New rear brake line install help

[Rob84KDX200]

Howdy,

I've a 96 kdx200, just recently went about changing over my front brake line. Purchased a set of Goodridge brake lines. I used the back bleeding/syringe method with great success.

However, I tried doing the same with my rear brake line, with no success at all. Firstly, I removed the old brake line, hardly any bleeding required as the rear reservoir was already dry and empty. So I then fitted the new brake line, as well as cleaning out the bleed nipple. Got my syringe full of new fluid, applied it through the nipple, and watched a few air bubbles and some old fluid come up through the reservoir. At that point when no more air bubbles showed and the fluid appeared to be clean, I shut off the nipple. Replaced the reservoir diaphragm and cap. Pumped the rear brake pedal - no action! No brake! Where did I go wrong? Any thoughts?

 

[mudpack]

I'd bleed the system in the normal way, if reverse bleending isn't working.

 

[Rob84KDX200]

Nothing is working, both normal method and reverse bleeding method. I even got a replacement rear master cylinder, and that made no difference. Is there something I'm missing? Do I have to keep the brake pedal depressed as I'm bleeding or reverse bleeding? About to tear my hair out!

 

[whenfoxforks-ruled]

Rebuild the master cylinder, unless you see it leaking around the caliper/piston? I have been under the assumption when something in the brake system goes bad, it leaks, except for the master cylinder, and worn out rubber lines. There are no more parts! The piston will move back and forth, without pushing, or not enough to engage the caliper properly. The brake lines will get soft spots, and a weak/no pedal feel. Vintage Bob

 

[sr5bidder]

put the bike on a stand and remove the rear wheel and the caliper, let the caliper hang down, remove th pads, take a c-clamp and put it on the calpers piston and push the piston all the way in, remove the 2 line clamps on the top of the swing arm.

now with the caliper hanging as close to vertical to the master cylinder try your reverse process again, when you feel the pedal stiffen up remove the c-clamp, install pads and reassemble the wheel/ brake and the keep the master cylinder full as you pump the piston outwards.

this shoud work for you.

 

[Rob84KDX200]

An update : disassembled the rear caliper. Had to blow out the piston with compressed air as it was stuck in there nice n good. The dust and fluid seals were trashed, so have new ones on order. The bore looks to be in good shape, but I did have to Dremel-polish the bottom of the piston. More to come...

 

[whenfoxforks-ruled]

Are you sure you do not want to replace that piston?

 

[Rob84KDX200]

It's an option - either a second hand rear caliper, or new OEM piston. Either option will cost me US$50.

 

[pesky nz]

At reassembly time I always use rubber grease on caliper seals because a lot of other lubricants react with the rubber seals and usually cause them to swell. Depending on the type of rear brake line used you can chech the master cylinder by clamping the brake hose near the bajo bolt on the master cylinder with normals pliers ( only works on soft rubber coated hoses not steel or kevlar braided lines). If the master cyl is good the pedal wil bleed is about three pumps and be hard, you can then open the bleed nipple on the caliper and chase the air out of the system by bleedinf through the pliers.
Whats was the original reason for changing the brake line? did the brake work properly with the old line? Master cylinders do 2 things commonly one is leak internally causing a soft pedal that depresses slowly until it bottoms out, the other is when the rubber seals swell and block off the internal bleed hole and no longer allow fresh fluid into the system to make up for pad wear causing the pedal to work at an ever lower point until it stops working. also if you mix different types of brake fluid they can react and cause seals to swell

 

[Rob84KDX200]

Yeah the rear brake was working before, surprisingly as the reservoir level was near empty and dry. Something I should've noticed upon pre purchase inspection. I purchased a new set of Goodridge braided brake lines, more as an upgrade. I had no problems setting up the front brake with the new line. It's just the rear I'm having issues with. I've since replaced the rear master cylinder - in near new condition - came off an '06 model (and worked out cheaper than getting a rebuild kit). That side of things is good. No more leaks at the cylinder. So now my main concern is the caliper piston. I did polish it nice n good, but hopefully not too much to alter the seal between piston and rubber seal.

 

[pesky nz]

If the caliper seals are leaking then the fluid will come out and be visible

 

[Rob84KDX200]

Ok sorry for the long delay. Latest update: replaced the caliper, tried reverse bleed again with the syringe.

Still the same result: reservoir fills up to a point. Then won't tale anymore fluid. Caliper piston will not budge. It's pushed in half way. I'm wondering if the caliper piston must be in a certain position (eg pushed in or extended out)? Thoughts? And how about after the bleed valve is closed, does one also close the reservoir cap before pumping the brakes?

 

[whenfoxforks-ruled]

The piston should be flush, not inside. The cap does not need to be on.

 

[Rob84KDX200]

A quick update. All is good now. First I reverse bled with the syringe. Then pumped the brakes and then did a normal bleed several times. Done by pumping the brake pedal a few times, and whilst pedal is down, quickly open and shut the bleed valve to let out air and build pressure. I did that until the brake pedal was firm, and voila! Rear brakes! Thanks for all your help and a few YouTube videos which helped shed some light on this issue. I'll post a link of the clip later.