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 Post subject: Camaro IRS into locost
PostPosted: April 25, 2020, 5:07 pm 
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I’ve been building cradles to adapt Gen5 Camaro rear ends to pickup trucks and recently found some old locost frame drawings. Of course, the two came together and here is the first cut. It’s my attempt
to adapt an IRS differential to a locost chassis. Damn, it ain’t easy. I took the route of putting the diff in a cradle and adapting that to all the frame tubes. I think the cradle came out OK, but how to tie it into the tubes? Ideas welcome!
Ps: My highest complements to those of you that have conquered this beast in the past!


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PostPosted: April 25, 2020, 5:10 pm 
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PostPosted: April 25, 2020, 7:59 pm 
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In a typical Locost book chassis, this is a very narrow area to start with. In a book chassis you have ~(40-6)/2=17 inches available for seating at your hips. Many builders find that very tight. FYI, I didn't but I am 5'8" and made my own donor seat mods. In your chassis you have a bit less, ((46-8-1.25)/2)-2= 16-3/8". It will be very difficult to find seats to fit without modifications. Passenger side will be even less when you make room for the offset u-joint flange not yet in the model. Only you can know if you and another will fit. I suggest you take some 2x2 wood and mock up this area to see if you can fit in the area. Many who use donor rear subframes move the rear wheels and diff back a few inches to clear intrusion into the passenger area.

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“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766


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PostPosted: April 25, 2020, 10:30 pm 
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Tried to make it smaller. Regardless, the front differential mounting ear will protrude.


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PostPosted: April 26, 2020, 2:47 am 
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Looks like a fun, but challenging idea you're toying with. A few things to consider for your next pass:

Perhaps this wouldn't actually be a part of your plan, but it is how it's drawn. If I'm not mistaken, that rear tire looks to be OE Camaro Sized. Based on the specs I can find, even if it was running 275's it would still have ~53" between the tires. Even with side clearance for geometric wheel movement, I bet you could widen the whole thing at the tunnel by another couple inches. And with those ~29" diameter tires, the chassis would also need to get proportionally taller at the rear bulkhead as well, especially if wanting to run rear fenders of a traditional-ish looking build, resulting in the rear wheel centerline moving back a bit as well.

The frame doesn't come to a point at the top of the bulkhead that the axle sits below. It flattens out and that portion of the frame is actually a trapezoid with a very narrow top, but it moves the shock mount pivot an inch or two back from the seating face of the rear bulkhead.

The rear axle center line does not actually need to be directly below the upper shock mount pivot. In fact, as opposed to a live axle, it would typically be less than desirable to do so on an IRS, as the axle would tend to interfere with the shock.

Due to the way our bodies and seats are shaped, the tunnel can flare out a bit in the last few inches before it hits the bulkhead.

The CV's have to accommodate a lot more articulation on a stock Camaro than they would a Locost. This otherwise unused travel could be utilized to move the diff rear of the wheel centerline until the combined angularity at max Locost travel is similar to that of a stock Camaro. Along these same lines, the diff does not actually need to be parallel with the vehicle center line. A little 'twist' could help gain some clearance for the flange.

Keep the ideas flowing! :cheers:

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PostPosted: April 26, 2020, 10:21 am 
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I understand that you have experience making Camaro subframes for other vehicles. Perhaps that has driven the approach of making a separate frame for the diff and then trying to put that into a Locost. Most people who use subframes, carry the diff and control arms and are using the donor's subframes not just the diff. If not using the donor's subframe, I would not recommend creating one to hold just the diff. Instead, use the Locost's frame members themselves as the sole support mechanism wherever possible. If not possible, try to see what changes need to be done to make it possible. Perhaps the basic Locost chassis would need to be modified somewhat.

I can envision using the rear panel of the passenger compartment as a sheer panel and supporting the nose of the diff directly. Along those lines, I'm not sure why you feel that you need some adjustment in the diff angle. Rather that incorporating adjustment capability, thoughtful design should be capable of ensuring the u-joint angles are within recommended limits. Whatever structure you design for the rear control arms could support the single rear mount of the diff.

These are just a couple of my thoughts. Simplify and add lightness is what the original Lotus seven was conceived around. Not a bad goal IMO.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766


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PostPosted: April 26, 2020, 3:18 pm 
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Here’s a drawing of the Camaro IRS fitted with fat 335’s. The frame could be widened a bit.
Looking at all this, I got to ask, ”Why the Camaro?” They're cheap and plentiful. There are parts of the country where a boy doesn’t become a man till he’s wrecked his first new Camaro by age 18. The dropout I last purchased was $400 and very low mirage. The law makes them keep a history back to the car it came from, complete with photos of the wrecked car.
The dropout includes everything out to the hubs, brakes as well, but no disks (legal again). It’s all wrapped with the control arms and all into a complex stamped piece of steel plate. Way too ugly and heavy to be considered putting into a locost. I considered hanging the diff from the locost frame tubes as suggested. A few hours spent on the builds section seeing what others had to do scared me away from that.
I have already designed uprights to fit these hubs, shown somewhere else on this site.
Which brings me to my next challenge. Yes, now to design some control arms for this.

Stay tuned and keep the comments coming.


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PostPosted: April 29, 2020, 3:27 pm 
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Made some more changes. Basically, the cradle fabrication will now replace the two rear locost crossmembers with 2” structural tubing. I lowered the front tube to keep it out of the cockpit but the differential front mount remains protruding. I fitted up some lower control arms. The sloped tube they attach to could be moved outward to change their length. I think they are too narrow now and I would like to lengthen the cradle a little to splay them out some more. The upper control arms are a mystery right now.
I’m trying to match this up with a “standard” locost frame and it seems the rear is different on many. So I’ll just finish up what I have shown. I haven’t done any structural on this but it will require support from the locost tube frame above.


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PostPosted: May 4, 2020, 6:27 pm 
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Driven5 wrote:
The CV's have to accommodate a lot more articulation on a stock Camaro than they would a Locost.


The axles on the deTomaso Pantera sweep forward at about 15 degrees to move the driveline back so only the water pump protrudes into the passenger compartment. ("Shifter falls easily to elbow...")

Lots of *serious* Pantera builds out there, not counting the Silver State guys with their 200+mph runs. CV failure is an absolute non-issue.

I've also noticed many FWD cars have the axles sloped down about that much while sitting at ride height. I would have thought they would be as level as possible, but apparently it's a non-issue there, too.


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