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... I wasn't sure about keeping the gold powdercoat, I was planning to repaint them in black. But it's really growing on me. Hmm, I'm starting to think of a livery change...
Like this, maybe?
 

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Discussion Starter #583
You will know if the new/old tires still have grip if you pick up OPR during your next track session. OPR: "Other Peoples Rubber"

I really enjoy reading about your progress with the Spider.
Thanks, George! If these new/old tires aren't sticky enough, I may douse them in a home brew of Xylene+Toluene.

I'm hoping there really is a significant benefit to 20 extra millimeters of rubber that would overcome the extra rolling and wind resistance, as well as the extra unsprung and rotational weight.

Leave the wheels gold, and paint your new roll cage to match.:surprise:
Dang you, Rick! Stop planting these ideas in my head!

Like this, maybe?
You reading my mind, Stoppie? I've always admired JPS colors, even as a kid in the '70's. Didn't even know they were cigarettes until later in life.
 

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Discussion Starter #584 (Edited)
Nature vs. nurture

I've been nurturing this car thru its development, but sometimes, nature takes its course.

Such as in fitting these wider wheels and tires to this slim body. I've shared with you all the tools that I've used in this build. Everything from cheap Chinese Harbor Freight, to higher end American Snap-On and German Knipex tools. Now taking it to the next level, I'd like to introduce you all to the ultimate in race car-specific, body working tools.

Behold, the Western Red Cedar. They grow in my front yard, and after having them professionally pruned, I'm left with a varied selection of logs in a diameter appropriate for rolling the fender lips of my race car. The moss is an extra, no-cost feature that perfectly adds additional cushioning to prevent creases in the precious Alfa lines as I carefully roll the fender lips to accommodate the wider tires.
 

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Perfect!

Absolutely a Northwest-dweller's solution.
 

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New or revised rollcage looks tidy.

Pete
 

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Discussion Starter #587
New or revised rollcage looks tidy.

Pete
Thanks, but that's the same old cage. The cage modification project may happen after the dust settles from this sliding block madness.

Speaking of which, I got most of it buttoned up today. I spend a lot of time visualizing how projects will play out. What materials and tools I'll use, what approach, back up plans, and such. In my mind, it was going to take an hour or two to fit everything together before proceeding to the last step of fitting and fastening the differential trailing arm.

But like most of my bigger projects, this one fought me at every turn. Things didn't want to line up just so, which is a must because everything has to fit together based on predrilled holes. And there are a crap-load of holes throughout the trunk to mount the yoke, diagonals, and brace.

So I spent a lot of time today shimming, cursing, massaging, persuading, and despairing. I even broke out the vintage Snap-On punch and chisel set to make holes line up. "The choice of better mechanics"? so what am I doing with them? What should have been at the most a couple hour task (in my mind), stretched into a whole day.

Ultimately, minus the trailing arm, it got done. Everything is where it should be. I have a trunk full of M8 fasteners to prove it.
 

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Discussion Starter #588
Here's how it looks almost done. Paint came out sloppy, but that's a minor concern. I've included some detail pics of how things mount, including the diagonals. They have pads that fit in the bracket between the bulkhead and shock tower. The nice thing is that if my setup is crap, and I can unbolt everything and swap back in the original T-arm. Nothing here is irreversible, and it can all be transferred into another chassis if so desired.

All that's left is welding a reinforcement plate on the body's sheetmetal to accept the mounting bracket for the differential's forward trailing arm. It will take some careful positioning, otherwise easy-peasy (famous last words).
 

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Discussion Starter #589
Made a reinforcing plate out of 1/8" steel and welded it into place. Compound curves to match the sheet metal where it joins the trans tunnel. The holes are welded in as additional attachment points. Kinda got sloppy with the primer spray on that second pic. I'll take care of that later.

Now I need to carefully line up the differential's trailing arm and bolt it into place at the right angle. Someone PM'd me about the importance of its location, and I'm thankful for that. I might have just put it any old place.
 

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I don't know if it's the same thing but I saw a live axel that instead of the sliding block there is a big bearing with two horizontal bars coming off the top and bottom off the bearing. It just may be a fancy panhard rod I'm not sure. Just wondering if you'd seen anything like that? Great work! Thanks!
 

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Discussion Starter #591
Gigem, I think you're describing a Watt's linkage. Alfaholics sells them. That was another option for this car, but for better or worse, I was set on doing a sliding block.

Glad you're enjoying the show!
 

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That does sound like a Watts link. Functionally the same as the Sliding Block. SB is historically correct as it was developed by Autodelta for the racing GTA's. It's limitation is that it did tend to jamb on long or hot races where the lubrication between the block and the slide frame eroded. (It got really exciting when it jammed in a hard turn!) We used to grease it every pit stop. Watts replaces that with a really big bearing.

Had one on my "street" Duetto for many years, and it was a PITA for regular maintenance, but it sure was cool!

Robert
 

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thanks for clearing that up. It was on a stock car Smokey Yunick built where I saw it. That guy did some amazing stuff. That is a big pucker factor having the block weld itself together in a turn! Has anyone ever tried having the block slide inside a stack of needle bearings on each side?
 

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The solution we used was to mill a rectangular cavity a few mm deep in each side of the bronze block, and insert a 3 or 4 mm thick delrin plate. That's like the UHMW slippery plastic used in many places today.

OF course, the wear and cornering forces were pretty hard on the plastic....

Robert
 

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Cornering forces with today's tires are significant. I have a Jack Beck Panhard bar setup on my autocross spider, and have fractured the chassis brace twice and also ripped the sides of the the axle mount.

Sliding block content: that's why the casting is so robust.

...
OF course, the wear and cornering forces were pretty hard on the plastic....

Robert
 

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Discussion Starter #596 (Edited)
Onto the final stages of this sliding block madness.

I needed to fab up a bracket to mount the trailing arm directly to the underbody's sheetmetal (since I'm choosing not to use the cross piece that replaces the stock trunnion arm). I previously made an aluminum bracket, back before I realized that the mounting surface is curved and the bracket wouldn't conform to the bodywork. So I'm back to using steel, which I can bend and weld to my heart's content.

I didn't have the steel stock on hand, so I cut up and welded an old Harbor Freight double-ball trailer hitch thing I didn't need. Remember, I never throw anything away. This isn't the first time a discarded piece of Harbor Freight metal has been repurposed/recycled into a part of my race car. This stuff can't be any worse than the lousy Russian steel that came in these cars.

Placing that bracket took a lot of measuring, and remeasuring. I wanted to replicate the mounting angle of the stock T-arm to the differential, which also matches the angle of the driveshaft.
 

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Discussion Starter #597
Somehow, the first part of this project became the last to be installed. Remember that titanium trailing arm I made a while back? It was buried under a pile of metal shavings, swarf, and detritus behind my machine tools. Dusted it off, and put it in its rightful place, at last. Just about done with this sliding block madness...
 

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Flat amazing, really nice work!
 

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Richard Jemison
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Upper link

Two things;

1- the attachment bracket you mounted to the chassis is not adequate for the load. It will flex and tear the chassis metal. This from experience
with several builds. You need a backing plate on the inside that is braced to the roll cage.

2- The mount for the upper link should have at least three positions for the upper link to mount. The highest being just below the OE trunion angle, so you can adjust squat/anti-squat to optimize traction and reduce rear lift under braking.

As well remember the pinion angle must be the same as the short front section of the driveshaft with the suspension loaded.(car sitting on its wheels.)

there is probably pics of the upper mount designs on both the "Montreal coupe" thread and my Duetto race car thread.
 

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Discussion Starter #600
Thanks, Richard. I took care to preserve the pinion angle while under load, and I located the bracket at a position that replicates both the stock trunnion as well as the transverse bar that should have replaced it in the sliding block setup.

I'm not much for experimenting with adjustable this or that. Aside from the obvious time suck, I can see myself tuning the car to a standstill by fiddling with things more than I already have. Know how that goes? In fact, I've adjusted my Konis exactly zero times from their initial setup. That may change if I swap in heavier rear springs. Just got the 225 pounders.

So that 3/16" mounting bracket up against welded 1/8" plate reinforcement won't be enough? I'll brace it up some more.

Jeeze Louise, I have an ugly driveway! You know, there's still traces of blue on the exposed aggregate from the time I painted the car there five and a half years ago. I think I posted a pic of it back then. That Briteside boat paint is good stuff.
 

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