TH400 Swap

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A couple of months ago I posted a question about finding a shop who could rebuild a TH400 walked in the door already out of the truck. The reason? My torque converter was failing, and I had two grimey TH400's sitting on the shelf that were questionable, so I wanted a shop that could possibly make one good transmission out of two if necessary, but at least rebuild a transmission with a quality shift kit and throw in a new torque converter (since neither of them had one and my existing one was hurtin').

The answer was Lakewood transmissions near Tacoma, WA. Enumclaw Autoworks is a small store in the home town I grew up in that got started sometime around 2001, and the guy who runs the shop knows a lot of people. I've been buying stuff through his shop for a few years now because he's local to my dad's place where I do most of the work on my truck.

He simply told me to drop the transmissions off at his store, and the Lakewood shop would come up there, pick them up, rebuild them, and return the rebuild plus whatever parts were left in less than 3 days. Perfect.

I made the arragements last week (the first week I've had off from work in 6 months) and dropped both of the transmissions off on Monday afternoon. Wednesday the guy at the store called me to tell me they were already back. Turns out the one they decided to rebuild was in good enough shape to not require opening the case on the 2nd one, so they left it alone. I put them in the back of the truck, and I drove to my dad's farm to get to work swapping the one out of my truck with the newly rebuilt one. It took me Wednesday night, all day thursday, and all day friday to get the swap done. Total it cost me:

$100.00 - Transmission Core (I bought from Wes about 4 years ago)
$856.00 - Transmission rebuild (including new torque converter)
$75.00 - Shift kit
$126.00 - 16 quarts Royal Purple synthetic ATF
~$100 - Tax
+$40.00 - Misc. parts and supplies
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about $1300

Here's some pics showing the rebuilt one next to the one that didn't get used in the rebuild. The rebuilt one used to look just as bad.

[COBALT]

The transmission I had in my truck had been leaking for a long time. Two years ago I pulled it out, resealed the front and rear seals, put on an aftermarket deep aluminum pan with drain plug, a poly mount, and cleaned it up before putting it in. However I made some mistakes with the pan, and it never would stop leaking. I didn't use any sealer with a cork gasket (bad call), and didn't use any thread locker on the bolts (another bad call). Fluid was everywhere, and the tail housing had not held up well with the modified mount setup I had put in two years ago.

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Another mistake I made was forgetting to lube the hub on the torque converter before I put the transmission back in the truck 2 years ago, but the flex plate was still in good shape. Overall I was lucky. I kept an eye on this transmission while it steadily leaked fluid and created a huge mess on the underside of the cab. I wasn't going to repeat the same mistakes this time.

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Two critical things I did differently this time were:

1. Thinking WAY ahead on how I was going to support the vehicle. Last time I tried farting around with my 4 ton jack stands and blocks of wood. The truck was unstable and scary to be under. I also had a terrible transmission jack that set too high, so my bell housing didn't clear the frame rail. I had to tip the transmission forward and roll it out on two wheels - mashing the hell out of my hand. I got a brilliant idea from the guy at the Autoworks shop to build some 6" tall 12" x 14" stands out of 2" x 4"'s. I made 8 of them; 2 under each wheel instead of the jack stands. I also spent the extra time to find a transmission jack I could rent that had a low profile, and was easy to move around. This setup worked a hell of a lot better.

2. I checked the aftermarket aluminum pan for leaks THROUGH the casting before re-installing it on the new transmission. Since it's cast aluminum it was sand casted, which means inclusions and flaws may exist in the casting that are invisible, and may allow a leak to develop anywhere. I took the pan, cleaned it really well, and poured some gasoline in it to sit over night on some clean towels. The next morning I came in to find a quarter size wet spot right at the base of the "U" in the "SUMMIT" letters under the pan. FOUND MY LEAK! I used some JB Weld smeared with a putty knife over the entire area, and set it under a heat lamp all night to cure.

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I poured 1 quart into the new torque converter, and lubed the front seal before sliding it onto the input shaft, and rotating it a bit until it seated completely. The torque converter needed to be deep enough so the mounting nuts were at least 1" from the edge of the bell housing, and I couldn't fit my fingers behind it to reach the front pump.

I installed the transmission in the truck using one of the old pans instead of the new one first. I bolted everything up so I could get the transmission jack and the jack holding the engine up out of the way. That included the driveline. I lubed up the rear seal and the slip yoke before installing it.

Once the JB weld cured I took some silicone RTV that works with aluminum, and used one of those thick paper gaskets this time instead of cork. I spread the sealer VERY thin on one side of the gasket, set it on the pan, pressed it into place, and then spread sealer on the other side - thin again. Then I used the same bolts as last time (stainless alan head screws) only I used red thread locker on the threads before installing them.

I had to replace the filter neck and screw with the filter neck and screw from the deep pan kit. It allows the filter to sit lower in the pan than stock.

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I let the pan with the sealer in place and the thread locker set up for about 6 hours before I started filling the transmission. Meanwhile I reconnected everything including the driveshaft.

I had taken all of the accessories loose from the front of the motor, and removed the spark plugs so I could rotate the engine over using simply my hand on the flex plate. It made turning the plate so I could access the torque converter bolts WAY easier, but I had to reconnect all of that. I had plenty of time while I waited for the sealer and thread locker to set up.

I also cleaned out the cooling lines and the cooler in the radiator. I used a small home made funnel, and some denaturalized alcohol, and ran it through until the red dissapeared. Then I blasted the lines and the cooler with the air hose.

Finally I was ready to fill the transmission and fire it up for filling and my first road test.

This is how I filled it on initial start-up:

1. 1 quart went into the torqe converter before I put it on the transmission and wheeled the transmission under the truck to install.
2. I poured 8 quarts down the dipstick tube into the pan and kept an eye on the dipstick to make sure I didn't max out the pan.
3. I started the truck to let the pump pull the pre-added fluid into the valve body and torque converter.
4. I then started adding more fluid shifting through the gears after every quart until the level on the dipstick was just under "ADD".
5. I did a quick drive test for a couple of miles and then came back and checked the level again. I had to add about 1/2 quart and it was full.

Total with deep pan: 15 quarts

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I only had one real problem. I failed my first road test.

My first road test showed me the value of a shift kit. Those crisp shifts plus the boost in power that my old torque converter didn't deliver made a world of difference. It was pouring down rain, and I had to drive the truck out of the shop and down the gravel driveway down to the road before I could adequately test anything. I was really excited because everything was working so well...until I got back and saw I had left a rainbow in the puddle in the driveway on the way OUT earlier.

Checking under the truck in the garage let me see what the problem was. My rear seal was simply letting fluid run out past the slip yoke and down on the ground. I had the wrong rear seal, and worse I had the wrong tail housing! Aparently there were at least two short tail housings on these trucks. They're almost identical. In fact they're only about 3/16" difference in diameter. There was less than 1/16" of play between the yoke and the seal. Just enough to let fluid run right out. My choices were to try and find a seal that would fit the housing AND the yoke (not going to happen), a new yoke (which means a new driveline. Nope.), or swapping tail housings. I voted to do the latter.

In short I had to take the pretty brand new cleaned-up tail housing off of the newly rebuilt transmission and re-use my old one off of the one I had just taken out of the truck the day before. I cleaned it up, and swapped gaskets. I also had to go buy a new rear seal. That took another 4 hours of work, but by the time that was done the leaks were gone.

I haven't had a single drop of fluid yet, and that rebuilt transmission is amazing. It's a little startling sometime putting it in reverse. I think the reverse band pin is a bit too short. It likes to bang into gear a bit.

My final problem is the speedo gear is too short. I need a taller one. My speedometer is showing me going 75-80 down the freeway when I know I'm only going 65-70, so that's the last thing to do...