1970 D100 leaf springs

[GTEEO]

I have a 1970 D100 short box that was a 6 and now has a 440. We pulled a 19' Retro trailer easily but now have traded that for a 24' Retro. The new trailer sits higher and weighs about #1500 more. We pulled it home (350 miles) and it pulled great. I have air bags but want to bring the truck back to original ride height. The door tag says 1250/1400 for the springs but I think the PO dropped it because it seems a little low. I have 2 springs up front and 3 springs in back. I have a few questions that I hope someone can answer.
-1) What is the original ride height and where do I measure it?
-2) How many springs stock?
-3) Checked the Eaton sight and they mention PV 3-1, what is meant by that?
-4) Was there a HD spring option?
Below are pics of the old and new. The black/white is new. Thanks, Eric.

[martincom]

-1) What is the original ride height and where do I measure it?

As ride height is not adjustable, there is no specification for it that I'm aware of. My '71 D100 LWB is stock, so if you'd like some reference measurements from it, let me know.

-2) How many springs stock?

See the page excerpts from the '69 - '70 factory service manual, below:

-3) Checked the Eaton sight and they mention PV 3-1, what is meant by that?

I do not know.

-4) Was there a HD spring option?

Yes, see the service manual specifications pages, above.

There were never trailer towing specifications published, that I'm aware of. I've checked both the owner's manual and the factory service manual. The gross weight of your travel trailer will impact things like the rear axle, U-joints, transmission, brakes, etc. I pull my aluminum car hauler trailer, with a vehicle, behind mine on an annual basis. I'm comfortable with a 6800 trailer gross weight, which is the heaviest I've attempted. The trailer is rated for 10K. My rear suspension is stock and is showing its age, so I have to pay attention to tongue weight, as it will really squat if I get remotely heavy. I have a 22' trailer, so I have some wiggle room on where I position the vehicle to moderate the tongue weight. That is a luxury you're pretty limited with. When the times comes for me to replace the rear springs, I may be tempted to step up to the heavier options. However, the truck really rides nice now, with the stock configuration. As it is my daily driver, I don't want it to become a buck'in bronco. So, please post your results.

[GTEEO]

Thanks, that answers my questions. I think I'll pull the rear leafs and add a leaf, then check the ride height. My front springs are not standard leafs, the main leaf is thicker in the middle than on the ends, I'll have to see what I can do there. Just by looking at your picture I can tell that your truck is a little higher. Nice truck by the way. That would be what I'm looking for. If you get a chance to measure your ride height, I'd appreciate it. My new trailers empty weight is #5500 so with water, food etc., I'll be close to your weight. I'll update the post when I start to work on it and relay all the info. I'll also post how it pulls the trailer next year, gotta live through 6 months of winter now. I should also be installing power steering if all goes well. I already have power discs to help in the brake dept. Thanks again, Eric.

[Wildergarten]

When the times comes for me to replace the rear springs, I may be tempted to step up to the heavier options. However, the truck really rides nice now, with the stock configuration. As it is my daily driver, I don't want it to become a buck'in bronco. So, please post your results.

I am assuming you considered factory overloads. One of my trucks came with them, which pushed the VIN tag axle rating to 5500#. There was apparently an annoyance with that setup when the springs "clanged" against the take-up bracket. The owner had added a pad there. I noted on ebay a couple of years ago that there were identical brackets available with rubber bonded on them as a F0rd part.

[martincom]

I'm rather surprised that all the front spring capacity ratings remained the same across all engines. Even though ride height is adjustable on passenger cars, torsion bar sizes were different for certain engine sizes. A 440 was never an option in a sweptline, the 383 was as large as they came. Though very similar, the 440 weighed significantly more.

I also note the rear spring capacity ratings changed between a 6 and 8 cylinder, if I'm interpreting the chart correctly. Why engine size would have an impact on the rear spring rating is beyond me. Perhaps someone more knowledgeable could enlighten us?

As ride height measurements would be impacted tire size, I made the reference measurements you requested between the bottom of the frame rail and axle member. Bear in mind my truck was built with the heaviest front and rear spring options.

I couldn't keep the tape measure positioned against the bottom of the front frame rail and take the photo at the same time. The measurement from the bottom of the frame rail to the top of the leaf spring pack is 5.5". From the bottom of the frame rail to the top of the axle spring seat is 7.25".

[GTEEO]

Thanks for going through the trouble and taking pics and measurements. Much appreciated. ... Eric.

[Wildergarten]

I also note the rear spring capacity ratings changed between a 6 and 8 cylinder, if I'm interpreting the chart correctly. Why engine size would have an impact on the rear spring rating is beyond me. Perhaps someone more knowledgeable could enlighten us?

I have a guess: leaf spring wind-up. Unloaded, there isn't much weight on the rear axle, putting less normal force against the tires, which reduces both friction against the ground and the size of the contact patch of the tire. With more torque, lighter springs may be subject to more "leaf spring wind-up," with the axle torque against the tires putting the spings into an "S bend" until the tire lets go, which would produce at least rear wheel hopping and possibly loss of control.

[GTEEO]

Bought 2 60x2.5" springs, cut and drilled them and now I'm adding 2 on each side in the back and 1 more each side up front.