Tag Archives: technical stuff about writing

OK getting down to brass tacks on this steering business

First, an etymology of the phrase “Getting down to Brass Tacks” because I know it and I think it will add to the conversation about the steering. The origin of the phrase relates to custom saddles for horses and cowboys, and literally refers to the size and number of the brass tacks used to secure the final seating surface to the frame of the saddle. This was important because too few or too small of tacks would cause the saddle to fall apart, and because the polished brass tacks were a decorative touch and too many was considered to be low-class, or <i>nouveau-riche</i>. And that should be in italics but I have to switch back and forth between editors so fvque it.

Anyway, this part of the design is very detail-oriented, in that the same parts from different suppliers will require different fitting because while they might be the same internally (spline count and/or shaft diameters) outside they are very different. Like about a quarter-inch different in outside diameter between basically the same U-joints from different manufacturers means some will clear the inside of the bellypan without relief dimples and some will require about an eighth of an inch or so relief dimple to not foul the U-joints when the steering wheel is turned. So I have to do a lot of catalog and website browsing to find the outside diameter of the various U-joints, so I can pick the ones that won’t require extra work on the bellypan.

Actually there is only one place where the outside size of the U-joints is at all important, the place where the steering shaft goes under the radiator, between the frame rails, and above the inside of the bellypan. The current plan is running a 3/4″ shaft under the radiator in the 1 1/2″ gap caused by the radiator having to sit on top if the bottom frame rails, and tucking that shaft up as close to the radiator as possible. I can get bearings that can be mounted so the shaft just barely clears the bottom of the radiator mount, meaning the U-joints have 1.125″ radius clearance without having to dimple the bellypan. Most of the U-joints I’m looking at will clear that with no problem, but there are some that don’t and I have to make sure I don’t get those. So I have to mark the ones that I know will fit and then cross them against other considerations, like how strong they are, and how much flex they have. Price is also a consideration, but there isn’t much leeway there. They pretty much cost what they cost, and there isn’t much difference between suppliers.

Anywho I have also figured out what to do with some of the leftover heavy angle stock: the panhard rod (or track bar, the two are interchangeable) needs a sturdy mount on both ends, and the quarter-inch thick stock will be perfect for that, being practically inflexible for the size needed for that bracket, no deflection at all as short as they are. And because right angles and flat surfaces, it’s practically self-jigging.

And I don’t know if I mentioned it explicitly before but because of the thickness required to prevent flex in the steering arm, the part is thick enough to be threaded for secure connection to the rest of the car. No extra nuts required, but I will use a safety nut on the bolt through the heim joint at the end of the drag link, because that bolt will be hanging down and could fall out of it wasn’t safetied somehow, which could cause a total loss of steering control. I don’t think saying that would be bad is any overstatement. The safety nut in this application would be equal to a double nut safety, as the threaded steering arm would function as the first nut.

And I’m getting a notification from my computer that my OS wants a shutdown to update, I’m starting to glaze over and try to faceplant into my keyboard because trying to think about something on-topic to write about. So this looks like a good time and place to stop writing this and publish and reboot.

I need to think out loud some more

And you get to read it, lucky you! This is one of the ways I solve problems, but I usually don’t keep the process after I’m done, but I’m thinking since this isn’t how to make a man-portable nuke, or how to shut down the stock market, or any other destructive thing that could cause chaos and destruction if I let it out in the wild, this one I will let people see the process.

The problem needing solution tonight is the question of will using a Powerglide transmission and a quick-change rear axle be better for the autocross and still usable for just driving? From known data the QC has about 10 pounds less mass than the 9″ Ford rear end or is way cheaper than an equal weight fabricated aluminum housing 9″ Ford, going back to the Eternal Triangle: Light, Cheap, Strong, pick any two.

The other thing is you can’t street drive with the PG without changing the final drive ratio from the race setup, the ratio is Too Low for any highway driving. The final drive for the autocross setup is top of the RPM band in first gear at 40 MPH. For an LS engine that would be 6500 RPM. Now because the PG comes in two low gear ratios, 1.78 and 1.82 you can see the problem. Even going from the 23″ tall race tires to the 27″ tall street tires that would make the freeway RPM an unbearable 3110 or 3042 depending on which ratio transmission I get. Either one would result in horrible mileage, horrible engine noise and added wear and tear on the engine. What I’m looking for is a highway cruise of 1900 RPM or less, so you can see what the problem is.

Now the reason I want to run the PG is weight, both absolute and rotating mass. My other options are the 4l60 and variants, or the 4l80, the first weighing in at almost 200 pounds with fluids, the second is 240± with fluids. A fully race prepped PG is [drum roll] 96 pounds with fluids so 100 to 140 pounds less weight on a car that would weigh 1800± pounds with the 4l80. And do I really need to show how much 140 pounds off an 1800 pound car is as a percentage? Plus I don’t have the actual rotating mass for all 3 transmissions but I know the 4l80 is the highest and the PG is way lower and the 4l60 is somewhere in the middle but closer to the 4l80. And going back to Commonly Held Beliefs About Rotating Mass For Hot Rodders every pound of mass rotating at engine speed is equivalent to 5 HP, so going from the 4l80 to a PG not only takes 140 pounds off the static mass and sprung weight, but it takes a Large Amount off the rotating weight. As an added bonus the PG is one of the strongest automatic transmissions you can buy for normal car engines. Of my two choices the 4l80 has the best power handling but slightly worse ratios which is why I was looking so hard at the 4l60 based transmission. But neither of them can hold a candle to the PG in torque capacity. The PG is pretty much the standard transmission for a Monster Truck with 1800-2000 HP alcohol-fueled big-block engines, so strong, and light, and low rotating mass.

But to use it with the Sprint-T I need a way to easily change the final drive, or invest in a truck and a trailer to haul it between races and pretty much resign myself to only driving to my local grocery which is close enough to not drive me crazy with the RPM and noise from the engine. That’s where the QC axle comes in, it takes about 15 minutes and about $70 for a different set of spur gears to set the highway cruise to 1900 RPM. Now the QC cost is about $1k over the Ford 9″ unless you try to get the Ford as light as the QC and carry two center sections to have the race and highway ratios because part most of the higher cost of the QC over the 9″ is magnesium and aluminum EVERYTHING. Also changing the final drive on the 9″ requires hours of work setting the lash and engagement depth on the gears, or carrying around a spare centersection to swap from one to the other, and also about an hour of laying on my back at the race track going from one to the other. The QC requires an extra set of spur gears at $70/set and about 15 minutes unbolting the rear cover, swapping the spur gears, and bolting the cover back on and putting the gear oil back in the housing. That last bit is very important if I want to keep driving more than a few miles from the track.

Now I have been thinking about it and I can live with a PG and highway gears without much problem beyond the one they made fun of back when the PG was a production transmission installed on common road cars, driving 70-80 MPH still in 1st gear, as there are only two plus reverse. Actually if I have my sums right the shift from 1st to high under full throttle would be at 131.5 MPH. Which is even funnier than the vaunted 70 MPH shift from 1st to high ridiculed in the magazines of the times. The engine would remain below 3500 RPM all the time and would rely on low RPM torque and the torque converter to run without stalling. Which is almost the same as the speed the engine would be forced to spin at 60 MPH with the race gear all the time, so from one extreme to another in engine speed. Engine speed in 1st gear at 40 MPH with the highway gear would be 1976. That is a swap I can live with. Especially with the benefit of 100 pounds less empty weight and a similar but lower reduction in rotating weight for racing the autocross. But if I decided I needed a higher engine speed for around town but not making long trips on a freeway, all it takes is consulting a chart, picking a gear set, plonking down another $70, and spending another 15 minutes under the back of the car changing the spur gears. Or maybe just swapping the gears top for bottom on the race gears, because that would be a thing that was possible because the spur gears for the race gear would be a reduction set to get the RPM that high for that slow is WOW! The race gear needs to be 6.11:1, and the highway gear needs to be 2.54:1 and there is no way to get from one to the other without using different spur gears. If I get the low-inertia (rotating mass) 4.12 ring and pinion I can get close at 6.08 and 2.79 with only one set, giving me 2083 RPM at 60 MPH, but if I get the more common and slightly cheaper 4.86 the 6.12 spur gears give me 3.85 swapped top for bottom, which would be a decent setup for around town but loud and drony 2875 RPM for highway use. The bad thing about the 4.86 is the tallest final drive I can get is 2.58 which is Really Close resulting in 1926 RPM at 60 instead of 1900.

I shall have to let this one percolate through the grey matter for a while, comparing the costs of the 4l60 variant that will support the engine I get with a 9″ rear housing to fit the Sprint-T, and the costs of a PG and QC to fit the Sprint-T including 2 sets of spur gears, or a 9″ to fit and another center section. And looking at the assembled and ready to go 9″ center sections the cheap ones with a spool are $620 plus tax, for a race-only application. The ones with the highway gearing higher than 3.00:1 are scarce and expensive because most vehicles are equipped with overdrive transmissions to bypass the need for such tall gears. They used to be very common in the ’70s before overdrive transmissions were common, but I’m only finding used gears above 3.0 and even those are way expensive, so I might have to run the QC if I choose to run a PG. Or it just might not be economical to run a PG because of how expensive the support equipment required to run it on the street especially when a 4l60 can get 6500 RPM at 40 MPH with a 3.62 rear end ratio on the 23″ race tires, and get 1900 RPM at 60 MPH with the same rear end ratio and the 27″ tall street tires. Now that’s not a standard ratio but the common 3.50 is super cheap (for a 9″ rear end ring and pinion) and gets the race ratio close (41 MPH) and is just a tiny bit tall for the highway ratio resulting in 1830 RPM instead of 1900. Even closer is the Ford 8.8″ rear axle which (some of them) came with a 3.55 and a limited slip. Much more thinking is required, and as you can see there was already much thinking and consulting of texts and web pages done to get this far.

OK Finished the Archive Crawl of QC

I finished the archive crawl of Questionable Content last night early early this morning and saw patterns in his creative processes, but I really didn’t help my problem. I did see an ongoing art evolution that gradually became more of a character evolution, but aside from taking my mind off the subject enough that I am able to post this about my observations I didn’t find anything that would break my creative block, at least as far as writing is concerned. Now for the Sprint-T and the Mini Sprint-T I have found a few things to move that design along, but only in details. So far the major parts of the build are pretty much set in stone, but there are a ton of details that have to be resolved before the design can move forward as the tiny details cascade backwards into major changes in other parts of the build.

One of those tiny details is the steering arm location and orientation on the spindle. There are two locations and two orientations that result in 4 different locations for the drag link connecting the pitman arm on the steering box to the steering arm on the spindle. This cascades into different locations for the steering box because the drag link needs to be pretty level, or close to it if other things get in the way, which basically means there are 3 different places I need to put the steering box depending on how I mount the steering arm on the spindles. That’s because there are 2 combinations of mounting position and orientation that put the drag link in pretty much the same place.

Actually there’s no real technical reason for making the drag link level. The drag link and the panhard rod or lateral link (same device, different names) need to be parallel to prevent bump steer, and ideally the lateral link should be roughly level with the ground to prevent excessive side-to-side motion which would change the way the car turned depending on ride height. In the end it just makes things slightly easier to finagle to have the lateral link level at design ride height, and as stated earlier having the drag link parallel to the lateral link prevents bump steer and other steering maladies.

Another tiny detail is mounting the alternator, and I think I have that one nailed down. The only belt-driven device on the engine will be the alternator as the power steering will be electric, so no power steering pump, no AC so no AC compressor, and the water pump will be electric to reduce total drag on the engine and also improve cooling efficiency by driving the pump at the speed for best cooling regardless of the engine speed. That only leaves the alternator that needs to be driven by the engine directly. As I pointed out a while back there are 3 bosses on the passenger side of the block that are designed to have a bracket for an engine driven device bolted to them, the bracket for the AC compressor specifically, but there is no reason why that device can’t be the alternator instead. What I was thinking is a plate that bolted to the side of the block and another plate that gets welded to that plate that the alternator bolted to with one bolt hole being the arced slot that the bolt that adjusts the tension of the belt slides through. That front plate can be just bent from the side plate to avoid a welded joint, but that’s more of a “what can I do with the materials and tools I have?” than the other kind of design question. Obviously both bolts that go to the alternator would have to be on the same plane or pretty close (talking washer thickness differences more or less) which means I need to do a little bit of measuring when I go to the parts store to pick out an alternator, but for the Mini Sprint-T I just pull one from the parts box and bend a bracket from sheet plastic to glue to the block and alternator to hold it. I just have to line up the crank pulley and the alternator pulley until the glue dries, then run a simulated belt around the pulleys.

And there is a valid reason the alternator goes to the passenger side of the engine that goes back to mounting the steering box on the driver’s side of the frame and leaving room for the box and the steering shaft. If you thought Tetris was fun wait until you have to package the front end of a hot rod. At least when I have to shave material off the model to make things fit a hundredth of an inch on the model is a quarter of an inch on the full size car, or what’s basically molding flash on the model is major structure on the real car. And the engine and transmission is going to be offset to the right to counterbalance my weight to the left, another design decision made a long time ago. I have to find good weights for the engine and transmission.

I have a weight from a GM technical publication of 255 pounds full of fluids for the transmission, and a weight from a GM parts catalog of 614 pounds for the fully-dressed version of the motor I will probably get from the junkyard but nothing accurate for the junk I will be pulling off. Anyway I can assume about ~50 pounds for AC and power steering and assorted junk brackets so 565 for the engine and 255 for the transmission and 30 for the full of fluids torque converter adds up to 850 (!) pounds for everything on the right side of the car, balanced by my 210 way further from the center on the left. Doing the math my moment is 210 pounds times my arm of 11.25″ or 2362.5 Pound inches of moment and dividing that moment by the 850 pound engine gives a 2.78″ moment to balance or 2.8″ to take the driveshaft into account. That works out to 0.112″ on the Mini Sprint-T which is enough to be noticed on the model. The inside to inside on the Sprint-T cowl is 26″ and the bellhousing on the back of the engine or front of the transmission is 19″ outside to outside and moving the engine 2.8″ to the right gives me 0.7″ clearance on the right side of the engine if I use a mini starter instead of the honking huge OEM starter that actually sticks out from the side of the engine, getting back to the subject of Tetrissing the engine compartment. And I know I did this calculation for an SBC a while back, but I didn’t feel like going through the archive to find it because I just finished diving the QC archive in the way early hours of this morning and diving a comic archive is much quicker than looking for specific words in a blog archive.

And it’s getting late because I have been watching YouTube videos between paragraphs and I have almost 1200 words according to the editing program that comes with WordPress. So this seems like a good place to wrap this and post.