Does anyone know anything about MICO brake locks ?
The one that I have plumbed into the rear brakes of my 1985 F-350 seems to have quit working; else, I have something weird going on that makes me think the MICO isn't working.

It has worked perfectly for thirty-plus years, holding truck and loaded trailer under all sorts of circumstances.

Just lately, I have discovered that, applied or not, the rear brakes aren't holding at all.

I guess anything can eventually wear out.

Can a MICO be rebuilt ?

I really miss it and it is a wonder that I didn't have a roll-away experience.

For what it's worth, the rear brakes are in excellent order, everything new a couple months ago.

 

It has been quite a few years since I worked on Mico-Brakes but from what I can recall they were not user serviceable.
Here is a link to their website, you may want to give them a call.
https://www.mico.com/welcome-mico-0

 

...and don't they use the EMER BRAKE for holding the truck?

 

Thanks for the link.
I did a bit of searching and found out that the old-school MICOs, such as the ones I have on several trucks, are indeed user rebuildable, at least so far as replacing the cam/lever and operating rod (and it's seals).
So far, I have found one source for the rebuild kit; and, it is priced at $94.50, more than twice what I paid for the whole thing when new.

No; MICO Locks are plumbed into the hydraulic brake lines and "lock" the brakes hydraulically.
They are most often plumbed in the rear brake line and lock the rear brakes.
They can also be plumbed in the front brake line and lock the front brakes; I have one truck that is equipped this way, the cable park brake locks the rear and the MICO hydraulically locks the front; that truck will for certain stay wherever I put it.
They also make a dual kit that has valves for both the front and rear brakes; I have always wanted one of those.

A MICO works very much like a check valve that can be turned ON and OFF.
To set the MICO, you flip the lever 180* over to LOCK position and then firmly apply the hydraulic brake; the fluid pressure can pass through the MICO to apply the brakes and is held there under pressure so long as the MICO is engaged.

The only weakness, or actually a strength, of a MICO is that the brake system must be completely leak-free between the MICO and the brake that it is locking; a leaking wheel-cylinder or pin-hole in a brake line will allow the pressure to bled off and the MICO will no longer hold.

Although I have never been in the wrecker business myself, every hydraulically braked wrecker that I have ever seen has a MICO.
I learned to love them because we pull extremely heavy goosenecks, most usually with cattle that are constantly surging around; a MICO, working along with a proper cable parking brake, gives you much better odds that your truck will be where you left it.
Of course, having genuine vacuum-over-hydraulic trailer brakes that can be locked helps a lot as well. I never trusted electric brakes.

 

Okay, a bit of an update in case anyone ever stumbles upon this seeking an answer to their situation.

I found several sources for a rebuild kit that replaces all the components that can be accessed while the MICO is still mounted, part # 02-600-001, about $95 shipped; to put this in perspective, I found a receipt where I paid just a bit over $40 for the last complete unit that I bought.

I got to mulling the situation over and decided before I shelled out for an over-priced kit, I would temporarily borrow the "kit" from one of my other known-working MICOs.

I took the "kit" out of a working MICO and installed it in the problem truck; before I put things together, I carefully measured and compared each component and could see no measurable nor visible difference between the two.

I went ahead with the switch and didn't gain a thing other than learning that a $95 kit is not going to fix the problem.....whatever it is.

During all this, I had been diligently keeping an eye on EBay and just did grab a complete NOS still sealed in the plastic and in the box for a very fair price, so fair that I clicked "Buy it Now" as soon as I saw what it was.

If this new MICO still doesn't hold, then it is going to be either a bad master-cylinder or whatever that combination valve gizmo is that limits rear brake pressure.

My next test is to get the hind wheels in the air and see how much rear brake I have, if any at all.

In all the years I have been running MICOs, this is the first problem I have had and I am beginning to suspect that the problem is not the MICO, but something else.

 

IIRC the micro switch fits between master and either front or rear systems.

If the master was bad and not building psi the pedal would go to the floor or close to it.
It sounds like you don't know what shape the brake system is in so I would pull all wheels and check everything.
Frozen wheel cylinders or calipers and good master could only have 1 part of the system working.

I would never use a micro lock as a parking brake.
If the system it is on leaks down no more brake and you may find the truck down the road in to a tree.

Yes I have used them on dump and tow trucks. Set jump out to hook up car or shovel some dirt then release and drive off.
just my .02
Dave - - - -

 

For what it's worth, everything about the brakes, front and rear, calipers, wheel-cylinders, hoses, rotors, drums, hardware, master-cylinder, etc., was all put in new not many months ago.

The only thing not replaced was the combination valve.

Just today, I had the rears off the ground, axles out so everything was free to spin; I had an assistant in the cab apply the brakes and I could actually turn the rear wheels while the brakes were applied; sometimes pumping the pedal another time would make them hold sufficient that I could not turn them by hand, but not every time.

This behavior can't be right.

I don't think sufficient line pressure is reaching the rear brake lines so I am going to start a thread in the other section to address this situation.

Right now, I don't think the MICO is bad, but that I have something else going on with the rear hydraulic pressure.

Thanks for your input.

 

Pumping the brakes and sometimes they stop Turing to me says air in the rear system.

Everything being new even more so.
I would start at the master cracking fittings working my way to the rear trying to get the air out.
Don't forget the micro line also.

A new system is hell to get the air out as I have done 2 or 3 so far.
Good luck.
Dave - - - -

 

Rule usually says to start at rear and work forward......

 

Check the rubber line between the chassis and axle. I have had them collapse inside and not allow any fluid to the rear brakes.

 

That is a good call and I have had it happen more than once myself; however, this truck has relatively new braided stainless flex-lines at all points.

As for the collapsing rubber lines, they will also act as a check-valve, allowing the brakes to apply and then not allow the pressure to release; this is quite common on disc-brake calipers.

It is like a million degrees outside and I must work on the rocks in the sun; so as soon as I recuperate from my last ordeal, I will see if bleeding again makes any difference.

 

You nailed it !

After a thorough vacuum bleeding of the rear system, the Mico holds as good as it ever did.

I have them on several trucks and I would not do without them; I am a firm believer in Mico Locks.