The Build Process

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Your brand new transmission was once someone else's core before it was rebuilt.  All cores are torn down in our shop, with every part inspected for wear and damage.  It is during this process that the failure mode of the core, if any, is determined, and this is usually reported back to the originator for information.  At BSA, we have many pallets and bins full of 4r100 parts.  Any part that is found to be damaged or defective is scrapped and replaced.

We have multiple cleaning stations.  For the cases, extension housings, and other really dirty parts, we use our industrial cooker.  It is a large cabinet that rotates parts while spraying them with high pressure 170 degree soapy water.  For small control body parts, the control bodies themselves, and front pump covers, we use an ultrasonic cleaner.  Everything else is cleaned in a more typical basin cleaner.  After all parts are clean, they are inspected once again for any issues.

We feel that since the customer can't see how beautiful it is INSIDE the transmission, we better make the outside beautiful too.  But more importantly, the paint provides protection from corrosion.  Aluminum corrodes much differently than steels - it dissolves when in a saltwater environment.  We have experimented with different paints, and have found a brand that works really well, and offers great protection.  While we don't take color requests, you can expect something in an earthtone shade, and we do switch it up now and then.  All parts are painted separately before assembly.  After the case is dry, we prep the case for build by cleaning up any gasketed surfaces and chasing all threads.

A variety of cutting and grinding machines do all the work - machines that can cut anything from a small valve piece in repetition to a large torque converter.  We use custom jigs wherever possible to facilitate the machine work of multiple parts one after another, so we usually wait until we have about 12 or more of each OEM part before we rough machine them in bulk.  Finish machining is done during assembly in order to meet our own clearance specifications for the clutch packs, which can be case or drum dependent.  This increases build time, but is worth it. 

 Pump and control bodies are ultrasonically cleaned, deburred, machined, rebuilt, and vacuum tested to ensure proper valve-to-bore clearance.  If a bore fails the vacuum test, it is repaired.  If it can't be repaired, body is scrapped.  We spend a LOT of time on the control bodies to ensure a consistent shift quality and maximum life without jamming or oil starving.

All solenoid packs are tested and inspected a few different ways before they make their way into a rebuilt transmission.  Click the button for a video I made regarding how I test them.  I only use good Motorcraft solenoid packs.  Any aftermarket packs I come across go right into the trash.

This is the rewarding part!  During assembly, we use Vaseline, TransLube and Synthetic ATF (MerconV compatible).  All frictions, bearings and seals are soaked in the ATF.  Translube is used sparingly on all seals, valves, and pistons.  Vaseline is used only in one place, and that's on the pump rotors.  Translube has a tack to it, so it is good for holding things in place.  To ease installation for our customers, we use vaseline on the pump rotors because we feel it makes it easier (less stressful) to fully install the torque converter by letting the rotors spin more freely and engaging the TC hub quicker.  The TC can be tricky...it is heavy and awkward, so we try to help anyway we can.

With the machines we have, we make all of our own special tools.  This includes bushing removers and installers, pullers, slide hammers, spring compressors, alignment pins, assembly fixtures and more. We employ all of them throughout disassembly and assembly.  This picture is less than half of the special tools we use for each transmission build.  All clutch pack clearances are maintained within a specific range for each pack to ensure longevity of the friction material, reduced slippage, as well as quicker engagement.

Before the controls are installed, all clutch packs are air tested to check piston motion, return to rest, and seal integrity.

Once assembled, the transmission is pressure tested to check for leakages in the control cavity.