Rear brake failure

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mimico_polak

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Was just on a ride and my rear brake is effectively non existent.

I didn’t pay much attention until I tried it at low speed (and bike is at temp) and zero. Full of play, and no reaction from the rear braking system.

Bike cooled off now and I can feel hydraulic pressure when I press on it….but at operating temp….zero.

Very concerning since the last time it was touched was a reputable mechanic that bled the system front and back….but since it’s been a year I don’t expect much. Front is great.

Rear…nadda.
 
Thinga to check:

Is there fluid in the reservoir. Are there any obvious leaks. Do pads have some life left. If you open reservoir, is there a vacuum in reservoir. If you pump brakes five times, do they build pressure and start to work.
 
Get a jug of water or bleach or something, pump the brake until there's pressure feedback and hang the jug off the pedal to keep pressure on. Do it for maybe 20 minutes, and see if it pumps up firm after that. There's probably air in the system.
 
Is the bleed nipple on the rear caliper oriented in such a manner that air won't get trapped somewhere in the caliper? There's a chance you'll have to remove the caliper and hold it in a position that actually allows you to evacuate trapped air.

Or maybe your rear master is $#!+.
 
Brakes are really easy to diagnose. First, bleed the back brake. Fill the reservoir, put a clear tube on the bleeder and have the dump end in a small clear glass to captor fluid. Pump 3 times then crack the bleeder on the calliper. Do this 5 times, watch for air bubbles on the tube. Once they stop, the brakes are bled.

If there is no pressure buildup on the pedal, most likely the rear master is pooched. $30 part, replace and repeat bleed procedure.

If there is still no pressure, it’s the calliper. Remove anc check the cylinder, piston for scratch marks, and the seals for cracks or deterioration. If these are present, rebuild or replace caliper.

Then list the Duc and buy a Suzuki.
 
You had me until the last line @Mad Mike kudos! I'll grab some new fluid and tubes tonight or tomorrow. Not sure if my cheapo brake bleeding kit from PA is functional even.
 
Common problem on Ducati's wherre the MC is by the engine and exhaust. Don't know how yours is set up with DSSA, but on SSSA where the caliper is underslung and goes through the other side and under the swingarm, the best way is to unbolt the caliper and elevate it while bleeding. Last time I bled my 998, I used my vac bleeder, then did it again manually for good measure.
 
The 20 second diagnosis we did probably won’t be that helpful, but it was literally zero pressure, only getting spring resistance.
Reservoir was full and no obvious signs of leaks in the system. Would have to have a lot of air introduced if it’s that bad since bleeding last.
I guess bleed it again and see, otherwise could be a M/C issue
 
Wind Shear said:
The 20 second diagnosis we did probably won’t be that helpful, but it was literally zero pressure, only getting spring resistance.
Reservoir was full and no obvious signs of leaks in the system. Would have to have a lot of air introduced if it’s that bad since bleeding last.
I guess bleed it again and see, otherwise could be a M/C issue
Click to expand...
If it's air in the system, rapidly pumping a few times should get you brakes. If rapid pumping doesn't help, I strongly suspect master (could be plugged port between reservoir and piston or failed piston seal). The solution for all master problems is just replace though so specific failure mode isn't all that important. With no obvious leaks and no pressure in the system, the issue being downstream of the master is very unlikely (although not impossible, pull caliper off and see if bellows is full of fluid as that can hide the leak).
 
I helped a friend with a similar problem recently. We got lots of air bubbles from the bleeder valve when just pumping the lever to bleed normally from the caliper, but we never gained much pressure that way. We eventually had to crack the banjos and bleed from the ABS unit, which sits at the highest point of the system. The ABS unit is of course situated in the absolute worst spot for access, so good luck with that. That bleeding was good enough to get through the day, but I'm not sure what the underlying cause of the air was. Might have been leaky seals on the master.
 
Ash said:
I helped a friend with a similar problem recently. We got lots of air bubbles from the bleeder valve when just pumping the lever to bleed normally from the caliper, but we never gained much pressure that way. We eventually had to crack the banjos and bleed from the ABS unit, which sits at the highest point of the system. The ABS unit is of course situated in the absolute worst spot for access, so good luck with that. That bleeding was good enough to get through the day, but I'm not sure what the underlying cause of the air was. Might have been leaky seals on the master.
Click to expand...
I forgot about ABS pumps. Took something so simple and made it such a pita.
 
GreyGhost said:
If it's air in the system, rapidly pumping a few times should get you brakes. If rapid pumping doesn't help, I strongly suspect master (could be plugged port between reservoir and piston or failed piston seal). The solution for all master problems is just replace though so specific failure mode isn't all that important. With no obvious leaks and no pressure in the system, the issue being downstream of the master is very unlikely (although not impossible, pull caliper off and see if bellows is full of fluid as that can hide the leak).
Click to expand...
Just trying it now at lunch….zero pressure buildup.

Found some tubing which should work and will play around with it tonight or tomorrow.

For now I’ll just move the stand to a better spot as it’s rather tight.
 
No pressure buildup. No bubbles showing when pumping. But since no pressure then releasing the bleeder just allows fluid to come out.

No leaks anywhere that I can see.

Brake pads are good and lots of life left.

At least I got to use my motorcycle lift for…lifting my motorcycle! So that’s a plus.
 
Wind Shear said:
The 20 second diagnosis we did probably won’t be that helpful, but it was literally zero pressure, only getting spring resistance.
Reservoir was full and no obvious signs of leaks in the system. Would have to have a lot of air introduced if it’s that bad since bleeding last.
I guess bleed it again and see, otherwise could be a M/C issue
Click to expand...
No pressure can be several things.

Air in system/low fluid
Bad master (most likely)
Bad line (check for bulges when under pressure)

If you diagnose it being the master, you can replace it with a generic version for about 1/10th ghe price of a Ducati part. In fact I’d probably do that given the volume of inter web stories about failed masters on Ducs.
 
mimico_polak said:
No pressure buildup. No bubbles showing when pumping. But since no pressure then releasing the bleeder just allows fluid to come out.

No leaks anywhere that I can see.

Brake pads are good and lots of life left.

At least I got to use my motorcycle lift for…lifting my motorcycle! So that’s a plus.
Click to expand...

Not to give you false hope, but it took me a LOT more than just 3 pumps to build pressure on the Ducati rear MC's I've bled starting from zero. Might have been because of the caliper being underslung below the axle and the line running around and under the single-sided swingarm. I'm happy to come by sometime to take a look, unless you want to drop by here.
 
Relax said:
Not to give you false hope, but it took me a LOT more than just 3 pumps to build pressure on the Ducati rear MC's I've bled starting from zero. Might have been because of the caliper being underslung below the axle and the line running around and under the single-sided swingarm. I'm happy to come by sometime to take a look, unless you want to drop by here.
Click to expand...
Stupid CT had 22 DOT4 bottles in stock...but zero on the shelf.

'I'm sorry sir, it's in the middle of a skid and I can't take everything off just for one bottle. It's been there since June and I'm not sure why they haven't unloaded it yet'.....

I'll pick some up tonight at another shop as I've been recommended to NOT use the DOT4 bottle I used at your place since it's probably got water after 2 years.

If you're available I'd appreciate it 100% as the bike's on the lift. Maybe next week or some evening this week, whatever works for you.
 
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