Author Topic: Front brake problem  (Read 190 times)

Offline Peter949

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Front brake problem
« on: April 10, 2021, 05:34:13 PM »
The dual front disk brakes on my 84 California no longer work, after I removed the front wheel and simply installed a new tire. The front wheel was off the bike for 4 weeks.

When I squeeze the brake lever it travels to the grip with no resistance at all. I topped up the fluid, bleed the brakes, the calipers and pads look perfect, and new braded brake lines a few years ago.  I tried to pump up the bakes by rapidly pulling the brake lever ... but absolutely nothing.  :undecided:

Any advice would be greatly appreciated, as I am no expert on hydraulic disk brakes.

Peter

1984  Cali II
Aprilia 125 Sportcity Scooter

Online Tom H

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Re: Front brake problem
« Reply #1 on: April 10, 2021, 05:51:55 PM »
If your bike has the stock braking system. The lever/MC on the handlebar only controls the right front brake. The foot pedal controls the rear and left front.

If your bike has been modified to de-link the brakes. The lever/MC on the bar would control both front brakes.

Does the rear brake work? Does the LH front brake work when you hit the foot pedal?

Tom
2004 Cali EV Touring
1972 Eldo
1970 Ambo V1000
1973 R75/5 SWB with Toaster
2007 HD Street Bob
1953 Triumph 6T (one day it will be on the road!)

Offline Peter949

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Re: Front brake problem
« Reply #2 on: April 10, 2021, 06:10:47 PM »
Thanks Tom ... I did forget about the linked brakes. I will certainly check to see if the front left disk brake is working from the rear brake pedal.
Peter

1984  Cali II
Aprilia 125 Sportcity Scooter

Offline n3303j

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Re: Front brake problem
« Reply #3 on: April 10, 2021, 06:48:54 PM »
If you pushed the pads way back when removing the caliper from the disk it will take a bunch of strokes to move the pads back to the disk. Each stroke only advances the pad a tiny bit. (Ratio of MC piston area to caliper pistons area). That's where all the power comes from.

I've also done much better moving pads with a moderately slow pumping action. Gives the fluid more of a chance to flow through its path in the master cylinder.
'98 MG V11 EV
'96 URAL SPORTSMAN
'77 MG 850T3 FB

Wildgoose Chase Moto Guzzi

Re: Front brake problem
« Reply #3 on: April 10, 2021, 06:48:54 PM »

Offline Peter949

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Re: Front brake problem
« Reply #4 on: April 10, 2021, 08:03:40 PM »
Partial Success!
The left front disk brake was operating normally with the foot pedal. Thank you Tom for the reminder about my 'linked' brakes. :thumb:

Also, I did push the brake caliper pads well back to help position the caliper back over the disk. After many many pumps of the brake lever, I am starting to feel some braking action.  Is there something I can spray on the brake caliper piston to help free things up?

Thank you for the helpful replies. 
Peter

1984  Cali II
Aprilia 125 Sportcity Scooter

Offline n3303j

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Re: Front brake problem
« Reply #5 on: April 10, 2021, 08:29:46 PM »
Partial Success!
The left front disk brake was operating normally with the foot pedal. Thank you Tom for the reminder about my 'linked' brakes. :thumb:

Also, I did push the brake caliper pads well back to help position the caliper back over the disk. After many many pumps of the brake lever, I am starting to feel some braking action.  Is there something I can spray on the brake caliper piston to help free things up?

Thank you for the helpful replies.
If the caliper pistons are not moving freely the caliper should be rebuilt or replaced. A binding caliper can lock up the associated wheel with dire consequences.
'98 MG V11 EV
'96 URAL SPORTSMAN
'77 MG 850T3 FB

Offline pehayes

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Re: Front brake problem
« Reply #6 on: April 10, 2021, 11:59:04 PM »
Likely it is not the pucks in the caliper but rather the piston in the hand master cylinder.  There are seals on that piston.  There are holes in the master cylinder bore which allow for exchange of hydraulic fluid.  When you squeeze the hand lever you send a bunch of fluid down to the caliper to move the pucks and pads.  When you release the lever, that fluid has to be replaced by gravity drainage from the master cylinder reservoir.  If the piston doesn't retract enough, it doesn't expose the bore sidewall hole and won't replace the fluid.  Make sure you have freeplay in the hand lever when it is fully relaxed.  Don't adjust it tight up against the piston.  You might need to remove the hand lever and gently grasp the piston to pull it outwards slightly.  You can clean and lubricate the piston bore with an ear swab Q-Tip and some fresh brake fluid.

Patrick Hayes
Fremont CA

 

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