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**dbeardslee** · 08-01-2008, 01:21 PM

Xcess11 - The line from the front master cylinder y's off behind the headlight and feeds both calipers. Squeezing the lever increases the hydraulic preasure to both calipers, so both should work. If you've only got one side working then you need to check the line and the caliper on the one that isn't.

Carb boots can be repaired with 10 or so coats of plastidip spray, or some members have used giant heat shrink tubing around them, tape, etc. I wouldn't throw the old ones away.

**Ken Talbot** · 08-01-2008, 02:55 PM

Welcome to the forum, Xcess11!

There's a great article here about the 1981 Midnight Special. The following extract from that article talks about the unified braking system:

The Midnight Special includes all the good features of this XS1100 family, plus some items that are elite onto itself. For instance, the Unified brake system. This braking system was developed by Yamaha to stop a motorcycle more easily and conveniently. Utilizing a triple disc arrangement, two at the front with a single at the rear, the Unified Brake System has a proportioning valve (P-valve) fitted in the hydraulic brake, line that links the left front and the rear brake calipers. The P-valve is connected to the master cylinder by a small metal brake line.

The Unified Brake System provides for simultaneous, proportioned actuation of the rear brake caliper and the left front caliper when the brake pedal is pushed. For the rider who has listened to the tales of "front brake "disaster", this system can make a difference in a panic situation where a rider who does not automatically respond in a panic situation with the application of both front and rear brake. For myself, being a longtime advocate of always using both brakes simultaneously when stopping, it was hard to notice much difference until I forced myself to use only the rear brake. The system worked well. The bike is very stable with either the use of only the rear brake, or both rear brake and front.

The system functions as the brake pedal is pushed so that the master cylinder pressurizes the input line to the P-valve. This valve will allow an equal amount of pressure output to both the front and rear brake calipers, as was generated during the application of braking. Beyond a predetermined point, the P-valve will automatically begin limiting output pressure to the rear brake caliper while maintaining direct input to the front caliper. The more pedal pressure, the more the ratio of front to rear brake pressure increase in a linear fashion. There is no doubt that this system improves stopping distance for those riders not inclined to use a front brake.

HTH....

How was that for #3000, Prom?

**dbeardslee** · 08-01-2008, 03:45 PM

Didn't know that. Sorry for the misdirection Xcess11. Thanks for putting us all on the path, Ken.

**FANNING507** · 08-01-2008, 04:36 PM

81' xs1100 sh

Welcome to the site. I have an 81' MNS also. This site is wonderful for all the various tips and advice. Most of the members have been around the block.
Make sure you flush the brakes by bleeding them several times over a period of time. The fluid is very caustic, protect the bike! If you have a Clymer manuel, it does not show the spiral front master cyclinder push rod. You can get rebuilds from several places, partnmore or georgefix is where I looked.
The manual say DOT 3 replacement fluid from a fresh can. I used some old stuff to start the bleeding and get rid of the coke color I had. After it cleaned up I put new DOT 4. Read the thread on opening the master cylinder holes. If plugged, it will shut your brakes after two or three days. I just went thru that. Also make sure your back brake isn't set too tightly. The heat will do the same thing.
Check your fuse block--if it's original--you will have problems. My fuse holders were brittle, and voltage readings changed with the temperature. TopCat will sell you a great solution cheap.
Read up on middle and final drive oil and spline grease. My splines are okay, but when I opened them up, there was only a film of grease. The two drives had dirty oil.
My brother rebuilds trenchers, and puts synthetic oil in all his rebuilds. It won't smoke, chatter, or wear the gears like gear oil. It costs more, but is worth it--runs much cooler.
Get familiar with the forum threads search tool. You may not embarass yourself like I did. The tab at the top of the Forum on Search is a wealth of information. Again welcome. If you need help you can send a personal message. Finding parts can be a bear. Kim

**Toolmaker Tim** · 08-01-2008, 05:33 PM

Welcome

Don't worry about embarassing yourself, thats part of the fun! I've only been a member for a short time and I've done it to myself at least a dozen times.
My bike is a mish-mash of parts, sort of a Frankenstein senario,soon to get worse. (some fool knocked my bike over in the bank parking lot, more parts) When I started rebuilding my rear brake M.C. the pictures in the Clymers manual didn't match what I was seeing. One of the gurus figured out that a Midnight Spec. rear M.C. had been grafted on by someone. Once I knew what was going on, things got easier. Having a bike that isn't a rebuilt basket case will hopefully make things easier, relatively speaking. One word of advice, treat your sidecovers like they are gold, the ends break off easily and they aren't getting cheaper or easier to find. Be gentle, don't ask how I know that.

Tim

**Xcess11** · 08-01-2008, 05:38 PM

Thanks very much for the warm welcome and all the replies.

The reason, in this case, I'm asking about linked braking is because when I replaced the brake pads in the right front caliper I was easily able (with the front master cylinder cover off) to push the piston back into the caliper. I could even see a little stream of brake fluid rise up from the top of the open master cylinder resevoir when I pushed the piston in.
When I tried to push in the piston on the left caliper it did not move a millimeter. I also could see no trace of oil filling back into the resevoir. The pads, however, on the left front caliper are very worn so it appears to have at least been working at some time previous.
I am now wondering if need to have the rear master cylinder cover open to allow the left front caliper piston to be pushed in to clearance the new pads.

I plan on spending some quality time wrenching my new scoot tomorrow and hope to have this sorted out this weekend.

dbeardslee, thank you for the tips about the carb boots. I won't throw the old ones away after reading that.

Ken Talbot, thank you for the referenced article about the linked braking on the Midnight Special. Glad to be your 3000th post!

FANNING507, thank's for the input. Yes, the brake fluid in there right now looks brown like coke and it also has what looks like brown algae chunks in it.

Honestly I don't think the fork oil or brake fluid had ever been changed. Makes me wonder what else has been neglected.

best to all

**Xcess11** · 08-01-2008, 05:45 PM

Toolmaker Tim, Thanks for the tip on the plastic side covers. I actually DO need the left hand side cover. The guy I bought it from ran over the left cover a few weeks back when he was getting the bike ready to sell. He gave me the cover with the bike but its many large cracks in it. Probably not worth attempting to repair if I can find another for the right $.

**Toolmaker Tim** · 08-01-2008, 06:06 PM

Side cover

Don't give up on the side cover yet! You would be amazed what you can do with JB Weld and a Dremal tool. My covers were a mess. The tab that fits into the lock on the left side was broken and they were all scratched up. I used the spray on filler/ primer stuff to fill in the cracks. I got a piece of plastic of a broken tail fairing and ground it to the approxment shape of the piece that goes into the lock mechanism andglued it on. then after the JB hardened I ground it till it fit in the lock with the lock in the open position ( you have to turn the key with one hand while fit the nose in the slot). Then I cut a notch so the latch would engage the side cover. I'm sure I'm not the only person to fix their covers with some sort of epoxy! I just like JB weld!

**Toolmaker Tim** · 08-01-2008, 06:22 PM

oops!
Sorry, the thread was about brakes.
Sounds like you will want to take your brake calipers and master cylinders apart to clean them. Its a chore, believe me I know. All that brown gunk you see is caked on everything inside the brake system.

Everyone here has been through it. When I first started working on the Yellowjacket, I would never have gotten it done without the help I got here.If you don't get the stuff out, your brakes can lock up, drag, and generally drive you nuts. That's a short drive for me. LOL These guys know everything there is to be experinced on these bkes. If a newbie like me can be coached thru a brake rebuild and a carb rebuild, anyone can.

**FANNING507** · 08-02-2008, 09:58 AM

The rear brake system is separate from the front, unless its been modified. Just be patient cleaning everything out. The manual says not to use solvents that aren't brake fluid, but if you are doing a rebuild, set the internal parts aside and soak them in brake fluid. I used starter fluid aerosol to clean the gunk out and off of the metal parts. It evaporates quickly after it eliminates the gunk. Won't interfere with your rubber parts after it evaporates. Carb cleaner in the spray can will probably do, but I don't know if it leaves residue. I wouldn't chance it--starter fluid is cheaper and works better in my opinion. Kim

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