ZF 8HP Identification Guide: Case Size, Generation and Tag Numbers

The ZF 8HP shows up under more badges than almost any other transmission on the road today — BMW, Audi, Jeep, Ram, Dodge, Chrysler, Land Rover, Bentley and others — and the part numbers behind that family name are not interchangeable the way the model number suggests. Order a valve body, a mechatronic unit, or even a filter kit by "8HP45" or "8HP70" alone and there is a real chance it does not fit the unit on the bench. The 8HP45 in a 2015 Chrysler 300 is not built the same as the Gen 2 equivalent in a newer model, because Chrysler/Stellantis quietly moved the whole family to a second generation in 2019 without changing the badge most people read off the case.

This guide covers how to actually identify what you have, in the order that eliminates the most wrong parts fastest: case size, model number logic, the Gen 1/Gen 2 split, the tag itself, and the valve body codes that settle it when the model name is not specific enough.

Recommended ZF8HP parts

Once you have confirmed the generation and valve body code, these are the parts that fit it. In stock, ships same day from the USA.

8HP70/8HP75 Transmission Master Rebuild Kit

$463.99View part

ZF 8HP45/8HP70 Mechatronic Solenoid Kit, 9-Piece

$175.99View part

845RE/8HP45/8HP55/8HP70 Zip Kit Valve Body Repair

$191.99View part

Two case sizes, then the model number

ZF builds the 8HP family in two physical case sizes, and that split is the fastest first cut. Per ATRA's Gears magazine, there is a smaller case for the lower-torque applications — 8HP45/845RE through 8HP50/850RE — and a larger case for medium-to-high torque applications, 8HP55 through 8HP95. The number that follows "HP" tracks the unit's torque class within the range ZF itself publishes for the whole family in its own product documentation: a torque capacity spanning 220 to 1,000 Nm across the lineup. That is why the base Pentastar V6 cars run a smaller-case 8HP45/845RE, the 5.7 and 6.4 HEMI cars and trucks step up to the larger-case 8HP70, and the supercharged Hellcat applications with the highest torque output of the family get the 8HP90.

Do not stop at case size. Gears is explicit that even within a case family, "there are enough subtle differences that could result in getting the wrong parts," and the safe assumption going in is that every one of these units is different unless you can cross-reference a part number through ZF or the vehicle manufacturer. Two transmissions that look identical on the outside, down to the bolt pattern and the fill plug location, can carry internals that are not interchangeable. The model number gets you in the right neighborhood. It does not get you the right part.

The generation split that changes everything (2019)

This is the identification step that actually decides whether the parts you order will work, and it is easy to miss because the badge on the case does not announce it. Sonnax technical specialist Jim Dial, writing in Transmission Digest, documents that in 2019 some Chrysler, Ram and Jeep applications moved to a second-generation ZF8. The designations split cleanly by generation: Gen 1 units are 8HP45, 8HP70 and 8HP90; Gen 2 units are 8HP50, 8HP75 and 8HP95. Same torque classes, same case sizes, different internals, different parts.

The internal differences are not cosmetic. The change was driven by a gear ratio revision that forced numerous hard part changes, and it reworked how the B brake applies and releases. On a Gen 1 unit, the B brake piston — located at the back of the pump housing — has two hydraulic circuits: an apply circuit (B1) and a release circuit (B2). On Gen 2, the B2 release circuit was eliminated entirely and replaced with a mechanical return spring assembly, and ZF added wave springs between the steel plates on both the A and B brake assemblies specifically to make them release faster.

The valve body changed to match. Per Sonnax's documentation of the same generational split, the B and D solenoids swapped physical positions between Gen 1 and Gen 2 castings. Gen 2 solenoids are visually distinguishable by cream and blue caps, but they are not interchangeable with 845RE solenoids because the snout diameters differ. And because the B2 hydraulic circuit no longer exists in Gen 2, the upper valve body casting lost five control valves that routed it in Gen 1. A Gen 1 valve body does not have a home for a Gen 2 case's return-spring brake, and a Gen 2 valve body has no B2 circuit to feed a Gen 1 case. They are not a parts-bin substitution for each other in either direction, no matter how close the casting looks on the bench.

Reading the tag and the stucklisten number

Every ZF transmission carries an identification tag on the case, and per Gears magazine, that tag "must be used when ordering parts" — it is the starting point before you trust anything cast or badged on the outside of the unit. Sonnax's general guidance on reading ZF tags describes two key lines: a serial number, which flags running changes specific to that individual unit, and a part number, called the stucklisten number, which is structured in groups of digits. The first digits identify the base transmission type, the next group identifies the design type (whether the unit has a transfer case, a specific electronic control configuration, or another special application), and the final digits identify the specific vehicle application.

On 8HP-family parts specifically, the type-code prefix that shows up repeatedly in documented service and valve body part numbers is 1087 — Sonnax's own separator plate chart lists stamped numbers like 1087-327-099, 1087-327-175 and 1087-327-221 across different 8HP valve body codes. But that prefix is not perfectly universal: the same chart lists one plate, OE code A187/B187, stamped 1102-327-188 instead. The lesson is to read the full stamped number off the actual part or tag in front of you rather than assuming a prefix pattern holds for every revision.

Valve body separator plate codes

When the model number and generation still leave more than one possible part, the valve body separator plate's own stamped number is the tiebreaker. Sonnax publishes an application chart for exactly this reason, and it states plainly that these plates are not specific by transmission model — they are specific by valve body code and by the stamped number on the plate itself:

Notice two things in that table that trip people up. First, the same OE code and stamped number can span three different model numbers (45, 55 and 70), which means a plate that physically fits is not proof you have correctly identified the model — it only proves the plate fits. Second, this chart does not include 8HP90, 8HP50, 8HP75 or 8HP95 at all. The Gen 2 and highest-torque variants use a separate numbering scheme entirely, which is one more reason the generation check has to happen before you go shopping for a valve body or separator plate by model number alone.

Vehicle application notes

On the Chrysler/Stellantis side, the pattern is well documented: the 8HP70 is the transmission behind the 5.7L and 6.4L HEMI Dodge Challenger starting in 2014, and the same unit carries the HEMI-equipped Durango, Grand Cherokee and Ram 1500 applications. The 8HP90 pairs with the supercharged Hellcat applications — the Challenger and Charger SRT Hellcat — because its higher torque rating within ZF's published 220–1,000 Nm family range is what the supercharged output needs. The smaller-case 8HP45/845RE covers the base 3.6L Pentastar V6 applications across the same model lines. ZF licenses the same basic architecture to BMW and to Audi, Porsche, Jaguar, Land Rover and others, each running their own badge and calibration on top of the same core gear set and shift element design — which is exactly why the tag and the stamped part number matter more than the name on the bellhousing.

FAQ

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