What are Caged Brakes or What are “Cage” Bolts and How To Use Them on an FMTV Truck

Before we jump into the Cage Bolts we need a quick lesson on Air Brakes for those who are unfamiliar.  And yes this Cage is different from a CAGE code for those of you who are suppliers to the Federal Government. As a bonus who knows what a CAGE code stands for?(See the bottom of this post for an answer)  Anyway on with our Cage bolt lesson.  If you have driven a truck with air brakes you can skip this part as you already know this stuff or should.

FMTVs have Air Brakes, that means air pressure is required to operate the brakes.  All air brake equipped trucks have a system for producing compressed air which consists of an air compressor, air dryer, air tanks, wheel brake cylinders, and various valves and hoses to control and distribute the air.  We are not going to go into details of exactly how the system works in this article but suffice to say approximately 90-120 PSI of clean compressed air is required to make the brakes work properly.

Air brakes are designed to be a fail safe system so if air pressure is lost the brakes are automatically applied to stop the truck.  If you are thinking what would happen if I had a sudden loss of air pressure while moving down the road…. Would I stop???………….Yep and in an immediate quick way.  That is why there are air pressure monitoring gauges in the truck and a low pressure warning horn.  If you get the horn while driving its best to pull over in a safe spot because if you don’t you will come to a stop when the air leaks out…… The reason the brakes are applied when air pressure is lost is the slave air wheel cylinders have a powerful spring in them that applies the brakes on full and it takes air pressure to compress the spring and remove force on the brakes.  This is what the Yellow Air Brake knob on the dash does.  Knob pulled out parking brakes on, knob pushed in normal service brakes in operation.  So knowing this and having zero air pressure in the system how do we move trucks that are not running or dead with the brakes locked full on?  Promise, you are not going to move an FMTV truck across the ground with applied brakes and no air pressure.  Since most of the FMTVs being sold surplus are non-runners we need a way to load them and get them on the road to a new home.

This is where the “CAGE” bolts come in. 

Serious injury, death and/or property damage may occur if you do not heed the following warning

*******Word of warning—-->>>> When all the brakes on the truck are caged the truck will roll and there is no means on the truck to stop it…….********

This means you need to have the truck properly chocked and/or a positive means of control or the truck will roll where ever gravity dictates.  THINK BEFORE you begin the brake caging process.  FMTVs should have Cage bolts installed in their storage positions if they have not been removed or lost.  Cage bolts are a T headed bolt with 1/2″ Acme threads that include a flat washer and nut (No Standard nuts will not work on Acme threads and you are not likely to find Acme threaded nuts in a basic hardware store Do not Lose the nuts!)  The Cage bolts are stored in a storage location on the brake slave cylinders on an a 2 1/2 ton LTV or in a storage holder mounted on the axle on the 5 ton MTV.   

LTV = Light Tactical Vehicle 2 1/2 Ton Truck Easily Identified by the single rear axle

MTV=Medium Tactical Vehicle 5 Ton Truck Easily Identified by the tandem rear axles

FMTV=Family of Medium Tactical Vehicles usually refers to either 2 1/2 or 5 Ton Vehicles and their variants

So how to Cage the brakes on an FMTV.  On the FMTV only the rear brakes need to be caged.  On the LTV there are 4 slave cylinders to cage on the rear axle.  On the MTV there are 8 slave cylinders to cage on both tandem axles. Cage Bolts require a 3/4″ wrench or socket.

Caging Procedure

  • Remove the plastic cap usually blue from the center of the wheel slave cylinder and save to reinstall when the cage bolt is removed.
  • Remove the Cage bolts from their storage positions.  Each slave cylinder has a holding space in the slave cylinder housing to store the long bolts. The short bolts are stored on the rear of the axle in a small box or in a holder built into the front of the axle.
  • Insert the T Head into the wheel slave cylinder hole the plug was removed from.  The T Head is then inserted into the match hole and slot inside the slave cylinder and then rotated 90 degrees to lock it in.
  • Verify it is locked in solidly and then slip the flat washer over the bolt and thread the nut down until it is finger tight.
  • Using a cage bolt socket (extra Deep socket) or a ratcheting box end wrench tighten the nut on the cage until it is tight.
  • On the FMTV 5 Ton there are 2 different length bolts required.  The short bolts go on the 4 slave cylinders located in front of the shocks the long bolts go on the other 4 slave cylinders.  You can use the short bolts on all cylinders but the long bolts will damage the shocks if jacked all the way out in the shock positions.
  • On the FMTV 2 1/2 Ton you can use either short or long bolts in any position.
  • Truck Missing the Cage bolts?  It happens……….they get lost, borrowed, or not put back.
  • Long Bolt NSN 5306-01-500-8736 PN# A4X1883
  • Short Bolt NSN 5306-01-479-1492 PN# 12422439

Missing Cage Bolts or need other FMTV Parts? Contact us we can help

Here’s Some additional info straight from the source:

FMTV MTV Cage Bolts 

Bonus Question Answer: CAGE is short for “Commercial And Government Entity” everyone who does business with the Federal Government is assigned a 5 digit alphanumeric code.  Think of it as your vendor number.  Now you know the meaning of another Government acronym!

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