Trailer hitch! Air Springs! Oh my!

[xsdg]

So, I finally bit the bullet and got a custom-fabbed Class III trailer hitch for Truckula.  I've been meaning to do it for awhile, and it seemed like the only options out there were U-Haul and custom.  The price for something custom was pretty close to U-Haul, and it meant I didn't have to sit through 20-30 days of lead time, so I jumped on it.

 

 

 

For any of y'all in the Bay Area, I got it done at A&B Trailer Hitch in San Carlos and was pretty happy all around.  I just got it done on Tuesday, and haven't really had a chance to play with it, but it seems pretty stout.  It's basically a couple pieces of square tube that are welded to the bumper supports.  The only downside is that it's also welded to the frame, but it's not clear what else you could do, given that the frame is fully boxed — it was hard enough getting the nuts in there for the bumper mounts, let alone having to get them even farther forward.  All things considered, I'm happy with how it turned out.

 

All that said, I've got some air helper springs coming in the mail pretty soon, and I'm wondering what the stock ride height is so I can set them up correctly.  I'm pretty sure my 30-year-old springs are sagging a bit, so "just measure" probably isn't what I'm looking for.  Ideally, I'd get some measurements from wheel center to fender lip, although wheel bottom or top edge to fender lip would work just as well — I've still got the stock 14" steelies.

[xsdg]

Oh, and if anyone's curious, here's the U-Haul hitch.  The instructions specifically call out all variations of the '85 720, so it's the real deal and is actually designed specifically for the 720:

https://www.uhaul.com/pubshandler.ashx?id=148535&digest=Oc2x9YG2NbMf5ZKYSB4xaw

 

That said, it looks like the actual receiver in that design would be pretty dang close to the spare tire, if it even clears.  That means you'd have to use an extender to tow mount pretty much anything, which would be a pain and would magnify tongue weight/reduce torsional strength.

 

 

The air bags I'm getting are these:

https://www.airliftcompany.com/shop/59529/

I cross-shopped those against the Ride-Rite (Firestone) 1130.  I picked the Air Lift bags because they're less expensive and lighter-duty — up to 1,000lbs per bag instead of 2,500lbs per bag for the Ride-Rites.  Given that the GAWR is 2540lbs, there's no way I'll even get close to the extra payload the Ride-Rites can handle.  The Air Lifts save me $65 for the kit ($365 vs. $300 at etrailer), and if I have to replace a bag, the Air Lifts are $70 per bag, versus $120 for the Ride Rite replacements.

 

The main downside for me is that the Ride Rites have a nifty tool-less install using bail clamps around the frame.  That said, they also require you to remove the bump stops, and don't incorporate any physical bump stop.  The Air Lifts install directly aft of the axle, and allow you to keep the bump stops, but you affix the upper bracket to the frame with self-tapping bolts, so you have to drill holes and then install the bolts without messing up.

[xsdg]

Bump!  720 stock ride height?  I'm planning on doing this install today, after I run and get some food.

[datzenmike]

It is, what it is, at the back. The 4x4 is higher than the 2wd but there is no published 'ride height', how can there be? Too many variables like gas tank size (full not full) wheelbase, options, spring sag over time, optional installed over size rims/tires. The front is adjusted by turning the torsion bars up or down to get a set distance from a known suspension component to ground and is critical for proper steering geometry.

[xsdg]

Go Go Gadget air helper springs!!!

 

The assembled air spring assemblies, in installed orientation. Red air fittings point towards the rear of the vehicle.

 

 

Lower bracket installed. Front of the vehicle is toward the right. One of the things I like about this kit is that you keep the bump stops.

 

 

All of the components (and tools) to mount the lower bracket on one side.

 

 

Getting things lined up to install the upper bracket.

 

 

Magically delicious! Drill 5/16" hole, then install 3/8" self-tapping screw. Thank goodness for impact wrenches

 

 

Fully installed with air lines routed but not yet fixed in place. 0 PSI

 

 

60 PSI. Note that the jack stands are supporting the axle and not the frame, so the air springs (plus leaf springs) are supporting the full rear axle payload. This basically shows the unloaded vehicle ride height at 60 PSI. System max is 100 PSI.

[xsdg]

I had meant to say: one downside is that even with the system at min pressure (5 PSI), there's still a pretty significant increase in spring rate over stock.  This is noticeable just driving around — it feels like the truck is slightly over-sprung in the rear, although part of that feeling might be the juxtaposition with the front, which is underdamped currently.

 

Also, the unloaded ride height has increased, which means that roll center is higher.  One result is that the truck seems to "fall over" in turns, whereas beforehand, it had plenty of body roll, but the roll was fairly progressive.  Because of the camber gain in front when the suspension compresses, it means that I have to watch out for surprise oversteer now, which is a trait that the truck didn't have previously.  Hopefully getting some stiffer dampers in the front will help to make the body roll more progressive again.

 

All in all, I'll probably get used to the new handling characteristics (and as mentioned, I have some ideas on how to make things a bit better then they are currently).  I'm still happy, because this means I can carry weight (including towing trailer tongue weight) that's cantilevered past the rear axle without losing as much weight off the front axle, so I'll still be able to steer and brake.  You never realize how nice turning authority is until it goes away :o)

[720inOlyWa]

I am really interested in this thread as I intend to pull a small outboard skiff behind my 720 in the future. (A Port Comfort 18 that I am currently building) Not a lot of weight, but enough that the compression needs to be fresh and the rear springs need to be right for the load. I have already learned, from putting 1/2 yard of manure in the back, that the stock rear springs are not going to be enough as is. It is pretty squirrely with 700 pounds of shit in the back (which is quite a bit more weight than the tongue of the trailer will bring to bear). Still...

 

I have a buddy with an 82 Toyota truck that is rear bagged and it seems to do the trick. He likes it, but hardly ever tows anything, so who really knows. I am also concerned about how stiffening the rear end will change the handling characteristics.

 

I wonder out loud whether it is better to put a 4x4 spring set in the rear, or bag it, like you did...

 

Thanks for posting. 

[datzenmike]

My 521 rode best with over 500 pounds in the back... didn't brake or accelerate worth crap but the weight helps make the springs actually move and this took the harshness out that you felt when empty. The 720 is rated to carry about 1,100 pounds of load. 

 

Generally the stiffer the rear springs (without cargo) the more the vehicle will understeer or plough into corners. It's very subtle and only when the vehicle is driven at the extreme edge of it's handling abilities (which you are not) Slippery roads (wet ice snow) might show this a bit more. Again this is why a truck rides better with some load in it.

 

As for towing generally you want (about) 10%-15% of your Gross Trailer Weight on the tongue. So a 2,000 pound trailer and load would only add 200- 250 pounds to the back of the truck. Like an adult riding in the back. Not likely to significantly sag the rear springs much.

[720inOlyWa]

My boat and trailer is about half of that weight, Mike.

[xsdg]

720inOlyWa: I think it depends on how much time you're going to spend carrying stuff versus not.  I generally drive around unloaded, so the air bags were the obvious choice.  If I were carrying loads most days, I probably would have done something with the leaf springs themselves (whether replace them, or add a helper leaf).  That option would be less adjustable, but more consistent.

[wayno]

Well this is something I know a little about, hauling weight and towing with a Datsun, these are not big trucks, so you basically have to build your truck to do what you want it to do, you cannot have it all.

I have built my truck to haul mass amounts of weight, and I tow a trailer that I would guess weighs somewhere around 1500lbs total, although it may weigh more, when I empty the truck and disconnect the trailer, it rides firm, it doesn't seem to bad to me, but I have been driving it this way for a decade or more, so I am used to it.

I added 2 extra leafs on each side of my leaf spring packs, they are basically motor home leaf packs now except not as flat, my stock 521 leaf packs have more arch than a motor home leaf pack, and I have both types to compare to each other, motor home leaf packs are more like 720 4X4 leafs than they are like 521 leaf packs, except they are way firmer than 4X4 leafs.

I also have shocks with coil springs on them, and I have over load bags, if I put any air in the bags it makes the rear of the truck bounce in the air when I go over a speed bump, so 99 percent of the time my air bags have zero pressure in them, the only time I put air in them is when I haul wood, lots of wood.

Here is a photo of one side of my truck, as you can see I have 7 leafs in that pack.

Here are the kind of loads I carry

You can also see my truck is a dually, the dual wheel rearend doesn't actually haul more weight other than having 4 tires to take the weight instead of just 2 tires, but it does tow things better, a lot better, I have towed with and without dually rearends, I will never tow anything without a dually rearend except maybe a couple miles, never again will I tow on a freeway without a dually.

You build a truck to haul weight, then it will never ride like a car again, and that is what a stock 720 2wd truck rides like, a car.

My truck has the best front disc brakes on the front that will fit, but to this day I still have the stock brake master on the truck, it works so I have not changed it out, but I really do think it should have a dual reservoir master, I just have not gotten around to it yet(10 years).

It really all depends on how often you plan to haul heavy loads, or tow with it, oh and how you plan to drive when doing/completing these tasks, if it is a weekend warrior, I would just get some air shocks, air bags might work also, but they should not effect the ride when at the minimum pressure, I have virtually no air in my bags except when hauling weight, meaning when the truck is empty I can push the spring/valve for putting air in the bag and no air comes out, but if I load the bed and push the spring/valve air does come out.

4X4 leafs lower the truck almost 2 inches, they are firmer, but allow a decent ride when truck is empty.

[720inOlyWa]

Wow, wayno. This is really great info. Thanks- a ton!

You nailed it when you said my 2wd 720 rides like a car. Now the base model 620 I had years ago was set up to carry a lot more weight than my 720. I put 1,000 lbs in that 620 regularly and it didn‘t hunt or act like the front end was going to leave the ground. No siree. That little devil was a BURRO! (Nothing like what you have, mind you. Holy cow!)

 

I have not tried to tow a little trailer and skiff yet, so I don’t really know how much stiiffening I will need. But I am pretty sure that I will need some. Maybe just air shocks would be plenty. I am never going to have a dually set up, though I sure can see how it works for you. But I do intend to drag my little skiff all over the place and I want either my 4x4 or 2wd 720s to do that job with ease. I am not worried about towing power so much as I am looking for solutions to beef up what I have. The more I think about it, the more sense a set of air shocks makes.

 

Awesome thread! Thanks!

[Spiff]

Isn't the 720 rated at more than 1100lbs? thats like 500kg's.... My 720 is rated with a gross vehicle weight of 2200kg, the truck weighs about 1100kg pluss me  thats about 1200kg leaving a whole 1000kg(2200lbs) of load capacity. It would probably bottom out though but still....

[xsdg]

Spiff: is that 1100kg wet?  What year?  I took my '85 (cali Z24) to a weigh station and it's 2750lbs with fuel, without driver.  So that's 1250kg without driver.  I have a spare and an aluminum toolbox.

 

Also, to Wayno's point, I did my couple-days-after-install pressure check and discovered that I had been misreading my inflation gauge — the last line isn't 0.  So it had around 10psi per side in it.  When I dropped that to 5psi (the recommended minimum), the ride improved pretty dramatically, so I'm basically completely happy with the setup now.

[Spiff]

My memory was slightly off, It's 1205 with a driver(which weighs 75kg's in the norwergian system), so add another 20 for me and that's 1225 wet, 1130 without driver. GVW is stated at 2300kg.

Although I'm not sure if this includes a full tank, couldn't find any info on that.

Mine is an 82 longbed singlecab.