The Glorious Renewal of Mikuvan and The Winter of Ven: Operation Give Me A Brake! Again

You might have seen Elf on a Shelf, but have you seen….

…dashboard master cylinder?!

I’m doing a lot of “van fill” here lately because… well, frankly, that’s what I’ve been up to for the most part, when I haven’t been working on Overhaul in the past few months. With these systemic repairs and some other work on the cooling system that also came along, Mikuvan is probably in the best mechanical condition it’ll be in for a long time. It’s great to be able to crank on things without being disturbed or getting rained/snowed on!

I’ve obviously been putting off figuring out how to structure now two entire build seasons of Overhaul progress. I can probably put together a legitimate e-book and sell it with how much there is to go through, with almost 700 build photos and over a hundred CAD screenshots. The problem in part is now I know what didn’t work, and so need to figure out if I should present the narrative as if I didn’t know yet, or cut to the chase and integrate it better.

This series of posts will be some more good ol’ Zen and the Art of Van Maintenance, covering brake system related things I had to do on Mikuvan from last fall into just a few months ago. It’s a time skip featuring work that was done in stages, but is better presented together as a narrative. So if you are into brake, axle, and master cylinder service on your 3rd-generation 1980s Delica, stick around!

The backstory to all this was explained in my post of everything. With as hard as I’ve been whomping on Mikuvan and driving it like a Miata, some of the systems are showing their age. The most pressing matter was a leaking brake master cylinder, which towards the end of summer began dribbling with every stop. As things got colder, it got worse, to the point where I should 1. uhh, probably stop driving it and 2. had to put shop rags around the steering column to catch the brake fluid.

So priority one was getting this thing replaced. I also replaced the front brake calipers and rotors again from their last round on this very site in 2013! But, that’s a more rote job so I’ll leave it for last. Details to come will also include diving into the slowly self-imploding power steering pump while it was apart and on jackstands with this master cylinder replacement.

Yeah, so about that master cylinder. I’m not sure when it began leaking, but it got pretty bad over the course of a few months. You can see how the brake fluid has eaten the paint off the booster cylinder on the upper left. While it never stopped stopping, I figured it was only a matter of time before it did!

Luckily, I ordered a new master all the way back in 2013 when I was scraping parts off Rock Auto for the first few times (is it still good, I wonder….), and it’s traveled with me to this day. Reading the shop book on how to replace it, though, was another “Damn, this thing is weird” moment.

Alright, the dashboard instrument panel area has to come off first. This is all fairly simple with unplugging cables and popping switches out of their housings. Hmm, the master cylinder is allegedly under here somewhere…

Ahh, there it is.

Connected to the reservoir (mounted remotely by the driver’s door) with some rubber caps, it sits with the brake booster facing you. The brake pedal linkage does a 180 degree turn and the pushrod pokes towards you!

I suppose that’s not TOO strange, as some earlier American full-size vans had a 90 degree linkage doing the same job.

Well, this thing’s lived in a plastic bag for 30 years probably. Let’s hope it’s still functional…

After moving the dashboard harness aside, I used the remote hose clip grabberator tool to move the brake hoses off the rubber caps. Before doing this, I used a leftover epoxy syringe to draw fluid out of the reservoir as much as I could, so it wouldn’t spill everywhere. Not that it didn’t do so anyway….

At this point I realized I didn’t actually own flare nut wrenches, so out comes the DIY flare nut wrench made from your least favorite 10mm box wrench. This is a counter-indicated activity, as flare nut wrenches are made to tighter fits and to grip more of the sides of the (usually soft metal like brass or plain steel) fitting. It worked out fine for me, however.

Also notice the little vacuum line caps I shoved over the fittings so I don’t spill out more of the fluid.

Once the wire harnesses and hoses are removed, the access itself isn’t bad. I used a 1/4″ drive ratchet with an unusually long handle for its size (for better leverage) and a small extension with a wobble drive end. The wobble is helpful due to the vacuum? line that runs across the assembly (it can be seen to the immediate right of the ratchet handle, in the center between the two master cylinder cap fittings), but I suppose you can also beast it.

Old master cylinder now removed. The area is pretty grungy, and there’s more eaten-away paint where it’s been leaking from the front seal. I cleaned up this area pretty thoroughly with teratogenic solvents and a small wire brush, wiping it all up with shop towels.

iNsTaLlAtIon Is ThE OpPoSiTe oF ReMOvaL – those dreadful words in every single shop manual. I mean, there’s not much trickery here, that’s really how it is. Before mounting the master cylinder, the fittings need to be oriented roughly how they’re shown here – front circuit pointed dead left, and rear circuit at the 45 degrees.

I’ve hooked the hoses and clips back up now and recovered all the dashboard wiring, previously shoved sideways. I took this opportunity while I was staring the speedometer cable in the eyes to force-feed it a bunch of 3-in-1 oil. This runs downwards and all the way to the transmission, and I figure any lubrication it had is long dry.

(Followup note: The cable is now so well lubed it has no damping left, and the speedometer needle has what I call “AC RMS” noise, furiously wiggling even at highway speeds around the actual average speed!)

In all, it either wasn’t as bad as the shop book made it out to be, or I’m jaded and consider this relatively simple van maintenance. The rest of this story is now about a brake job:

The draggy brake caliper on the front right got drastically worse after a weekend mountain run, and was bad enough that I was smelling brake pad (and took a noticeable mileage hit). So, Mikuvan got to sit on the bench for a few weeks before I got to the caliper replacement and the master cylinder work shortly thereafter.

I decided to just order more new (well, remanufactured) calipers instead of rebuild kits for the existing ones. With something as uncommon as the USDM Mitsubishi Delica, I’d rather have more parts than not enough. I ordered the rebuild kits anyway, but will be hiding them with the old calipers in case I or someone else needs them some day. And this is how it begins – the seed of my “Warehouse of assorted car parts someone will neeed” that my estate will surely one day have to auction off.

One quirk of “obsolete van” service? The parts you get for the left and right hand sides are probably not going to be the same. At all. These two brake calipers nominally had the same part number and were both branded the same rebuilds, but they are definitely different from each other. One had an original Mitsubishi star on it, the other was…. something else.

These brake rotors, too. Maybe the same thickness, OD/ID, and bolt pattern is all that matters, but it’s just funny to have one that has twice the number of cooling vanes as the other.

Disengaging these old truck brakes is very simple. No special tools needed save for a simple C clamp!

This took…. a lot of effort. Why?

Looks like the culprit is this torn rubber shield for the brake cylinder. This would allow weather in, and probably caused this piston to seize in the bore once corrosion started ruining fits and finishes.

Check out the well-cooked patch of brake pad that’s been burnt onto the rotor, as well as the heat-crazing that’s starting to form on the surface.

A lot of effort was needed to break the nut and bolt apart. They’ve had over six years of Natural Loctite buildup from Boston winters, after all. I didn’t consider the hardware useable at all after busting them apart, and so I ordered new JIS-standard hex cap screws and nuts.

Why specifically JIS? Well, JIS fasteners have smaller head and drive sizes than the more typical “metric” found in the US which is more likely to be DIN or ISO. The head of the screw had to fit fully inside the counterbores on the wheel hubs, and the nuts had to not interfere with the hub as well.

While I was waiting for the SPECIAL BOLTS OVERNIGHTED FROM JAPAN!!! (McMaster) to show up, I did…. what everyone expected me to do.

Consider it an act of rust prevention, or vanity. No, it’s not high temperature paint. No, I don’t care all that much, why?

The next day, JIS bolts! Besides having different drive sizes for hex and sockets, JIS also has a different fine and coarse thread definition. In M10, the typical pitch for coarse thread is 1.5mm and the fine thread is 1.25mm. Recall my adventure with repairing the exhaust manifold where I found out someone babooned a 1.25mm nut onto a JIS 1.0mm fine threaded stud.

See what I mean about those counterbores the heads had to fit into? Strictly speaking, a regular ol’ 17mm head would have fit here, but…. there would be no way to put a socket on it to install!

I discovered a folly immediately after test fitting the new bolt arrangement. I got screws which were the nearest 10mm to avoid having to get special automotive screw lengths. Well, they stick out just a little too far compared to the previous screws….

And that meant the ends of the screws hit this irritating high spot in the brake caliper castings.

I had to demolish my brand new Miku Magenta painted calipers with a grinding wheel to free up this fit!

So there we have it. Hot pink calipers installed on both sides.

The calipers did come with the slide pins greased, but I didn’t know how long they’ve been sitting in a box – the grease felt pretty dried out. I therefore unscrewed the slide pins and refreshed the grease with some copper filled grease.

After the master cylinder install, I took the opportunity to fully flush the brake lines, something I only did before in 2013 when I first went through the brake system. Plenty of “Brakerade” was generated once more. Delicious, delicious skin cancer.

Finally, while the dashboard was taken apart, I refreshed all the slowly dying Inexpensive Chinese Van Lights.

And we’re back together. At this point some time in January, stopping was fine, but turning was questionable. The power steering pump is next!

The Belated Equals Zero Christmas Special: Restomodding a Tomy Omnibot and Vintage Futaba AM Transmitter

Here’s a funny little side road I went down over the course of the 2020-2021 holiday season when nothing was open, nothing was shipping even if it were open, and I had otherwise nothing build-wise going on. It was a good trip back to the days when I did these little hacky things more often, building and making something without really a purpose except to see it happen because it needs to happen. Even better that I ended up with a mobile, displayable simulacrum of the current trendy 80s-90s nostalgia that has fully engulfed pop tech culture.

It all started during one of my random van adventures (of course) up to North Georgia. Having passed a lot of what I call “knick knack stores” on the way to and from the Blue Ridge and Smokies, I decided one weekend to just spend my time perusing their wares.

You know what I mean – the “antique markets” and “junk stores” that pepper state highways and county roads, well outside of metro areas. I’ve some times collected vintage tools or neat mechanical things from them.

But this little place on the side of Highway 515 was special. That’s because when I walked in, this thing was just sitting right there on the main display counter:

What is that!? Well first of all, it’s a Dr. Inferno, Jr. After that, it’s a Tomy Omnibot, one of the outfalls of the 1980s robot toy craze after the first microcontrollers became economical enough to put in (at least high end) toys. This was, it seems, an over $1000 (in modern dollars) toy back in the day, and it had all the 80s computer trappings – a tape drive that you could record movements onto and play back, for instance.

There was no remote or other documentation or original packaging to go with it. Without the paired remote, there wasn’t really anything it could do besides “Be Collectible” which isn’t really my thing. I thought “Well, I already have several 80s vans, so why not add an 80s robot to the mix”? The thought popped into my head then that it would be fun to drive around at shows and meets, like #RadwoodBait but for robots.

And so this is the story of how I turned this Omnibot and a vintage AM radio into a contemporary dance duo that never actually was.

There’s really two independent parts to this story: The AM radio conversion, and the buildout of the robot itself. I feel like the radio conversion is actually the neater technical contribution, but nonetheless, here’s the index:

1. Repairing and Upfitting the Omnibot

2. Converting the T4NL AM 4-channel radio to a 2.4Ghz 7-channel radio

Fixing up the Omnibot

I heard lap belts in the back rows are no longer the recommended way to keep your children safe in the car.

Anyways, besides the Omnibot, I also picked up a few old knick-knacky tools, including the pictured brass hammer for the Master of Benches.

The robot itself was in good shape – it had one of the arm guide links broken off at a plastic boss, and the wheels were missing small chunks of tread. Nothing major exterior-wise besides a few blemishes. The drivetrain took a little bit of wiggling to become ‘unstuck’, frozen grease and grunge if I had to guess. Much like my M.O. with vans, if it’s vaguely robot shaped at all, I can probably get it to drive.

The back lid pops off with a screw to reveal the battery bays. The main battery for the drive system and lights was a 6V sealed lead acid battery (which is long dead). The ‘computer’, timer, and tape deck were seemingly operated from 3 volts of AA batteries, the terminals of which were also long corroded off.

It’s a bit gross everywhere, like it clearly sat in a basement/attic with bugs for years. At each juncture I took the opportunity to try and get the detritus out with some bleach wipes and rubbing alcohol.

This thing actually pops apart very quickly once the six or so screws holding the body together are removed. There’s a LOT of what appears to be hand-wiring inside. I can imagine the assembly line for this thing being a jig holding all the body pieces in position as technicians install the wiring, and then the whole thing is closed up.

More corroded wiring and bug detritus abounded inside the shell. How’d y’all even get inside?!

To my dismay, the arms were not motorized. They’re all held in place by friction washers backed by springs. I was at least expecting the shoulder to be a lifting axis or something, as that’s all you’d really need to make the thing more animatronic. Alas!

Maybe this can be a future upgrade path if I choose to dive in further – adding an arm axis that never was!

The shoulder joint in particular is a mounted on an insert in the main body and has a set of O-rings to give it some more friction over just the spring loaded washer.

Two follower linkages keep the forearms parallel; one of these, as you can see, broke off its stud. It didn’t affect the operation all that much because there were three others, especially the one on its same side. I’ll likely just epoxy this boss piece back on.

As I was taking all of these joints apart, I was also cleaning up any worn plastic debris (powder) and then lubricating each joint with silicone grease as I was reassembling it. The grease didn’t make each joint looser so much as less grindy and prone to squealing.

This is what each arm looks like once disassembled. The claws are also unpowered, and just have a open and close lever that snaps the ends apart or together. I could see this end having a small servo embedded in the wrist joint to pull on this lever, if I went the full animatronic route.

I decided that the most immediately helpful replacement for the 6V lead acid battery was a 6.6V bank of A123 cells! Conveniently, two cells in a row was basically the same width and height, so this was a no brainer.

I whipped up a quick battery pack using the original plug cut off from the lead-acid battery, and a repurposed 3 pin servo connector as a balance tap connection so I can throw it on one of my 2S dedicated mini-chargers.

To get the bot base driving independently of the onboard controller, I decided to embed two of my leftover Vex 29 ESCs into the motor power path. This meant I had to tap power from the main board, and it was actually pretty nontrivial to find where.

Unlike most new PCBs, there’s no obvious “power bus” because the components are all through-hole and the power has to snake around to get places, using jumpers. I had to follow the original power input wire around on the board until I found where on the multi-position switch terminals it ended up.

Now when I turn the robot on, my newly appended JST battery lead gets power.

I had these de-husked Vex 29s left over from beetleweights of long ago, either Colsonbot or the first Stance Stance Revolution. They’re still my go-to for “Random small bidirectional DC motor driver that doesn’t need more than 12 volts and like 2 or 3 amps”.

The wiring was deceptively simple here. Because the receiver needed power as well, I just stuck the battery connector through a servo connector conversion into the receiver. The Vex ESCs are supposed to receive power and signal through that same connector. It’s only 6.6 volts anyhow!

(I’ve done the exact same thing for Stance Stance and Colsonbot, mind you. The receiver’s power trace is thick and short enough that on the order of single digit amps isn’t a problem)

I’ve closed the robot itself back up now after polishing the dome a little to get rid of blemishes.

For extra cheekiness, I gently peeled the original label off the lead-acid battery and then applied it to my newly made pack!

Converting the Futaba Conquest T4NL Transmitter

Here’s what I think is the bigger meat and thicker potatoes of this little holiday boredom project. A long (long) time ago (in a MIT far far away, at least now it is!) I collected a box of cruft which had a Futaba Conquest T4NL transmitter in it. It hailed from the era of “boxy and chrome” transmitters, and I always figured one day I’d shove a 2.4Ghz radio into it as a restomod. This was probably at least in the 2010-2011 timeframe, and it traveled with me through my multiple great cruft moves.

Well I think finally it’s time to do it! The idea came to me immediately when I brought the Omnibot home.

Like the Omnibot, it was in good mechanical and cosmetic shape, even if the batteries were long missing.

The radio of choice I was going to swap in is the “Microzone MC6C“. It’s one of many lower-end market 2.4Ghz basic model radios hailing from the vast ungoverned high seas of Jack Ma. I originally picked up two last year when I was putting Trashcopter together, since I wanted to see what the evolution of cheap radios has been like over the past roughly 10 years since I’ve owned two HobbyKing T6Av2s (which are still working, mind you, and exist for sale still!)

The upside of this MC6C radio, which made me select it over just getting another T6A/CT6B model to use as the transplant, was that it had mixing and servo reversing switches right on the front panel, something the FlySky/Hobbyking radio lack.

I’ve always been annoyed that you had to use a computer and USB programming cable along with a horrible VB6 application (or an open source one like DigitalRadio) just to do servo reversing – like mixes I can understand, but that’s some serious cost cutting to not even put reversing switches in. I’m hoping that maybe my exposé about these will help push them a little more mainstream in the robot community as a starter radio or a “class set”, like we used the HobbyKing radios for back in the 2.007 days.

So I went ahead and cracked open the spare one. There sure isn’t much going on inside the MC6C compared to the old Futaba. Miniaturization! Push the problem into software!

On the left side of the Futaba unit is the “RF Module”, so to speak. The larger motherboard on the right performs the sticks to servo PPM encoding. That encoding is done by a dedicated IC, the OKI MSL9362RS, specifically made for 4 channels of digital proportional RC PPM encoding. The combined PPM signal is modulated with the 72 or 75mhz carrier that’s generated by the RF module, and off we go to the races.

Before I started unsoldering things, I decided to do a little poking and prodding with the MC6C. See, there were unpopulated connectors inside on the main board, and unpopulated connectors mean “expandable features”. I figured I would see if the radio could be capable of more. By following traces, I determined that the unpopulated connector was an unimplemented Channel 7, and that it was 3-position (or potentiometer) capable, even. This was confirmed by putting a servo on the receiver’s Channel 7 as I fiddled the contact with tweezers.

I determined at this point that my plan of attack was to go a lot more in depth than the usual “Old Radio Revival” which seems to largely entail putting a modern radio’s RF module’s PPM input on the PPM output stream of the old radio. That would limit me to 4 channels only because of the fixed-function ASIC handling the encoding.

With the T4NL’s chassis containing a whole lot more holes than it actually had buttons and switches (as the same chassis would be used for several different models, such as 6, 7, and 8 channel ones, with dual rate settings or other functions), I decided to do it the hard way and fully embed the now 7-channel MC6C control board and transplant all the switches over, to make a retro 7 channel radio!

The problem to solve now was to decypher the wiring of the potentiometers that make up the joysticks. There was an additional complication, too. The MC6C is a modern computer radio and has digital button trims (click the button, move the servo center a little, save it in flash). The Futaba T4NL had analog trim potentiometers.

Separate ones, even. Most cheap radios that still have analog trims just have the potentiometer body on the trim lever so you can manipulate it separately, but it’s the same pot. This thing, however, had the separate potentiometers on each channel feeding into an analog voltage summation circuit on the motherboard.

The dual row of resistors on the right near where the wire to board connector comes in is the voltage summation. Between the three resistors in each junction are four pads, making the four channel voltages. Through some poking and probing, I discovered values and voltage levels for this circuit while under operation:

I dunno who else would do this, but if I’ve learned anything from this website, it’s that someone else will. So here’s the handy dandy wiring guide I’ve made! It’s interesting to note that the servo reverser switches just flip the polarity of power supply to the channel in question.

The next step is going to be deconstructing the T4NL’s joystick circuit and making it compatible with the MC6C inputs.

So here’s the wiring cleaned up into something that’s spliceable. I’ve made a few wire jumps to power the pots from the same wire, for one.

The next step was to discretize the voltage summation circuit of the mainboard onto the joystick’s trim potentiometers. They now feed the main pot via a high-value resistor.

What this does is let the trimpots influence the voltage output, but not by that much because the main pots have a much lower resistance and dominate the output range.

Through some trial and error, I found that a 3.4K resistor piping the trimpot into the main potentiometer gave me about 20% adjustment range in the signal, which is more than enough as a “Trim” function.

So the “hard electricity bits” of this conversion are actually done. By this point, I had 4 channels of joysticks which had known voltage output ranges.

The next steps were largely mechanical integration. I decided to take a hint from the T4NL case and stick the servo reversing switches out the back of the transmitter (Those 4 little slots were their locations). This area would interfere with the sticks, though, so I decided to hang them out of the battery compartment since I was planning on using a much smaller lithium battery.

The cut was made with a Dremel and a regular carbide burr bit in multiple passes to slowly whittle the line down further each time, until it broke through.

The MC6C reverser switch board used to be attached to the main board using some rigid standoff pins. Because of their move to the back of the radio, I replaced these pins with some jumper wire so they can make a 180 degree turn and fold over.

A little 3D printer nugget will hold the top of the MC6C board level, and its bottom will sit against the former telescoping antenna mount.

I also made two little nuggets to space the servo reverser board apart from the battery compartment’s rear panel. It turns out the switches stuck out really far into the battery compartment if I didn’t. This spacing gets them basically flush with the underside, enough to still manipulate.

See? As another cheeky relabeling, I removed the servo/mixer panel sticker from the front and glued it to the backside.

At this point, I had the transmitter powered on for power testing. Everything seemed to check out, so it was safe to proceed with adding the additional channel switches in. However, what I found was that the servo centers and travels were way off. Obviously, there’s not going to be any guarantee the potentiometers are going to be the same value, or in the same position at all between two radios separated by around 2.5 decades.

Here’s what the final integration looks like on the inside. I ended up removing the board spacers for the servo reverser board and letting the switches stick out again, after finding that it interfered with closing the case all the way. I transferred the switches from the MC6C case, and added a third 3-position switch. Maybe in the future this would be my flight mode select switch if I made some kind of retro-drone.

My last “Hmmmmm” moment was trying to sort out the stick calibration problem. What would I do if I were the enterprising managing designer/engineer of a board that had to take four analog inputs from potentiometers which weren’t guaranteed to be 1. in the exact same center position once mounted or 2. give the exact same range of travel, and 3. can’t be tested and calibrated individually for assembly/expediency reasons?

I’d make the final assembled device capable of running a calibration. My more expensive radios have this as a function, selectable from the questionably designed UI of the LCD screen. But what are the chances the MC6C just has a “Hold this button or close this jumper to run a stick calibration”?

100%, really. I noted a set of mystery jumpers when I first took the thing apart. At the end of the day, you want the factory calibration method to be accessible and easy to use for the assembly workers. A single big 0.1″ jumper is pretty damn out of place given everything else on this board is small surface-mount components.

So why not. I plopped the jumper in and booted the thing up. Immediately, it went into a flashing and beeping mode, which is obviously special. I swirled all the sticks and switches around a few times and left the sticks and trims centered, then powered it off and removed the jumper.

And that was it. All 4 channels now gave the same outputs for my test servo.

To really sell the look, I reached out on the robot combat Facebook groups to see if anyone had in the depths of their cruft piles a “rubber duck” antenna for use with these old 72/75mhz systems. It turns out someone did, and it was glorious. It looks extremely period correct when off, but of course once I hit the power switch, the orange and blue LEDs of the MC6C control board shine through the old battery meter.

Of course, this antenna isn’t connected to anything on the inside. The MC6C has a small internal PCB antenna, which I dropped behind the mainboard once it was mounted in the T4NL chassis in the same orientation. On my other MC6C (used on Trashcopter) I actually unsoldered it and added an external WiFi antenna using an RP-SMA fitting.

And that’s how we got this seriously #RadwoodBait photo at the January “Not cars and definitely not coffee” show. I’ll just say that the Omnibot is excruciatingly slow outdoors – it’s a fine speed for a house toy, I mean, but it took a good long while to get anywhere out here in the parking lot of the mall.

Plans for this thing? I’m not sure If I actually want to go back and try to engineer a movable shoulder joint. While it’ll be neat and all, this is a very reversible hack and it’s nice to just have. This project will, for the foreseeable future, just live in the house and be a thing I can pull out and demo. When the Radwood events come back around, I’ll bring it by!