A904 Transmission Tear Down

Time to rebuild the transmission!IMG_0336

I removed the speedometer gear first.   Looks like it can go in one of four ways depending on the diameter of that little black gear.  Presumably this is so you can  compensate for different diameter wheels which would affect your speedometer reading.IMG_0338

Next, the extension housing came off.  I had to reach in  with a pair of clip ring pliers through a slot in the bottom of the extension housing to spread apart a clip ring.  This released the output shaft bearing and allowed the extension housing to be removed.IMG_0340

Time to remove the shift and kickdown levers.IMG_0341

The pan comes off.IMG_0343

I removed the filter and valve body as a unit.  The valve body is the brain of the transmission.  Fluid travels through lots   of little passages and is governed  by valves, springs and ball bearings.  As the engine speed increases, the fluid pressure increases, causing the valves to move and allowing the fluid to flow through different channels, eventually actuating the servos.  An actuated servo tightens a band that’s wrapped around a clutch assembly preventing the clutch from moving.  Tightening and releasing the bands in different combinations gives you your different gears (1st, 2nd, 3rd, reverse and neutral).IMG_0345

Removing the accumulator piston and spring.  The accumulator provides you with smooth shifts.IMG_0346

Removing the oil pump bolts.  I noticed two of them had washers while the rest didn’t.   They  marked the holes equipped with special threads fit for a slide hammer to aid in removal of the pump.IMG_0348

Out comes the front band adjustment screw and the cooler line fittings.IMG_0349

With tension removed from the front band, the  front band strut falls out.IMG_0351

A few whacks with the slide hammer and the oil pump pops out.IMG_0352

Next I proceeded to remove the two clutch assemblies and planetary gear assemblies.  They just slid right out one after the other.IMG_0353 IMG_0354

Well, except for the one snap ring.IMG_0365 IMG_0366 IMG_0367 IMG_0370 IMG_0371 IMG_0372 IMG_0373

The sprag and rear band.IMG_0374 IMG_0376

I slid the output shaft out.  That big gear is the park lock gear.  When you put the car in park,  a lever swings down and engages the teeth of that gear.   I always like to put my parking brake on first then put the car in park to save wear and tear on this gear.  That way you don’t have the entire weight of the car resting on  it.IMG_0379

I removed the governor support next.IMG_0380

Rear servo actuating lever and associated components.IMG_0381

Rear band comes out.IMG_0382 IMG_0383

Here’s another shot of the sprag.  It keeps the transmission from freewheeling in the event of a broken drive train component behind the transmission (u-joint, drive shaft, etc.).  It also only allows rotation in one direction.  Kinda cool how it works.  Each roller has a little spring pushing it into  the tight walls of a “V” shaped channel.  Rotation causes the springs to compress slightly and the rollers can move.  When I pulled that center ring out, all the springs and rollers went flying (I knew that would happen).  I collected them all and stashed them in a safe place for reassembly later.


Here are all the parts that came out.  It’s amazing to think that all of these were designed before there was any CAD, rapid prototyping, simulation software, 3D modeling, etc.  Just pure mathematics, brain power and perhaps a lot of trial and error.


Removing a wire clip from the housing.IMG_0391

Front servo actuating leverIMG_0392

Retaining clip removed.IMG_0394

Using an air compressor, I put some back pressure on the piston which caused it to pop out.IMG_0395

Front servo completely removedIMG_0396

Rear servo removal.  It helps to compress the servos slightly using a C-clamp or equivalent.  Then removing the retaining clip is much easier.IMG_0399

The output shaft bearing retaining clip comes out.  This is what I had to release by reaching through an opening in the extension housing with a pair of clip pliers early on in the disassembly.IMG_0400

Output shaft seal comes off.  I’ll be replacing all seals and gaskets with new ones.IMG_0401

Here’s the lever that engages the parking gear.IMG_0402

After removing the pivot pin, the lever comes right out.IMG_0405

An old shift linkage bushing.  It will get replaced with a new one.IMG_0406

Old shift lever seal comes off.IMG_0408

And there we have it.  A completely disassembled Torqueflite A904 transmission.  Time to clean up this mess, clean these parts and start putting it all back together with new parts!IMG_0409