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Book 3

My third book is released! Learn what you'll need to know in order to become an embedded engineer.

Book 2

Check out my second book; learn practical stuff about building robots and control systems around Linux PCs and the Atmel AVR.

Book 1

My first book gives you all the intro you need on developing 32-bit embedded systems on a hobbyist budget.

Day 15 - Transmission Rebuilds and Cadavers

05/20/07 - Work is proceeding from the events of Day 14. I had originally intended only to replace the gaskets in this new transmission, and possibly clean off the outside a bit. However, when I separated the transmission from the transfer case, I forgot to open up the t-case and undo the bolt that holds the connecting shaft into the t-case. So when I tried to pull the two pieces apart, the sections of the output shaft separated and plink! all the rollers fell into the soup inside the transmission. Since this means more or less completely disassembling the trans anyway, I decided to pull it completely apart, clean every speck of dirt off the castings, and paint it.

It transpires that this was a blessing in disguise, because it allowed me to inspect a lot of surfaces I wouldn't otherwise have seen. I found that a couple of the rollers in the needle bearings were broken, and the input and output ball bearings are scratchy. The second gear was also worn enough to justify replacement, and there were little chunks of metal debris all over the trans, impacted into the soft metal (like inside the synchro rings). All these parts are included in the standard T90 rebuild kits, so this doesn't mean any extra expense. I also found that the oil collector had been omitted by someone who had rebuilt this transmission in the past. This is a common, foolish step; without the oil collector, the geartrain doesn't get as much oil as it should; there is more foaming, and an increase in leakage.

Cleaning this thing was a REAL bear, partly because I've never done it before. The next one will be much easier. Autozone sells a bunch of different degreasing compounds: forget them all, because they suck. I've tried roughly ten different products from there and they were all COMPLETELY worthless. The secret turns out to be Zep Industrial Purple Concentrated Cleaner and Degreaser (about $30 for a large plastic bucket from Home Depot). This is a combination of 2-butoxyethanol and sodium hydroxide, and it's fairly concentrated. You'll feel it turning your fingers into soap, so wear rubber gloves! I used about a 10% mix of this stuff with really hot water, and a wire brush. Once you know how to do it, I'd say it's about two hours' work to completely strip off the dirt. The next time I do this, I think I will be able to get it completely apart, cleaned and primed in a day.

From left to right, here are the stages in this cycle (so far). The first picture shows the unit fully assembled, in the back of my Jeep when I got it home. Second picture shows these parts in mid-disassembly (just after my "sproing!" moment). Third picture shows the case with all old paint, underbody coat, grease, dirt and rust wirebrushed off it down to gleaming cast iron. Fourth picture shows the case primed with Rustoleum Stops Rust primer. You have no idea just how much hard work went into this thing between the second and third pictures. Click to zoom.

What about the cadavers mentioned in the page title? In an hour or two, a truck will be rolling up to my door with a donor Scout. My mouth is watering at the thought of what parts can be salvaged from this vehicle. The most exciting thing is, I can pull off whatever piece I want, and take as long as I want to clean and restore it.

Go on to Day 16... and all original content herein is © Copyright 2007 by Lewin A.R.W. Edwards. "" is a trademark protected under U.S. and international law. Infringement or attempted dilution of the intellectual property rights held by Lewin A.R.W. Edwards will be prosecuted to the fullest possible extent.