OK, drive to my house with the bike and we can fix it together
Bad news I bled and bled today and took a very close look at the pistons... I think one of them is cracked. When I squeeze the lever, I can see a small bit of fluid leak out between the piston head and body (the silver part and the black part on the OEM pistons).
It's a small bit of fluid, but I suspect that it's also drawing air back in.
May have to wait a couple more days while I order some new ones Most unfortunate.
I just did the CR conversion on a YZ I built. Here is what I did:
1. Complete rebuild kits for master and caliper, new brake line, banjos, copper washers.
2. Cleaned both components, soaked in waste gas for a few hours. Sprayed off with brake clean.
3. Put new seals in caliper.
4. Filled lower piston cavity with dot 4, slid piston in and out to push air bubbles to upper piston cavity.
5. Filled upper piston, repeat until bubbles are out of banjo and bleeder holes.
6. Make sure the pistons are not stuffed in. 1/4-3/8 out
7. Pour more fluid into holes.
8. Install hose and banjo.
9. Install bleeder valve.
10. Push pistons in forcing fluid into brake line. Keep it elevated above caliper.
11. Same with master, fill plunger cavity with fluid, and stuff new seals and plunger in.
12. Install hose and banjo.
13. Fill reservoir with fluid.
14. Elevate caliper over master and install brake pads.
15. Install caliper on a rotor or equal thickness above the master.
16. Pump, hold, release bleeder, tighten bleeder, release lever.
Did this to my sons CRF (without the rebuild) soft brake, and bam, lit new gripped.
I have just started out by sticking some flat stock between the pads and hanging the caliper on the ceiling beam in my garage and bleeding. Doing the cr to the yz 125 was the last time I did that in fact.
As far as I can tell, that definitely helped. I had someone hold the caliper higher than the master and then I pulled the bleeder under vacuum a couple of times.
It's way firmer than I've been able to get it so far but now I feel like I have forgotten how stiff it should be I've zip tied the lever to the bars for the night, but what's the best way to test the lever? A normal grip no longer takes me to the bars but I nice hard one with 3 fingers and I can still pull it back.
Thoughts on best way to test this?
In two occasions, I have rebuilt the master cylinder and bled for hours... I mean hours... to no avail.
Stumped, and not one to throw money at a problem, I tried a different master cylinder. Instant fix. There was no air in the system.
The immediate remedy was replacement of the master cylinder. Not a typical result.
Something was physically wrong with the original master cylinders and they could not be rebuilt.
Not saying this applies to your case, but in the 100s of brakes I've bled, on two bikes I wasted a lot of time.
-BIG DAN