Ducati.ms - The Ultimate Ducati Forum banner

1 - 20 of 27 Posts

·
Registered
Joined
·
319 Posts
Discussion Starter #1
I've got an 00/01 ST4, and since new the rear brake has been about a millimeter short of useless. The issue of ST rear brakes has been on this forum a fair bit, and now I THINK I have found the problem.

While dismantling the rear caliper, I pulled open the Ducati Workshop manual and came across a section on "re-attaching the hose lines". It stressed that the banjo connector for the rear brake line, where it attaches to the master cylinder, must have an angle of 24 degrees to the cylinder. Mine was running exactly parallel to the master cylinder, which is how it came from the factory.

Twisting the banjo to the requisite 24 degrees (ish) caused the OEM stainless brake lines to rub the swing arm pinch bolt. But tell you what, I have a rear brake again!!

At the local Duc shop I had a look at some ST2s (no 4s in), and they had the banjo turned off at 24 ish degrees - though they had rubber lines.

Worth a look if you hate the way the rear brake doesn't work... this has had me scratching my head for years, and no Duc shop has ever pointed it out, which I understand - as you can't imagine it'd make the difference.
 

·
Registered
Joined
·
1,910 Posts
That seems kind of odd. Do you know why? I thought that the brake fluid would flow through the banjo bolt at any brake line angle. It would be tough to align the banjo bolt port to the hose line and keep a tight seal. Do you think there was a restriction in the fluid path or does the 24° position allow air in the brake line to be purged? Was your brake pedal hard, without rear brake grip or was it soft/mushy? Just curious.
 

·
Registered
Joined
·
319 Posts
Discussion Starter #4
I have to agree that logically it makes no sense. Banjo connectors, by design, should allow the fluid to enter the holes in the banjo bolt and thus flow back and forth. It's why, over the dozens of times I've thought "must fix that brake" that I never thought to re-position the connection.

I've always put the connectors back as I found them. It just so happened that this time I thought I'd double check the torque figures for the calipers (only to find that the workshop manual says 'don't take them apart'). It was only then that I noticed the couple of lines that I mentioned. It also stresses that the connectors onto the caliper must be at 90 degrees to the perpendicular (which it is).

The text also mentions an angle for attaching the front hoses, except that there are tangs on the calipers that ensure the 'proper' angle.

So, in short, I have no idea why this would make the improvement. However, problem now is that the brake line rubs up against the swingarm (where it curves under and over it) - which is because the angled banjo connector raises the line too high. On ruber hoses I notice that the connector is barely 'bent' upwards, on the OEM stainless lines, it angles up by about 30 degrees, which is what causes the problem with contacting the arm.
 

·
Registered
Joined
·
36 Posts
Very interesting, I have (I hope) attached two extracts from shop manuals

one from the ST4 workshop man and one from a 996 shop man - interesting that both do mention the correct positioning of the banjo angle and in fact the extract from the 996 shop man is more explicit

You may have unearthed the answer for sure - all we need to do now is get around the issue of the brake line fouling with the swingarm

thanks for the info
 

Attachments

·
Registered
Joined
·
1,910 Posts
I guess I can understand why they would specify an angle for brake or clutch lines at the steering head, but still can't come up with a reason for it at the rear brake. It's not worth taking it apart just to visually inspect it, but it did solve the braking problem and that's what's important. Maybe you should move or copy this post to the Halls of Wisdom, I think other members with different rides have complained about their rear brakes.

To protect your swing arm/brake line, try wrapping the brake line with some of the spiral plastic electrical wire wrap. Probably available at Home Depot or Lowes, it's used to keep loose electrical wires together.

One last question Ward, was your rear brake pedal hard or mushy?
 

·
Registered
Joined
·
319 Posts
Routing the brake lines a certain way is done for multiple reasons. Here are some of those reasons:

a) Interference with other parts (specially moving parts such as the fork sliders and swingarm). For example attaching the lines on the front calipers a certain orientation will allow you to put a wrench on the bleeder valve easier to bleed it. It also may prevent the lines bending a certain way, interfering with rotors or other moving parts when the front forks are compressed. On the rear master cylinder the proper orientation of the line will help the brake line go around the pivot point of the swingarm.

b) The most common place for air bubbles to get trapped is where there is a sharp change of direction for fluid movement (not a linear smooth surface) or where there is a small cavity for the bubbles to get trapped or where the air bubbles have to move --down-- first --before-- they can move up and can escape a local cavity or local maxima. As you have guessed by now the region where the line is attached to the master cylinder and calipers via the banjo bolts are the prime locations for air bubbles getting trapped because of all the above. Proper routing of the lines can provide an easier path for air bubbles to escape for the fluid to move easier.

c) Certain routing also reduces severe bending of the lines that can result in reducing the inner diameter of the brake lines which can affect how well the brake fluid can move back and forth through the reduced area.

I personally think the best routing of the of brake lines should provide an easy path for the air bubbles to move out of the system or to move to a place where they can be removed by bleeding. For example this means that --one-- or --both-- ends of the line that are connected to the master cylinder and calipers should be the highest point(s) of the line and there should not be a loop in the line where a local maxima is formed to trap the air bubbles. For example on the older superbikes, the rear caliper is mounted below the swingarm and the bleed valve on the rear caliper is the lowest point of the circuit. This makes it almost impossible to get all the air out of the system. To properly bleed that setup, one needs to remove the caliper from its mounting bracket and rotate it up so that the bleed valve is pointing up and not down and it is also above the rest of the brake line.

On the ST series because of the angle of the handlebars, the first elbow after the front master cylinder, is the highest point of the circuit. To get all of the bubbles out of the system, one needs to remove the master cylinder from the handle bar and rotate it so that the bubbles can escape back to the master cylinder and to the reservoir.

I have put a bleed valve on all of my banjo blots where the lines are connected to the master cylinders (both clutch and brake master cylinders). This allows me to get the last air bubbles out of the system. The difference is significant. On a friends bike, bleeding the clutch master cylinder (not slave cylinder) using this technique has allowed him to find neutral while the bike was running but not moving. He later told me that in all the years that he owned his ST2, he was never able to find neutral while stopped and had to always try to get in neutral before coming to a full stop.

-Fariborz
 

·
Registered
Joined
·
11 Posts
I'm puzzled by the apparent problems with getting the air out of the hydraulic lines. I haven't had any problems with finding neutral on by ST2 either. I bleed the brake and clutch lines using a hand vacuum pump and haven't had to do any extra disassembly or tricks. Also the rear brake isn’t great but it works as I would expect. I guess I’m either real good or real lucky!
 

·
Registered
Joined
·
319 Posts
Discussion Starter #9
Well it just gets curioser and curioser as Alice said to the rabbit or the rabbit to Alice or...

Some responses:

My rear brake pedal was 'hard' - not soft or spongy, but no "feel" and certainly no activity at the pad end!! Now it is still hard, but there's a tad more feel AND I can lock the rear up on dirt!! Have to stamp though.

While I understand the routing issue with lines, putting the line into the position stressed by the manual actually makes it worse in terms of possible trapping / rubbing. As fitted it cleared the arm, in the 'correct' position (manual-wise) it now presses slightly against the swing arm pinch bolt. It would NOT do this IF the banjo connector at the end of the hose wasn't angled up so high.

Additional Confusion:
A friend with an ST4 that has a working back brake looked at his for me, and his (OEM steel) line attaches as mine used to - viz, parallel with the master (not at 24deg).

As mentioned in my original post, looking at ST2 rear brake lines (rubber OEM hoses) they angled off the requisite 24deg.

Sigh.
 

·
Registered
Joined
·
36 Posts
Ward

Since posting those extracts from shop manuals last night I have checked my bike also as I have had the same experience as you. The brake pedal has always felt hard (read as absolutly no air in there baby) but yet the rear brake has always been next to useless - very wooden feeling.

Anyway checked mine and just as you had found the line going to the rear master was lying parrallel to the master cylinder. I noted the drawing in the ST4 shop man shows the line orientated at 24 deg in towards the swingarm, yet looking in the shop man for the 996 it is orientated at 24 deg the other way.

And short of pulling this fitting apart to inspect I think it must be to properly align the drillings in the banjo bolt with the port in the banjo itself - this would allow for a direct path with less restriction for the oil to take.

My result has been the same as yours - I now have rear brake with some more grunt and better feel which is very nice but I turned my line 24 deg out (as per the diagram in 996 man) and all is good no fouling and not enough difference to be in the way of a number 9 boot

thanks for finding this
 

·
Registered
Joined
·
1,910 Posts
Ward, since the brake is finally working now, maybe the pads need to be scuffed or bedded in. Others had complained about poor rear barkes and said a pad change offer big improvments. FWIW, www.spieglerusa.com has banjo fitting with all types of angles and bends to accomidate tight locations.
 

·
Chilehead
Joined
·
6,982 Posts
Fariborz said:
On the ST series because of the angle of the handlebars, the first elbow after the front master cylinder, is the highest point of the circuit. To get all of the bubbles out of the system, one needs to remove the master cylinder from the handle bar and rotate it so that the bubbles can escape back to the master cylinder and to the reservoir.
Not it it's on the side stand, with the bars turned to left lock!

Tom
 

·
Registered
Joined
·
319 Posts
st2lemans said:
Not it it's on the side stand, with the bars turned to left lock!

Tom
Tom,

I used to think that was good enough but after removing the master cylinder off the handlebar and holding so that the end of the lever was pointing up and pumping it few times, I was able to see bubbles still going to the reservoir from the master cylinder. By adding a banjo bolt with a bleeder valve to the master cylinder I solved that problem all together.

BTW, you have set your ride height so that your rear tire touches the ground when on the center-stand. That means that your bike leans significantly more when on the side stand, which in turn will have an impact on the angle of the master cylinder. This can make it easier for you to get the air out.

-Fariborz
 

·
Registered
Joined
·
319 Posts
Discussion Starter #16 (Edited)
LOL. Dontcha jus' love dees bikes. ;)

Don: I'll spin it out the other way and see what happens.

My next hypothesis (developed because of the fellow ST4 that has a) parallel line/cylinder AND b) working brake) is that the holes are not all machined the same - different hose / connector providers? And actually moving the lines around (not necessarily 24 deg) might improve things further?

Jack: No, this is the third set - first off replaced with standard, presumign glazed or whatever - no difference. Second, replaced with HH. No real change.

Line dem 'oles up....

!! UPDATE !!

I just switched the line from the angled "inwards" to angled "outwards" (as per Don's 996 suggestion) and think I should stress that the angled inwards (as per the workshop manual) is NOT good, not with the OEM fittings anyway. I knew it was close to or touching the swingarm pinch bolt, but after just 100 kms or so, the black rubber sleeve on the braided lines had been 'torn' and scored. Suggests strongly that leaving it there would eventually (soonish?) make a hole in the line. That'd be no good coz then we'd be back at the start with no rear brake! :( It might also be dangerous!
 

·
Registered
Joined
·
36 Posts
Ward

Wondering if after you changed from having the banjo angled inwards to now having it angled out - Is the braking performance still the same as when angled inwards?

regards
 

·
Registered
Joined
·
319 Posts
Discussion Starter #18
Hi - sorry for the slow response, been away.

Yup, braking is improved with the connector angled outwards. Problem solved!
 

·
Premium Member
Joined
·
260 Posts
Does anyone have any pics of the m/c bleeder valves that Fariborz suggested installed?
 

·
Registered
Joined
·
319 Posts
PaulST4s said:
.

Does anyone have any pics of the m/c bleeder valves that Fariborz suggested installed?
Paul,

The stock Brembo Gold series brake master cylinder on Ducati superbikes already comes with a bleed valve. I am attaching a picture of brake master cylinder from my '99 748. As you can see the bleed valve is above the banjo bolt with a black rubber cap. The other three pictures show the Yoyodyne bleed valves on my '03 ST4S. I hope this helps.

-Fariborz
 

Attachments

1 - 20 of 27 Posts
Top