Rebuild or replacment TH400

Yapay

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As the title says I'm thinking of doing one or the other. Now as a little info the truck is my daily I have no other vehicle. I live in an apartment, but work at a dealership. So I have the place to work just I can't leave it overnight. It'll be the first time I've gotten the trans out of the vehicle and first time tearing it down if I go that route. I would only get about 6-7 hours in one day to rebuild it on a Saturday. On the flip side its the original one. It doesn't matter if it's numbers matching, because the engine was swapped from 305 to 350 in the early 90's by the original owner. I've got experience pulling and replacing trans at work, but not tearing one down for a rebuild. Also I doubt I have all the special tools, but could get them if I knew what I needed.

My question really is this. Do I rebuild or just swap in a new one? I'd really like opinions from people who've worked on TH400 transmissions before. Though any opinion is welcome.

Thanks!
 

Nonstop

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I have never been into a th400. With that said, I have put them in. Honestly, I would go with replacement. 6 to 7 hours to pull, clean, rebuild, and put it in is not much time. R&R would be the most straightforward and possibility the easiest. You also do not know what hard parts you might meet to order once you get into it.
 

Matt69olds

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If you only have one day to make the repair, get a replacement. There’s always the chance you cut a seal, tear a gasket, or need a part that doesn’t come in your standard overhaul kit.

Could you tear the trans out on a Saturday, build it thru the week, and reinstall it on another Saturday? Obviously, if the truck is your only ride, that’s not an option Every dealership I worked at didn’t mind working on their own cars, as long as the customer stuff didn’t suffer.

Get it out, work on it during your lunch breaks and days off. When it’s done, reinstall
 

HotRodPC

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Yep, with the limited time you need a replacement. If you're speedo is accurate, be sure to take the tailshaft off and save your drive and driven gears. I'd also keep your governor if you like the current shift points.
 

Yapay

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Thanks guys for the replies. So with that what or where would I find the best replacement? Obviously I could go junkyard diving but I’d prefer a slightly used or rebuilt transmission. Nothing fancy. I don’t plan to build a speed demon.


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HotRodPC

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Before you go ordering or looking, I'd just make 100% positive you have a Turbo 400. I don't know your knowledge and maybe you are certain but an 87 1/2 ton pick up with a 350 should have come with a 700r4 or maybe even a Th350 if it doesn't have overdrive. Now that doesn't mean someone hasn't converted it to a Th400. Just saying, Make sure you know what you're looking for so you don't have to get into driveshaft and yoke issues making changes.
 

Yapay

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Before you go ordering or looking, I'd just make 100% positive you have a Turbo 400. I don't know your knowledge and maybe you are certain but an 87 1/2 ton pick up with a 350 should have come with a 700r4 or maybe even a Th350 if it doesn't have overdrive. Now that doesn't mean someone hasn't converted it to a Th400. Just saying, Make sure you know what you're looking for so you don't have to get into driveshaft and yoke issues making changes.
The truck came stock with a 305 actually and then was swapped to a 350. I’ve done a trans service already so I know it’s a 400. I don’t mind changing to say a 700r4 but would that be better or worse? I have enough knowledge on my truck to get me in trouble but enough experience to get out lol. I like my 3 speed but I don’t mind adding the 4th gear.


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Matt69olds

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Did you decide to go rebuilt, or to get a core and build yourself? If you go rebuilt, your at the mercy of the builder as to what was replaced.

If your looking for a core to build, basically any 400 is good. From about 1973 and earlier they used aluminum pistons as opposed to the later stamped steel. They also used plastic accumulator pistons, definitely replace them with aluminum! The early smooth race direct drum is preferred, but a mild 350 isn’t going to hurt any drum in good condition.

To answer your question, any 400 that will fit your application is a good one. All the cheap upgrades can be done during a basic rebuild. Get a thrust washer kit, bushing kit, and bearing kit, and that should cover all the basic wear issues.

A 400 is pretty easy to build, what tools are needed are easily built from scrap steel or other materials. Just work slowly and cleanly, don’t force anything.
 

HotRodPC

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700r4 is going to cost you quite a bit more at this point. First you have to acquire a core. The rebuild kit is more, not to mention the very bare minumum upgrades that need to be considered, torque converter core charge you'll have to pay if you don't have one so it'll be alot more not to mention losing reliability.
 

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