Front Brakes No More

Had knee surgery 4 weeks ago. Finally able to get out on the bike today.
Midway thorugh my early Saturday morning ride, I noticed the front brake lever getting softer and closer to the throttle grip so I turnd around and headed for home. By the time I got home, no more front brake. Lever touching grip. Not so easy using rear brake on hills. Anyway, I don't know where to start with the troubleshooting. I don't see any signs of a leak. Everything looks clean. I don't even know where the master cylinder is, what it looks like. I haven't worked on brakes for 25 years since my 68 Merc Cougar, so I'm not sure where to begin with the troubleshooting and repair. Pads seem fine. Plenty of meat left. Hoses and cables seem ok, but I'm not fully sure what to look for. Anybody got any step by step troubleshooting tips. Describe where and what Master C looks like. Also, my "manual" doesn't specify the type of brake fluid to use. I can change pads, but not sure how to troubleshoot why they failed. Please advise...I need to get on the road or I'll go nuts!! JG

 

It's typically a square-looking box mounted on the right handlebar with one of the lines coming out of it. Says "YAMAHA" in big letters on the cover.

As for hoses, I'm sure Len (Chacal) will tell you that if they haven't been replaced at some point, they should be; apparently they're meant to be replaced every few years. (As it turns out, mine appear to be factory stock.)

Now, I've had precious little experience with working on brakes, but offhand what you're describing surely sounds like it's either got no fluid, or a problem with the master cylinder itself. (BTW, I think DOT3 fluid is typically called for.)

Perhaps someone else who knows what the h*** they're talking about can chime in here?
***Edited by Robert. ***

 

81 Seca 750 doesn't have a MC on the bar. I've submitted pics. The bars typically have a plastic "decorative" cover. One pic shows the left side with the plastic cover and the right side with the cover removed. The switch control on the right side is the only thing on the bar. A short brake cable is attached to the lever. This goes down behind the headlights to some kind of a cast manifold. Brake cable attaches to an actuating lever on the manifold which engages two hydraulic lines. Two lines run from here down to the brake assemblies on the wheel. I can't really see where the MC is. I can't figure out how you'd fill the sucker. Could it be on the brake assembly on the wheel? I can't tell.

 

Take the cover off the Master Cylinder and check-out the level and condition of the Brake Fluid and interior of the Master Cylinder.
On the Seca Model the Master Cylinder is mounted to the right side of the Frame behind the Headlight. Removal of the Headlight is necessary to access the Master Cylinder for service and repairs.

If the Fluid Level is low and there is a discoloration to the Fluid; it's highly likely you need to either Overhaul or replace the Master Cylinder to have one that will contain Hydraulic Seals capable of applying pressure to the system.

With the availability of moderately priced reproduction Master Cylinders it might be a good idea to order and install a new one.
If the Cylinder Bore of your Master Cylinder isn't damaged by moisture and age pitting; it can be rebuilt with a Kit containing all the Internal Parts and Seals.

Obviously, a great deal of time and labor will be saved by simply swapping the old M/C for a new one.

You'll have to install the New Master and bleed the System; anyway.

So, if you need to other Brake maintenance now would be a good time.
Replacing Brake Hoses and Caliper Seals, along with overhauling and lubricating the Caliper will go a long way toward restoring your Front Brakes
to their full efficiency and safety.

 

RickCoMatic
OK, Excellent!! Thanks...I'm going to check it now. JG

 

This isn't fun anymore. You have to remove the headlight and the guage pack in order to even look at teh master cylinder. It's kind of scarry. What sick and twisted engineer devised such a diabolical place to put the master cylinder? :twisted:
I don't know how I'm going to remove the cover and examine the internals of this thing. There is one screw exposed, but I can't get a driver to bear down properly without fear of stripping the head. Now the other screw is burried under the handlebar/yoke assembly. There is no way to fit a driver in there. THis is starting to look expensive $$$
Any other advice on this one?

 

OK, so you have to drop the entire headlight/guage pack framework which is bolted to the forks and upper yoke. The whole thing comes out as one wirey mess. The brake cable is still attached and I think it's possible to actually brake pump and bleed. So at this stage it's finally possible to remove the other screw and take the cover off for inspection. The master cylinder does have fluid and it looks clean. My next task is to bleed the sucker and hope that's all I need for now. The parts all look pretty clean, but my bike only has 14K on it. So then the next issue is that if I can't get it to work, then I have to remove the MC assembly as a unit and rebuild or get a new one. A new one sounds pretty good about now. This wasn't how I imagined I'd be spending my first day back on the bike. :x

 

If you intend replacing it with a new one why not get one that will mount to your handlebars like most bikes have, it would however mean some new brake lines as well but it would make any future maintainence far easier

 

A handlebar mounted Master Cylinder would spoil the styling of the Seca look.
The Seca has handlebars covered with plastic bodywork.
Cutting the bodywork to install a handlebar mounted MC would mean removing a section needed to keep the bodywork in place.

Hopefully, after doing the repair or replacement of the Stock MC ... you won't have to revisit that job for some time.

Routine Maintenance ... removing the Cover and adding fluid as needed can be done with a small-handled ratcheting screwdriver.

 

I cleaned mine up about 3 months ago and our bikes are the same. I removed mine and cleaned it all out because my bike had been sitting for quite some time. The one tube wih the nylon cover with allen head is actually the fill tube. In the Haynes manual for the bike they recommend using a hyperdermic needle with tubing on the end to put brake fluid in. For brake bleeding I used a mightvac vacuum pump and they work really good. You can pick them up at autoparts stores for about $30.00 and they are so worth it. When bleeding the brakes on the XJ 750 Rs you should start at the anti dive units first and then proceed to the calipers.

 

I think there are some really small holes / orfices inside the mc that could get clogged over time. Even though the fluid looks clean small narrow passageways can get clogged. It became clear that after I took mine apart that it needed a good cleaning. I did not have to purchase any new parts so the repair was not expensive, it just took some time and patience to clean everything. Dot 3 is the correct fluid to use. Remove your bleeder valves on the calipers and anti dive units and make sure they are not clogged. I wrap the threads of my bleeder valves with teflon tape to assure its a good seal. Although these brake systems are sealed I think over time the brake fluild absorbs moisture from hot / cold cycles, it gets contaminated and needs replacing.

 

GEHIV: Thanks for your input. I'm going out today to buy a pump. I've put everything back together and I can see the allen head tube you mentioned. Since I don't have a Haynes manual yet, I have questions for you and anyone else who would care to answer them.

When you say that you did not have to purchase any new parts, do you mean you did not even need to buy a rebuild kit? Did you just remove it and clean it without replacing any parts inside?

How and where do I attach the pump? Did you rig any special adapters or connectors?

If the pump is forcing brake fluid out the bleeder valves, then wouldn't that indicate the MC is clean enough to function? I will eventually rebuild/replace the MC but I'd like to see if just a good refill and bleed with do the trick for today since I'll have to wait for a kit or a new unit to be shipped.

Thanks in advance for any input. JG

 

Well, a fried of mine came by and checked it. The advice is that since there is no evidence of leakage, and the brake lever never achieves any kind of pressure at all; the master cylinder is shot. Can anyone confirm this diagnosis? It makes sense. I haven't removed the calipers or any of the brake parts yet, but it looks like I'm going to sink some money into a MC rebuild kit, new brake pads and maybe a brake caliper rebuild kit. And also maybe new hydraulic lines just for peace of mind. Any input of anyone?

 

That's the right thing to do.
You might find a New Master Repro for short money.
Check around.

When you get down to the Caliper ...
Remove the Piston
Remove the Piston Seal
Scrape-out any Crud within the Seal Channel cleaning the surfaces of the Seal Channel right down to bare aluminum.
Use fresh Brake Fluid to lube New Seals and for lubing the Piston to replace it.

 

Talk to Chacal he has both OEM and aftermarket (repro) stuff in stock.

 

Let me start by saying I never experienced the same problem you are having with the brake lever never achieving any kind of pressure. The problem I have is one of the calipers doesnt retract all the way in its bore and my front brakes admit an annoying little chirp for every wheel rotation. I know that I need to pull the calipers and replace the piston seals. Since my bike sat for so long i wanted to clean out the mc to check its condition. It sounds like your friend is giving you good advice and a rebuilt kit is needed. With the mighty vac pump you do not need special adapters although mine came with several quick disconnect adapters. You dont need to use the adapters you can just take the end of the tubing and place it over you 're bleeder valve. Pump it up about halfway on the vacuum gauge then open you're bleeder and the fluid will pull through the brake system from you're mc. As you are pulling the fluid through the system the vacuum pressure will drop. Once the flow of fluid stops and the vacuum pressure on the gauge drops you should close the bleeder valve. Add fluid to the mc and pump the lever a few times to see how it feels. I went through this process about 16 times on my bike after cleaning the mc and it felt very good. mc is on right side of headlight so start at the bottom left anti-dive unit, move up to the left side caliper, over and down to the right anti dive unit and up to the right side caliper. I did mine twice per bleeder valve, so eight total the first time around. Then I went around again and repeated. Remember the DOT 3 brake fluid is extremly corrsive and will eat paint quickly. Be very careful and try not to spill any, have rags / cleaner close by just in case. I covered my tank up since the fill tube is right next to it. It's worth a try to see if it improves lever feel but also a good idea to rebuilt the mc for piece of mind. Front brakes account for 70 % of your motorcyle stopping power so its important they fuction correctly

 

All that Brake Bleeding will be for naught if the Hydraulic Seals in the Master Cylinder are compromised.
Before you start a complete bleeding of the entire system; check the Master Cylinder Seals for their Hydraulic Integrity.

Find the first Banjo Bolt on the feed line exiting the Master Cylinder.
Remove the Banjo Bolt and substitute a Bolt, washer, rubber seal (slice of inner tube) ... at BOTH sides of the Banjo Fitting ... making the Brake Line "Fluid Tight"

NOW, with the Brake Line SEALED -- Test the Master Cylinder Seals.

Add some Brake Fluid to the Master Cylinder Reservoir.
Pump the Brake Lever to see if it is CAPABLE of achieving some pressure.
Loosen the Fluid-tight seal you fashioned at the first Banjo SLIGHTLY and TEST the Master Cylinder Seals capability of FORCING Fluid OUT of the Master Cylinder.

If the Brake Master Cylinder remains "Mushy" and is unable to create sufficient pressure to force some Fluid out of where the Brake Line is Sealed;
the Hydraulic Seals within the Master Cylinder (and/or) the Bore of the Master Cylinder is compromised and corrective measures must be taken before any Bleeding of the System will be effective.

Save yourself a whole lot of time and aggravation by KNOWING the condition and ability of the Master Cylinder ... first!