Brake fluid - ok to top up?

[CDFloss]

Hey. My rear brake fluid is low, so I wanted to top it up. I've been servicing & tinkering with my cars for years, so know more or less about the various DOT specs, etc. Is there any issue with topping up using a new bottle of brake fluid? Obviously I dont know whats in there at the moment, so wont know if the new stuff matches.
Does this matter? Do bikes use a specific fluid? What should a get?

Thanks in advance,
Dave

[Subike]

All brake systems use the same fluid.
Just bikes need flushing more often.
I suggest that you flush you rear brake with new fluid and check the rear hose for that "spongy" feel.
If its spongy replace it.
New pads at the same time would be a good investment.

[skidMark]

Hey. My rear brake fluid is low, so I wanted to top it up. I've been servicing & tinkering with my cars for years, so know more or less about the various DOT specs, etc. Is there any issue with topping up using a new bottle of brake fluid? Obviously I dont know whats in there at the moment, so wont know if the new stuff matches.
Does this matter? Do bikes use a specific fluid? What should a get?

Thanks in advance,
Dave

I would kind of question where it went

[MaxB]

I would be more concerned with what is in there now. Why not bleed the brakes and replace the fluid? One reason the fluid level drops is pad wear so maybe check that out too.

[Katman]

All brake systems use the same fluid.
Just bikes need flushing more often.
I suggest that you flush you rear brake with new fluid and check the rear hose for that "spongy" feel.
If its spongy replace it.
New pads at the same time would be a good investment.

All brake systems definitely don't use the same fluid. Dot 5 is not compatible with Dot 3 or 4.

[skidMark]

I would be more concerned with what is in there now. Why not bleed the brakes and replace the fluid? One reason the fluid level drops is pad wear so maybe check that out too.

**sits there with a stoopid look on his face**

dammit you're right

[Subike]

All brake systems definitely don't use the same fluid. Dot 5 is not compatible with Dot 3 or 4.

read the first post before you put your foot in your mouth

Hey. My rear brake fluid is low, so I wanted to top it up. I've been servicing & tinkering with my cars for years, so know more or less about the various DOT specs, etc. Is there any issue with topping up using a new bottle of brake fluid? Obviously I dont know whats in there at the moment, so wont know if the new stuff matches.
Does this matter? Do bikes use a specific fluid? What should a get

I was replying to a man with prior knowlage

not to an idiot who just thinks hes know everything

[sinfull]

read the first post before you put your foot in your mouth
Obviously I dont know whats in there at the moment, so wont know if the new stuff matches.

No matter what issues you guys have going on, Katman does have a point !

Mate if yr unsure as to whats in there at the moment just flush it right through so you know for future top ups !

[FilthyLuka]

If its gone down because of pad wear, then you COULD top it up, but i would just replace the pads if it has gone down noticeably far.

Bear in mind that if you fill it up to the full mark now, when you press the pistons apart in the rear caliper, the fluid may overflow and leak onto something (like bodywork) and damage it.

[FROSTY:Me]

What I was gonna say--Basicly if fluid isn't at the low level check your pad thickness first before touchin the fluid.

[Katman]

read the first post before you put your foot in your mouth

I was merely addressing this statement.

All brake systems use the same fluid.

I am genuinely concerned with the amount of bad advice and misinformation that is so commonly seen on technical forums such as this. You do realise that others will be reading your posts - not just the original poster - don't you?

[Katman]

Bear in mind that if you fill it up to the full mark now, when you press the pistons apart in the rear caliper, the fluid may overflow and leak onto something (like bodywork) and damage it.

And furthermore, it's advisable that, when you force back the pistons, you crack open the bleed nipple and drain the excess fluid out through the nipple. Otherwise, if there's shit in the brake system it can be forced back up into the master cylinder and can result in catastrophe if a bit of shit gets caught between the bore surface and the seal lip.

[CDFloss]

Thanks for all the advice. Yes I do know (more or less) what DOT specs are (being glycol\silicon\synthetic based, etc), but I'm no mechanic or engineer. Hence the reason I ask these things.

I've just recently bought the bike, so dont know its entire history. I do have a service history, but nothing I can see specifically says that the brakes have ever been bled. I noticed that the level is closer to the lower mark than full, but its not quite there yet. The front looks sweet.
Havent checked the pads closely (they've got a plastic cover-thingy you have to remove to inspect the pads I think) - but they seem to be ok from what I can see.

I'm taking it in for a service/tyres/WOF/etc soon, so will ask them to check it out.

In case I decide to bleed the brakes myself in future - I guess its much easier than a car? No bleed sequence or ABS to worry about. Just each one seperately, no catches? I'll search the forums as Im sure there'll be something on this already. Thanks again...

Cheers
Dave