soft rear brake pedal.

[WingingEd]

I am not a beginning mechanic, but it's been a long time since I've been in the profession. So over the last year my 2002 GL1800 has developed a soft rear brake pedal on the first press. Let it up and hit it again and has a full pedal. So today I replaced all the pads, front and rear. Also replaced all the fluid although it looked good and clean. I followed the bleed sequence using the old pump up and bleed method. All this changed nothing at all. I never got air out if any of the bleeders and had good spray pressure when opened. I know I could be looking at replacement of one or more components. What have you found that's most likely the problem in a situation as this?

[WingAdmin]

Assuming there is no air in the system, 90% of the time you need a rebuild - either the caliper or the master cylinder. The rubber bits in them just wear out.

The other 10% I have seen due to bound-up caliper slider pins not allowing the caliper to slide - particularly if only one is bound up, in which case the caliper is actually bending to engage the brake rotor.

[WingingEd]

OK, thanks!
I think I'll start with the rear master cylinder replacement. I'm wondering... I noticed that the left fork seal is blown and has lost a lot of fluid. Since that's the side that also has the anti-dive unit, is there a chance the soft rear brake pedal is related to that?

[Andy Cote]

I don't think so.

Many folks will disable the anti-dive during a rebuild.

Have you checked (with a dealer, not online) to see if all recalls are up to date? Specifically, numbers 20, 22 and 23 deal with brake pedal master cylinder. Although the symptom the recall addresses is a sticking brake, this may be related but will at least get you new parts for free from Honda.

There is also a specialized bleeding procedure that adds a step to the Honda service manual. Did you use that?

[WingingEd]

The sequence I used that seems to be the most recommended according to my search is,
1) Using the Front Brake Lever - Front Right caliper Upper bleed nipple
2) Using the Front Brake Lever - Front Left caliper Lower bleed nipple
3) Using the Rear Brake Pedal - Front Left caliper Upper bleed nipple
4) Using the Rear Brake Pedal - Front Right caliper Lower bleed nipple
5) Using the Rear Brake Pedal - Rear caliper Lower bleed nipple
6) Using the Rear Brake Pedal - Anti Dive plunger
7) Using the Rear Brake Pedal - Rear caliper Upper bleed nipple


I did these steps several times trying to get a good brake pedal. When I wasn't successful, I buttoned everything up and took it for a test ride. To my surprise, and beyond my explanation, I had a great pedal and the brakes worked almost good as new. I now even have good stiff pedal sitting still in my driveway. Can't explain it, but I'll certainly take it. So now I will order the fork seals and bushings. Hope that gives me a smoother ride. I bought the bike new 19 years ago but our family situation changed shortly after and it has sat a lot. Only has 30k miles on it so a lot of things have deteriorated. Now I'm trying to restore it to it's former glory.

[Andy Cote]

The sequence I used that seems to be the most recommended according to my search is,
1) Using the Front Brake Lever - Front Right caliper Upper bleed nipple
2) Using the Front Brake Lever - Front Left caliper Lower bleed nipple
3) Using the Rear Brake Pedal - Front Left caliper Upper bleed nipple
4) Using the Rear Brake Pedal - Front Right caliper Lower bleed nipple
5) Using the Rear Brake Pedal - Rear caliper Lower bleed nipple
6) Using the Rear Brake Pedal - Anti Dive plunger
7) Using the Rear Brake Pedal - Rear caliper Upper bleed nipple


I did these steps several times trying to get a good brake pedal. When I wasn't successful, I buttoned everything up and took it for a test ride. To my surprise, and beyond my explanation, I had a great pedal and the brakes worked almost good as new. I now even have good stiff pedal sitting still in my driveway. Can't explain it, but I'll certainly take it. So now I will order the fork seals and bushings. Hope that gives me a smoother ride. I bought the bike new 19 years ago but our family situation changed shortly after and it has sat a lot. Only has 30k miles on it so a lot of things have deteriorated. Now I'm trying to restore it to it's former glory.

Glad to hear all is better. I thought there was a How-To post on this but I didn't immediately find it.

For future reference, there is a junction block near the steering stem that sometimes can trap a bubble. You can loosen the brake line to bleed this block as well as loosen the banjo bolt on the secondary master cylinder. Use a proper line wrench. Just be extra careful as there is no bleed nipple and fluid can go anywhere.

Besides damaging plastic parts, brake fluid can cause blindness!