How to determine spring rate for torsion bars?

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Herbie
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Re: How to determine spring rate for torsion bars?

Post by Herbie »

We hit a snag on trying to get "standard" dimensions.

There are a number of different part #s, and there's more variation in the measurements than I expected. The possible interchange options kinda muddied the waters - since we weren't sure whether the samples I sent would even work for *my* van. (Since they were from two different junkyard vans in two different years...)

Frustrating hurdle, for sure. Not giving up, though!
"My minivan is cooler than your bro-truck"
2003 Astro AWD Astrolander/ZMB - GTRV Top Transplant, 4" OLV Lift, NP233 T-case, evolving interior
1995 Safari GTRV Organ donor - gutted and gone.
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Re: How to determine spring rate for torsion bars?

Post by Astrophysics »

Hi Again,

The torsion bar itself is similar to an anti sway bar, but the torsion bar has a higher spring constant
Since it must suspend 2800 lbs divide by 2 = 1400 lbs.
Where 2800 lbs is max weight of front end.
A high g turn in an Astro is estimate at , take a guess, 0.6 g? There fore we need to calculate sway bar twist needed to limit front body roll to say, 15 degrees off horizontal at high g turn. Assume body weighs 2,500 lbs? And frame and drive train 2500 lbs.

Wow maybe sway bar engineers know the calculation.

I will call Mike at Journeys Off Road Monday to ask him about torsion bar spring rate.

Wow, maybe we can think outside the box... how about welding an extra cross bar to the exposed portion of Astro torsion bar. Each side of this cross bar would be fitted with a compact coil spring from a heavy motorcycle . Then as the torsion bar tries to twist, the coil spring adds more spring rate. Just 100 to 200 lbs more spring capacity could help firm the front end on heavy Astro.

AP


I will draw a sketch,
The upper spring perch could be an issue,
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Herbie
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Re: How to determine spring rate for torsion bars?

Post by Herbie »

Yeah, I'm sort of well past the initial queries of this thread.

Now I'm at the point where I'm working with the Torsion bar manufacturer to spec out new bars, but the problem seems to be a diversity of both lengths and end-dimensions.

Ensuring compatibility with the maximum number of vans means understanding what changed, what will interchange, (and what won't), and what parts we can include (if we opt to do the splined adjuster solution).
"My minivan is cooler than your bro-truck"
2003 Astro AWD Astrolander/ZMB - GTRV Top Transplant, 4" OLV Lift, NP233 T-case, evolving interior
1995 Safari GTRV Organ donor - gutted and gone.
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Re: How to determine spring rate for torsion bars?

Post by Astrophysics »

Good points. On front torsion bars. We need a college mechanical engineering student to do a summer project in ProE or AutoCAD etc, and
It would be super if one of the Velocity channel car shows like Texas Metal, or Garage Squad, or Kindigit Designs Utah, would use the Astro AWD as a vehicle to improve.

The fella Mike at Journeys Off Road in Prescott AZ does his own CAD computer drawings for bumpers, etc. But a torsion bar spring and all the math and calculations and heat treating does take a specialist I suppose.

JOR does have a great hidden winch tray $399 which allows use of OEM plastic bumper guard. I plan to get one in January. Then I can discard my DIY, heavy bolted bumper and trail gear winch plate. This could save 60 lbs on front of my 2003 Astro.

Merry Christmas

AP

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Re: How to determine spring rate for torsion bars?

Post by Astrophysics »

Hi Herbie,

1. It sure would be nice to get the stiffer torsion bars.
I remove the winch and winch plate and my heavy plate bumper . This saved about 150 lbs.

2. My neighbor gave me the OEM front bumper from his 2014 Jeep Wrangler sport 4 door. The frame spacing on Jeep is about 35", whereas Astro is about 41". So I added another bumper bracket.
The OEM Jeep bumper fits the Astro with the 2” lift brackets and a bit of extra brackets.
The Jeep bumper has built in fog lights. The metal portion of Jeep bumper has a neat design with built in recovery hooks on top.
I will post some photos.
The plastic slide on Jeep bumper cover is very nice too. Jeep bumper + cover weigh about 36 lbs. the tow hooks are 4.5 lbs each, then add about 10 lbs for extra brackets and grade 8 bolts.

AP

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Re: How to determine spring rate for torsion bars?

Post by Astrophysics »

Hi,

2014 OEM Jeep front bumper.’’

Install into 2" lifted 2003 AWD Astro

AP
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2014 Jeep Wrangler bumper on 2003 Astro
2014 Jeep Wrangler bumper on 2003 Astro

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Re: How to determine spring rate for torsion bars?

Post by Astrophysics »

Hi,

The metal portion of Jeep bumper has clever round impact absorbing cylinders welded on which also support the plastic bumper cover.

AP
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Jeep Wrangler  thin steel bumper
Jeep Wrangler thin steel bumper

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Re: How to determine spring rate for torsion bars?

Post by Astrophysics »

Hi,
Jeep OEM horseshoe shaped tow hooks attach to bumper mounts and protrude up on top of bumper.

AP
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Jeep Wrangler OEM tow hooks
Jeep Wrangler OEM tow hooks

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Re: How to determine spring rate for torsion bars?

Post by Astrophysics »

Hi,

I still plan to install 35" wide cross bar 1/8" thick steel angle 4" x 2" from Astro L to R side frame mounts to stiffen up bumper where tow hooks attach.

AP

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Re: How to determine spring rate for torsion bars?

Post by Astrophysics »

Hi

Bumper needs cross bar

AP
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Astro bumper frame mounts need cross bar
Astro bumper frame mounts need cross bar
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