1981 KZ1000J FRONT BRAKE ISSUES

Hello fellow riders, hope everyone is well and COVID free. Here is my issue: My master cylinder was pitted so I purchased one that was used but "bolt on ready". NOT That was pitted also sooo I went to Ebay, put in my bike info and purchased a dual brake Master Cylinder Brand new. Bench tested and didn't hold pressure with 1 caliper hooked up. I removed the caliper and blocked off the master cylinder outlet and it held pressure. OK so I disassembled the calipers, found the pistons with mild pitting, I bit the bullet and spend $110 for 2 new OEM pistons and new seal kits. Reassembled everything, bled the brakes and no pressure at the lever. Disconnected the calipers and hooked up the hoses to the junction block and I have pressure at the lever. I purchased another new master cylinder from a different vendor with the same results. My opinion is that the "new, dual caliper master cylinder" isn't for a dual caliper brake system. If anyone has any ideas on how to proceed please speak up lol. Thank you and please stay safe.

If you happen to get a single caliper MC (1/2” bore) it will work with dual caliper setup. The performance will not be optimum but will hold pressure and function. So I’d be looking at brake lines or something blocking the splitter. You should be looking for a 5/8” bore or 16mm MC. Your existing MC can be bored and a steel sleeve installed. I’ll try to find the company name, if I remember correct another member (asphalt900) mentioned they are in California.

www.karpspb.com/index.htm

I sent the master to Karps after calling them. The said it would be about $95 to put in a new sleeve. I will update after I find out more. Thanks to all who replied. Jon

Master cylinders are dead simple components. You can buy a brand new 5/8" or 16mm bore master for dirt cheap on ebay. I wouldn't bother with sleeving and buying a master kit when you can get a new master for about $35 shipped.

I bought 2 new masters from 2 different sellers.. Neither one would hold pressure. I bought new caliper pistons and seal kits so I know they aren't the issue. The brake lines appear to be working fine, not leaking or bulging anywhere. I thought maybe the 2 that I bought weren't for dual brake systems so I checked and they were. The original master had a few pits in the bore so I assumed it was leaking by the piston seals. I'll check back after I get the master back after the new sleeve is installed. Thanks for your reply.