Part 1 Rebuilding the Transmission Main Case: Installing the Overdrive Clutch Piston Retainer

Now that the overdrive unit is done, I can move on to the main case. Finally! (I've been at this rebuild for a month now. Time to get it back in the truck!)

I start with the overdrive piston retainer. While conceptually part of the overdrive unit, the overdrive piston and retainer reside on the back of the main transmission case.

I decided to upgrade the overdrive piston retainer is well. The upgraded unit has an o-ring on the outside bore that allows more lube to flow to the intermediate shaft bearing surfaces which in turn allows more lube to the overdrive gear train. It also claims to be made of a better, more durable material. The OEM unit is on the left. The upgraded unit is on the right.



The lower groove is what the o-ring goes in. The OEM unit doesn't have this.



A recommended, but not necessary, modification to the case is to drill a small hole to allow better lube flow to the overrunning clutch at the rear of the case. The clutch would normally get lube from the overflow coming from the clearance between the intermediate shaft and the piston retainer. Since the o-ring has been added, that bleed-over will be stopped. So Sonnax, the manufacturer, recommends drilling a .040" hole from one ATF gallery to the inside of the case.

Here's the case in the drill press. The bit is so small, I figured I'd break it if I tried to drill it by hand. It's an .040" or #60 drill bit.



Here, the drill bit is posed above the gallery (the dark one).



Here you can see the hole at about the 9 o'clock position. Well, 8:30 really.



A closer view.



And from the inside.



Now I'm ready to put the main case on my bench and start "doing stuff" to it. First, here's a shot of my way-cool "overhaul mount." I just bolted a piece of angle across the top front of the bell housing. This way, I can flip the case over and fix it solidly to my bench with a couple of clamps. I happened to use vise-grips.



Then I just put a piece of scrap 2x6 under the rear of the housing and I have a nice stable unit that's just the right height for working easily without too much back and neck fatigue.



Now to the real work at hand: installing the overdrive piston retainer. I begin by sliding the new gasket over the sleeve of the new piston. Then install the o-ring on the upgraded retainer. I little assembly lube under and over the o-ring is good.



Then some assembly lube on the rear bore of the main case where the piston retainer slides in and the o-ring interfaces with.



Now gently slide the overdrive piston retainer into the rear of the main case.



Make sure the boss for the governor tubes from the overdrive unit line up correctly and that the gasket is still aligned.



Make sure the piston retainer is seated fully against the main transmission case.



Put in the 6 bolts that hold the retainer to the case.



Torque those up to 13 ft-lbs.



Now install the overrunning clutch on the inside of the case. Here's the new clutch.



Smear a little assembly lube on the clutch cam inside the case.



Carefully slide the new clutch into its position inside the cam (the rollers and springs can sproing ANYWHERE). It only goes in one way.



Seat it fully against the back of the case.



Next: Installing the upgraded rear band servo.