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Bad Moon Rising

Maybe I’ve switched over to being a little more serious about all this car building shit. Maybe it’s because someone in China is constantly probing my Home Page and I want to give them premium content and cover pics to probe. Fucking Chicomms. Who knows. Smells like a sellout to me…anyway enough of that horse shit.

One thing a day on the race car and juggling Pedro’s EVO VIII engine/race car build with that and other work at the shop for race car money is going well. Supply chain shortcomings aside the build is progressing. I’m glad to say I’m finally seeing results from all the planning. We switched over to classic southern and arena rock, maybe that mellowed me out a bit. But maybe, just maybe it makes me want to harass fuck heads even more.

Last issue we talked about mating the engine and tranny together. This issue I think we are going to talk about locating the engine and tranny into the chassis. Locating, not mounting. If you want to talk mounting please get into your DeLorean and go back to the future.

So, the jig is all square and perfect. The chassis is mounted to the jig, squared and trued within 0.79375mm (1/32″). Without giving away my specs its sitting at ride height. (104.775mm ((4.125″))) That’s frame ride height. Locating the engine/tranny assembly knowing all this information becomes a very, very simple task. It simply requires more jigging. Given my designed axle centerline height of 322.58mm (12.7″) it becomes even more simple.

I rifled online through the McMaster Carr catalog to see what I could come up with materials wise to set up my axle center for the proper jigging to the frame. Getting no results I decided it was time to just design something…

Unassembled fore/aft jig

Being that I’m using the STI 6-speed in transaxle configuration the most obvious choice was to use the “Front” axle output shaft holes. These after all are what locates the axle in the driveline, thus locating the axle centerline in space. So I started there. I popped the axle seals out of the preload discs after removing the “front” diff from the bellhousing. We’ve got a bore diameter of 49.991mm(1.965″) to pass a rod through to simulate the axle line. No one makes that. No one even makes anything close to that for a location interference fit. So I made this:

Axle adapter

A simple little plug for each side of the trans that presses lightly, but snug enough to stay, into the preload adjuster on the side of the trans. And not to over complicate things, the center bore is a simple 31.75mm (1.25″) location fit to slide a piece of off the shelf 4130 through. And talk about price effective, about $1.00 and 4 hours on the 3D printer each. So that’s that. My axle center-line simulator.

Next I needed a jig to actually set the height. So I designed this:

Height jig with forward indicator arrow

A triangle axle mount that attaches to the chassis jig and sets the center-line height to my exact measurement. Simple to assemble too, that’s all tab and slot. This is the power of CAD. I’ve got about an hour of design between both units and the accuracy on the manufacturing end is always spot on. This way there is no guessing, no countless hours of fiddle fucking with horseshit. Just make, print or cut, and assemble.

Next up was the location of that axle center-line fore/aft in the chassis. Back to my original design sketches and my numbers in Suspension Analyzer v2.4 and I all the sudden remember the spec on the fore/aft location. 444.5mm (17.5″) from the rear chassis cab bulkhead tube. Another jig designed:

Terrible pic of fore/aft locators

Tab and slot just like the other one.

Let’s repeat the whole process to center the drive train left to right within the chassis.

This, however, has led to one minor flaw in the rear space frame. The rear frame rails are too high. I’m glad I didn’t weld those in yet. Minor redesign and we’re all set.

Wrong frame rail
Hanging assembly

All that accomplished and the drive train is hanging in free space. Now I can stare at it for hours on end and decide if that exactly where it needs to be. And think about axle shaft angle and it’s relationship to torsional loading and unloading of the rear tires under acceleration and deceleration. But that’s another topic for another time.

Corrected frame height and bottom rectangle installed

Edit: I did end up moving the axle centerline slighlty down and slightly back. I’m hoping to get a little extra traction when accelerating out of corners.

theDoc View All

Chassis builder, engine builder, cynic

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