Rear brake Master Cylinder - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 8 (permalink) Old Aug 1st, 2019, 10:10 am Thread Starter
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Rear brake Master Cylinder

I just replaced the rubber lines on my '96 SS with Venhill braided stainless. Fronts went together easily but the rear is being a problem. My vacuum bleeder will not pull fluid out of the reservoir and through the cylinder or out of the bleeder. Yes I have the caliper rotated around to the top of the rear rotor. I doubt it's the new lines or banjo's so it's either the master or the caliper and I suspect the cylinder. I searched the forum and found a post by Ducvet saying careful with air pressure so as not to blow out the lip seals. I'm wondering if I can safely put air in at the output side of the master cylinder and see if it comes out the bleeder on the caliper. I will mention that before the line change the rear brake was useless, had a hard pedal that moved but did nothing like it was stuck. When I pushed the pedal really hard it seemed to snap and come unlocked and work with normal pressure so maybe something in the cylinder is bad? At about $50 to replace the cylinder that might be the least expensive fix option if it is the cylinder. Also the rear pads were worn nearly to the backing plates whereas the fronts were not even 1/2 worn out. 8500 miles on the odometer. Both sets of pads were Brembos and probably original equipment. Maybe the previous owner rode the rears? Maybe the hard/useless pedal was actually dragging the rear? Any ideas?

Also can anyone tell me the thread pitch on the banjo bolt for the clutch slave. M10 X 1? Venhill didn't supply a bleeder banjo only a regular one and I will obviously need a bleeder valve.

Thanks!

Terry

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post #2 of 8 (permalink) Old Aug 1st, 2019, 11:40 am
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10 x 1.0 on Brembo should be right I only see course threads on Japanese bikes and then Harleys.

You may have a bad master and if you can replace for $50 with new Brembo I would do so. Normally these units are quite reliable but that master is now 23 years old so for the cost of dinner out you can be done with it. I must add though due to routing the rear CAN be a bear to bleed, check bleed down is not closed off by debris or someone adjusting the pushrod too far. Make the bleed at the high point and push/pull fluid through, most times if it is not the ports in the master it is a bad master.

I see plenty of riders who come from non-sport bikes and use 90% rear brake which as we all know on a ducati is only good for 10% brake power. Front OEM organic pads often will often last to 40-50,000 miles before needing to be replaced so 8,000ish miles are just bedded in. Rears pads will struggle to last 4,000 if that's all you use.
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post #3 of 8 (permalink) Old Aug 1st, 2019, 4:20 pm
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Just Remember one Important thing--Brakes Only Slow You Down lol---this can be both good & bad depending on your situation

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post #4 of 8 (permalink) Old Aug 1st, 2019, 5:14 pm
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I just replaced the rear master on my 998, it was under $50 from Motowheels. My rear pads were 50% worn after 3500 and I very rarely used the rear brake. I suspect it was all kinds of screwed up. My initial symptom was excessive lever travel.

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post #5 of 8 (permalink) Old Aug 3rd, 2019, 9:28 pm
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Originally Posted by StraDuc View Post
I just replaced the rubber lines on my '96 SS with Venhill braided stainless. Fronts went together easily but the rear is being a problem. My vacuum bleeder will not pull fluid out of the reservoir and through the cylinder or out of the bleeder. Yes I have the caliper rotated around to the top of the rear rotor. I doubt it's the new lines or banjo's so it's either the master or the caliper and I suspect the cylinder. I searched the forum and found a post by Ducvet saying careful with air pressure so as not to blow out the lip seals. I'm wondering if I can safely put air in at the output side of the master cylinder and see if it comes out the bleeder on the caliper. I will mention that before the line change the rear brake was useless, had a hard pedal that moved but did nothing like it was stuck. When I pushed the pedal really hard it seemed to snap and come unlocked and work with normal pressure so maybe something in the cylinder is bad? At about $50 to replace the cylinder that might be the least expensive fix option if it is the cylinder. Also the rear pads were worn nearly to the backing plates whereas the fronts were not even 1/2 worn out. 8500 miles on the odometer. Both sets of pads were Brembos and probably original equipment. Maybe the previous owner rode the rears? Maybe the hard/useless pedal was actually dragging the rear? Any ideas?

Also can anyone tell me the thread pitch on the banjo bolt for the clutch slave. M10 X 1? Venhill didn't supply a bleeder banjo only a regular one and I will obviously need a bleeder valve.

Thanks!

Terry
I've had similar problems with mine - usually due to moisture buildup in the rear caliper. That'll seize up the piston, and give you a hard pedal, with no response. I've also had problems getting the rear caliper to bleed (usually at the same time) - having to completely remove the bleed nipple and then pump on the pedal to blow the crud out (into a paper towel to catch it). Once I get that clear, I can put the nipple back in and then bleed as normal.

I suspect a seized (or partially seized) piston in your rear caliper is the cause of the pad wear - my wifes bike had that problem...

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post #6 of 8 (permalink) Old Aug 4th, 2019, 7:33 am Thread Starter
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I suspect a seized (or partially seized) piston in your rear caliper is the cause of the pad wear - my wifes bike had that problem...
Thanks Steve. I just ordered a new master cylinder but before it arrives I will remove the rear caliper and investigate it further. Before I obtained it the bike spent it's entire life indoors and was obviously very well cared for so with only 8500 miles on it I'm hoping the caliper is good.

Can anyone confirm that the rear underslung caliper is a model 32G Brembo?

'73 Ducati Bevel Drive 750 GT |'74 Norton Commando Roadster |'96 Ducati 900 Super Sport/SP | '06 Sport 1000 Monoposto

Last edited by StraDuc; Aug 4th, 2019 at 7:39 am.
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post #7 of 8 (permalink) Old Aug 7th, 2019, 6:20 pm
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I'm sure you already have --but remove the bleed nipple and clean it out well make sure the holes are not clogged --I see that all the time on older bikes where the brakes have not been flushed on a regular basis

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post #8 of 8 (permalink) Old Aug 9th, 2019, 12:28 pm Thread Starter
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Problem solved!

Thanks to all who offered advice. I did check the rear caliper before the new $52.65 rear master cylinder arrived and I didn't see any issues. Pistons moved with finger pressure. So this morning I popped in the new master and connected my vacuum bleeder. It immediately sucked out the entire reservoir of fluid. Refilled and pulled it down to the minimum line twice more and job done. Solid pedal and rear brake functioning as good as you can expect from a Duc. I had removed the torsion arm and rotated the caliper to the top of the rotor and held it there with a bungee. Easy bleed. Time to turn some fuel into noise and break in the new brake pads and tires. Three out of four bikes now in road worthy condition! So w00t! as the kids like to say.
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