Brakes stiff (hard to apply) on 1981 Honda CM400C Custom

danthesk8er · 10-01-2010, 09:39 PM

I will do my best to describe the issue and the things I have done to try to solve it.

The problem:
I bought the bike a few months ago and the front brakes were hard to squeeze. What I mean by that is that it takes a lot of hand force on the brake lever to get the calipers to squeeze on the pads. I can only squeeze the brake in about half way total. As far as I can tell the brakes don't drag when the are disengaged. The caliper releases smoothly.

What I have tried:

Checking the pistons:
I pulled the caliper off and checked the brake pads... the look good and are not worn. I then pulled of the pads and noticed the pistons were a little dirty and were extended about 1/4" from the caliper. I pumped the lever a few times to push out the calipers. I have a dual piston system. I cleaned the brake powder residue from the pistons and sanded then down with 1500 grit sandpaper to make sure they were smooth. When I went to put the pads back in I used a C clamp and attempted to squeeze the pistons back into their original position. The pistons required a lot of force to compress down. I have repaired calipers before and they were not that difficult to get down. Put it back together and didn't fix anything.

Changed brake fluid:
I opened the reservoir and noticed that the brake fluid was a nice brown caramel color. I decided to switch out the fluid by gravity bleeding the lines. I bled the lines with brand new DOT3 brake fluid. The handle was very easy to squeeze while bleeding the lines. I cleaned the lines out and now the fluid in nice and clear. But I still have the problem of stiff lever.

My Thoughts:
I don't think the brake line is clogged, since the fluid flowed so easily. What seems to happen is the master cylinder pumps more fluid than the line needs and the fluid can't get back into the master cylinder.

I am willing to replace the master cylinder and rebuild the brake caliper, but I would like to ask your advise first. Please let me know your thoughts on this.

Easy Rider 2 · 10-02-2010, 12:12 PM

Quote:

Originally Posted by danthesk8er

My Thoughts:
What seems to happen is the master cylinder pumps more fluid than the line needs and the fluid can't get back into the master cylinder.

I am willing to replace the master cylinder and rebuild the brake caliper, but I would like to ask your advise first. Please let me know your thoughts on this.

That first part is "interesting" but not possible. ALL the fluid that the master puts out goes toward pushing the pistons and the calipers. There can't be "too much".

Do the calipers first. I think you will be amazed at the gunk you find when you get them all apart.

It could be a fault with the master but that would be a rare occurance, given the symptoms you described.

danthesk8er · 10-03-2010, 07:59 PM

Well the reason I thought it might be the master cylinder is I read this site:
fireblades.org/forums/honda-cruisers/73126-honda-1981-cm400-brakes.html

I will pull the caliper apart and see what I can find... and then post the results
Hopefully I won't need a rebuild kit.

Thank you for your reply... If there are any other suggestions, please post a reply.

10-01-2010, 09:39 PM	#1
danthesk8er Motorcyclist Join Date: Oct 2010 Location: Houghton, MI Posts: 7	Brakes stiff (hard to apply) on 1981 Honda CM400C Custom I will do my best to describe the issue and the things I have done to try to solve it. The problem: I bought the bike a few months ago and the front brakes were hard to squeeze. What I mean by that is that it takes a lot of hand force on the brake lever to get the calipers to squeeze on the pads. I can only squeeze the brake in about half way total. As far as I can tell the brakes don't drag when the are disengaged. The caliper releases smoothly. What I have tried: Checking the pistons: I pulled the caliper off and checked the brake pads... the look good and are not worn. I then pulled of the pads and noticed the pistons were a little dirty and were extended about 1/4" from the caliper. I pumped the lever a few times to push out the calipers. I have a dual piston system. I cleaned the brake powder residue from the pistons and sanded then down with 1500 grit sandpaper to make sure they were smooth. When I went to put the pads back in I used a C clamp and attempted to squeeze the pistons back into their original position. The pistons required a lot of force to compress down. I have repaired calipers before and they were not that difficult to get down. Put it back together and didn't fix anything. Changed brake fluid: I opened the reservoir and noticed that the brake fluid was a nice brown caramel color. I decided to switch out the fluid by gravity bleeding the lines. I bled the lines with brand new DOT3 brake fluid. The handle was very easy to squeeze while bleeding the lines. I cleaned the lines out and now the fluid in nice and clear. But I still have the problem of stiff lever. My Thoughts: I don't think the brake line is clogged, since the fluid flowed so easily. What seems to happen is the master cylinder pumps more fluid than the line needs and the fluid can't get back into the master cylinder. I am willing to replace the master cylinder and rebuild the brake caliper, but I would like to ask your advise first. Please let me know your thoughts on this.

10-03-2010, 07:59 PM	#3
danthesk8er Motorcyclist Join Date: Oct 2010 Location: Houghton, MI Posts: 7	Master Cylinder Well the reason I thought it might be the master cylinder is I read this site: fireblades.org/forums/honda-cruisers/73126-honda-1981-cm400-brakes.html I will pull the caliper apart and see what I can find... and then post the results Hopefully I won't need a rebuild kit. Thank you for your reply... If there are any other suggestions, please post a reply.

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