IRS 5spd Occmans Razor

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Larry Coreth
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Re: IRS 5spd Occmans Razor

#31 Post by Larry Coreth »

Jacques,
Where do the parallel arms connect ?
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Jacques Lefriant
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Re: IRS 5spd Occmans Razor

#32 Post by Jacques Lefriant »

Hi Larry
i was going to let you figure it out. I can't have all the fun. What is missing from the picture is the inboard bearing housing. It looks like it will require a longer stub axle and an even shorter axle but it can provide the two attachment points for the outboard rod ends and the bolt pattern to bolt the upright to the spring plate. An alternate solution comes to mind is that we substitute a Macpherson strut (integral with the upright) for the shock then we only need one lateral radius rod and the spring plate attachment must rotate. The upward wheel travel in both cases is comparable to the SWB 911 arms that are used. Using short stub axles and the 69 911 wheel brg may allow the CV joint to be outside of the wheel arch on the body but we would have to use disc brakes. Yes we could make weird backing plates and have the drum go on the hub like a rotor now my head really hurts.
j
 

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Larry Coreth
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Re: IRS 5spd Occmans Razor

#33 Post by Larry Coreth »

What's the old German saying, "Why make it simple when complicated works too ?".
BTW, isn't a McPherson strut located in the rear called a Chapman Strut ?
I need to go to bed my head is spinning with options !
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Martin Benade
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Re: IRS 5spd Occmans Razor

#34 Post by Martin Benade »

Will a shorter axle be able to handle the maximum angles arising from suspension travel?
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Jacques Lefriant
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Re: IRS 5spd Occmans Razor

#35 Post by Jacques Lefriant »

Hi Martin
we will evaluate that. In offroad racing they have horrendous angles.they even let the cv joint move with respect to the axle.
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Jim Nelson
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Re: IRS 5spd Occmans Razor

#36 Post by Jim Nelson »

Have you evaluated a Spicer joint vs the CV ?

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Larry Coreth
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Re: IRS 5spd Occmans Razor

#37 Post by Larry Coreth »

Jim Nelson,
What is it about a Hooke (Spicer) joint you like over a CV joint ?
In a Hooke joint you'll need a splined section in the shaft to allow for the shaft length increase as the suspension moves up & down. Not necessary with a CV joint.
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Martin Benade
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Re: IRS 5spd Occmans Razor

#38 Post by Martin Benade »

Also the Spicer is not constant velocity. Not likely you would feel the difference but it is not a better joint.
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Ashley Page
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Re: IRS 5spd Occmans Razor

#39 Post by Ashley Page »

I have enjoyed following this thread.

IMHO I like the idea of a link bolted to the hub carrier and running to a bracket that could be clamped onto the torsion bar tube next to the transmission mount bracket. The bracket could be located with a dowel.

A new hub carrier could be fabricated or machined to use an existing stub axle and bearing assembly. Or there may be an existing trailing arm that could be modified to work.

If making a new hub carrier then the spring plate could be used or, better, replaced with a part machined from aluminum since there would be no need for a spring plate. The spline for the torsion bar could be crowned and barreled to allow some camber and toe adjustment. A new torsion bar with crowned spline would give more adjustment.

This kluge would be 99% reverseable.

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Jim Nelson
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Re: IRS 5spd Occmans Razor

#40 Post by Jim Nelson »

Larry Coreth wrote:Jim Nelson,
What is it about a Hooke (Spicer) joint you like over a CV joint ?
In a Hooke joint you'll need a splined section in the shaft to allow for the shaft length increase as the suspension moves up & down. Not necessary with a CV joint.
I have probably not described it correctly, though we did find a replacement in the Spicer catalog.
In 1989 Tyrrell (the F1 constructor) used CV joints at the gearbox and the hub, allowing for the fore and aft, up and down movement essential for suspension to be properly utilized. In 1990, though, they changed the layout to a spicer-type arrangement. I'll have to go get some pictures so that you can properly visualize this, but it was a really elegant, much more simple solution to the same issue. The bearing was shaped a bit like a rounded triangle, with rounded rollers at the edges, that moved in and out (and up and down) on the one-piece hub.

So I was wondering if that might be one possible piece of Jacques' puzzle.

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Re: IRS 5spd Occmans Razor

#41 Post by Ashley Page »

Jim, what you are describing, plus the timing of it in 1990, sounds like what is commonly referred to as a "tripod". They are common in racing today and started appearing on race cars around 1990. I believe they are common in road cars too.
Is this it:


jim nelson wrote:
Larry Coreth wrote:Jim Nelson,
What is it about a Hooke (Spicer) joint you like over a CV joint ?
In a Hooke joint you'll need a splined section in the shaft to allow for the shaft length increase as the suspension moves up & down. Not necessary with a CV joint.
I have probably not described it correctly, though we did find a replacement in the Spicer catalog.
In 1989 Tyrrell (the F1 constructor) used CV joints at the gearbox and the hub, allowing for the fore and aft, up and down movement essential for suspension to be properly utilized. In 1990, though, they changed the layout to a spicer-type arrangement. I'll have to go get some pictures so that you can properly visualize this, but it was a really elegant, much more simple solution to the same issue. The bearing was shaped a bit like a rounded triangle, with rounded rollers at the edges, that moved in and out (and up and down) on the one-piece hub.

So I was wondering if that might be one possible piece of Jacques' puzzle.
Attachments
tripodjoint.jpg

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Jim Nelson
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Re: IRS 5spd Occmans Razor

#42 Post by Jim Nelson »

No, Ashley, it isn't, (and I could also be dead wrong, the concept is the same) but I'll try and get a couple of shots today or tomorrow, the F1 shop's 40 miles away and I do have some fab to do here on a '53 non-Porsche project. Trying to get the interior back in the car, and the wind lace/headliner combo is a bear.

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Re: IRS 5spd Occmans Razor

#43 Post by John DeWitt »

When I acquired my '57 A, (an empty shell), the previous owner wanted an IRS rear suspension, so when the car came to me, I thought "Why not?" So I welded in the center part of a 912 torsion tube, complete with anchors for the trailing arms, installed the trailing arms, used a 902/02 trans, disc brakes, etc. The IRS is 3 or 4 mm wider than stock 356 on each side, but not much of a problem. Installing an IRS is not necessarily a piece of cake, but it isn't rocket science, either. The three main items I had to deal with were 1) since 902 transmissions are longer than stock 356 transmissions, I found it necessary to cut the shift rod shorter, 2) using the trans mounts on the IRS suspension to locate the trans also means the engine will be moved 2.25" (plus or minus) to the rear, and the rear deck in the engine compartment will have to be modified to compensate for the extra distance, and 3) because the 902 trans (obviously) does not fit the hoop, I did some measuring and drilling in the bell housing to allow the 902 trans to be suspended by the hoop. But, knowing it wasn't the best set-up, I also installed a 912 rear motor mount to give added stability, anchoring it to steel plates I had added to the engine compartment before actually beginning the project. All in all, this set-up seems to work very well. I have put about 800 miles on the car since the installation, and haven't detected any IRS-related problems. Using a rear engine mount does require use of a 912 third piece.

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Jacques Lefriant
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Re: IRS 5spd Occmans Razor

#44 Post by Jacques Lefriant »

Hi John
Doing the 901 conversion now is problematic since the prices of early 911/912 are catching up to 356 values. besides it is not easily reversible. other than that it is a great job congratulations.
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Re: IRS 5spd Occmans Razor

#45 Post by Jacques Lefriant »

Hi David
in the engine choices you inquired about an IRS conversion with a 5 speed. The 901 transmission is an excellent choice for the transmission but you don't have to use the entire rear suspension of a 900 series car. the IRS can be accomplished reversible and even the 4spd original tunnel trans can be used. Conversely Wevo is contemplating a swing axle conversion for the 901 but that does not interest me.
j
 

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