I have an 07 RG and have attempted a brembo upgrade using 08 parts on the front brakes. I am having an issue getting the brakes to work properly. The lever will pull firmly and the brakes grab. If I continue to hold the lever, it will gradually, slowly pull all the way down to the grip. It will eventually let the pressure off the disc, allowing the front wheel to spin. I have used a mityvac to bleed the brakes, putting teflon tape on the bleeders, getting good fluid flow to the reservoir. Tried reverse bleeding, using a syringe to force fluid from the caliper bleeder up to the master cylinder, no bubbles coming up. I did not "bench bleed" the master cylinder when I did the install. Is this what is giving me a problem? If it is, how would I correct this? Take the m/c off and start over? I am really frustrated and want to find the problem here and get it taken care of. I appreciate any help and or ideas. Thanks,

Posted this in the DIY forum too but since I hang out here and it is a touring model....
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This does not sound like a bleeding issue to me.

Bleeding eliminates the air which caused sponginess in the system. Even with air (and associated spongy lever), once pressure is built up it should hold.

You almost certainly have a bad seal (or seals)

By the sound of things it is probably not your caliper piston seals as you have not reported external leakage. On this basis I would check your master cylinder seals.

There have been numerous threads about this, but you need to ensure you used the same grade brake fluid that the replacement components are made for (sealed for) and you need to ensure all compononents in the system are compatible with that same grade

 

I would take the teflon tape off, it serves no useful purpose and may be preventing the bleed nipple from reseating properly.

 

My understanding is he used the tape during bleeding.

If there was an ongoing problem with the bleed nipples seating that would manifest itself as an external leak

 

Correct, I used the teflon tape to get a better seal when using the mityvac. I was getting too much air past the threads and not pulling the fluid down from the m/c.

If by saying there is no visible leakage at the calipers, then those seals are ok, wouldn't it have to be a physical leak somewhere else in the system to loose pressure? I did put a rebuild kit in the master cylinder, thought maybe I put the previous one in wrong. When I took the older one out, I did find a small cut in one of the rubber seals. Thought "that must be the issue, fluid getting past the seal", but no, still looses pressure. The m/c, calipers, and discs are 08 spec for the Brembo brakes. Everything I could find said to use Dot 4, so I am. The only thing I didn't change was the lines. Those were already upgraded to braided awhile back.

 

Forgive me as I do not know, is it possible that I should be using Dot 5 fluid? 2008 was the first year of the new Brembo system on the baggers. Did they use Dot 5 and then go to Dot 4 after that? This is really beginning to get frustrating......

Thank you for helping out...

 

Sounds like back flow by the caliper piston seals in the MC plunger as Diesel suggested. This is an "internal" leakage and not external. DOT 4.

 

You could reinstall the original M/C and this will isolate the issue. No leak=problem in the 08 M/C. Still having a leak= problem in the connections or one of the calipers. Just a thought.

 

I would think you need to rebuild the master cylinder. You have no leakage and air usually makes it spongy. Not sure if they are rebuildable though. Probably had the problem before and just noticing it because you are testing it. Just my thoughts on this.

 

I did rebuild it if putting new plunger/seals/spring and retaining ring in is rebuilding....



I did buy this m/c from a chromer on ebay. Is it possible there could be something inside the seal/plunger area causing it not to seal and hold correctly? Would that cause the problem I am describing? Fluid getting past the m/c seals and releasing pressure....