Rear Suspension Mod's For Big Blue?

[85lebaront2]

I used to haul a 30' 5th wheel trailer, 10K loaded and I think it was 1710 lbs pin weight and it would just bring the truck down to touch the overload spring. I have also twice had the proverbial "ton of bricks" in the bed with no problems whatsoever. I keep my rear tires at the recommended 65 psi (215 85R/16 LR D) for dual rear wheels. My axle is rated 7400 lbs.

[Gary Lewis]

Interesting.  Darth has a 7400 lb axle and Big Blue has a 6250 lb axle.  But both of them show spring code K for the rear springs, and in both 1985 and 6 spring code K called for E3TZ 5560-T springs.  But, in 1985 the catalog shows that those were replaced by E7TZ 5560-A's, although the catalog doesn't say they were for 1986.  

If General Spring is correct and K's are 3100 lb springs, then your overloads must be good for about 600 lbs each to get the total pack to 3700 and match the axle.  Does that make sense?

[85lebaront2]

That would make sense since 3100 X 2 = 6200, 6200 + 2 X 600 = 7400. Maybe if could get the information on the individual leaves you could arrive at a viable option. As far as ride quality, Big Blue is a standard cab or 133" wheelbase, Darth is a crew cab or 168" wheelbase, that extra 35" goes a good way towards making it feel smoother. Also keep in mind Darth is 2WD and as such has big COIL springs which probably help the front ride feel over leaf springs.

My 1958 F100 rode like a buckboard, 110" wheelbase and 4 leaf springs.

[Gary Lewis]

Yes, Big Blue has leaf springs in front, and that doesn't help the ride any.  But we've watched (felt?) and the biggest jolt on bumps is when the rear axle hits.  So I'm hoping to soften the blow(s) some with de-springing him a bit.

But, that isn't going to happen very quickly as I have a ton of things to do first.  However, I will get it done.

[Ford F834]

I don’t know if it helps, but here is the certification label for my 4x4 F350. Interesting that the rear spring code is the same as DRW???

[1986F150Six]

Gary Lewis wrote

But, that isn't going to happen very quickly as I have a ton of things to do first.  However, I will get it done.

Appropriate wording for this subject matter!!

[Gary Lewis]

David - Pun intended.  

Jonathan - Interesting!  So we have the following with the same spring code "K":

'85 F250HD regular cab rated at 5922 lb GAWR w/a 6250 lb axle and LT 235/85R16E tires

'86 F350 crew cab rated at 6084 lbs GAWR and with a 6250 lb axle and LT 235/85R16E tyres

An '86 F350 crew cab DRW rated at 7400 GAWR and with a 7400 lb axle and 4 215/85R/16D tyres

Turns out that LT 235/85R16E tires are rated for 3042 lbs, and two of those would get you 6084 lbs, which is what yours is rated at.  But Big Blue is only rated for 5922 with the same axle, tires, and main spring pack, so apparently the overload is standard on an F350 and boosts the spring rating to over the rating of the tires - to at least 3700 lbs given Darth's rating.

But Big Blue is running LT285/75R16E tires, and they are rated for 3750 lbs, so with the right springs it would be limited only by the 6250 lb axle.  Given that, if I downgrade the main pack and then install F350 overloads or air bags I'd be there.  Right?

[85lebaront2]

Ok, here is what I am running for tyres right now old bean, the tyres have 112/115 on them since all the old load ratings seem to have been devoured by DOT. I am running 58 psi front and 65 psi rear, these may be equivalent to LR E as they give a load rating for 80 psi but it was too dark to read it clearly (more tomorrow) These are the same size and tyre that the counties use on school buses, probably the E350/GM3500 ones.

[Gary Lewis]

Those are LR E's with either a 2380 or 2680 lb rating, and you have far more tire than you have rear axle.

[85lebaront2]

That was my thought too. They do not ride badly at all and wear seems fantastic, I will get a picture of the front tread later today. One item I found in the past, DRW tire ratings are lower per tyre than SRW, probably due to greater heat buildup with the tyres so close together.

Better more rather than less.

[Gary Lewis]

I didn't realize that the same tire used in DRW applications is rated less than in SRW app's.  Perhaps that's the 115/112 bit?

[85lebaront2]

Don't know, my last set (Sears) had the load ratings as xxxx single and xxxx dual. As long as I have a minimum of 1850 lbs per tyre on the rear I am fine. These were actually a good price and readily available and the company has the equipment to handle the Alcoa rims without damaging them and can balance them.

[Nothing Special]

Coming a little late to this party.  I had Firestone Ride-Rite air bags on my '95 F-150.  After I bought that truck I got a slide-in camper and the truck didn't handle that weight very well.  Rather than get the right truck for that load I put air bags and load range E tires on a half-ton.  Note that I do not recommend that (that would be Wrong).  But it did work out pretty well.  The truck handled the weight quite well.  So I'd say that overall you have a good plan.

I never noticed any significant wear from grit or anything (not that I did any off-roading with that truck).  But the bags did have sort of an accordion pleat to them that could have trapped grit when the suspension was compressed a bit.

Lack of suspension travel was a bit of an issue in my F-150, but I don't know if it would matter in an F-250HD.  I tried to set mine where the air bags would bottom about where the bumpstops hit, and set like that the air bags were the limiting factor in droop.  that never seemed like a good thing, but again, without taking the truck off-road it wasn't really an issue.

You can set up air bags do work differently based on how you plumb them.  I really wanted roll stiffness in my 3/4 ton F-150 so I didn't connect them together.  That meant I had to inflate them separately, but it also meant that air couldn't transfer from one side to the other, which was good in my situation.  On the other hand, I've thought about using air springs on a dual axle trailer with BIG air lines connecting the front and rear bags on each side together (but still having right separate from left).  That should give the same sort of effect as the equalizing shackle set-up on leaf sprung trailers.  By connecting right and left air bags you could get more or less roll stiffness by changing the size of the air lines.  Just some rambling thoughts.

[Gary Lewis]

That's my thinking as well - separate fills so it gives as much roll-prevention as possible.  And, that allows for inflating/deflating one side when crossed-up on the trail to get traction.  But, for that to be effective you have to have soft suspension.  As it is, Big Blue's suspension is so stiff there's little movement.

The bags I'm looking at have bump-stops in them, but that might be a limitation as it minimizes the available travel.  So, if I could rely on the stock bump-stops then I wouldn't need the top-of-the-line bags.

And, there's the stock spacer that comes on the 4x4 trucks, which I might take that out depending on how much the truck sits down with softer springing.  I say that because Air Lift says there needs to be 5 - 7" between the brackets, and 7" is better than 5".  I'll have to check, but right now I'm sure there's more than that.

[85lebaront2]

As discussed earlier, further tyre pictures:

[Gary Lewis]

Yup, 2680 SRW vs 2470 DRW.  But you still have 620 lbs/tire of reserve.

[85lebaront2]

FWIW, here is the left front after 3 1/2 years and quite a few round trips to Newport News VA and Pittsville MD.

[Gary Lewis]

Looks like it is wearing quite evening, Bill.  But, what are those curly things in the pic?  Doesn't a "real truck" have the buckboard style leaf springs?

Seriously though, why did Ford think a 4wd F250/350 needed leafs and a 2wd could use coils?  I've never understood that when that wasn't the case in the F150's.  Was the radius arm not up to the task of keeping a heavier front axle in check?

[85lebaront2]

First, in 1986 the crew cab DRW trucks could not be ordered as a factory 4WD, In fact I am not sure any 1986 F350 DRW truck could be factory 4WD, Ford did sell a number of cab & chassis 4WD models, but they have the Dana 60 rear and a narrower track.

Second, if I had wanted 4WD, I would have opted for a mono-beam front end with the Dana "king pin" style as it has cone roller bearings top and bottom so no ball joints.

As for "real trucks" lets not talk about Blue Jeans, with its FWD sedan front end, or "dad's" with the twin traction beam coil spring system.

I like the ride the coils give up front having driven 4WD F250s and my 1958 F100, the scout camp cornbinder, and any number of Mxx USMC trucks from the old Jeeps to a 5 ton wrecker.

If I really wanted a 4WD truck, I would try to find an old M37 Dodge built 3/4 ton, either build a bigger MOPAR flat head for it or shove a 318 Polyshere head in there, power steering and better brakes. Those things I think could climb a wall straight up if you could get traction.

[82F100SWB]

Looking at the shape of the end cut and the thickness of the leaves, I would be inclined to believe that those springs in big blue aren't factory pieces at all and that may well explain your ride issue.