If you’re driving around at a fairly constant weight and no constantly loading and unloading I would bypass all that stuff and run a line with a schrader on it to each bag and then land the schrader somewhere easily accessible.
That’s how I run the bags on all my rigs(heavy heavy 1 ton rigs). I check the pressure with a gauge the same time I check my tire reassure. I have a compressor on my truck to air up if needed. A little 12v tire inflation compressor will work just fine. But you can air up at a service stations also. I drive a LOT of brutal rough roads and don’t have any issues with leaks. It’s simple and reliable
https://www.amazon.com/dp/B08BJ57PDS/ref=cm_sw_r_cp_awdb_imm_VHCX3CCCACV3XQ465R94
Run the lines directly to your bags and don’t T them together. One line for each bag.
I have like 300lb of stereo and tools in my trunk. I put in air lift 1000's and it raised the car back up 2" and you can vary the pressure from 5-35psi. Had them in since April 2017 (approx 25-30k km) with no issue.
EDIT: here's the link https://www.amazon.ca/gp/product/B000CFQ34A/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Here's the Amazon link. They were relatively easy to install if you find the YouTube videos and they work great. I have a 7,000 lb travel trailer with a tongue weight around 500 lbs and with these inflated, it rides perfectly level.
AIR LIFT 60818 1000 Series Rear Air Spring Kit https://www.amazon.com/dp/B001OMVCIC/ref=cm_sw_r_cp_apa_IV4JAbG89VXB3
So I went ahead and order this kit from amazon. Will be here Sunday. I can’t imagine it will hurt anything but it could certainly help.
Air Lift 80753 Air Lift 1000 Front Air Spring Kit https://www.amazon.com/dp/B0047DTDH2/ref=cm_sw_r_cp_api_i_mO1XEbEKHC93P
They fit inside the springs and can be inflated/deflated to add extra support and resistance to the suspension. Maintains ride height and prevents the suspension from bottoming out with the weight of a trailer on it, so it can still do its job and soak up rode bumps. The difference in handling and comfort is night and day with and without them, and if you're not towing, just deflate them to around 5 psi or so and it's like they're not even there.
The ones designed for coil springs are universal based on the measurements of your springs. This is the kit that I used for the EUV.
The air lines are normally a kind of thick plastic shown in the link below. I personally perfer metal tees but due to winter we use plastic often.
https://www.amazon.com/Hromee-Suspension-Fittings-Replacement-Components/dp/B08BJ57PDS
Make sure you center the weight over the axle but slightly forward so you have decent tongue weight. Go watch YouTube videos on tongue weight demonstrations if this is your first trailering experience.
If you're going to do this frequently, I'd suggest adding Firestone airbag kit inside the rear coil springs. Backs of 4Runners are very softly sprung. I did this to my 2021 TRD after my experience with my 17' and 1000s of miles towing my off-road camp trailer. Kit you want Firestone W237604135 Coil-Rite Kit , BLUE https://smile.amazon.com/dp/B000JK0XKI/ref=cm_sw_r_apan_i_G8PF359HSA2Q8J75KN2V?_encoding=UTF8&psc=1
That's how mine (2004) is oriented as well, and it rides/handles fine. However, I have the battery on opposite side and an air spring kit like this one , which has been a fantastic help to keep the rear suspension fairly level side to side as well as front to rear.
2018 Highlander XLE V6 AWD
Had a shop put the tow-hitch on with a proper 7-pin and brake controller.
I put in the airbags myself (AIR LIFT 60732 1000 Series Rear Air Spring Kit). These are for a Sienna but fit inside the coil springs. I keep 5 PSI in them at a minimum and towed with them at 15/20 PSI. You don't have to take the suspension off (just remove the tires). Just have to lift the flap that covers the rear springs and use an angle socket to remove the nut on the bump-stops. You can use pry bars to separate the springs enough to get them out but it's a bit of a bitch so be prepared to cuss. Once they were in, I ran the tubing up to the small flap in the back (not the brake light flaps). You can get fancy and mount an air gauge if you want but I only towed for the summer as we bought a truck in prep of a bigger trailer as we camp a lot with the kiddos.
Air Lift 80753 was the kit I got.
Amazon has them...pricey though. Think I paid around $90 a couple years ago.
Air Lift
Jack stand the rear of the car, pop out the rear springs, deflate bags, squeeze in, pop coils back in. Easy job. I ran the air line out the bottom of the control arms and into spare compartment. Left a tag end for easy access to the Schrader valve.
If you are trying to take up sag, have you looked into bagging the rear shocks? WE did that with our Previa and it made a world of difference for balance and handling.
We used this kit. Obviously you need the one to match your vehicle...
Yes I installed myself. Etrailers.com has great instructional videos. You can buy them from Amazon for $95 if you can wait a couple weeks. If it’s gotta be quick etrailers.com has them for a little more and if you need it they have quicker more expensive shipping options.
Here they are on Amazon
AIR LIFT 60732 1000 Series Rear Air Spring Kit https://smile.amazon.com/dp/B000CFS028/ref=cm_sw_r_cp_api_glt_fabc_QK580QRVFFKN17BRW6RK
These are the ones I got. There are some different brands that all seem to do the same thing, but this is what I found. Has worked great so far.
Only the one tow, but they've helped a half dozen times level out the back end when loaded down with all our shit and dogs. I think they were totally worth it, and easy to install.
We tow with a Toyota Sienna. we bagged the rear shocks and it made a huge difference to handling. No more rear sag and way better braking and cornering.
A kit like this does amazing things. You just stuff the red air bags inside the rear shocks and inflate when you are towing something heavy.
Yeah, adjustability is kindof a requirement; I don't want to raise my CG and compromise everyday handling. I've been looking at a coil-rite kit for the rears and something like this on the front struts, but I'm not sure those are the right parts.
The controls seem pretty straightforward if you don't need 'em to be nimble. One valve per corner that either connects or isolates it from a common manifold. And then the manifold gets a gauge, a vent-to-atmosphere valve (with needle orifice for speed control), and a compressor inlet probably also with a check valve. I could automate it, but for as often as I'd adjust it (once when approaching the trail, once when leaving it, once before a blizzard, once after the snow's gone), I'm not sure that's prudent -- I don't mind taking a minute per corner to dial it in.
Trouble is, it's my daily driver and I'm leery of adding complexity and points of failure that're outside my field of expertise.
Nah it's super easy. I used a sawzall to cut the rings off the bumpstop. Cut 1 at a time or you'll have a big chuck of rubber that you can't remove. (ask me how I know)
Push the airline up through the rubber bumper from the bottom and run it where you like. I run mine through frame and out the ends. I use foil back sound deadener to wrap around airline near the exhaust and where it goes through the frame. There is a hole in each bumper where the side pieces meet the center. I put my valve stems there. I prefer to have each airbag independent so you can adjust the pressure if you have an unequal load in the cargo area.
Just collapse the airbag by squeezing all the air out, and push it in with the air line connection going up.
Put the barbs on the airline, connect to the airbag, put the valve stems on, and you are good to go. Should take an hour tops.
I have had the kit on my 1999 since 2014. I run 5psi when unloaded. Run up to 50psi when loaded down with a trailer or gear in the cargo area, or heck, even if you have your whole family in there.
https://www.amazon.com/LIFT-60743-1000-Air-Spring/dp/B001F15Z08 - This is the kit I used. I paid 83.85 on Jun 26, looks like the price has gone up by 10 bucks.
https://camelcamelcamel.com/product/B001F15Z08?context=search - This site lets you flag Amazon for price alerts and tracks pricing history. Looks like the price has been up and down as low as 72 bucks in March!
Here is the kit I used, Amazon says it doesn't fit my vehicle but on my 2008 P71 it was the perfect fit.
https://www.amazon.com/gp/product/B001OMVCIC/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
I put these on my ram. Makes a big difference in sag when putting weight on the rear axle.
Not too hard to install.