TH350 vs TH400
Rebuild Cost Comparison

The Turbo-Hydramatic 350 and Turbo-Hydramatic 400 get talked about like they are two halves of the same story, and mechanically they share a design language. But on the bench they are not the same rebuild, and they are not the same bill. The TH350 is the lighter, shorter, cheaper unit that lived behind small blocks and mild big blocks. The TH400 is the heavy-duty three-speed built to survive behind 454s, diesels, and race motors.

If you are pricing a rebuild, the short version is this: a TH350 is the cheaper unit to rebuild in parts, but the gap is smaller than people assume once you add a converter and account for hard-part wear. The real cost driver is not the transmission model. It is whether the hard parts survived, and whether you are doing it yourself or paying a shop.

The Quick Answer on Cost

Doing it yourself with a mid-grade master overhaul kit and a new converter, expect roughly:

The TH400 runs 20 to 30 percent higher across the board. That premium comes from a larger converter, more friction material, a heavier direct clutch pack, and a core that is harder to find clean because so many were run hard.

Where the Price Gap Actually Comes From

Clutch and band count

The TH350 uses a two-band-style design with an intermediate sprag and forward/direct clutch packs sized for lighter torque. The TH400 deletes the low band in favor of a heavier clutch-and-sprag arrangement and carries more frictions in the direct drum. More friction plates and more steels means a bigger master kit, which is most of the parts-cost difference.

The torque converter

A stock TH350 converter is smaller and cheaper to reman or replace than the larger TH400 unit. If you go to a higher-stall performance converter, the TH400 side climbs faster because the heavier unit and its billet options simply cost more.

Core condition

This is the sleeper cost. A TH400 that lived behind a big block towing a trailer often needs a direct drum, a center support, or an output shaft, and those hard parts turn a $250 rebuild into an $700 one in a hurry. A TH350 pulled from a mild small block is usually just tired frictions and a worn pump bushing.

Line-Item Parts Breakdown

Here is what actually goes into each rebuild and what those pieces cost individually, so you can see where a "cheap" kit cut a corner.

Browse TH350 master rebuild kits

Browse TH400 master rebuild kits

Kit Grades — What You Are Really Paying For

The word "kit" covers three very different boxes. Buy the wrong grade and you either overpay for parts you do not need or you tear it down twice.

• Banner / gasket kit ($40-$80): gaskets, seals, and sealing rings only. For a valve body reseal or a leak fix, not a real overhaul. No frictions.
• Basic overhaul kit ($70-$160): adds the friction clutches and band(s). Fine if your steels, bushings, and hard parts measure good.
• Master kit ($150-$320): adds steels, the bushing and thrust washer set, filter, and often a modulator. This is what most rebuilds should start with. Buy the master.

Brand matters more than grade at the friction level. Raybestos and Alto frictions hold up. The no-name frictions in a $60 eBay kit glaze and slip. If you are only doing this once, spend the extra $40 on a known-brand master kit.

Check Raybestos and Alto branded kits

Which Is Cheaper to Rebuild — And When to Pick Each

Pick the TH350 when

You are behind a stock or mildly built small block making under about 400 lb-ft, you care about parasitic loss and fuel economy, and you want the cheapest reliable rebuild. The TH350 is lighter, spins easier, and the parts are everywhere and cheap. For a street cruiser or a daily-driven classic, it is the value pick.

Pick the TH400 when

You are behind a big block, a diesel, or a boosted combo, you tow, or you are building for real power. The TH400 costs more to rebuild but it survives torque that shreds a TH350 direct clutch. Building a high-horsepower TH350 to TH400 strength ends up costing more than just starting with the TH400, so do not cheap out on the wrong unit.

One honest note: the TH400 costs a few percent in the quarter mile and a mile or two per gallon on the street versus a TH350, because it is heavier and takes more to turn. That is the trade for its strength. If you do not need the strength, you are paying to rebuild and then carry weight you will not use.

Labor — The Number That Actually Decides Your Bill

Parts are the small half. A shop rebuild bills bench time. Expect 6 to 10 hours of labor for a clean TH350 and 8 to 12 for a TH400 including R&R, and at typical 2026 shop rates of $120 to $180 an hour that labor alone is $900 to $1,800. That is why a DIY rebuild that costs you $400 in parts is a $2,000 job at a shop. The transmission model barely moves labor; access to the vehicle and how badly the core is worn move it far more.

FAQ

Is a TH350 or TH400 rebuild kit interchangeable?

No. They are different transmissions with different friction sizes, steel counts, band setups, and pump geometry. Order the kit for the exact unit. Verify by case length and pan shape before you buy anything.

Can I rebuild either one in a home garage?

Yes, both are among the most DIY-friendly automatics ever built. No electronics, no solenoids, mechanical governor. A master kit, a set of snap ring pliers, a spring compressor, and a service manual get you there. The TH350 is slightly more forgiving for a first-timer.

Why is my TH400 core worth more?

Good TH400 cores are harder to find because so many were abused behind heavy motors, and the hard parts cost more new. A clean TH400 core commands a premium, which also raises the all-in rebuild cost if you have to source one.