible.
Shimano are Mineral Oil ans Hope are Dot Fluid (4 or 5.1)

Also not sure what you mean? Is it an expansion that is causing the brakes to lock on? What sort of temperatures?

Shimano uses mineral oil instead of Dot fluid.

Personally i'm not convinced it's down to the heat you're having issues, but i'm not going to argue... but anyway, Shimano use a completely different type of fluid which may be what you're after.

They're all pretty decent, from the Deore to the Zee.. .

As for temperatures Mike my bike sits in the sun all day & the other day I released some fluid & could cycle home as I live in Sydney, Australia.

Thanks both for the help

Really don't think this will be down to the fluid. What do you use in cars down there?

Possibly there is air in the system which expanded in the heat or if the brakes were over filled then it's possible that liquid expansion caused it, but now that you've released some it shouldn't recur as there's space for it to expand into.

Living in Hobart, we get hot here too, rode through the mainland and never had issues - heaps of avid brakes out here so I don't think thats the problem.

As noted by others, whatever your problem is, its not the DOT4, at least not in a way that would be solved by 5.1 or mineral oil.

Have you bled them recently? If no, then bleed them, although most bleeding related problems tend to result in a soft lever not hard. If you have bled them recently, then there is too much fluid in there which is locking the brakes on, as long as no air got in then letting some out will have helped or even solved this.

Ok team some helpful things to try out I'm just waiting on a bleed kit arriving so I can rebleed my brakes which will hopefully be cheaper than new brakes

You lot really are a bit slow.

This is just an elaborate ruse to justify new brakes. It's nothing to do with a poor bleed. It's all about the fluid expanding massively when it heats up by 25 degrees, filling the reservoir then squeezing the pads out until the brakes are jammed on. That's just unsafe, he needs new brakes. Hydraulic fluid that adds a significant fraction to its volume with just a 25 degree temp shift is just lethal.

Maybe he needs to start a new thread and we can all agree with him so he's at least got a thread to show the finance controller.......

I had this twice during the summer , had to let a fraction of fluid out each time

What brakes are you using Holyzeus ? & where do you live ?, Yes I'm after fixing the problem Ghostlymachine if I'm going to buy new brakes I'd like honest opinions on good brakes that won't fail when it gets hot weather & value for money.

Thanks team

My Avids do this, but only if bled incorrectly, there's a sequence of alternately pressurising and pulling a vacuum with the lever open/closed to follow with Elixirs. Getting it wrong pushes too much fluid into the reservoir and locks the brakes on (or at least gives zero lever throw).

I suspect it's because "in the good old days" brakes had a master cylinder, which filled by gravity from a reservoir above it, and that was that. These days brakes are mostly ambidextrous with the master cylinder inside the reservoir, and the fluid expansion is dealt with by a bladder design. Which means air no longer rises to the top and it's far easier to overfill the system.

Has the problem come back since you released some fluid?

I'd like honest opinions on good brakes that won't fail when it gets hot weather & value for money.

Brake fluid boils at around 200C-250C, it's entirely possible to have it reach those temperatures in use (which is when the brakes fail completely). It being 5-10C warmer ambient temperature in summer in Sydney Vs Barnoldswick isn't going to affect a properly functioning brake.

Not saying there's not something wrong with your brake(s), but it's a problem with your brakes, not DOT fluid in general, and my money's on overfilled and the difference in temp between morning/afternoon was enough to expand it that last little bit and lock the brake on.

I'd like honest opinions on good brakes that won't fail when it gets hot weather

If it's an open design with bladder to allow expansion is it possible the breather hole is blocked? That and a bit of overfilling could cause what the OP describes.