Buyer’s guide
Reading Subaru STI six-speed gearbox numbers
A used six-speed is sold on a title written by somebody clearing a shelf. The part numbers are the only thing in the listing that was not typed from memory, and they will tell you more about what is in the crate than the description does — including, fairly often, that the description is wrong.
Written from our own sourcing experience. Last checked 24 September 2026. Related parts: Drivetrain & differentials.
The two numbers that matter
A Subaru STI six-speed carries a transmission code beginning TY856, and an assembly number beginning 32000A. They encode different things and you want both, because the interesting cases are the ones where they disagree.
The TY856 code identifies the gearbox specification — which generation, and what is inside it. The 32000A assembly number identifies which car the assembly was built for.
TY856 transmission codes
The prefix tells you the family and the suffix carries the spec. The two characters worth learning are the model-year digit and the specification letter.
| Code | What it indicates |
|---|---|
| TY856W… | The GDB-era six-speed family — the box that suits a GDB install. |
| TY856U… | The following generation, fitted to GRB, GVB and VAB. Not a GDB box. |
| …6… | Model-year digit. A 6 here reads as MY05. |
| …K | Specification letter. K reads as DCCD with a Suretrac front LSD. |
| TY856WB1CA | The early GDB six-speed without DCCD. |
A TY856U code is the next-generation box. It is not a cheaper way into a GDB six-speed — it is a different gearbox.
A worked example
Take TY856WB6KA, quoted alongside assembly number 32000AH090.
TY856W puts it in the GDB-era family. The 6 reads as MY05. The K reads as DCCD with a Suretrac front LSD. The assembly number beginning 32000AH confirms GDB rather than the following generation — so the code and the assembly number agree, which is exactly what you want to see.
That much is settled before you have looked at a single photograph: a GDB six-speed with the earlier purely-electromagnetic DCCD and a Suretrac front differential. What is left to check is all physical — kilometres, whether it has been apart, and the casting tag matching what the listing says.
When the transmission code and the assembly number agree, you are reading a gearbox. When they disagree, you are reading a mistake — find out which kind before you bid.
The 32000A assembly number, and the contradiction to watch for
The assembly number is the faster check of the two, because the letter pair after 32000A maps to a car generation.
A GDB assembly reads 32000AH followed by three digits. A GRB or GVB assembly reads 32000AJ. So a listing titled as a GDB box that quotes an assembly number in the AJ range is telling you one of two things: somebody transposed a digit, or the box is not the generation the title claims.
Neither is a reason to walk away on its own, and both are a reason not to bid until you have seen the casting tag. Ask for a photograph of it. A seller who will not photograph a number that is stamped into the part is answering the question anyway.
- 32000AH### — GDB.
- 32000AJ### — GRB or GVB.
- Title and assembly number disagree — get a photo of the casting tag before bidding, every time.
DCCD generations
Not all DCCD is the same DCCD, and the listing will almost never tell you which one you are looking at. The generation follows the model year.
The MY05 unit is purely electromagnetic, with a 35:65 front-to-rear default split. From MY06 the system is a hybrid — mechanical and electromagnetic together — with a 41:59 default. Both are fully driver-adjustable, and the earlier one is a perfectly sound gearbox; it is simply the older system, and worth knowing you are buying.
| Generation | System | Default split |
|---|---|---|
| MY05 | Purely electromagnetic | 35:65 |
| MY06 onward | Hybrid — mechanical plus electromagnetic | 41:59 |
Propshafts are their own part number
The shaft that connects a six-speed to the rear differential is specific to the six-speed cars. A five-speed GC8 or GDA shaft is not it, an automatic shaft is not it, and the following-generation item is not it either.
Length and flange are the two things that decide whether it bolts up, and they are the two things a listing never states. Have them measured and checked against your gearbox before anything ships, particularly where the donor is an early non-DCCD car and yours is not.
Questions we get asked
- The seller lists a part number I cannot find anywhere. Is that a red flag?
- Usually not — a lot of dismantlers quote their own stock number rather than the Subaru part number, and it will look like nothing you can search. Ask for the number stamped on the casting instead. That one is Subaru's and it is the one that answers the question.
- Is an MY05 DCCD box worth buying?
- Yes, as long as you know that is what you are buying. It is the earlier electromagnetic system rather than the later hybrid, and it is fully adjustable. The thing to avoid is paying hybrid money for it because the listing did not say.
Why we wrote this down
We source these parts for our own cars, which means working through listings written by people clearing a shelf and deciding what is worth the risk. None of the above is theory — it is the checklist we actually use. No prices here on purpose: they move weekly, and the hammer price was never the real number anyway.
More guides
- Why a GDB needs a 3.545 rear diffThe final drive has to match the transfer gear, or the centre diff destroys itself. The arithmetic, and how to read it off a listing.
- Buying used drivetrain parts sight-unseenWhat a listing has to state before it is safe to bid, why clutch-type beats helical on stage, and the Japanese terms that carry the real information.