2004 EV brake system Q

[jrt]

Background on this-  my rear brake isn't working (air in line, I'm sure).  I tried the old-fashioned method of pumping the brake pedal to push fluid, but nothing comes out the front brake.  nothing.  I put a (admittedly light) vacuum on the line and I get nothing out of the front brake.  My first thought is I am not overcoming the proportioning valve for the linked system (#18), but I've also got this part that I don't know what it does-

On the linked brake system for the California EV (2004, but applies to other years)- 
What does the "Braking Correction Device" do?  Is it a valve?  There is a spring loaded... something in there. It is #21 in the parts fiche.

[rocker59]

It's a proportioning valve that varies the amount of front-rear bias based on swingarm angle. 

[guzzisteve]

That is your proportioning valve for the rear brake system. The more swingarm squats the more fluid goes to rear caliper.

Rocker beat me.

[Tom H]

You may have a bad master cylinder?

Try loosening the banjo bolt at the MC and gently push on the brake pedal. If fluid comes out like it has some pressure, move to the next banjo and so on. This will tell you where your fluid is stopping at.

I had a MC go bad seemingly overnight. It felt normal the day before and the next day the pedal went all the way down.

One thing that worked for me when bleeding the brakes was to do the rear first, THEN do the front.

Good luck,
Tom

[John A]

I’ve had the spring come off and escape so check for that

[pehayes]

I have seen those proportioning valves corrode and lock.  I may have a couple of spares of unknown quality.  For testing purposes, it might be possible to buy or fabricate a female/female fitting, disconnect both hoses from the proportioning valve, and direct connect the two hoses via the bypass fitting.  That would allow you to bleed both front left and rear brakes to verify that your master and slaves are in good order.  From your description I suspect the proportioning valve is locked.  I never heard of anyone dismantling one for rebuild.

Patrick Hayes
Fremont CA

[Frenchfrog]

Sounds about right Patrick....I think I read a rebuild of these valves a while ago : likely to be somewhere here.Perhaps on Greg Bender's excellent site?
Might be just worth unbolting the front caliper, inserting a sufficiently wide wedge between the pads and raise the whole lot higher than the rest of the line prior to giving it a bleed. For years that has been my go to bleeding method but with earlier Tontis without that valve.

[pehayes]

Might be just worth unbolting the front caliper, inserting a sufficiently wide wedge between the pads and raise the whole lot higher than the rest of the line prior to giving it a bleed.

That sounds good for a bleeding issue when you can't purge an air bubble.  But, in this case from the PO, he can't move any fluid at all.  Bleeding air isn't his problem.

Patrick Hayes
Fremont CA

[guzzisteve]

Better off to replace it to an earlier splitter or later CalVin which is like the older one w/a bleeder on top.

[jrt]

Thanks for the replies everyone.  I had no idea that there was a valve based on the swing arm angle.  Crazy. 
Yes, it sort of happened overnight, but it also happened the night I replaced the rear brake pads.  Coincidence?  Or conspiracy?

I'll check at the connections and suss this out.

[moto]

Part #21 is a brake proportioning valve, as said before. The cylindrical housing on it doubtless contains a stepped piston that reduces the proportion of line pressure sent to the rear brake beyond a certain system pressure, called the knee point. Its lever arm attaches to the swing arm to change the knee point at which the reduction in rear pressure begins, depending on the load on the rear wheel.

Part #18, "valve 4,5 bar," is not called a proportioning valve since it doesn't reduce the proportion of force going to the rear brake beyond a knee point. Instead, it provides a fixed, nonproportional force reduction of 4.5 bar (65 psi) to the front brake line at every level of system pressure. It is a fixed reduction valve.

The reduction valve acts like a small master cylinder in the line that has an extra-powerful return spring. This spring is designed to produce 65 psi of resistance into the front brake line, thereby reducing pressure at the front master wheel slave cylinder by just that amount at every system pressure. The spring doesn't need to be very strong. (Edit: this because the reduction piston is very small; if it were a tenth of an inch in diameter a spring exerting 0.51lb or about 8oz would do. (65x3.14x0.05^2 = 0.51.)

If the reduction valve has a bypass in it like a master cylinder it will be possible to bleed the front line when it is cycled, but very, very slowly because of its size. A constant line pressure on it will not produce a constant flow. I  would recommend prefilling the front line and raising the front caliper, suitably blocked, overnight, to remove bubbles.

I have never touched one.

By the way, the split between the front and rear lines occurs at the simple splitter or manifold that the reduction valve (18) screws into.

[jrt]

Yep,  I've got both slave cylinders hanging as high as they will go.  I upped the vaccuum and it pulls fluid through both front and rear pretty well- the front had lots of really small bubbles, so I am suspecting (hoping!) it is a simple matter of having air in the line.
I bled front and rear, and it is better, but not still not very good.  I have something, somewhere in the line still.  I didn't have a lot of brake fluid, so I had to stop.  I'll get more tomorrow.

[pehayes]

Some years ago I installed shorter shocks on Regina's EV.  This changes everything related to brake proportioning.  I found a factory diagram which explained the system.  I fabricated a modified upper mount for the external spring so that I was duplicating the factory dimension for swingarm deflection.  See here:  https://www.guzzipower.com/IntegEVBrakes-Pat_H.html

Patrick Hayes
Fremont CA

[Tom H]

Sometimes "really small bubbles" are caused by a leak in the vacuum bleeder hose and the bleeder nipple, a hose clamp can help. Been fooled by that a few times myself.

Can you pump the pedal and get fluid out of the front or rear slave? Or ONLY with vacuum?

Tom

[Wayne Orwig]

You need to eliminate all air just ahead of the valve #18, or you will never get fluid to the front.
I have had good luck loosening the valve a bit during bleeding. A vacuum bleeder may not overcome that valve.
As mentioned, I have actually seen that valve for the rear brake lock up from corrosion. Clean it up and verify that the spring is in place.

[Frenchfrog]

Yep,  I've got both slave cylinders hanging as high as they will go.  I upped the vaccuum and it pulls fluid through both front and rear pretty well- the front had lots of really small bubbles, so I am suspecting (hoping!) it is a simple matter of having air in the line.
I bled front and rear, and it is better, but not still not very good.  I have something, somewhere in the line still.  I didn't have a lot of brake fluid, so I had to stop.  I'll get more tomorrow.

Running the engine for a short while might induce enough vibration to merge some of the small bubbles too...at least you seem to be getting there slowly!

[moto]

It is the reduction valve, number 18, that causes a problem, and Wayne's advice seems excellent. You should be able to bleed the rear line in the usual way, and then move to the front.

[jrt]

OK, I wanted to close this out.  First, I appreciate all the responses and suggestions. 
I think my issue was a stuck proportioning valve.  I was using a vacuum and couldn't get any fluid out from the front caliper.
Ultimately- I dressed all the fittings (bleeder valves) to make sure they weren't sucking air, improved the vacuum source and some light tapping on the valve (I don't know that actually helped) and I got a good flow from the front caliper.  Did this, followed by the traditional open bleeder valve-pump-close a couple of times and now I have some really good brakes.  Better than they were.  Part of that is I replaced the rear pads with new ones, but this was an air-in-line issue.  So- in the end- I have replaced ALL the pads, ALL the fluids and the bike runs and stops great. 
I just noticed a slight weep on one of the pressurized fuel lines, so that's the next thing to address (it's a loose clamp- all the lines are new). 
The Yardbird is back on the road!

Thanks y'all for your help- it was much appreciated.