Rebuild Your TH700R4 at Home

Lacking anything that even...        read full caption Lacking anything that even resembled a “proper” transmission shop, we bought three big plastic tubs from Home Depot for $20 and began our transmission teardown on top of a set of tires in our backyard. There was still a ton of fluid in our core transmission that would have ruined our workbench (er coffee table) so we did the messy stuff outside and used one tub to hold the entire transmission and two more to lay the internal parts in.

Knowledge is power. Consider...        read full caption Knowledge is power. Consider these three things—the Technical Video for TH700R4s, the Haynes General Motors Automatic Transmission Overhaul manual, and a factory service manual—your crash course in 700R4 rebuilding. It’s enough to give greedy transmission shops all over the country fits, and more than enough info to guide you through your own rebuild.

We know it looks absolutely...        read full caption We know it looks absolutely terrifying, but this is every single part that was inside our TH700R4. We recommend that you lay each part out left to right in the order that you removed the components to help you identify the parts later (our picnic table er “transmission shop” wasn’t big enough). We were confident that between the Haynes manual (PN 10360) and the Technical Video we’d be able to make it all go back together.

When you pull the pan off...        read full caption When you pull the pan off any GM transmission you will find nasty stuff stuck to the bottom. The grit that feels like sand is actually friction material from the clutch packs. It’s nothing to worry about. The paste you find stuck to the magnet is from worn pressure plates (you get new ones in the rebuild kit) that are also part of the clutch packs. Again, no big deal. What you don’t want to see are big chunks of steel or long shreds of aluminum that could be from the housing, planetary gears, or apply pistons.

The biggest benefit to doing...        read full caption The biggest benefit to doing a job like this is that you know exactly what went into your transmission. We’ve seen early model pumps, planetaries, and input shafts retrofitted into later-model cases by transmission shops because they had the stuff laying around. That is exactly the kind of thing you want to avoid! When selecting a rebuild kit, you want to specify a master overhaul kit with all the clutches, steels, seals, gaskets, and band. We chose the TCI Pro-Super Kit ($209) that comes with a shift kit and all the wearable items for the transmission. You’ll also want to replace the torque converter with one of the proper stall speed. Again we went right to TCI to get the correct converter for our diesel application ($269).

With the transmission disassembled...        read full caption With the transmission disassembled you will have to meticulously clean every part. We used a friend’s parts washer to do the big stuff like the case, pan, and valvebody. The rest of the components were cleaned with the cheapest cans of carb cleaner we could buy. You can’t clean the parts too much, so make sure you remove all grit, grime, and gasket material before you start reassembly. We’ll let the Technical Video and books walk you through the assembly from here. Take your time, don’t be scared, and you’ll be back on the road in no time.

There is no need for any Mission Impossible theme music here because what we are about to tell you is completely possible and utterly doable. We are going to take all the fear out of the internal workings of an automatic transmission, and even go so far as to tell you that you can rebuild your GM TH700R4 at home without being ASE-certified in anything!

Automatic transmissions are not filled with magic voodoo no matter what the local transmission shop tells you. We called around to see what a rebuilt TH700R4 would cost us if we brought the unit down to the local shop and had them go through it. We were quoted prices from $550 to $1,500. Dang! That’s a lot of money. Being the inherent cheapskates that we are, we’re always on the lookout for ways to do things cheaper, and we are huge fans of doing things ourselves whenever possible.

But how can you rebuild an automatic transmission at home, you ask? We know what you’re thinking, “Nobody can do that!” Well, we’re going to show you how. Actually, Paul Zank, of Technical Video is going to show you how. Paul has produced a series of videotapes designed to empower the average home mechanic with the ability to rebuild his own transmission. We called Paul at Technical Video and ordered up the 700R4 tape (about $40) to see if we could actually pull this off. We received a 90-minute, step-by-step tutorial video that shows Paul taking you through each step of the teardown, cleaning, inspection, and reassembly process of the transmission.

Most importantly, the video took away our fear of getting in over our heads on something we have never done. Along with the video we referenced our factory service manual, and a Haynes General Motors Automatic Transmission Overhaul manual to build our confidence before we started in on the project. We recommend you watch the video over and over until you can almost quote Paul Zank word for word.

When you have digested the video completely you should schedule a weekend to do the rebuild. You’ll need a transmission overhaul kit that includes all new clutches, steels, seals, and gaskets like the 700R4 Pro-Super rebuild kit we got from TCI Automotive. If your core tranny is really worn, you may need some “hard parts” like gears, drums, or even a pump that could add big bucks to the cost! So try to get a good core. There are also a few specialty tools that we got from Technical Video that you’ll see in the photos.

Select a big enough work area that you can lay out all the parts in a logical order as you disassemble the transmission. We did it outside on a picnic table. If you’re worried about screwing up, you can even make your own video of you disassembling the transmission to use as a reference for when you have to put the whole thing back together.

Take your time, but don’t walk away from the project until you are done. When the whole thing is reassembled, reinstall it in the truck. If you followed all the instructions there won’t be a need to cross your fingers. It’ll work. Drive it for 200 miles, then change the fluid and filter. You can thank us later. We can’t begin to show you the assembly process, but trust us when we say the Technical Video will hold your hand through the whole deal.