Independent Rear Suspension. Heidts+LS427 = ?

[CobraB]

I have been keeping up with the 4.6L on the Ffive forums. They have been using the T-bird IRS in some of their builds for lower cost. The shafts are not as strong as the cobra and need to be replaced to handle the torque.

[LS 238]

Prof, I have a car lift in my garage if you want to take a look at the car we can set that up, just leave me a PM with your cell # . I live in dallas just north of downtown off the tollway.
Eric

[427HISS]

The looks, strength and the name factor of the Heidts is what I would like under my cobra. That's one hell of a nice IRS.
I mean, look at the difference guys. I don't think I need to start a poll. lol

The problem I have,...... I WANT IT NOW !

I'm sure with the mechanical knowledge and ability of Paul and Brian, they'll work out the bugs, like with any Hot Rod builder goes through.

[Prof]

All,
Raised the frame up on my lift. Plumb bobs hang down marking driveline center.
I'm having the welding shop here at the University mig/tig the round ends onto the main crossmember. Permanently welding the main crossmember assembly onto the frame is the last step in the manual; it sets the ride height.
I will probably powdercoat a few pieces of the IRS so that folks who "look up my skirt" will get an eyeful. Just the housing and lower arms. I need this to function hard and not bind if I bounce it on a berm in a corner--looks are for the other guys.

In the end, I will most likely notch the frame approximately 1.75" exactly where the lower bracket/mounting hole is for the 4-link. This is a very strong area on the outer frame. I am setting up the strut rods for a 58" unit (thanks Lakeway Cobra!)--ordering the whole IRS enchilada, or at least the remaining stuff that I don't already have--next week on my 50th birthday. (I gotta do SOMETHING to make that birthday feel less obnoxious.)

More later,
Paul

[Lakeway Cobra]

50!! You don't look a day over 39

I'm expecting to see this thing in San Marcos.....

[Prof]

All parts that move (articulate) with the suspension have arrived and are being powdercoated. I have a fresh 31 spline 3.5 TracLok pumpkin (awesome!). Mounts, lower control arms, housing, struts, etc. all ready to go.

Plans are to c-notch the frame a certain amount for some of the 2.5" to 3" of suspension compression. The coilovers I have been told to use have 6" of travel. I might do something a bit stiffer with less overall shock travel.

Weight is an issue. The afore mentioned coilovers use #400 springs to account for all of the extra weight in the IRS.

I need to crawl under a few Lonestars to determine where the top frame rail is in relation to the rear wheel center/hub. I can easily run a straight line back along the bottom of the framerail and see where the hub is in relation. Centering the wheel in the opening (Up down/fore aft) is unknown-- I guess the assembly is raised into the rear frame to a permanent location AFTER the body has been mounted to the frame. Currently working with 93.25" wheelbase setting.

Assembly will start after Easter. I will start a new thread for the build log. Lots will be explained at that point.

Later,
Paul

[Prof]

LATEST UPDATE:
I have many hours (pleasant ones) in the installation of the Heidts Ind. Rear Susp. Many decisions have been made--58" width, driveline centering, c-notching the frame to provide some room for the soft 2 1/2" compression of the rear shocks, etc. BUT, along comes Murphy's Law just when the end was in sight. The PINION IS OFFSET 1"on a Ford 9". Thus, centering the pinion in the trans tunnel results in setting the lower control arms short on one side (screw heims in all the way) and long on the other (leave 1" of heim's threads showing).

I have talked to Heidt's engineers and they scratch their heads because every other builder wants/assumes/accounts for the offset pinion. The other thing they told me is that 1" in the difference of the lower control arms is acceptable. AND different length half-shafts are essential. This is basically what Ford has designed in their rear axle housings--one side axle is shorter than the other.

Today I will talk to Smiley's Racing and explore other options (moving the LCA LONG SIDE mounting point 1" further out on the housing for equal articulation of the lower control arms).

I suppose I could fudge some of the difference and move my entire driveline 1/2" off-center to accommodate some of the differences. (BTW--u-joint failure happens when the joint tries to pivot more directions than up-down. For example, I can't have a centered transmission output shaft and a 1/2" offset pinion that's 19" away).

Whew! All of this is for zero binding on the race track. It is worth it.

Many have asked about other brand's complete cradle assemblies and how they would work vs. Heidt's. I suspect the cradles made by Factroy Five and Hurricane have already accounted for the offset in their design. They use Ford factory pieces and assemblies. To tell you the truth, I am close to calling one of them and having a complete cradle shipped down here--to end this search for IRS euphoria without the headaches.

Will keep you posted and provide a build log when all the kinks have been solved.

Best,
Paul

[Barnsnake]

A u-joint doesn't know sideways from up or down. As long as the pinion and tailshaft are parallel, the driveshaft will offset X degrees in some direction. It's a single angle, not one vertical and another lateral. The direction relative to the ground (or whatever) is immaterial.

Jim

[Luce]

And with the diff fixed instead of jumping around like in a live axle, there should be very little angular movement in the driveshaft. I would be less concerned about the offset in the driveshaft than asymmetrical suspension travels. I had a 280z with a messed up rear suspension. White knuckle stuff when you least expect it.

Thanks for your work and post. I'm interested in getting a LSC after this option is on line

[Data Recovery]

Hi

Here is the link for some Heidts parts. Hope that may help you out for finding your required part.

http://www.walterswebs.com/heidt.htm

Thanks
Britt
File Recovery

[427HISS]

It's coming along.