Before embarking on a Ford automatic overdrive building project, you’re going to need a proper work setting and the tools required to do the job. Because automatic transmissions encompass numerous tiny precision parts such as clips, balls, pins, valves, springs, and other items, your shop environment must be neat and orderly, not to mention well lit. Some parts are so small they’re easy to overlook, especially with poor lighting and a lot of clutter. With automatic transmissions, there are no unimportant parts. If there are parts left on the workbench when the job is done, you’re in trouble.
This Tech Tip is From the Full Book, FORD AOD TRANSMISSIONS: REBUILDING AND MODIFYING THE AOD, AODE AND 4R70W. For a comprehensive guide on this entire subject you can visit this link:
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Cleanliness is never more important than with automatic transmissions. Even the smallest particle of dirt or grit can disturb an automatic transmission’s precision tolerances, causing malfunction and poor performance. All it takes is a tiny grain of sand to cause a valve to stick or a seal to tear. Even house dust can be detrimental to transmission function, which is why transmissions should always be bagged whenever they’re not being worked on. If you live in a dusty environment, consider taking your bagged transmission inside a clean storage room.
Automatic transmission building creates its share of safety issues. Remember, automobiles and components can maim or even kill if you are not careful. Here are a few suggestions to avoid that.
Use Nitrile gloves, which are similar to latex gloves used in hospitals, to protect your hands from harsh chemicals. Solvents can dry out your skin and may also pose a cancer risk.
In addition, you will want to protect your skin from sharp edges. Iron and aluminum castings have their share of sharp edges, as do stamped sheet-metal components. Grind ragged edges smooth to protect yourself from injury and to remove stress risers from castings that can crack.
High-frequency noise from power equipment can damage hearing, so make sure to use earplugs or muffs. Even the background din of shop equipment, electric motors, gear and belt drives, air compressors, and the like will damage hearing over time. Cleaning and drying parts with compressed air, which isn’t always recommended, is loud enough to damage hearing.
Eye protection is of utmost importance. If you’ve ever had metal or other foreign matter removed from your eye, you understand why. Use goggles or safety glasses to protect your eyes from flying debris. Ideally, use wraparound face protection that keeps debris well away from your eyes. And if foreign matter does get in your eyes, go to an emergency room or source of medical care immediately. The longer a piece of metal remains in your eye, the greater the risk of vision loss. Metal corrodes in your eye, causing further damage.
Always use face protection (a full face shield) in addition to eye protection when working around power equipment. A stray bolt launched by a bench grinder can do permanent damage to your eyes or face. Metal particles from a hand-held grinder can cause the same kind of damage. The combination of eye and face protection can prevent the risk of serious injury.
Remember too that how you hold a grinder, cutting wheel, or part determines how safe you are. Always make sure the grinder/cutting wheel rotation is away from you.
Whenever using harsh chemicals such as petroleum or alcohol-based cleaning solvents, protect your lungs with a good respirator. Dust masks are not sufficient protection. A good respirator with charcoal cartridges keeps all chemicals and particulates out of your lungs. The same rule applies to spray paint. Always use a respirator regardless of how well ventilated your shop or driveway is.
Now that you’ve got a nice clean place to work, you can get started on your AOD/AODE/4R70W build. The main consideration is order, with a place for everything. Pick up a package of cheap disposable containers for parts and label them accordingly.
Clutch friction discs and steels must mate with precision smoothness. Sliding valves must glide through the valve body smoothly. Servo pistons and seals must be clean. These parts will bind if dirty because tolerances are extremely tight to provide proper containment of hydraulic pressure. Seals can also be damaged by dirt and friction material, which causes internal hydraulic leaks, line pressure loss, and malfunction. When you’re not working on your transmission, keep it bagged inside a large plastic trash bag.
Tools, Supplies and Equipment
You will need a variety of tools, supplies, and equipment to work on your AOD transmission. Some of these items can be rented, especially if you intend to do this only once. You may need to buy others. In some cases, you already have a common household item that can be used.
Most professional transmission shops have transmission-holding fixtures to support transmission cases during disassembly and assembly. Not many of us can afford such a fixture or will even need it again. However, equipment like this can be found at auctions, eBay, Craigslist, and other sources. If you can’t find one, you’re going to need a hard work surface on which to build your AOD. Although you might think you need a holding fixture, it really isn’t necessary for the home garage technician.
Transmission disassembly and assembly get tricky when in the “stack” position, which is standing the transmission on end at the tailshaft end when it’s time to load components. Transmission shops generally use tailshaft housings as holding fixtures and have been doing so for decades. If that’s not possible, you can always bore a hole in your workbench for vertical assembly. Tool supply houses and home improvement stores offer inexpensive general-purpose holding fixtures designed for most transmission types that work well for disassembly and assembly.
Rebuilding any automatic transmission requires compressed air to clear debris and check servo/clutch pistons for proper function. It’s also necessary for the removal of parts such as clutch pistons and sliding valves. During assembly, compressed air is used to check component function. A huge industrial compressor is not required; a 10- to 30-gallon portable compressor that operates off 110/115/120 volts provides plenty of volume. Getting 220 for the more powerful compressors isn’t always easy.
Air tools make transmission building faster and easier. A 1/4- and 3/8-inch-drive air wrench and ratchet are sufficient for the job; a 1/2-inch-drive air ratchet would be overkill for automatic transmission repair. If you use an air grinder, take extra care not to damage cast-aluminum contact surfaces. Use air tools for disassembly, but never use them for assembly. Use a torque wrench on every fastener.
Because automatic transmissions have dozens of tiny parts, organization is very important. Use small disposable kitchen containers and mark them for identification purposes. Magnetic parts trays are also a good idea. Baking sheets work well for larger parts such as fasteners, and the sheets can be reused.
Old-fashioned metal coffee cans are great for cleaning parts. Petroleum-based solvents are a good choice because they minimize the risk of rust and corrosion and make excellent grease cutters. Once the heavy crud is gone, lacquer thinner and brake cleaner are best for final prep work because they have a high evaporation rate.
For items such as the main transmission case, tailshaft housing, and bellhousing, dishwashing detergent and a high-pressure washer work very well. A pressure washer can be rented for a modest fee. Use a pressure washer and compressed air to cleanse and clear passages.
Although hammers are common-place, a hard mallet is handy for items such as servo covers and pistons. A mallet provides passive-aggressive force without inflicting damage. Forcing any component into place is usually cause for concern. Although servo covers and pistons must have a snug fit, installation by force means something’s too tight or seals and parts have not been properly lubricated.
Transmission work calls for specialized tools depending upon the type of transmission you are building. You may need to modify snap-ring pliers to get at certain snap rings in your AOD/AODE/4R70W. Although clutch piston return spring compression tools are the best to use, you can use C-clamps instead, which are available at any hardware store.
As mentioned earlier, some tools must be purchased to do the job properly. Teflon seal installation tools are a must-have. Bushing removal requires the appropriate tool or tool modification to drive a bushing out. A slide caliper is necessary to measure steels and frictions. Simple tools can be modified or fabricated, such as long headless bolts to make front pump installation easier with less chance of seal damage. You can make a pick from a common screw-driver by heating and bending the tip; this can be accomplished with a variety of screwdrivers.
To rebuild an AOD-, AODE-, or 4R70W-series transmission, you must first remove it from the vehicle. Because you want a clean job with a minimum of fuss, drain all fluids from the transmission sump and torque converter. Allow the fluid to drain overnight with the pan removed if you can. Disconnect the cooler lines and allow them to drain. Always recycle old, dirty fluid responsibly.
Whenever you rebuild or replace an automatic transmission, you should replace all transmission cooler lines and, if possible, the cooler, to eliminate any chance of debris damaging the fresh transmission.
Transmission removal should begin with safe vehicle support: large-capacity jack stands in all four corners that can get the vehicle high enough for you to work freely underneath. Never trust your life to a hydraulic jack and never jack on an incline. A floor jack or low-profile transmission jack can be used for removal and installation. To ensure your safety, it is best never to under-take transmission removal and installation alone.
To save time, determine what you will need and make sure you have the appropriate tools before getting started. Few things are more frustrating than being underneath a vehicle only to have to make several trips to the toolbox.
Prepare for Removal
Step 1: Remove Items in the Way
Transmission removal normally begins with items that tend to get in the way, such as exhaust systems, wiring, and parking brake cables. H-pipe assemblies are normally easy to remove unless they have been welded together. This 1993 Mustang GT has a bolt-on Flowmaster cat-back H-pipe.
Step 2: Remove Crossmember
Once the transmission is properly supported, the crossmember is unbolted and removed. This is the time to replace the crossmember bushings and mount along with anything else time and mileage may have worn.
Step 3: Remove Driveshaft
On the driveshaft, make reference marks at the flange and yoke so you can reinstall them in the same position with the reference marks aligned. This is the time to have the driveshaft rebuilt and balanced with new universal joints and a slip yoke. The driveshaft should be checked by a professional for run-out and any stress issues.
Step 4: Disconnect Accessories (Professional Mechanic Tip)
Disconnect the shift linkages and TV cable. Note the TV cable adjustment and installation before disassembly. Do the same with the cable manual-shift linkage.
Step 5: Remove Exhaust Heat Shield
Next, remove the heat shield, which makes the transmission easier to remove. The heat shield is there to keep extreme catalytic converter heat away. Reuse this heat shield when it’s time for installation.
Step 6: Disconnect Battery and Remove Starter
Disconnect the battery’s negative cable, then remove the starter. This is a reduction-gear Denso starter, common from 1992-up. The smaller trigger lead fires the solenoid in this application. Before 1991, expect to see a Motorcraft light-duty starter.
Step 7: Remove Bellhousing and Dust Shield
Remove the torque converter/flexplate dust shield, which reveals the converter-to-flexplate studs and locknuts. There are four locknuts. It is a good idea to replace the locknuts with new ones. You can access all four nuts by rotating the engine manually.
Step 8: Disconnect Flexplate and Torque Converter
Remove the flexplate locknuts to free up the transmission and torque converter. During installation, use a good thread locker, along with new locknuts.
Step 9: Disconnect Cooler Lines
Disconnect the transmission cooler lines. Even if your transmission didn’t fail, the lines and cooler must be flushed or replaced. Debris such as clutch and band friction material and metal can become trapped in the lines and cooler and damage the new transmission.
Step 10: Unbolt Bellhousing and Lower Transmission
Most applications call for a 5/8-inch socket to remove the bellhousing bolts. Most bolts can be removed from underneath. You may have to use a box-end wrench to remove the top two bolts, depending upon firewall clearances.
Step 11: Inspect Flexplate
The flexplate should be inspected for cracks, proper installation, and ring gear damage. The starter drive should also be inspected. While you’re under there, look for rear main seal and pan gasket leakage on the engine. This is the time to correct any problems before reassembly.
Step 12: Prepare for Teardown
After you remove the AOD, it is ready for teardown. Teardown is an opportunity to learn why transmission failure, if any, occurred. It is also a chance to examine wear patterns that could cause problems in the future.
Step 13: Remove and Inspect Electrical Components
All fittings, switches, and sensors should be removed at this time. The transmission case should be stripped completely bare for cleaning. If you’re performing a transmission build at home, have all of the parts professionally cleaned or, at the least, pressure washed with a good solvent. This is something you can do at home, especially if you’re on a tight budget.
Written by George Reid and Posted with Permission of CarTechBooks