Proportioning valve disassembly?

[CatatonicBug]

I'm trying to figure out my braking issues (seems to be a hot topic lately ), and I got all the way to the point of realizing that the proportioning valve on my rear MC is not sending pressure to the rear caliper like it should. I took the cover off of it and removed the spring, but the actual valve body did not seem like it wanted to come out. To prevent myself from ruining it, I figured I would ask you guys first. How is that thing supposed to come out? Should I just grip it with some needle-nose and pull firmly? Is there some kind of retaining clip I am missing? It wiggles in the hole, and even spins with only finger grip pressure, but I want to pull it out to get it cleaned and re-seated. What do I do next?

[CatatonicBug]

I gave up waiting

Well, since nobody chimed in with an answer, I decided to dig in blindly. Turns out, the part is just a brass post with a funky rubber stopper/bumper on one end. I just grabbed it lightly with needle-nose pliers and really didn't need to pull much at all. Just enough to break the surface tension, and the post came right out. I cleaned it off and put it back in. I bench bled the MC and finally had fluid coming out of the rear port. All putback together, and I finally have good rear brakes.

[petejw]

glad u got it sorted out,
i didnt think the 81 had a proportioning valve,
thought they were only on the xj models where the
front and rear brakes were linked.

[CatatonicBug]

glad u got it sorted out,
i didnt think the 81 had a proportioning valve,
thought they were only on the xj models where the
front and rear brakes were linked.

Yep, I believe both the '80 and '81 have the linked brakes. As far as I am concerned, it's the best safety feature on these things. I don't know why anyone would want to remove it, though I know that's a common practice.

[DGXSER]

I do not think my 81 Special has linked brakes, I think it is a Midnight thing until you hit the XJ models.

[trbig]

As far as I am concerned, it's the best safety feature on these things.I don't know why anyone would want to remove it, though I know that's a common practice.

I don't know how much riding experience you have or what your riding style is, and not trying to be arrogant, but the different brakes affect the bike in completely different ways. If you're coming hard into a corner and hit the brakes hard with a linked system, the proportion valve shoves most of the stopping power to the front brakes, which stands the bike straight up and you'll probably not make the turn. Rear brakes won't do that to you. There may even be times when you'll need to skid the back end a bit to get the front pointed where you want to go. Most would think you were out of control, but there are controlled skids. I don't make it a habit, but I have gone around corners in a slide like a flat track with the transmission skipping and jumping. A linked system never would have made it.

The point is, when I want back brake, I want that and know what affects it will have.. as well as the front. I don't want a 28+ year old valve deciding how much front brake to use when I really need back. It's like an automatic transmission.. nice to have for the average driver.. but not a lot of control. Not too many racing style vehicles will have them. If the bike is automatically going to push 70% of the pressure to the front, when I want 70% going to the rear and the other 30% to the front, how are you going to do that with it being linked?

It all comes down to me being able to control a bike better having them seperated. The average rider is going to be just fine with a linked system... I'm just not an average type of rider.


Tod

[DGXSER]

... I'm just not an average type of rider.

Thank god for small miracles.

[CatatonicBug]

Well, as you can see from my signature, this is my first bike. So, that kinda tells you what my experience is like. I admit that I am a VERY green rider, and know very little about the detailed ins and outs of riding. However, if my bike EVER went into any kind of skid, I can tell you I would not be happy about it. I would definitely not intentionally lock my brakes. I ride within 10 MPH of the speed limit, with at least a 2-second following distance, and don't plan on ever getting close to dragging the pipes on a turn. I guess I AM just an average type of rider.

[TopCatGr58]

Hey there Bug,

Sorry you didn't get a reply, but there aren't as many XJ'ers on here as XSers, and then, don't know how many have taken the valve apart? A review of the Microfiche doesn't show an exploded view of the valve, just the rear MC/plunger, so we couldn't tell from that either!? Glad you figured it out, and now it can be added to the collective knowledge base here!

It's not just in situations like Canyon Carving that Tod's talking about. It can also be a problem on city streets in mild driving situations. With linked brakes going around a nice sweeper or slow turn and you are already leaning a bit, you apply the brake, but there's a fine layer of dust/sand/something slippery that you can't see well, and with braking to the front wheel, it could cause it to grab/lock and then the front wheel will slide out throwing you down!

Whereas if you had just the rear brake, and going thru turns you want to apply mostly the rear brake, even if it started to slide a little, you could let off allowing it to grab again, but you might have slid a little but not enough to go down because your front wheel still had grip and control. Ever see those MOTOGP type racers, when they loose the front wheel grip, they go down very quickly, but if the back tire breaks loose, they are often able to regain control and keep it upright! This is why Tod and others are not proponents of the linked braking system.
T.C.

[Jerry]

On the other hand, linked brakes show up on high-end bikes like the Goldwing, Honda VTX and a BMW LT1200. In addition, ABS systems I've read about link the front and rear brakes. it may be that people who ride these bikes are "average" riders; it may also mean that there is some real advantage to having linked brakes.

From the NHTSA:
"As found in the Hurt Report, in a situation the motorcyclist typically overbrakes the rear and underbrakes the front, even though weight transfer means the front brake must do the majority of the braking. Overbraking can either cause loss of steering control or total loss of control. If the rear wheel is locked, the rider typically loses directional control. If the front wheel locks, the rider is likely to crash due to loss of stability."

The key phrase may be "typically", which covers all cyclists regardless of skill level. Likned brakes are one of 2 common methods (the other being ABS with wheel sensors) to help balance front to rear braking power.

I like the linked system of the XJ; it gives me controlled, no fork-dropping stops from any speed and with any load.

From memory, the shop manual has a discussion on how the XJ proportioning system works. it starts with the rear brake, adds front brake, then will proportion the brake force between front and rear. Key here is that the proportioning varies under load and is not a straight split front to rear across the braking range. I'll see if I can find this again (explanation includes a chart of proportioning pressures) and scan/post the pertinent part of the manual.

Racing conditons are very different, I agree, and a linked system may be more hinderance than help. However, for standard riding, more and more bikes are offering or have as standard equipment, some kind of linked system. There has to be a good reason for it.

[trbig]

Overbraking can either cause loss of steering control or total loss of control.

Which is a problem with or without a linked system. Knowing most of your stopping power is in the front is the key. Most average riders in a panic will lock up the back brake. Under hard deceleration, the back has very little stopping power.. if any since it may actually be slightly in the air.

However, for standard riding, more and more bikes are offering or have as standard equipment, some kind of linked system. There has to be a good reason for it.

I agree with you. Just as I mentioned.. automatic transmissions are a good idea for the average driver/rider, but not for someone who wants more control of their vehicle. Same reason you won't find the linked brakes on true sport bikes. I can see a problem though under hard braking where the linked system throws a big part of the stopping power to the front.. and you grab a handfull of additional front brake from the right handle.

I'm not knocking the people that keep the linked system. It's fairly idiot proof in 99% of the situations... but I like to ride like an idiot. It's that other 1% of the time where I like to ride a lot of the time, and I run in to those situations at a much higher occurance than most will. But even if I wasn't, I just feel that I have much more control of the bike than I do when it was linked.


Tod