Rear Master cylinder plunger size

[maugliavus]

Hello folks!
I am a new owner of 1998 SE that is a BARN FIND. Been sitting since 2010. Just pulled a tank.( pain ... big pain). While the tank and exhaust is off the bike a decided to rebuild rear master. I ordered two kits from eBay and both came in with a smaller diameter plunger. What am I doing wrong?

Input is very appreciated.

[maugliavus]

Just learned how to add images

This is a second kit I have purchased. Mine is on the right. There is a big difference in diameter. The firs one was even smaller.

[Rambozo]

Hello folks!
What am I doing wrong?

Expecting proper parts from ebay?

43520-MG9-305 is the correct kit for that application. Of course, if someone has swapped the master for something else, you are on your own.

[maugliavus]

That is a part number i have used. But you could be correct about someone swapping the parts. Ideally the smaller the diameter of the plunger the higher pressure achieved at the Caliper.
Considering this is the heaviest bike Honda makes, i will agree with the idea that it was swapped.

Thank You for your input.

[Thombar]

I ordered ebay rear master cylinder kit gl1500 and recieved piston that was too small too, for gl1200. That seller, gadgetstopstore, knew piston was wrong but seller keeps listing it for gl1500. I ordered new master cylinder +-$50 w/ reservior on ebay. Helps to fill cylinder before install and I still had to make a reservoir pump to inject brake fluid into master. I had reservoir lid from a gl1200 that I drilled a 1/2' hole so I could hot glue a rubber tube and slid syringe into. Filled syringe, pushed plunger forcing fluid into reservoir and master until I started feeling pressure in pedal. I was also able to insert a tube into syringe and attach a vacuum pump to syringe without plunger to pull air out. My 93 gl1500 w/ 14k miles sat since 2001 and had hard obstruction in front left brake line. Detach line from front left caliper and blow out BEFORE you attach line to new master.

[Rambozo]

Anytime you install a master, it's always best to bench bleed it beforehand. So much easier when you can tilt it so the air rises to the ports.
The only exception might be if you plan on either forward or reverse pressure bleeding. But even then, I still like to verify the master is working properly before installation.

[maugliavus]

Thombar,
I just looked at the name of the vendor I purchased it from... and guess what? I think I got the kit that you have returned.
I have ordered a new kit from a different guy. You know what they say - third time is a charm.
I also buying a whole new setup but where is a guaranty that the internal diameter is the correct one. I looked all over and did not find the explanation for the different plunger size for the bike.

[maugliavus]

Rambozo, agree with you on bench bleeding 100%. I actually purchased a new small device for bleeding from the site called Temu.com. It consists of small cylinder with a check valve in it and a hose on both ends. Will be trying it as soon as the master is back together.

[Thombar]

That seller knows kit not for 1500s. I never found one that was so I bought new master. Also theres a place on the old one that I couldnt get to to clean, under a pressed in metal disc. The kit didnt come with replacement disc that I would have had to damage to remove. Everything else on my old master was pristine except where I couldnt get to under that disc. Sure enough when I reinstalled, same problem, no pressure on pedal. The new master, $50, came with a new brake light switch as well. As hard as it was to R & R old master Id go new not half rebuilt.
On barn finds like ours fuel pump change in order too. Buy one like I pictured #4 in previous message, osiasautopart_us.
Dont buy air filter from Caltric, warped.
Blow out your lines,
Tom

[maugliavus]

Well, the fuel pump assy and the tank is a totally different story. I pulled the tank already and the FP assy just disintegrated in my hands as soon as i pulled it out. But i will start another topic on that issue.