M&G Tow Brake Installation Tips and Pics

[Cruzer]

After having the M&G tow brake on my Grand Cherokee for a while now it was time to add one to the Wrangler.

The M&G Tow Brake is a great setup. It utilizes the existing air brake system of any coach with air brakes to proportionately actuate the toad's brakes. For RVs without air brakes they do offer an air compressor setup, but this does add to the cost. The beauty of this system is that there are no electrical connections and no decelerometers. When descending a grade the jake brake will not engage the toad's brakes. The only time the toad's brakes work are when the coach's brakes are on. Being totally proportional the amount of braking depends upon how hard you step on the brake pedal so the toad and coach are always in sync.

Installation on the coach is very simple. You simply tap into one of the brake service lines at the rear axle with a tee fitting, then run the extra nylon line to the rear of the coach where you intall a quick disconnect coupling. Tapping into this line is no different than feeding a tag axle. In the event of a failure the brake system's isolating valves would still give you 3 wheels worth of braking and the air pressure loss by a severed line would be very minimal because it's the service line, not the "hot" emergency line.

On the toad end you first have to install the M&G adaptor.



This adaptor fits between the master cylinder and the vacuum booster. It consists of a housing with an internal split shaft. Where the shaft is split the piston on the frontmost half is acted upon by the air pressure input. Whenever you are not towing, this system acts as a large pushrod allowing the brakes to function normally. This is a fail-safe design so even if the M&G module was to fail you would still have manual braking. However, when towing, there is nothing pushing on the pedal. Instead, the air pressure from the coach is applied to the M&G module which works the front half of the split shaft to apply the brakes evenly and in direct proportion to the coach.

The RV connects to the front of the Jeep with a short nylon hose with a male and female quick disconnect fitting. I find that running it inside the coiled trailer light umbilical makes it nice and simple. There is nothing to hook up or install inside the towed vehicle and once installed it's totally invisible. You just plug in the hose and go.



I also ordered the optional breakaway kit. This kit consists of a small air reservoir tank that will supply air to the M&G module should the toad come loose from the RV.



This tank is charged up after 3 good pushes on the brake pedal. It is connected to a 3 way solenoid valve.



This valve allows the tank to charge up while driving and directs normal braking air pressure to the M&G module. Upon breakaway, the valve dumps the contents into the M&G module and locks it up to keep the toad from going ballistic. This does require wiring in a breakaway switch. One wire goes to ground an one goes to a battery "hot" source. I mounted both the breakaway switch and the air inlet fitting on the front bumper of the Wrangler.



M&G recommends that you just leave the hose loosely coiled up under the hood of the towed vehicle, then hang it out the hood when towing. I wanted something more stationary so I mounted everything in the bumper. Besides, it's a Wrangler, not a Ferrari.

The only drawback to this is that you can get dirt into the fitting. M&G states that the end of this hose should not be capped off or else air pressure could increase within this hose as things warm up under the hood and you might find your brakes dragging while driving. To rectify I took a right angle spark plug boot and inserted a short whip of the nylon brake tuning into it. This gave me a vented dust cap which keeps dirt out, yet allows venting of the system.



After having a Brake Buddy and US Gear unit previously I am very happy with the M&G system. It's the most foolproof system out there and reacts just as you'd expect, when you expect.

[Cruzer]

After having the M&G tow brake on my Grand Cherokee for a while now it was time to add one to the Wrangler.

The M&G Tow Brake is a great setup. It utilizes the existing air brake system of any coach with air brakes to proportionately actuate the toad's brakes. For RVs without air brakes they do offer an air compressor setup, but this does add to the cost. The beauty of this system is that there are no electrical connections and no decelerometers. When descending a grade the jake brake will not engage the toad's brakes. The only time the toad's brakes work are when the coach's brakes are on. Being totally proportional the amount of braking depends upon how hard you step on the brake pedal so the toad and coach are always in sync.

Installation on the coach is very simple. You simply tap into one of the brake service lines at the rear axle with a tee fitting, then run the extra nylon line to the rear of the coach where you intall a quick disconnect coupling. Tapping into this line is no different than feeding a tag axle. In the event of a failure the brake system's isolating valves would still give you 3 wheels worth of braking and the air pressure loss by a severed line would be very minimal because it's the service line, not the "hot" emergency line.

On the toad end you first have to install the M&G adaptor.



This adaptor fits between the master cylinder and the vacuum booster. It consists of a housing with an internal split shaft. Where the shaft is split the piston on the frontmost half is acted upon by the air pressure input. Whenever you are not towing, this system acts as a large pushrod allowing the brakes to function normally. This is a fail-safe design so even if the M&G module was to fail you would still have manual braking. However, when towing, there is nothing pushing on the pedal. Instead, the air pressure from the coach is applied to the M&G module which works the front half of the split shaft to apply the brakes evenly and in direct proportion to the coach.

The RV connects to the front of the Jeep with a short nylon hose with a male and female quick disconnect fitting. I find that running it inside the coiled trailer light umbilical makes it nice and simple. There is nothing to hook up or install inside the towed vehicle and once installed it's totally invisible. You just plug in the hose and go.



I also ordered the optional breakaway kit. This kit consists of a small air reservoir tank that will supply air to the M&G module should the toad come loose from the RV.



This tank is charged up after 3 good pushes on the brake pedal. It is connected to a 3 way solenoid valve.



This valve allows the tank to charge up while driving and directs normal braking air pressure to the M&G module. Upon breakaway, the valve dumps the contents into the M&G module and locks it up to keep the toad from going ballistic. This does require wiring in a breakaway switch. One wire goes to ground an one goes to a battery "hot" source. I mounted both the breakaway switch and the air inlet fitting on the front bumper of the Wrangler.



M&G recommends that you just leave the hose loosely coiled up under the hood of the towed vehicle, then hang it out the hood when towing. I wanted something more stationary so I mounted everything in the bumper. Besides, it's a Wrangler, not a Ferrari.

The only drawback to this is that you can get dirt into the fitting. M&G states that the end of this hose should not be capped off or else air pressure could increase within this hose as things warm up under the hood and you might find your brakes dragging while driving. To rectify I took a right angle spark plug boot and inserted a short whip of the nylon brake tuning into it. This gave me a vented dust cap which keeps dirt out, yet allows venting of the system.



After having a Brake Buddy and US Gear unit previously I am very happy with the M&G system. It's the most foolproof system out there and reacts just as you'd expect, when you expect.

[PDB]

Cruzer,
I much enjoyed your writeup on the M&G system. I have it on my Grand Cherokee, and I had it on my old Alero. It's a great system.

I have a question. I lost my spark plug boot so I bought a rubber cap at an auto parts store. It does not have a right angle bend, nor does it have a hole in it. It is strictly a rubber end cap. Am I to undrstand that since this cap won't "breathe" that I could be causing myself a problem with my GC brakes?
(Believe it or not, the auto parts guy had no idea what I was talking about when I asked for a spark plug boot!)
Thanks.
Paul

[Cruzer]

Hi Paul,

M&G's reasoning behind leaving them open is because of expansion. If the line were capped off there would be no room for any air to go when it expanded. Naturally, when air warms up, it expands and it can get pretty warm under the hood when an engine is running. This expanding air would then cause the piston to move which would begin to apply the brakes, causing them to drag as you were driving along.

In theory this makes sense. However, I don't know how much actual expansion would occur under typical operating conditions. Still, the brakes are a pretty critical part of a vehicle so I tend to assume M&G considers it a definite possibility opr else they wouldn't mention it. Sticking a spark plug boot on it gave me coverage and using a leftover chunk of the poly brake line let me vent it to a clean location - right behind the bumper rather than sitting out front. When using a right angle spark plug boot you just need to be sure you don't cram the air line all the way into the boot or else it won't be able to vent. If your local guy can't find you a spark plug boot let me know and I'll send you one. I have a drawer full at work.

[M&EM]

I used a right angle pvc fitting from an old pvc valve. Connected it with some neopreme tubing with a bit of gauze stuffed in it as crude filter.