What do do with those bl*%dy brakes?

[PasoRoo]

Hi All,

I think I have tried about everything to fix my brakes and it's getting the better of me. Jaffa kindly offered to help me and came over to render assistance. After installing everything we started bleeding the system. After no more air came out there is still no pressure at the brake lever. And I literally mean: no pressure.

We did the following:

• I took apart every single part of the front brakes and cleaned them.
  Put an overhaul kit in the master cylinder.
  Put new seals in the calipers.
  Used the supplied grease on all the seals.
  The pistons were OK.
  Added Goodridge 'speed bleeders' on the calipers.
  Added HEL stainless steel brakelines.
  Added a banjo bolt with bleed valve on the master cylinder.
  Tightened everything up (to exact torque where possible).
  Filled the master cylinder with DOT 4.
  Started pumping until fluid appeared from the valves at the calipers.
  Started bleeding the left caliper (furthest from the master cylinder).
  Then the right one.
  Then the bleed valve at the master cylinder.
  All three were repreated till no more bubbles appeared

Result: hardly any brake pressure. When you squeeze the brake you can feel the pads move but not enough to even stop the wheel from rotating.

No fluid is leaking out from any connections
The master cylinder is pumping because I get the usual 'fountain' coming out of the cylinder if I leave the diaphragm and lid off.
After leaving the lever tied to handlebar overnight only a few little bubbles came out. Given that there is hardly any pressure to start with I'm assuming that leaving it overnight doesn't do a lot in the first place.

One thing I'm wondering: if air got sucked into the system somewhere, wouldn't I keep getting bubbles coming out when bleeding (and fluid leaking out)?

Any advice would be greatly appreciated because this thing has me (and Jaffa) stumped.

Cheers,

Mike

[higgy]

Many brake systems can be difficult to bleed

The best way to deal with this sort of issue is to reverse bleed them
Instead of of pumping the fluid down from the master cylinder get situated to bleed from the calipers up.
It can be done with a brake fluid pump or by raising the fluid supply up above the master cylinder and using a long tube to supply the fluid to the caliper bleeds. A pump is by far the quickest way and they are not overly expensive.

Here is an example of one such pump

http://www.amazon.com/Dorman-9-910-Brak ... B0024G9QX0

I'm sure you can find a similar one from any good automotive supply shop down your way

[paso750]

a big syringe would work fine too and could be used also when changing the fork oil.
http://www.amazon.com/Motion-Pro-Fork-L ... 912&sr=1-5
If that doesn`t work you should try another brake pump. The pump squishes out fluid to the top also when it`s not ok or the seals would be put in the wrong way as that doesn`t require a lot of pressure. This doesn`t have to mean it actually puts full pressure on the system.

G.

PS: had you touched the lever adjusting screw ?

[PasoRoo]

Hi all,

I normally use a syringe but the one-way valve on the speed bleeders prevents this.

I probably did touch the adjusting screw before the overhaul to try and get a bit more action at the lever. Should it be in a particular position?

G, your remark about the master cylinder pressure makes me think about the direction of the primary seal in it. The instruction sheet helpfully tells me to mount it with 'the lip facing the interior of the cylinder'. So: does that mean the 'open' end (the part with the largest diameter) of the seal is facing towards the banjo bolt on the master cylinder or away from the banjo?

One consolation: if it IS the the wrong way round I wasn't the only one fooled by the Italian instructions...

Thanks for not giving up on this cause (if not a lost cause, then at least a wandering one)!

Mike

[Fraser]

Mike,

I had something like this when changing the F08 caliper and installing a master cylinder rebuild kit on a Moto Guzzi; beld and beld the thing till no bubbles, but the lever was still really soft. The brakes did work but the lever was hopeless. Now, being that the Guzzi had intergrated braking and the foot brake operated the left front disk and the rear disk I went out for an experimental ride (as still had 2/3 braking available).
Anyway, in 5 minutes the front brake lever (which did only the right front disk)was good and firm. Only conclusion was that some vibration/bumps etc pushed air through the system into the master cylinder.
Is it possible for you to safely go up and down your street a few times, assuming there is some braking available even if it is difficult to feel?

Cheers,

Fraser.

[ducapaso]

just a quetion.. you are SURE that the rebuild kit was EXACTLY the same?

[paso750]

So: does that mean the 'open' end (the part with the largest diameter) of the seal is facing towards the banjo bolt on the master cylinder or away from the banjo?

As stated in your other topic of course the open side of the rubber seal has to show inwards (towards the banjo) When the piston is pushed in by the lever the seal has to "open" and press itself against the cylinder walls. Only this way it can create pressure. If showing outwards the brake fluid may pass between seal and cylinder when pulling the lever and press it in the pump when releasing it.

I probably did touch the adjusting screw before the overhaul to try and get a bit more action at the lever. Should it be in a particular position?

I think so. If I remember well brake issues due to the lever adjusting screw were posted already.

G.

PS: I do have one or two old pumps. I can open them if you need pics.

[PasoRoo]

Hi all,

OK G, seeing your reply I thought that the seal was mounted the wrong way round. Hooray! Easy to fix. Took the master cylinder off and took the internals back out. Turned the seal around and put it all back in the master cylinder.

After I topped up with brake fluid I tried the lever: disaster! The lever goes in but does not come out. Pulling out the lever actually seems to suck brake fluid back.

Here's how I put it together (the master cylinder is in the foreground so squeezing the lever would move the piston towards you):

Master_parts1.JPG

(257.25 KiB) Downloaded 771 times

and from a different angle (the master cylinder is on the left):

Master_parts2a.jpg

(172 KiB) Downloaded 771 times

So either everything was in the right order in the first place (but didn't build any pressure) or something else is going on.

This thing really has got me almost beat.

Nicola: the kit is exactly the same as what was in the cylinder originally.

Fraser: I have no brake pressure at all so I would hesitate to ride it anywhere.

Thanks again for all your advice guys!

Mike

[riascns]

If the master cylinder is very worn, then a new seal can make things worse. I have had this happen before on a clutch, originally was soggy, new seal kit - result no clutch at all. Solution was a new master cylinder.


As far as bleeding, I have always had success with the following method which requires no special tools other than 3 hands.

1. Fill the system with fluid by pumping with the bleed valves open until fluid comes out
2. Close the valves and pump
3. Hold lever in whilst releasing bleed valve
4. Close bleed valve and pump again
5. Repeat 3 & 4 until success
6. If no success, pump system and tie lever aginst the bar over night
7. Repeat 3 & 4 until success

Never had a failure with the above procedure.

For safety best have a tube over the bleed valve venting into a suitable container as otherwise may get brakefluid everywhere as it will be under pressure.

[PasoRoo]

I suppose a worn master cylinder is quite possible. If I replace it I would like to start upgrading to newer parts as I have been planning for some time.

Would a 916 or 996 master cylinder work with the original F08 calipers?

Mike

[Fraser]

Mike,

If you need a new master cylinder Bevel Heaven have them for USD$115.
http://shop.bevelheaven.com/detail.aspx?ID=206

Cheers,

Fraser.

[Jaffa]

I suppose a worn master cylinder is quite possible. If I replace it I would like to start upgrading to newer parts as I have been planning for some time.

Would a 916 or 996 master cylinder work with the original F08 calipers?

Mike

Really, having inspected the master cylinder, I dont think it needs replacing. There is very minor scoring on the inside, with nothing particularly evident on the old piston. I would have not hesitation in reinstalling on my own bike and this is what we did with Mike's. The rebuild of the master cylinder and calipers was I think text-book and cannot understand why this has not fixed the problem.

Riding the bike in its current condition isnt really an option.

The only conclusion I can come to is that there is still some air in there somewhere, either at the splitter or some other joint.

[paso750]

what about that o ring, shouldn´t that sit on the piston, in the groove behind the seal ?

G.

[PasoRoo]

G,

The inner diameter of the O-ring is about the same as the outside one of the piston. When I took the cylinder apart it seemed to sit on the recess furthest into the master cylinder. Do you think that is incorrect?

I will check what the drawing on the Brembo instructions shows (if anything).

I'm going to have another go at putting all this together but I'm also considering alternatives. Do you know if a 916/996 master would be able to operate the F08 calipers? I would like to upgrade the brakes to goldlines at some stage. If I'm replacing the cylinder I may as well buy the one I want to end up with.

Cheers,

Mike

[paso750]

Mike,

I`ll look through my parts boxes right now and if possible disassemble one pump today to let you know.

Of course other pumps will work. Generally.
The smaller the piston diameter the more aggressive the pump usually is.
Bigger pumps like a PS16 will need more hand force to create the same pressure but this will give the rider a better feeling for the brake.
The question may be the relation between brake pump piston diameter and brake caliper piston diameter.
4 or 6 piston calipers have pistons with different diameter. The smaller pistons react sonner on pressure than the slightly larger ones which makes the brake more sensitive.
4 piston calipers usually need a pump PS16 or bigger. The caliper pistons are smaller than the ones of the 2 piston Paso calipers.

What I`m trying to say is that I don`t know if there`s a kind of "gear ratio".
It may be that a caliper with bigger pistons may need a brake pump with smaller piston. Anyone who knows ?!

I`ll look for the brake pump now ...

G.