Direct and Forward clutch

Again, as with many aspects of the TH400, current internet wisdom can vary greatly when it comes to clutch setup. One of the beauties of this design is that all 3 of the clutches can be easily setup just as you'd like, to suit any possible end use. For general street performance use, I've read it's not really necessary to add another friction to the direct drum, but at a minimum you should have at least 5 frictions. I think passenger cars pretty much came with 5 frictions in the Direct and Forward drums, and 3 in the Intermediate. If adding an extra friction, machining of the pistons might be required, and you'll probably need a thinner retainer plate. Extra frictions also mean thinner Steels, which are generally said to be susceptible to burning up much easier. Thicker seems the way to go with steels, unless this was to be a track only transmission. As far as clearance wisdom goes, as very general rule, .010 per friction will work. That being said, .050 should be the number. With a wave plate I think it's safe to assume the number can be reduced a little, due to the built in .020 of cushion.

So in the Direct clutch I went with one factory Wavy or cushion steel. 060 thick, .079 tall on top of the wave. So really... a built in .019 of cushion in the plate. It was in very good unburnt shape, so I just did the circular medium/fine Scotchbrite, then a fine steel wool to finish it. So it's evenly smooth, but not completely polished. Some surface roughness won't hurt, just not too much. I could have bead blasted all my steels, but I didn't want to contaminate the area with dust.

The Direct pack, from the left; .060/079 Wavy, 5 Red Alto .080 Frictions, 5 .080 Kolene Steels and the stock end retainer plate. Pretty much as the factory would have sized things for 5 frictions.

As far as any preparation before final install of the frictions and Kolene steels go, soak the frictions in trans fluid for 20 minutes and vigorously wipe the Kolene's off with a rag with some trans fluid on it. You'll find a LOT of brown oxide will come off them, and when clean, they'll feel much smoother than as found. Again, there's a ton of opinions on Kolene's out there. Some guys hate them, they are what I had with my kit, so I just did what seems logical with them. 

Clearance,

First you'll need to determine how much play you'll get with the endplate. Installed into the drum with the retainer ring, it will have some endplay between the plate land and the retainer ring. Set the drum in a vice with a Dial indicator in place. Ensure the retainer ring is clean and fully seated. Push down on the plate, zero the indicator and pull up on the plate evenly on two sides. Keep doing this until you get a repeatable number. This is your first part of the clearance measurement. Record the number. I got .014 here.

Forward Drum shown in image, but measurement method will be the same for the Direct endplate play,

Basically, now set your stack into the drum less the end plate, all dry, then try different feeler gauges to determine clearance to the end plate land. Butt the shim up to the land, push the frictions all towards that land, apply light pressure downward to the friction all around (2 fingers will do it) and one on the shim, then lightly scribe back and forth across the land to the shim. You'll know when the two are even. When they match, you've got your second measurement needed for the pack clearance. Record it. I got a repeatable .026 here.

So .026, plus the retainer plate .014 and I have .040 Direct clutch clearance.

So at this point I installed the Direct drum into the trans. I did it with no plates installed, as it's far easier to manipulate and fuss the Direct sprag gear into the Intermediate clutch stack. With the clutch pack installed, the drum weighs considerably more, and you really can't get a handhold on it. You'll know the drum is fully into the Intermediate stack when you get a solid "thunk". The Direct drum splines rest or stop on a small land at the bottom of the Sunshaft splines. Make sure it is fully home and not hung on a Intermediate steel. Also, make sure your new Center support ring seals are lubed and oriented correctly. Go easy when setting the Direct in place. You don't want to damage these little seals, they seem pretty delicate. One bonus is the Direct drum has a very wide taper where it meets the Center support oil tower, so there is no real danger of hooking them.

Direct fits into the intermediate (right). Forward band must be installed before the Direct. It can't be done after,

Build the Direct in place with your selected stack. It's easier this way,

Edit; another popular mod to the Direct drum that I decided to forego, is the drilling of a tiny drain hole in the drum. My drum has a drain and checkball,  and I will not be spinning the engine to extreme RPM's. It's said that at 6000 RPM for a sustained period, the direct drum will spin so fast that any leftover fluid will drive out to the ends of the drum and begin to compress the apply piston, causing drag and clutch burnout. I don't plan on exceeding 5600 but for a brief period, if ever. I'm also installing the HD Direct springs included in the TransGo kit. They should help to reduce this effect.

Another popular mod I'm not bothering with is the removal of the lip seal on the direct drum itself, and one of the 4 Teflon seals in the Center support. This is the popular "Dual Feed" mod to allow more piston apply force to the Direct clutch. My shift kit comes with a valve body spacer plate to allow this to be done internally, and I don't have to tap and plug a case feed/return hole to make it happen. It's said the TransGo 400 Pro kit does a pretty good job of this, and will be fine in all but a competition build.

Forward Clearance,

Forward drum fully seated, bushings in place, getting .004-5 with the kit included .115 Nylon select washer behind the pump.

Handy this one. A small Phillips fits right into the Input shaft oil hole. Prying it up lightly against the pump stator gives a dial result. Use the regulator half of the pump with gasket in place to set initial clearance. Using this half only gives a good flat to Mag onto, and will have no effect on the overall clearance. Use one bolt to lightly secure the pump half to the case.

Too tight at .004 with a .115 shim. Target .007-.019. Need a washer about .005 smaller. My next one down is a .095 to replace the thick one...which will be too loose...Hmm...

Spoke with my trans guy today. He says .004-5 input shaft clearance will be fine in a new build provided you have sufficient rear clearance, says you'll gain a few thou on break in. So I'm fine with the .115 nylon washer at the pump, and the two .060 bronze washers at the forward hub. I've also just noticed the factory 1967 manual indicates the clearance can be as tight as .003", whereas ATSG book says .007.

After torqueing the pump down (which I hadn't done initially)...all the clearance was lost. I then ended up getting an appropriate .010 shim from my tranny shop, and put it between the pump and a .095 selective washer. Perfect!

Here's a .115 select washer in position between the pump and forward drum,

So while I figure the shim, I decided to tap the forward pump half Converter feed hole 5/16-18 to accept a plug, which I'll drill out to .040. This is to reduce excessive forward Hyd pressure on the converter. All TH400's will drive the converter out a little, sometimes with enough continuous force to max out the flexplate, bottoming the converter into the crank, and thus driving the crank into the main thrust bearing, wiping it out. This is what would be known as the "Crank killer TH400". Bad. This 400 will keep it's stock regulator spring, shim and pressure, regardless, this is seen as a common mod on any performance 400 build today. And another reminder to make sure your converter pilot will always register freely into the crank.

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Drilled the plug out to .152. Larger than originally planned but should be good with the stock pressures. Used a setscrew. Big mistake, it's hardened and was a bugger to drill.

Straightedge across the pump gears shows a tight clearance, calls for .001-.0025 here. My 002 feeler won't fit, so it's very close to .001. Gears and running surfaces are in top shape, so I think it's good to go.

So pressed in a new bushing and a new front pump seal, cleaned and lined up the two pump halves, bolted them together, installed the new D ring, inserted and lubed the two Teflon sealing rings.

Then assembled the shift shaft, rooster comb and parking mechanism. If you don't do this now, you'll not get the shaft pin in with the pump in place, it slides in from the front and is blocked in by the pump. Funny how the pin looks just like a nail...and it probably is. Clever GM. You can see the pump regulator retainer just below the head of the nail. It can be gotten to with the pan off if a spring change is desired.

Fitted the pump, torqued her down and rechecked endplay. I get .010. I'd call the internals done! So satisfying!

I think that for many non mechanics, the transmission will always be seen as a dark art,  but really, with some research, decent skill and patience I think anyone could do this. Funny how actually being hands on can change things. It inspires you to seek something more challenging. My cousin and I now want to invest in a used up 4L80e just to open it up  "to see". If I can find the right one, I'll go for it.

The best part of all this, is when I get it all on the road, I can say I basically built the entire driveline myself. I don't think it can get any better than that.  Cheers!

Valve body, shift kit and the final items,

So I went through almost 3 cans of Walter brand "SlapShot" chlorinated solvent to clean the valve body. I never took it apart but for the 1-2 valve, the second accumulator valve and the valve body accumulator. I think I was able to get it pretty clean, which is pretty important. I don't think I would ever disassemble the entire unit.

As per the TransGo Pro 400 kit, I added the 1-2 command shift spool, the heavy valve body accumulator spring and the recommended springs on the 2nd accumulator valve. A new accumulator piston comes with the shift kit, but it must be matching to the forward band apply piston. The two types cannot be mixed...as I found out after assembling the new piston into the body! I think they supply a new piston to replace the later plastic crap. Also added the heavy spring in the big rear servo.

I then drilled the shift kit separator plate as recommended, Spot A, B, conservatively at .093, and left spot C as is. The kit does not come with a .093 drill bit.

Edit; After doing more research, I went back, opened it up and drilled position A/B to .116".

Then set in the 5 checkballs as recommended, a gasket, plate, gasket, then eased the valve body with governor feed tubes into place. Used to home made pins to help align it all. Don't forget to align the selector pin into the direct valve. Go easy, you don't want to distort the tubes. Then bolted and torqued it down. Don't forget the selector detent roller! I did, and had to pull the pan again. Doh!

The forward band apply piston, that must be used with the smooth accumulator piston.

The crowned replacement accumulator piston (below, bottom in photo) cannot be used with a crowned apply piston. One of the two must be smooth.

5 checkballs in place per shift kit instruction,

Two gaskets and drilled separator plate in place showing alignment pins.

Valve body in place along with the kickdown bleed solenoid and electrical pass through fitting,...and (edit July) the parking rod lever bracket (seen below the solenoid) ASSEMBED BACKWARDS! Can't get park. Easy fix, but pan must come off.

Installed the taller fluid pickup tube, filter spacer and filter. To get a good seal at the tube grommet, the filter must sit at an angle. Is this normal? I've heard that the filter needs to float, is this true? Makes more sense to have it mounted solid. Of all the things, I find this setup cheesy. Filter is a high flow brass screened unit.

Inserted the governor (yellow gear) and speedometer drive with new O ring,

Pink spring on the modulator spool as per the shift kit instruction, and inserted the adjustable modulator with new O ring that came with the rebuild kit,

Edit; I removed the pink spring, as according to web wisdom, it will just speed up the shift points way to early. Everyone doing the pro 400 leaves it out.

Installed the pan, removed the pan...installed the pan again (for the missing detent roller). Attached the tail extension, capped the governor and added the dipstick tube, added the line fittings with new copper washers...she's pretty much done and finally free of the bracket!

Hey CP,

Thought as an epilogue to this post I would make comment on the actual performance of my diy transmission,

Well, since this was my first "black art" transmission build, you're never really sure it will work well, even at all when you have it up on stands, fill it and put it into gear for that first time. Well, I was pleasantly surprised that it did indeed work, the wheels turned, and as the whole package has begun to break in, I must say it works perfectly, just as I had envisioned it to! And no leaks so far. Early on I head a whining sound, but that just turned out to be the flexplate cover contacting the ring gear. Thank goodness!

One major consideration; If you look back at the post, you'll see I included a factory wave plate in each of the 3 clutch packs. I did this to take out some of the extreme harshness that can be felt with a shift kit. The transmission shifts just right, progressively firm, but no slam in any gear. The more you give it, the firmer it becomes. A little chirp under WOT into second. Normal easy cruising it upshifts nice and easy but no slip or hunting. Putting it into reverse brings none of that usual clank that I'd feel with my old TH400 (most will do this).

I went middle of the road with springs and drilling when adding the shift kit. I think a lot of guys will go right to the upper end of the kit. I say keep it moderate to start, you can always go in later for more firmness.

You read talk on the web about guys not liking the red alto frictions and Kolene steels. I can say no wrong about them. They shift and feel absolutely perfect, no slip under heavy power whatsoever. But I did carefully clean prepare the Kolene steels before hand.

One thing I did do wrong was install the parking rod/pawl bracket backwards. So no park. Rookie mistake corrected with removing the pan and switching it. I'm just glad the big pan has a drain plug.

On a side note, I feel I chose just about the right stall for a converter for this combo. Its a Coan street series said to stall at 2900. I chose this because I didn't want a constant heavy slip that would build excess heat. 2900 is a high enough slip compromise that the engine doesn't load up too bad at idle when in gear. Anything lower much and the engine would drop down too much in idle in gear. Givin' her from a standstill seem to really put the engine right in the meat of the powerband, and the thing really seems to hook. I could have had a converter built, but I simply chose an off the shelf Coan because of the reputation of that company. Got it through Jegs.

One more consideration is go with a good aux transmission cooler, preferably a stacked plate design, properly placed as close as practical, centered in front of your rad. Feed out to the rad cooler, then into the aux trans cooler back to the trans. Make sure the lines have the least amount of restriction possible. One thing I did find out was that I had my stacked plate cooler upside down. I was feeding and exiting from the bottom of it. Found out it must be fed from the top, or if mounted sideways, feed into the bottom fitting. Top feed will cause a air lock, and will reduce it's cooling capacity. I have since flipped it over.

So bottom line is, with patience, I feel anyone with reasonable skills and a willingness to learn, can do this themselves. Read everything you can, take lots of pictures during disassembly, work clean, be prepared to build and break down the components many, many times to get it just right, pay close attention to clearances. Enjoy it and be proud when it actually functions like you hoped it would. I truly don't think any shop would have taken the level of care I gave it. That's the beauty of a labor of love with no time limits.

Cheers and happy shifting,

Mark

I am sure glad you are building all these special tools so I can pick your brain when I do the rebuild on my Turbo 400 this spring. I would even be prepared to burn my gas to take my trans from Kitchener down to your place. Nice of me eh !!

Bill.