May need to rebuild front break master cylinder...need some advice.

My front brake was getting 'spongy' for lack of better words. As I would pump the lever, it would get slightly harder so I figured there was an air bubble in the line. I popped off the top of the resevoir to find about an 1/8 of an inch of brown residue and the fluid was much darker than normal. It leads me to believe that either A) it had never been changed in the past 25 years or B) someone mixed the DOT's.

After I got all the gunk out of the resevoir, I flushed out the lines with about 300 ml of DOT 4 and put it all back together. It was still spongy so I bled the lines again and got the same results. Im wondering if the piston and other rubber components in there are bad?

Has anyone ever rebuilt their front brake master on their VF500? If so, can you give me some pointers? Is it as easy a just buying the parts or, based on what I mentioned above, does it sound more serious? Do they make a rebuilt kit and if so, how much should I be looking at paying for this?

Thanks for your help and yes, I did search but couldnt find much on this topic.

 

I did this to mine last summer. Took about 5 minutes and $10 in parts. Kits are available. Did you completely drain the system? You may still have some air in the lines. As long as it's safe to ride I'd let it slide for a few days and see if it improves as the remaining air bleeds out. If nothing changes then you can look at rebuilding things. New stainless steel lines would probably help too.

-Jake

 

Wow...$10? I just called the dealership and they have a 'kit' for $56. Apparantly this is common but $56 seems a bit steep. Im driving there in a few mins to have them diagnose it and if its the kit, Ill put it in. I dont mind spending the money on brakes. Rumor has it, they are important

Did you replace the spring, piston, cups? Is that what youre talking about? did you have to remove the unit from the handle bar or can I service it on the bike?

 

Before you buy anything try this:

- Pull the lever all the way to the grip.
-Zip tie it that way. (Ensure it's pulled in all the way)
-Leave it like that overnight.
-Next morning hold the lever and snip the tie.
-Slowly release the lever

See if that helps.

 

If you pump the BRAKE lever and the pressure improves ,you need to rebuild the master cyclinder.

The parts are one rubber cup mostly. Go to Japanese Vintage Motorcycle Parts | Motorcycle Parts, Bike Accessories & Motorcycle Apparel For Honda, Kawasaki, Suzuki & Yamaha- Old Bike Barn $56 dollars is too high considering we are in a depression.

 

I needed a master cyl kit for my clutch and found it for 19$ on ebay. They also offer the Brake master kit for the same price. Shipping was reasonably fast, and free.
PM me if you want their info.
I ordered the wrong part initially and they let me return and exchange it for the correct one even tho it was my fault.
I am doing all of my own minor repairs now, but back then I was not, and TOE CUTTER did the repair for me, so I cannot attest to the level of difficulty to the job, but he called it a five minute job.
However, he is a master mechanic. So I can't help you on the labor side as far as how hard it is or how long it takes. The parts were all good tho.

 

depending on how stock your bike is, you can always mount a more modern master, as long as they share the same piston dia, i think my vf and 11f were both 5/8s? anyways the upgrade to new cbr stuff was a no brainer, the downside, i have no mirror mount. but thats what crg bar ends are for

 

A blanket statement like that is flat out stupid and I'm surprised it's coming from a mechanic with as much experience as you claim to have. If he still has air in the lines we can expect the exact symptoms you describe without it being the fault of the M/C. If we can be 100% sure the system is bled then we can start looking at other things.

I honestly don't remember what I paid for my rebuild kit but I'm pretty sure it was less than $30. This was a year ago so they may have gone up in price or I don't recall correctly at all. Take Slowbird's advice and see if that improves the situation.

-Jake

 

I did make the assumption that he had checked the usual things.
He did not say it had been sitting around.
I did assume it was a bike that was in use.
Next time to avoid this kind of ridicule I will cover the subject from bottom to the top.
But you will have to read all that stuff.

 

Well, considering I wanted to go riding today, I purchased the kit from the dealer and rebuilt the master. I'm sad to say that it didn't help much. It was needed though since the dust boot was torn and it was getting corroded. I fear that the same setiment that was found in the master may also be in the calipers. It looks like I will be taking those off and cleaning them out. I'm assuming that I will have to replace some warn parts there as well. Any advice before I take on this project? I sure wish I could find some inexpensive Galfer lines to put on it since i've gone this far.

 

If you're going to pull the calipers apart to clean you may as well rebuild them as well. I suspect that your problem is either air or flex in the lines. Air can work itself out but it can take some time. Also, if you're going to spring for caliper parts I'd just suck it up and get the Galfer lines. Last I checked they wasn't that expensive. Depends on you definition I suppose. I've never priced replacement OEM lines. At least you know your M/C is good now...

-Jake

 

Most likely you still have air in the system at the banjo bolt on the master cylinder. The way the mc is mounted that connection is not lower than the fluid level. Loosen the mc and tilt it forward so the connection is pointing downward. With the mc cover off and a little bit of fluid in the reservoir slowly pump the mc lever. You should start to see a small amount of bubbles coming up thru the bled hole in the bottom of the mc. This is a gotcha that happens to just about everybody that rebuilds the brake system the first time. It's that way on the older 750's and I'm assuming the 500's are the same.