MICO brake lock problem

[Doc Dave]

I found an older MICO lever lock and thought it would be a good addition to my '52 B-3 PW resto I am doing. This is the model of lock without the electronic low pressure warning system, and with one bleeder on top.
I have a (new) stock single chamber MC under the floorboard, and a frame rail mounted Midland vacuum booster (professionally rebuilt).
I got a kit for the MICO that consisted of a new piston and lever assembly. I cleaned the MICO well and put it back together.
I plumbed everything correctly, I believe. WHen I went to use it, the MICO built/held pressure well and held the truck on a slope. BUt, when I release the lever, the brakes remain locked. To release the brakes I have to crack a bleeder a bit.
I have been talking to the MICO tech, and he suggested I do a test involving cracking the line at the MC outlet. If it releases the brakes, then it isolates the problem to the MC he said. I did this and indeed the brakes released.
If I do not use/activate the MICO, the brake system seems to work fine, although I am simply driving it a little on my farm, it is not road legal yet.
I read a post in some archives about having to pump the brakes hard when dropping the lever to release the pressure, but when I tried that it did not help. I also increased the brake pedal free play to see what that did , but it did not help either.
Is is possible it is a MICO issue? Ideas welcome.

[Tom Petroff]

Hi Dave,
From what your saying I would lean toward a problem with the micro brake.
The way it worked if I remember,(long Time ago) you raise the lever apply the brake to set. To release you lower the lever.
Don't remember any "pumping" to release.
The harder you Pump the pedal while locking the brakes the harder it is to release.
Now I just had a "brain fort" and I think maybe you do push the brake hard not pump after the lever is lowered to release the valve in the unit.
Tip, when you set the brake with the lever on I would go softly, really don't take much effort to lock the wheels,then release the lever and push hard and see if it releases.
TGP

[Charles Talbert]

Doc, check this

We don't install these much any more, used a lot of them years ago however. When doing an installation, I recall one issue always being a point to watch.

To better explain, the lever lock type works like this; apply the brakes by pressing the pedal, while holding pressure on the pedal, raise the lever upward into the lock position, release the pedal. System is now locked. What this does is block fluid return back to the master cylinder holding constant pressure between the lock & the wheel cylinders. No pressure is retained on the master cylinder during a system locked interval.

When ready to release; simply move the lever 180* downward to the fully released position. The valve piston plunger is pushed fully inward by the lever fulcrum & the brakes should immediately release completely, no pedal action required for system release of the lever lock type.

Here is what the installer has to pay close attention & look out for. The valve body of the unit is a separate part from the lever mechanism. The design of the unit doesn't leave much room for correct adjustment of the lever fulcrum/piston plunger relation when fully assembled. How far the lever assembly screws onto the valve body threads is the adjustment procedure. What I'm saying is this; the lever mechanism must be the correct distance from the piston plunger so it receives the correct amount of travel both ways via lever movement. If the unit is installed on a thick panel for instance, when the lever is screwed tight against the panel, it may not be close enough to the piston plunger to push it all the way in allowing the brakes to release. The piston plunger must be fully depressed or it will not release pressure. I can recall mounting one in a pre-existing panel hole once, the hole was a little to large in diameter & I used a washer to cover the hole. Ok, nice neat installation, brakes wouldn't release. The space taken by the washer pushed the lever too far away from the piston plunger, removed the washer & instead used a thin shim to cover the excess diameter hole, screwed the lever assembly farther onto the body threads & tight against the panel, great, everything functioned normally. If you used a nut on the back side of your panel on the valve threads, run the nut down exposing longer thread length to the face side of the panel. The lever assembly will now screw farther onto the valve body threads placing it closer to the end of the piston plunger. Adjust this until you see the plunger push in fully via lever pressure with the lever in the downward position.

To check out whether this theory is the problem with yours; lock the brakes, (moderate pressure only, it doesn't take a lot of pedal pressure to securely lock the system), move the lever downward to the full released position. If brakes don't release as you described is happening, carefully use a small flat blade screwdriver & wedge between the end of the plunger & the lever assembly fulcrum applying pressure to push the plunger in as far as it will go, (CAREFULLY). If the brakes release when you push in on the plunger, what I have described is your problem, readjust for correct plunger travel & you are good to go. Watch this adjustment for opposite or outward plunger travel also, the lever fulcrum should not touch the plunger at all when in the locked position.

If this test & adjustment procedure does not correct your problem, my vote goes to an internal lock mechanism malfunction. I see no way at all that your master cylinder could be at fault here. Master cylinder issues come into play when the system won't remain in the locked position, (brakes release unexpectedly) while the lever remains in the locked position, a totally different story not related to your issue.

Let me clarify this point also, older MICO locking mechanisms used a push button to activate instead of a lever. To activate that system, the button was pressed & held in while a single brake application locked the system. On this type, a second brake pedal application was applied to release the system. This system was standard equipment on Military wreckers for years, up until full air brake systems became the norm. I mentioned this system because someone had talked about the possibility that a brake pedal application might be required to release the system. That is correct when using the push button type, does not apply with the lever lock type that you have.

[Tom Petroff]

Thanks Charles

For clarifying the procedure.
It's been a very long time for me since I have used a brake lock.
Should have stayed with my first thought that you simply release the lever.
Then you reminded me why I thought you pushed the pedal also.And your correct that was only on the electric solenoid type's that you needed to do that.

I still can't say which one, electric or lever was first. I seem to remember they were both around at the same time,with the lever type around a little earlier.
TGP

[712edf]

It's posts like these that make this forum such valuable asset! I'd rather have a "been there done that" experienced person in my corner than all the new-fangled "information systems" in the world.

You guys know your stuff!

[Charles Talbert]

I recall seeing the electric push button units first & seeing that type used up into the 70's. I know the 2 1/2-ton M60 military wreckers, cranes of the early to mid 50's vintage used the push button type. These disappeared in favor of the lever type later on in civilian use. Lever type was deemed less prone to problems; reasonably so, I certainly found that to be true. Not sure when they were first introduced though. The later MICO units purchased today are much different & more costly. They have an electronic unit on the rear of the valve body that must be wired to an alarm of some sort that sounds if brake pressure is lost. The system will not lock unless the alarm switch has power to it, so it can't be bypassed & used as the early units. This is simply a safeguard to warn the operator if the lock system pressure has failed for any reason. Like many other devices, this is now OSHA regulation. They older style without the pressure switch is no longer offered for retail sale.

[Charles Talbert]

After reading original post again??

I found an older MICO lever lock and thought it would be a good addition to my '52 B-3 PW resto I am doing. This is the model of lock without the electronic low pressure warning system, and with one bleeder on top.
I have a (new) stock single chamber MC under the floorboard, and a frame rail mounted Midland vacuum booster (professionally rebuilt).
I got a kit for the MICO that consisted of a new piston and lever assembly. I cleaned the MICO well and put it back together.
I plumbed everything correctly, I believe. WHen I went to use it, the MICO built/held pressure well and held the truck on a slope. BUt, when I release the lever, the brakes remain locked. To release the brakes I have to crack a bleeder a bit.
I have been talking to the MICO tech, and he suggested I do a test involving cracking the line at the MC outlet. If it releases the brakes, then it isolates the problem to the MC he said. I did this and indeed the brakes released.
If I do not use/activate the MICO, the brake system seems to work fine, although I am simply driving it a little on my farm, it is not road legal yet.
I read a post in some archives about having to pump the brakes hard when dropping the lever to release the pressure, but when I tried that it did not help. I also increased the brake pedal free play to see what that did , but it did not help either.
Is is possible it is a MICO issue? Ideas welcome.

I'm wondering if you have it plumbed correctly. I say this because you said you cracked a line nut at the M/C outlet & pressure released. There should be no pressure between the lock valve & the M/C when in the locked position. There should be no significant pressure there unless the pedal is depressed. Rethink that plumbing also, feel free to give me a call if I can help you.

[Doc Dave]

Charles,

Thank you so much for your very thoughtful and detailed posts on this.

I will try your suggestions in the first posting, starting with seeing the result of using the small screwdriver.

As to plumbing, I think I have it right, although I had no schematic or instructions with the old lever lock, so I got a sheet on the modern version, that shows the input being closest to the lever, and output at the back. That is how I plumbed it, it could have been switched over the years.

The Mico tech rep, Mr. Tupper, asked me to make sure the lever part was screwed all the way possible to ensure good contact (but did not mention whether a thicker steel mounting surface could be a factor). He also wanted me to check my brake free play to make sure it was adequate, which I did - and I even tried backing off even more - which did not help.

The other thing I will try is to only apply a small amount of brake pressure to set it. I used a firmer pressure previously, perhaps too much.

I will post the results of my experiments, and perhaps call you, thanks.

[maineSS]

There's another thing to check if everything discussed so far doesn't work. 4-wheel drum and drum/disc bake systems have a "residual pressure valve" (RP valve) that keeps enough pressure in the line to keep the drum brake springs slightly extended- just enough to let the shoes just barely touch the drum. In drum/disc systems, the RP valve is combined with the proportioning valve, and is called the "combination valve". Disc brakes don't need an RP valve- it keeps them partially applied all the time.

The RP valve is part of the PW master cylinder- it's a little perforated concave disk with a rubber diaphram, and has to be oriented with the flap forwards to prevent backflow. When I bought my truck, the previous owner had given up trying to get the brakes to work- the pedal just sank to the floor. He'd bought a new master from VPW, installed new wheel cylinders, had no line leaks. I finally found that the RP valve had been installed backwards. When I turned it around, I had brakes.

When I added the Helitool disk brake kit, I took a ride about three miles out of town. The truck sounded like it was working really hard in all gears. I pulled over, and saw my rotors were blue. I called a flatbed, and returned home. Unfortunately, the Flatbed Guy flattened one of my front brake lines with the axle hook, so between replacing that, removing the master cylinder RP valve and fitting an inline RP valve on the rear brake circuit, it was awhile before I took any more country drives.

Since the Mico Lock was designed for use with 4-wheel drum systems, it shouldn't have a problem with the RP valve if it's working properly. If it's not working properly, the RP valve pressure MIGHT be a consideration. NEVER underestimate the problems this little part can cause....

[Doc Dave]

Now you got me thinking. I can't remember the orientation of this RP valve in the MC. I had it apart when I got ready to bleed it and put it back together.
If this is backwards, would you have normal acting brakes like I have, except when the MICO is activated, though?

[Charles Talbert]

Now you got me thinking. I can't remember the orientation of this RP valve in the MC. I had it apart when I got ready to bleed it and put it back together.
If this is backwards, would you have normal acting brakes like I have, except when the MICO is activated, though?

Only 2 ways the check valve inside the original M/C can be installed; correctly or backwards. If it were installed backwards, system would not build pressure. My guess is that is not your issue.

[maineSS]

I also have a Mico lever lock I'm going to install to lock my front brakes when I go to a dual master cylinder, so I'm following your problems with interest. Like Charles said, the RP valve is a check valve, so it only works one way, and if you have brakes, it's ok. What I'm wondering is if you have a sticking valve in the Mico, and you are still applying pedal pressure after you flip the lever. You may have more pressure between the MC and the Mico than you have between the Mico and the brakes, and if a return spring is weak, or the valve is gummed up, it stays applied? I would think a properly working Mico wouldn't have a problem with this if it's hooked up right, since it was developed to work with 4 wheel drum brakes and M/C located RP valves.

[Doc Dave]

From all the advice I got on this thread, and the associated tests, I have decided I had a bad MICO (it was the only brake component I had that was used.

I went ahead and just won a vintage NOS MICO in its box on ebay. Very nice, and does not have all the electronic alarm stuff on it, etc., like a modern one.
I am going to plumb this in when I get a chance, and will report on the progress.

BTW to all who have followed this thread. I have an Imperial brand double flare tool. In spite of being careful, it still is not foolproof; some flares leak.

The people that make the Kunifer brake line have a deal where you can borrow their several hundred dollar commercial double flare tool for free, simply for making a deposit (if you are a customer). Are these tools appreciably better than the Imperial or others like it?

[maineSS]

I called Mico and talked to one of the Techs regarding the installation of the older lever lock types- he said the line to the MC is plumbed to the side port in the housing, and the port at the end goes to the brakes. He also said when the housing is screwed onto the lever assembly and bottoms out, you don't back it off to accomodate mounting concerns- you turn the lever & housing until the lever swings upwards, and bend your lines to fit the position it came to rest in. Also, there is no internal seal kit- when the factory-machined tolerances are gone, so is the unit.

Orme Brothers in California sell dead-soft copper brake line washers that do a great job fixing leaky flares. I used them on a front caliper and on the high-pressure side of my Toyota steering box line- worked like a champ both times.

[Doc Dave]

Thanks Maine,
I have those washers, and I think I will use them here. It seems like the MICO, being that it "holds" pressure, really "shows" if the joints are not perfect. In a way maybe that is a good test device for your flares.
With the next truck project I have, I am going to bend all the lines and then "borrow" the professional flaring machine from the Kunifer people. I really dislike making double flares.