Possible Faulty Master Cylinder/2000 GL1500SE

[T.A.S.T.1977]

I'm having an issue with the rear & front left brake system. Noticed a few weeks ago that my GW brake pedal was loosing it's firmness when braking. Eventually lost all brake pedal firmness. Performed brake bleeding to front left caliper, followed by the rear brake caliper. The front left caliper purged well, after performing a vacuum purge using a MityVac. But the rear caliper assembly would not clear up after several attempts to evacuate. Also the vacuum gauge could not pull more than 8-10 inches of vacuum. At this point, I'm suspecting a faulty master cylinder. Any & all input would be greatly appreciated. Many thanks!

[robb]

Or it could be a piston seal. Seals get hard and crack with age.

[T.A.S.T.1977]

If you're referring to a piston caliper seal, I also thought about the possibility of a bad piston caliper seal(s). But I did not have any brake fluid loss, front or rear. The brake pedal reservoir was full. There is no fluid leak at either brake caliper assembly. I removed the old brake fluid from the reservoir, then added fresh DOT 4 brake fluid before proceeding with a brake system vacuum/purge. I thank you for your input/suggestion.

[dingdong]

Try bleeding the old fashioned way by pumping the pedal. I can't bleed the rear brakes with the vacuum bleeder. It pulls air around the bleed valve threads and won't pull the fluid through. I have to do mine manually.

[T.A.S.T.1977]

I will attempt to manually bleed/purge the rear brake caliper, but first will remove bleeder fitting and apply some thread sealant to fitting. I have read that there can be an issue with air being drawn in through the threads of a bleeder fitting. I thank you for your suggestion.

[Mh434]

I'd take dingdong's advice & do an old-fashioned manual purge. It's awkward, messy, and requires a helper, but it's the most sure way. I have a top-of-the-line MityVac kit (the aluminum set) and I've had almost zero success on doing bike brakes with it, for the reason stated - air gets in around the bleed nipple. A tiny bit of crud in the nipple itself, and it resists fluid movement out, so air sucks in around it.

If that doesn't work, I'd consider rebuilding the master cylinder. It's a pain to get it out, I know, but the rebuild itself is easy. Since the pedal is getting soft, without fluid loss, either a fair bit of air has been introduced (which you're dealing with, with the bleeding) OR the fluid is bypassing the master cylinder piston seal.

I suspect the latter. Assuming the fluid level has not been allowed to get very low during riding (i.e., air has sucked in to the master cylinder), any hole elsewhere in the system big enough to let air in would let fluid (under hydraulic pressure) escape, and fluid loss would be very noticeable. The first place I looked online showed a GL1500 rear m/c rebuild kit for under $30.

[T.A.S.T.1977]

Thanks so much for your input/advice on the issue. I will proceed with a manual purge/bleed of the rear caliper assembly. Since this GW is in fact 15 yrs old, it is my belief that the master cylinder may indeed be in need of a rebuild, but first things first. May I ask any/all GW operators on this website if there is a preference for online parts suppliers? This is my first umdertaking for repairing a component of my GW. I do own a factory GW service manual specific for this model year, but I have learned to always ask other operators in such matters. I thank you all for your comments/suggestions.

[Mh434]

Well, I've used CycleMax, Cruiser Customizing, and a host of others, and I've had good success with all of them. I try to use site supporting vendors when I can.

What you might consider, though, if time is a factor, is contacting your local Honda dealer, as they probably have a kit in stock. I've done this myself (and I live in a city a LOT smaller than Houston!) and was surprised to find out they had what I needed, right on the shelf, for the exact same price as online suppliers...but without ordering, waiting, shipping costs, etc. Returns, if necessary, are a lot simpler, too. I know, it's a little "old school", but there's something about handing over your money and having the parts in your hand, immediately, confirming they're correct, that is strangely satisfying!

I'm NOT trying to be condescending here! I sometimes find myself thinking that buying online is the only way to purchase things. It's easy to forget that the part we need may be just down the street from us...

[T.A.S.T.1977]

Thanks for the suggestions. I'll contact the local Honda dealership(s), as well as CycleMax. I very much appreciate everyone's advice/suggestions. I'll definately perform a manual rear brake caliper purge/bleed before I consider rebuilding the rear master cylinder. The issue that has me perplexed is that I was able to purge/bleed the front left brake caliper assembly of air, but i was not able to purge/bleed the rear brake caliper properly. I'll remove the bleeder valve and add a coating of thread dope to the threads before once again attempting to bleed the brake caliper assembly. Many thanks to everyone for their assistance!

[ct1500]

There is not a vehicle manufacturer on the planet that puts sealer on bleeder screws that I can remember and if there was it would be specialized for the application.

Don't do that.

As everyone has stated bleed the brakes the normal way. You are getting jammed up because of the 70/30 brake split in the valve from a linked system.

[T.A.S.T.1977]

Your explanation for the issue that I'm experiencing makes total sense to me. Thank you for the explanation/suggestion. I will fore go the use of thread sealant and perform a manual purge/bleed on the rear caliper assembly.

[wiredgeorge]

There are several brands of speed bleeders; they have a check valve that allows you to hook them up and not have to screw them in between strokes on the pedal. They don't work perfectly but they can be helpful. Almost ALL speed bleeders I have seen have a red thread sealant installed from the factory, by the way. The simplest way to bleed brakes is to go to a feed store and buy a BIG hypodermic and get some small clear hose and glue onto the nozzle (it will pop otherwise) and a piece of hose just large enough to press fit onto a REGULAR BLEED VALVE (speed bleeders don't work in this direction). Remove cap/cover from master cylinder and keep and eye on it. Push the hose piece onto the bleed valve and after sucking up some brake fluid, inject into the bleed valve and it will force itself through the caliper, hoses and into the master cylinder reservoir. No air, just fluid as the air is purged out the reservoir as fluid is pushed. You may need a small hose clamp on the hose end when installed on the bleed valve. Put towels down to catch any fluid out of the m/c as brake fluid and paint remover are 1st cousins.

[T.A.S.T.1977]

That is a dandy idea! And it can be done without a second pair of hands! Thanks so much!