Brake bleeding confusion.

[Stevieabz]

Do I at any point need to unscrew the cap on the master cylinder when bleeding the brakes if I'm not planning on adding any more brake fluid into the system? I have just bought 500ml of DOT 4 just in case if I need it, but I only want to get some air out of the system, not do a full fluid change. Thanks.

[Jookeone]

You're going to lose an amount of fluid, depending on how much air there is in the system to bleed. Wont hurt to ensure its topped up again once you finish... Just make sure that the level doesn't drop below the bottom of the cylinder when bleeding as you'll force more air into the system. As long as you keep an eye on it you'll be fine.

[Stevieabz]

Thanks for that. My only confusion is: Once I've bled the system, I'm assuming with the cap on, you then take it off and just add some more fluid in? Wont this just put more air into the system? I had to take that cap off today when I was changing the front pads and that's the reason I now have to bleed the system. It's not making much sense to me, unless I'm over complicating things here? Thanks

[Stevieabz]

Ah, I'll add to my comment. I quest if you pour the liquid in slowly enough not to cause any bubbles, its going to remained sealed bubble free? I think I see now..

[gromgsxr]

yeah making it complicated if the level is low pour more in, no air should have got in to the system just from removing the cap when changing the pads.

[harry_p]

You don't need to bleed brakes just from pushing the piston back when changing pads, unless you've disconnected the caliper from the car or undone the bleed nipple while doing it.

[Brianmoooore]

The bleed nipple should always be opened when pushing the caliper piston back (to avoid pushing the crap that collects in the caliper back into the rest of the system, and the possibility of reversing seals), but as long as the nipple is tightened again before removing pressure from the piston, no air will enter the system.

[Stevieabz]

Thanks for the help guys. I didn't release the bleed nipple on the calliper.. So I defiantly have air (and crap) in the system. I already have 500ml of DOT 4 on the way. How much am I going to need to do a full flush and refill? I'm going to use the two person method of pressing the brake pedal over and over again until brake fluid leaks out all round. Thanks.

[Jookeone]

Make sure you only have the bleed nipple open when you have the brake applied, nipping it again each time it is released. If you don't do this you'll be drawing more air back in each time your mate releases the pedal. 500ml should be enough, just ensure you don't let the reservoir run dry at all like willnz said.

If you have any fluid left get under the car and really spoil her with a flush of the clutch fluid while you're at it, bet that's gone for years with no attention!

[Brianmoooore]

If you did not open the bleed nipple, then there is absolutely no way that air should have entered the brake hydraulic system, or that it should need bleeding.
If there is air in the system, then you have a fault with the brakes that needs addressing.

[Stevieabz]

I have literally no idea how they are worse now after the change. My brakes were fine / a little numb before the change. So I defiantly wanted something sharper and more 'there' if you get me. Looking at the old front pads, they had quite a bit left on them but were liked polished bits of glass.. so I put in the new TRW pads and now my pedal travel is much greater and so is the stopping time. Kind of feels like there's something on the disc. I really don't know what I should do.. other than bleed the whole system with new stuff, or just try bleeding any air that might be in there out.. or just do the back pads when its in raining and just see how it feels after that. I'm not sure.

[Brianmoooore]

If you are using old discs, the new pads won't be worn to them yet, and the pedal will be longer until they do.

[Stevieabz]

Okay, so this could all be as simple as that? aha oh dear I over complicate things. It does say no hard breaking for 150 miles. I'll do the rear's and then do 150 miles and then I'll decide if anything needs doing like bleeding ect.. Thanks for all your help guys. Sorry for being a noooob.

[Brianmoooore]

Measure the thickness of your discs (file off a small section of the ridge around the outside first, so that you can get an accurate measurement of the thickness of the shiny bit). I come across loads of discs that are worn way past their limits.
If the discs have any substantial grooves or ridges in them, or are anywhere near the limit, they should be replaced.
Pagid discs are dirt cheap from the likes of CP4L.

[Stevieabz]

Thanks for that man. Never seen this site before, so thanks for that also! Think I'm going to do the check and then buy new disc's, they certainly don't look new.

[Stevieabz]

Could someone tell me the difference between these two. I'm very limited on cash atm but am going to buy some cheap disc's.

http://www.ebay.co.uk/itm/BMW-3-SERIES- ... 5d44cfdeb7 - £28 for just the fronts. Can't find rears.

http://www.ebay.co.uk/itm/300986420613 - £75.56 all round.

[Brianmoooore]

Presumably one is a vented and the other a non vented disc.
Eicher is a brand aimed at back street traders 'doing up' cars and selling them on quick with no comeback.
I strongly recommend you stretch yourself to Pagid, which is an OEM BMW brand.
http://www.carparts4less.co.uk/cp4l/c/B ... 44c&000027

This is the non vented disc used on 316i/318i saloons without ABS.

[Carmo13]

Just to back up what has been said really, the brakes definitely wont feel as good until the new pads have bedded in.

[Stevieabz]

Got four Pagid's disc's, front two vented. Thanks guys.