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03 RKC - Front Brake Lever Travel

RibEye

RibEye

Senior Member
My front brakes are not spongy. Once the lever gets to the active point, the function is nice and hard. The problem is that it takes over half of the lever travel before compression is detected. I have rebuilt my master cylinder, and fully replaced all fluid during bleeding. Some improvement, but I did not see much wear on the MC seals. Before the rebuild, ineffective lever travel was around 2/3.

I'm told that accumulation on the caliper pistons can cause this. I can't for the life of me figure how that could be. Being an engineer, I need to know the failure mechanism. It seems that if the pistons were dirty, the pads would not retract, causing drag, but I can't see how that would account for the ineffective brake lever travel.

Last unrelated repair operation, the tech at the dealer did something I did not get charged for, that made the brake operation almost immediate in lever travel, but I did not get charged, nor did it get put on the invoice. I did seem to get quite a bit of brake drag in that state, until the lever travel worked its way back down a bit, over a few hundred miles.

I need a mental model of the failure mode, and its correction. Can anybody help?

Enjoy,
Rich P
 
RibEye said:
Once the lever gets to the active point, the function is nice and hard.
Click to expand...

Rich,
The 1st thing I would do is determine what the physical clearance is between the Hand Lever contact point & the hydraulic piston contact point. Only a SMALL amount of distance is needed to assure that the compensation port will remain uncovered during "Brakes are Off" times.

With your fingers, gently push the brake lever AWAY against it's final outward stop. Then Gently pull the lever IN (as in applying the brakes) until you feel the "lever contact point", contact the "Piston contact point". How much "play" or mechanical lever movement do you have that must be taken up BEFORE the piston even begins to be pushed in?

On my bike, I would guess it to be about .020".

Now, ONCE the piston begins to move,,, how much distance can you sink the MC piston into the bore? . Mine is near nothing,, tops .010".

All the mechanical "lash" in the brake lever and piston needs to be as little as possible but still have the compensation port remain uncovered. Once the piston in the MC starts moving, "near nothing" in distance should be required to push out the caliper pistons. Since the caliper pistons use quad seals, the piston/pad relaxed state is a very close distance to the rotors.

I do not have ABS, therefore my lever movement is VERY VERY small before I am trying to compress a liquid.
 
Seems we are having a lot of brake problems lately, makes me wonder of the vendor HD is using for master cylinders, just thinking out loud here.
 
If you have never cleaned the pistons in the calipers. Then that is your problem.

The reason it causes the brake lever to have so much free play is because only one or two of the pistons are pushing on the pads. The others two or three are not comping out of the caliper. When all four pistons are coming out of the calipers at the same time you will not have excessive lever travel. You will see when you take them apart and check it out.
 
I like Hoop's analytic approach; do check out the actual mechanical lever stroke, pivot and lever for any elongation or wear. Then work your way from the calipers, rebuilt/renew all new seals and hoses (steel braided ones are smaller teflon lined means less swelling or mushiness). Not to worry, you will find the problem.
 
Last edited:
OK. Here is what I found, and it did solve the problem...

Apparently, when the caliper pistons get dirty, they hang up on the caliper seals. If they hang-up on the way back in (retraction), they drag. If they hang up on the way out (actuation), then when you release the brakes, the seals, which do provide just a bit of pad retraction pull, pull the pads back too far. This causes you to have to actuate the lever more, to get the pads in contact with the rotors.

Since you can push the fluid back into the master cylinder from the bottom (some bleed this way), that explains why the brakes do not auto-adjust for brake wear.

I had a combination of dirty caliper piston issues, some pistons hanging on the say out and some on the way in, resulting is both, light dragging (cutting my mileage measurements), and excessive lever motion to the friction point (my primary problem).

Spongy feel at the friction point is still air in the lines. I did not have that.

Thanks folks. I needed to understand the failure mechanism, and now I do. The brakes are as good as new...very little lever to get to the friction point, and no brake dragging at all.

Enjoy,
Rich P
 
I am Happy you got your front brakes repaired.

But some day someone has to explain to me how the failure of 1 in 4 pistons to move,, will increase the needed hydraulic fluid remaining in the other 3 pistons. The dispensed fluid saved from the frozen piston gets applied to the other 3 pistons. All I see is dragging brakes and nothing else caused by a frozen piston.
 
RibEye said:
OK. Here is what I found, and it did solve the problem...

Apparently, when the caliper pistons get dirty, they hang up on the caliper seals. If they hang-up on the way back in (retraction), they drag. If they hang up on the way out (actuation), then when you release the brakes, the seals, which do provide just a bit of pad retraction pull, pull the pads back too far. This causes you to have to actuate the lever more, to get the pads in contact with the rotors.

Since you can push the fluid back into the master cylinder from the bottom (some bleed this way), that explains why the brakes do not auto-adjust for brake wear.

I had a combination of dirty caliper piston issues, some pistons hanging on the say out and some on the way in, resulting is both, light dragging (cutting my mileage measurements), and excessive lever motion to the friction point (my primary problem).

Spongy feel at the friction point is still air in the lines. I did not have that.

Thanks folks. I needed to understand the failure mechanism, and now I do. The brakes are as good as new...very little lever to get to the friction point, and no brake dragging at all.

Enjoy,
Rich P
Click to expand...


It is a horrible design by Harley. Hence bremo brakes in 06n or 07. You can win some bets betting on the solution. People will hit every other potential problem first.
 
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