Part 2 Rebuilding the Transmission Main Case: Installing the Rear Reverse/Low Servo Piston

Now the first thing I'm going to actually do in the main case is to install the reverse/low servo piston. It's the servo at the rear of the case. I decided to upgrade this piston. The OEM piston is quite thin, and, apparently, can have a tendency to twist in its bore. The new piston is thicker with more contact surface in the case bore. The OEM piston is on the left. The upgraded piston is on the right. The components in the middle are OEM parts that are re-used.



You can see that the new piston is quite a lot thicker. I first thought it had a double seal. But the instructions indicate that the metal ring is for support only.



Here's the seal installed. The lip of the seal points down into the bore in the case.



To install the center piece and spring I put the new piston in the vise. This isn't as scary as it looks. The jaws of the vise aren't clamping on any surface that is going to contact another surface. Then I install the OEM snap ring to hold the 3 pieces together.



Here's the assembly so the spring is visible.



Apply some assembly lube to the seal surfaces.



Lube the servo bore with some fresh ATF.



Drop the piston into the bore with the spring up and the seal lip pointing down.



I used a .010" feeler gauge to help work the lip of the seal down into the bore correctly. Easy does it here.



Slide the larger servo spring into the bore and on top of the piston. Place the servo spring retainer on.



Now compress the spring and install the associated snap ring. The spring is light enough that I was able to compress it by hand - no c-clamp required.



Next: Installing the rear drum, reverse/low band linkage.

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.

Part 7 Rebuilding the O/D Section: Measuring for the Intermediate Shaft End Play Spacer and O/D Piston Thrust Plate

Now that I've got the overdrive unit assembled, I'm ready to take the final measurements in order to determine what size sims I'm suppose to use.

I ended up buying two more tools for this. I could have "faked it" with one of the measurements, but I didn't have the right tools (specifically a lathe) to make the tool for the second measurement. So I popped for a 2-tool set from TransmissionPartsUSA.com. It was JT-1301 and included a "transmission overdrive shim & intermediate shaft spacer tool". You'll also need a dial caliper for this measurement. Here they are.



You could easily make these tools if you have access to a machine shop. I don't, I'm grumpy about that fact. But I guess I'll make do.

The shaft-looking tool (on the right) is for determining what size o the intermediate shaft end play spacer you need to use. It's the same diameter as the intermediate shaft and exactly 5.50" long. That's the important part.

The bar-looking tool is for determining what size overdrive piston thrust plate to use. You use this tool for the first measurement as well. You can fake this tool by using a rigid bar of an exact thickness. This bar is exactly .500" thick. The .500" thickness corresponds with the tables in the repair manual. So it's a little easier to use. Length isn't important as long as it spans across the overdrive housing surface.

I start by taking the shaft tool and inserting into the bore in the overdrive gear train.



Make sure it's seated all the way against the shoulder. It has a positive "stop" when it's seated. It sits right atop the splines at the planetary gear.



Now lay the bar across the mating surface of the overdrive housing.



Insert the end of your caliper into the slot in the bar and let it make contact with the end of the shaft tool.



There's a certain technique to this. I extended the caliper past what the measurement would be. Let the caliper end contact the shaft and then settle the caliper shoulders onto the bar. I made sure it was square, and then rocked the end of the caliper back a forth a little across the top of the shaft. This way, the measurement won't be greater than it's supposed to be. And it's near impossible to get a reading too small as well.



My reading came out as .746". According to my FSM (factory service manual) that means I need a spacer for the intermediate shaft that's .158" thick. There's a little chart in the manual for determining what size spacer to use.

End Play Measurement | Spacer Thickness | Transtar Part#
--------------------------------------------------------
.7336 - .7505        |    .158 - .159   |   12708A      
.7506 - .7675        |    .175 - .176   |   12708B      
.7676 - .7855        |    .193 - .194   |   12708C      
.7856 - .8011        |    .211 - .212   |   12708D       

BTW, I searched and searched to try and figure out what the "intermediate shaft end play spacer" was. None of the manuals showed it in the exploded diagrams. I only found it by searching through a parts catalog on the Transtar website. Transtar supplies almost all the rebuild parts to shops around the country. They don't sell retail! I didn't check with my online supplier, PATC, since I wanted the parts ASAP. I've had to develop a relationship with a local transmission builder, AAMCO of Brighton. They are willing to get the parts for me. I'm grateful for that.

This is where the intermediate shaft spacer sits. It's just to the left of the splines on the rear of the intermediate shaft in this photo. I totally missed it during the tear-down! Never saw it.



Now I'm ready to take the measurement for the overdrive piston thrust plate. This plate nests in the overdrive piston (we haven't talked about that yet) and pushes against the thrust bearing that sits atop the overdrive direct clutch hub.

Use the same bar used in the previous measurement. Now measure to the clutch hub thrust bearing seat (WITHOUT the bearing installed) in 4 different places 90* apart.



Average those measurements. (Add the four measurement up and divide by 4.) Then select the correct spacer from the chart.

My measurements where:

 1.804"
 1.806"
 1.811"
+1.811"
-------
=7.323"
    ÷4 
 ------- 
=1.808"

From this measurement I determined that I need a spacer that's .153" thick.

Here's the chart:

End Play Measurement | Spacer Thickness | Transtar Part#
--------------------------------------------------------
1.7500 - 1.7649      |    .108 - .110   |               
1.7560 - 1.7799      |    .123 - .125   |               
1.7800 - 1.7949      |    .138 - .140   |   12706A      
1.7950 - 1.8099      |    .153 - .155   |   12706B      
1.8100 - 1.8249      |    .168 - .170   |   12706C      
1.8250 - 1.8399      |    .183 - .185   |   12706D      
1.8400 - 1.8549      |    .198 - .200   |   12706E      
1.8550 - 1.8699      |    .213 - .215   |   12706F      
1.8700 - 1.8849      |    .228 - .230   |   12706G      
1.8850 - 1.8999      |    .243 - .245   |   12706H       

Next: I get to move on to the main case! I'll start with the overdrive piston retainer.

Part 6 Rebuilding the O/D Section: Installing the Overdrive Clutch

I met with some difficulty with this step. It all turned out fine in the end, but, MAN, was I ever pullin' my hair out!

As always, soak the friction components in some fresh ATF. At least 30 minutes is recommended.



First off, I decided to upgrade this clutch pack. Everyone seems a little shy about pulling loads in O/D. So I figured it would be a good idea to have as much ooomph here as possible.

The original clutch pack had 5 steel pieces, 5 friction pieces, and 1 reaction plate. The frictions were really in pretty good shape. The steels show a little wear.



The new clutch "power pack" has 6 steels, 6 frictions, 1 thinner reaction plate, and 1 thinner snap ring. This will give me a 20% increase in surface area over the OEM setup.



The old reaction plate measured right around .215" thick (give or take).



The new reaction plate is .185" thick.



The old snap ring was about .078" thick (again, give or take).



The new snap ring is .060" thick.



Now this is where my headaches started. I started stacking up the components of the clutch and it was obvious, rather quickly, that it was just too thick! Here, the groove the retaining ring is supposed to fit in is covered by the last steel. There's no way to get it in. Even if I could force it in the pack would be waaay too tight and burn up in a hurry.



Head scratching. Lots of head scratching. Maybe some cursing.

So after some consulting with the boys over at the Diesel Truck Resource forum (which has invaluable advice on most subjects), and a call to PATC (where I purchased the parts), I discovered that I was NOT supposed to put in the wave snap ring at the bottom of the stack as the OEM configuration had. THAT would have been nice to know from the beginning. Maybe somebody (PATC) should include some instructions on what to do with their upgrade power packs.

I did some more reading over at the Diesel Truck Resource forum. Most noteably, there's a thread that user BC847 wrote up about his transmission rebuild. I'm doing most of the upgrades he did, and he said he had .050" milled off his reaction plate for teh overdrive clutch. I thought about this for minute and headed out to the garage with my micrometer.

This is what I found. The new clutch pack DID fit without the wave snap ring. But there was only about .010" clearance between the top steel and the retainer ring. That didn't seem like enough to me for lube clearance when the clutch is disengaged. So, voila, add .050" to this figure and you get .060" clearance, or about .010" clearance per clutch.

I had a local machine shop take .050" off the bottom of the reaction plate. Just enough for the snap ring to fit in.

(BTW, I used an simply CAD application from eMachineShop.com to draw up a model of what I wanted done. It worked fairly well...enough for the machinist to know what I was talking about. It generates a nice 3D image as well. Give it try.)



OK. NOW I'm ready to assembly the dern thing!

Place the new flat snap ring in the groove at the bottom.



Make sure it's fully seated in its groove.



Now, normally you would install the wave ring on top of the snap ring. But in my installation I'm NOT doing that because of the upgraded clutch pack.



Flip the reaction plate over, so the machined shoulder fits next to the snap ring, and place it on top of the ring.





Now, start installing the frictions and steel. Start with a friction.







Now install a steel over the friction.





Alternate friction, steel, friction, steel until you have all 12 componants installed. (This photo has the wave ring at the bottom. I didn't install it in the final assembly.)



Install the associated retaining ring in its groove. It's a wire type.





Here's the .060" clearance between the top steel and the retaining ring.



And the whole clutch pack in its final assemblage.



Next: taking the final measurements for the intermediate shaft shim and the overdrive piston thrust plate.