Trailer Tires & Suspension Pressure Monitoring

I pull a trailer almost constantly for work and I was looking for a clean way to monitor the pressure of my Air Lift suspension. I haven't seen anyone else do this yet and it took a little research and figuring, so I thought I would share what I did.

I came across the Careud U912 TPMS that fits in a standard switch slot. I got the version that screws on to the tire valve cap, since my air bags inflate via standard schrader valves. I could only find that version through aliexpress, but it showed up and works just fine.

I decided that the top two numbers would be for my airbags and the bottom two numbers would be for my trailer tires.



Turns out that those valve cap pressure sensors are a pain to take on and off, and I kept losing a bunch of air trying to get it back in place. The airbags don't hold much air, so a little bit of air makes a pretty big difference in pressure. I wanted to add another schrader valve to the line, under the truck, to keep the sensor permanently mounted.

After educating myself on schrader valves, Push-to-connect fittings, and NPT thread size options, and an epic internet search, I finally found the push-to-connect T fitting that would work with

$9 GASHER 2PCS 1/8" NPT Tank Valve Anti-Corrosion Brass Schrader Valve with 1/8" Male NPT,Using with Air Compressor Tanks

the correctly sized schrader valve that I wanted.



That worked out perfectly. After confirming that the fittings were holding pressure and that the unit was receiving the information, I took off for work...

...and was rewarded with the very loud alarm sounding for the 7 hour trip!! I knew that there would be an alarm for over pressure, under pressure, and over temperature. All of those can be set so that the limits are well outside of the working range to prevent the alarm.

What I failed to notice in the instructions was that there is also a "rapid pressure change" alarm. That would be great for tires, as it would let you know within 3 seconds of your tire starting to deflate if you got a puncture. The issue is that the airbag pressure constantly changes every time I hit a bump, go around a corner, change lanes, accelerate, decelerate, etc, etc...

I figured I had two options. Either figure out how to get rid of the buzzer or add a switch to the unit. Adding a switch would allow me to check the pressure before starting the trip and then turn it off to prevent the alarm. That would be a bummer not to be able to keep tabs on the system throughout the trip. I figured I'd risk it for the biscuit and worst case, I would just have to order a new one.

Hot tip: Don't push this receiver into place until you are ready to have it permanently in the dash. It is a very tight fit and super hard to get back out. I popped the switches out on either side of it to reach in and press the little releases, but no dice. I ended up having to take the whole dash apart again.

Tearing the receiver apart was another learning experience that I can get into if anyone else ever wants to try it. I ended up breaking mine open and gluing it back together afterwards. Removing the buzzer was straight forward with a soldering iron.



It was a little more work than I expected, but I think it's a super clean solution.

 

My compliments. That is a CLEAN install. Well done.

 

Thanks. I was especially glad not to need to run any hoses or wires into the cab.

 

interesting solution, i haven't seen those dash modules before. i'm interested specifically for my brz-- it just has an 'idiot' light for the tpms which drives me nuts, to the point i taped it off, and removed the sensors. i don't mind tpms where i can actively see the pressures, just can't stand the light...


what kind of air ride do you have installed on your trailer that the system hooks up to?

 

The airbags are actually on the rear axle of my truck. That keeps the truck level if the trailer tongue weight gets a little heavy. I am using this Air Lift kit.

 

Slightly better picture:

 

ah, too bad.

i was really hoping you'd converted a trailer or your truck to a 4-link airbag setup...

it's in my plans for the future, but there's not too much in the way of information on anything outside of extreme-travel trail pigs.

 

@ThisBen so the pressure sensor just screws onto the valve stem of the trailer tire?

 

Yes. That's right.

 

I'm intrigued. I'd like something like this as well.

Just be clear, you bought 4 sensors off Alibaba. 2 are used for the 2 wheels on the trailer and 2 are used for the bags on the truck?

 

Found them on Amazon too. Going to get one for my 2 axle TT.

$84 U912 Tire Pressure Monitor System TPMS Real Time Pressure Temperature Monitoring 4pcs RF Sensors Internal/External Default Slot 5 Year Battery (W/4pcs External Sensors, for Toyota)

Amazon.com: U912 Tire Pressure Monitoring System Customized for Toyota Honda Mazda Nissan Real Time Monitoring Pressure Temperature (W/4pcs External Sensors, for Honda) : Automotive

 

Thanks for saving me the trouble, was just about look there.

 

I just realized that I hyperlinked the wrong site above (now fixed). This is the TPMS that I ordered.
https://www.aliexpress.us/item/3256...il_item.3.79f8f19cL64M3k&gatewayAdapt=glo2usa

 

Nicely done. Enjoy seeing folks work creatively instead of just bolting stuff on out of a box

 

Please do elaborate on the buzzer removal .

I'm sure it's not rocket science, but I do have a thirst for info.

If I do this, and I'm sure I will, that buzzer will be yanked

 

just ordered one. Arrives in Feb

 

Out of curiosity, why do you want real time updates on the air pressure in your air bags?

 

I guess I don't really need the real time updates, but I want to keep the numbers in front of me so that I don't forget about it. The system seems to leak about 5% to 10% per day, regardless of whether I'm driving or not. I've troubleshooted (sp? troubleshot?) the whole system. Both sides leak about equally, so I think it just "is what it is" for the cheapest system I could find, and I can live with that. I just like to know where I'm at so that it doesn't get too low.

 

Allow me to answer for the OP?

I have air bags on my Tundra. They require manual inflation, as in I can't inflate them from an on board air compressor. The pressure gauge is not very accurate at these low of volumes and you will lose air pressure when you test. You can really only get " close" to the pressures you need.

Air bags work great for leveling the truck after you drop a trailer into the truck hitch.

The draw back is it takes very little air pressure to raise the back of the truck. It also takes very little to drop the rear of the truck.

20 psi is about the maximum pressure the bags can take, give or take.

The difference between maximum air pressure and a leveled bed pressure is pretty small. 5-6 psi maybe.

There is no need for max pressure once the truck is leveled with a trailer in the back. It just stresses the air bags and the ride will be harsh if you max out the bags.

With experimentation, the perfect psi can be achieved.

With this tool it will be easy to achieve the correct position with repeatability, since the trailer is not always on the truck.

In addition, because of such small volumes of air, the psi will fluctuate with temperature. This tool will tell you pretty quick if you are in need of more or less psi.

Also, like any air system, leaks are the weak link. You will know pretty quick if one of the bags had a plumbing or bag leak.

For people that tow and are really bothered by a squatting rear end, this tool is a pretty cheap upgrade.

 

Good answer!