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 Post subject: Lincoln 8.8 IRS
PostPosted: April 2, 2018, 1:09 pm 
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Joined: January 12, 2012, 6:17 pm
Posts: 7
Currently working on the CAD design of my rear suspension and have a couple of questions....

1.) If you design anti-squat into the rear IRS by tilting the inner pivots of the a-arms, won't this create a binding of the bushings on the uprights as the a-arms swing at different angles?

2.) I have all the energy suspension bushings to replace the original Ford rubber bushings in the uprights, what is a good size bushing set to use for the inner pivots on the a-arms?

3.) Has Stu at IRS Machining closed the business? The website has disappeared?

Almost forgot,

4.) What are good lengths for the a-arms to start with? * I'm using Lincoln 8.8 IRS center section with FFR shorter axles and the Explorer rear diff cover/mount

Thanks
Bungi


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 Post subject: Re: Lincoln 8.8 IRS
PostPosted: April 2, 2018, 5:20 pm 
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Joined: January 10, 2008, 4:47 pm
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Anti-squat on the rear suspension of an IRS car comes from the fore and aft movement of the spindles as they move up and down. So you can tilt both the wishbones the same amount to avoid the binding. This would make it easier to get the desired amount of anti squat too, but it may not be a lot of anti squat. Are you sure you are not thinking of forces from the brake disk which would be anti-lift?

Quote:
I'm using Lincoln 8.8 IRS center section with FFR shorter axles and the Explorer rear diff cover/mount


I think you'll have to mock it up a bit. You may not want or need the shorter axles. I think in a Cobra the rear wheels are behind the driver but in a Locost the driver is between the wheels. It also depends on what you pick for wheel offset. I tried to get a lot of backspace on my wheels to avoid scrub on the front end. So it may be harder to fit them in the rear, I will know soon.

I also noticed that the IRS machining place seemed to have closed.

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 Post subject: Re: Lincoln 8.8 IRS
PostPosted: April 3, 2018, 1:51 am 
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Joined: April 26, 2008, 6:06 pm
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Bungi wrote:
1.) If you design anti-squat into the rear IRS by tilting the inner pivots of the a-arms, won't this create a binding of the bushings on the uprights as the a-arms swing at different angles?
If you don't keep the a-arm pivot axis parallel to each other, yes you'll have binding. Regardless, IRS doesn't have very strong anti-squat anyways, so I wouldn't put too much effort into it.


Bungi wrote:
2.) I have all the energy suspension bushings to replace the original Ford rubber bushings in the uprights, what is a good size bushing set to use for the inner pivots on the a-arms?
If going poly bushings, I'd look a the energy suspension universal bushings (http://energysuspension.com/universal-products/link-flange-type-bushings-universal-mounts-isolators.html) and pick it by a combination of outer tube size (diameter larger than a-arm tubes, easily sourced DOM wall thickness in that diameter, and long enough that a-arm tubes at necessary angles won't overhang) and fastener size (1/2" or maybe 5/8").


Bungi wrote:
3.) Has Stu at IRS Machining closed the business? The website has disappeared?
Unfortunately, I have recently come to the same conclusion, even though I've found no mention of it on the Factory Five (or other) forums.


Bungi wrote:
4.) What are good lengths for the a-arms to start with?
I too have Factory Five axles, and believe that with careful planning they should result in a close, but acceptable, clearance on up to a +2 width chassis with up to 40mm (or was it 45mm?) offset wheels. Of course, this is all still just math based, and has not been physically built/confirmed, so don't trust anything in this reply to work 100% at face value. In this setup though, I was looking at the outer (spindle) pivots being ~24.5 outboard of the centerline and ~10 vertical from the ground for the lowers, and ~23.75 outboard of the centerline and ~17.75 vertical from the ground for the upper for the ~25" OD tires I'm planning for. If I were to go with a conventional IRS, my early design work was narrowing in around the inner pivots being ~9 outboard of the centerline and 10 vertical from the ground for the lowers, 12-12.5 outboard of the centerline and 16.5 vertical from the ground for the uppers. But the compromises in a suspension design are very individualistic, so numbers that I found appealing you may find less so.

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