VFR 800 FI 1998 Rear Brake Seizing On

Mid year I decided I needed a new sprocket and chain. I did the swap and while I was at it I changed all the brake pads. On the first big ride back I noticed some weird braking and pulled over to find the rear brake had seized on and basically ruined the pads and rotor. So after a trailer ride home, I rebuilt the rear with a new rotor, new pads, new rear brake lines. All back together and after a bleed the problem was repeatable while on the centre stand. Applying the rear brake would result in a lock that would clear after about 20 min of sitting there. Next I rebuilt the MC, SMC, and Rear MC hoping that would fix it. No luck either. I even found a post about that little ball bearing release port on the front left rotor and rebuilt that, still no luck. A test ride around the block this morning resulted in a few min of good riding, followed by the rear locking and the front having a very 'pressurised' feel. Again 20 min of waiting and the bike will roll freely again.

Any thoughts? I am thinking I will give new pistons and seals on all the calipers a go. With the final either being a de-link or taking it to a mechanic.

 

Search the forum. Your answer lies there. It is not calipers/pistons/etc.

 

Lots. But they are all negative about Linked Brakes on a VFR.

Sure sounds like the tiny bleed port is plugged on one of your Master Cylinders. There's only like 7 or 8, right?

Seriously, good luck. I think it is thoroughness of cleaning and attention to details, not hardware like pistons and seals.

 

A couple of links from the other forum that may help.
I don't have a linked system on my 5th Gen, can't really help with answers beyond the links below.
Good luck, hope you sort it out.


https://www.vfrdiscussion.com/index...ar-brake-locking-up-rear-center-piston-fixed/
"Everything pointed to the inside of entry port of the SMC. Or what's known as the "green filter". Reading ST-owners forum and an anecdote from our own Duc2V4, simply cleaning the "green filter" or rebuilding the SMC doesn't solve the problem. Honda technician on ST-owners forum, Igofar, recommends replacing the SMC rather than trying to clean it or rebuild it. So, that's what I did... 06454-MBG-425"

https://www.vfrdiscussion.com/index...en-linked-brakesslave-master-cylinder-needed/
"I went through this same drill last year with a friends 01. We ended up replacing the SMC (complete) and the issue went away. He had the exact same issue as you're experiencing, rear brake locking up. I completely tore apart the SMC and cleaned it up, down and sideways. When I opened the SMC there was a very fine pasty film on the inside of it, I believe that whatever this was must have contaminated the green item you picture above. Long story short, we found the issue to be somewhere in the SMC. Although I like your investigative approach, you'll probably end up with the same conclusion. The SMCs are still available BTW but your call as to whether you still want to do your forensics. Anyway you slice it,please update us as to your findings."

 

For the rear brake to lock on when the bike is stationary, the only brake pressure is coming from the foot pedal. You can diagnose whether the SMC circuit is involved by seeing which of the rear calliper bleeds is needed to free the brake. The outer pistons are direct from the pedal master, the centre piston is driven via the SMC. Based on your symptoms it sounds like the rear master is where the pressure is trapped.