Brake line replacement

[ahebron]

Hi DA
Sorry to hear the nipples are playing up.
My experience is the generic nipples from BNT don't fit right.
It seems that aftermarket manufacturers ideas of diameter and pitch is different from BMW.
The local BMW agent supplied me with a new nipple ex Auckland of course with in two days of ordering it.
The new nipple came with the rubber boot all about $17.

Adrian

 

[Disaster Area]

I wonder if the place here in Dunedin which does the servicing for BMW would have any? Worth a shot I suppose. It's not like I use the back brake anyway.

 

[ahutcheon]

Dunno if they would have the bits in stock, but I've always found them pretty helpful so got to be worth a try?

 

[Disaster Area]

If they don't have them in stock I'll order them from Auckland. I'll try the ones from BNT and see what happens.

If you're around and want to help bleeding them let me know. As I said earlier, it's a job I loathe doing so someone to bounce ideas off is always welcome.

 

[Disaster Area]

Just a couple of quick questions from a paranoid brake bleeder: If I've replaced the hoses, just how much air should be in the system? How long should it take before no more air comes out? It seems to be taking a long time! Also, it feels as if some of the bleed nipples are moving around in their socket, allowing air to get through the threads. Is that a realistic thing?
I just seem to be getting lots and lots of air without, even though (for the front) the fluid drops in the reservoir. The rear just seems to be giving me lots of air with no drop in fluid level.
Over to the experts!

 

[ahutcheon]

If they don't have them in stock I'll order them from Auckland. I'll try the ones from BNT and see what happens.

If you're around and want to help bleeding them let me know. As I said earlier, it's a job I loathe doing so someone to bounce ideas off is always welcome.

Replied to your PM...

 

[nigel tailyour]

if you have positive pressure as you crack open the bleed valve, it will not matter that the thread is loose. fluid out prevents air in. So its probably good to have asecond person on the brake lever while you are cracking open the nipple. Close the nipple before they release the lever.

 

[Slipperyeel]

+1 for the above instructions/comments.

Just another thought. Do you think there are bubbles in the fluid? I have this idea that if the bottle isn't allowed to settle and is handled gently thereafter (with the cap on I mean) you can find yourself pouring bubbles into the system, tiny bubbles. But maybe I'm talking rubbish?!

 

[ralphy]

No need for a bleeder or special prep for the brake fluid (though neither will hurt). Just tie back the brake lever after initial bleeding and leave it overnight. Worked for me when changing m/c and hoses on separate occasions.

And this has just worked for too, after new lines and careful bleeding there was still a bit more ‘sponginess’ in the feel than I liked, but your tip has cured it completely.



R

 

[Slipperyeel]

Someone needs to explain why that technique might work? I mean as opposed to just leaving it overnight which has worked for me in the past (that was until I started taking care of the new fluid bottle... which seems to have eliminated any spongyness when finishing).

 

[Disaster Area]

Someone needs to explain why that technique might work? I mean as opposed to just leaving it overnight which has worked for me in the past (that was until I started taking care of the new fluid bottle... which seems to have eliminated any spongyness when finishing).

Perhaps tying the lever back squashes all of the bubbles?

 

[Slipperyeel]

Yea, but then they don't go anywhere. They just get squashed!

I can't yet see why it's different from just leaving it overnight?

 

[Disaster Area]

Yea, but then they don't go anywhere. They just get squashed!

I can't yet see why it's different from just leaving it overnight?

But if the bubbles are pre-squashed, they won't be able to compress again when you press the lever, getting rid of the spongy feel.
Simples.

 

[Slipperyeel]

Well, I like the idea, but I think there's a flaw in there somewhere like when you take the pressure off the lever they become 'unsquashed'...

Personally I think they just vent out during the period they're left so doesn't really make any difference squashed or 'unsquashed'. Though I wouldn't have expected it to be able to vent worth the system pressurised?

But would be good to hear some other theories. It's an old problem!

Glad they're fixed though!

 

[ralphy]

I’m assuming the compressed trapped air rises to the highest point i.e. the reservoir, from there it exits out as that component isn’t pressurised (to anywhere near the rest of the system).
R

 

[topcat2006]

Someone needs to explain why that technique might work? I mean as opposed to just leaving it overnight which has worked for me in the past (that was until I started taking care of the new fluid bottle... which seems to have eliminated any spongyness when finishing).

The master cylinder is a spool valve which by pushing it in joins the ports between the reservoir and the brake lines. By tying the lever in you are keeping the connection their and that allows the air to bubble up.

 

[fatnfast]

Gravity will allow the air bubbles to rise even if you do not tie the lever back. However, air can still stay trapped in certain parts of the brake system depending on caliper types, hose routes etc. Tying the lever back overnight and the resulting high back pressure this creates, helps to shift any remaining pockets of air. Obviously the system is sealed whilst the lever is pinned back so the air will not be able to vent direct to air. Once you release the tied back lever in the morning the air, which has now travelled to the master cylinder, can vent into the reservoir.
Well, thats my theory

 

[Comfy Old Boots]

Maybe get a pro to do it?