48RE Identification Guide: How to Confirm What You Have

A core shows up on a pallet with "48RE" written on the bellhousing in paint marker. The customer swears it came out of an '04 Cummins. Maybe it did. Maybe it is a 47RE that someone relabeled, or a 48RE that has already been apart with a 47RE valve body stuffed in it. From the outside these units look almost identical, and ordering parts off a guess is how you end up with the wrong kit on the bench and a truck that comes back in three months with a cooked converter clutch.

This is how we identify a 48RE before we quote it, order for it, or tear into it: the stamped numbers on the case, the external tells, the valve body markings, and the ratios and clutch counts that confirm it once it is apart. Specs come from the Chrysler 48RE service manual and Sonnax's identification data. Sources are listed at the bottom.

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Start With the Stamped Numbers

The factory answer is on the case. Per the Chrysler 48RE service manual, the transmission identification numbers are stamped on the left side of the case just above the oil pan gasket surface, and the manual tells you to refer to that information when ordering replacement parts. The same figure calls out three separate numbers in that area:

• Part number — the assembly number that ties the unit to a specific calibration and application.
• Build date — when the unit was assembled, which matters on a family that changed hardware mid-stream.
• Serial number — unique to the unit.

On a truck that has lived its life in salt or mud, that pad is usually buried under a crust of grime and fluid seepage. Scrape it gently with a plastic scraper and wipe it with brake cleaner; do not hit it with a wire wheel, because the stampings are shallow and you can erase exactly what you came to read. Take a photo of the pad before you do anything else and keep it with the work order. When you call a parts supplier, the part number and build date settle most arguments in one sentence.

If the pad has been ground off or the case was replaced, you fall back on the truck and the hardware described below. A replacement case is not unusual on a diesel that has been through a few shops, so a missing or odd stamping is a reason to verify more carefully, not a reason to panic.

Confirm the Application

The 48RE is the heavy-duty member of the RE family. Sonnax notes the 48RE went into production in 2003, with changes to the clutch packs and gear train compared with the 47RE, and that the 48RE and the 46/47RE look extremely similar from the outside. In the Ram lineup it lives behind the 5.9L Cummins in 2500 and 3500 trucks from the 2003 model year until the 68RFE took over; ATSG's application chart lists 2003-07 Ram pickups with the 5.9L diesel and also the 8.0L V10, and Chrysler's 2006 Ram Body Builder spec sheet calls it the "Auto 4-Speed HD 48RE" on the heavy-duty trucks. So a V10 core is not automatically a 47RE. If your unit came out of a 1500 with a gas engine, you are almost certainly holding something else, and our 46RE / 47RE / 48RE guide covers how those family members split.

The trap is a 2003 truck. Production changeovers do not line up neatly with model years, so a truck titled as an '03 can carry either unit depending on when it was built. That is exactly why the stamped build date on the case outranks the year on the registration. If the paperwork and the case disagree, believe the case.

The Throttle Linkage Tell: Cable or TTVA

The quickest external clue on the truck is what is driving the throttle valve shaft. Per Sonnax's write-up on TTVA codes, in 2005 Dodge started using a transmission throttle valve actuator (TTVA) instead of a TV cable on the 48RE in diesel 2500 and 3500 Ram trucks. The actuator mounts to the case above the throttle valve shaft and carries two potentiometers that report to the ECM plus a DC motor that the ECM drives. The bottom of its shaft has a D-shaped opening that fits over the throttle shaft. ATSG's 48RE manual puts the change at the start of production for model year 2005 on 5.9L diesel trucks, and notes the actuator replaced the TV cable and all of its linkage. The same ATSG text dates the push-in transmission range sensor, which replaced the screw-in Park/Neutral switch, to model year 2002, so every 48RE should have the push-in sensor.

So, in practice:

• Electric actuator on the side of the case, no TV cable: a 2005-later diesel 48RE.
• TV cable running to the throttle lever: a 2003-2004 48RE, or a 47RE. The cable alone does not separate those two; you need the case stamping or the valve body.

This matters for more than identification. The 2005-later unit uses a different pressure regulator spring bracket setup. Sonnax specifies 0.905 in. between the bracket and the inside edge of the throttle shaft adjustment bolt head on a TTVA unit, and notes that some cable-type brackets have as little as 0.820 in. Build a TTVA truck with a cable-style bracket and you can set P1751 and P1752 because the actuator cannot find its full span. Per Jeff Parlee's writeup in Transmission Digest, the ECM wants at least 48 degrees of travel from minimum to maximum span to satisfy its calibration, and that calibration runs on every key-on, which is why the TTVA has no manual adjustment of its own and must simply be initialized by holding the ignition on for at least 30 seconds after install or reinstall. Identify the unit correctly and you order the right bracket the first time.

Valve Body Identification

Once the pan is off, the valve body is where you separate a real 48RE from a 47RE and from a 48RE someone has already "fixed." Sonnax's 48RE valve body identification chart gives three checks:

1. Closed casting. 48RE valve bodies have a closed casting at the location Sonnax marks, so the spring at that spot is not visible. Sonnax also warns that some 47REs have a closed casting, so this check alone is not proof.
2. Large separator plate ID number. Check the stamped ID on the large separator plate. For the 48RE converted valve body (Sonnax CHR135, '03-later), the number is 27.
3. Channel plate part number. Sonnax lists the channel plate part number as 52854129AA.

Take all three together and you have a confident answer. Here is why it is worth the five minutes. Sonnax documents that the 48RE valve body is calibrated differently from the 46/47RE: the pressure regulator raises line pressure roughly 22-28 psi in lockup and fourth gear on the 48RE, versus roughly 10-15 psi on the 46/47RE, to clamp the converter clutch and overdrive clutch harder behind the diesel. The 48RE also feeds the TC solenoid from the manual valve in any Drive position, which allows converter clutch apply in manual second. Sonnax's warning is blunt: a 46/47RE valve body in a 48RE seems to work at first, but the truck comes back with a failed converter clutch or overdrive clutch.

If a core arrives with the wrong valve body in it, that is often the root cause of the failure you are looking at. Our 48RE valve body testing guide walks through the bench checks once you know what you have.

Confirm It on the Bench

Once the unit is apart, the factory specifications close out any remaining doubt. From the 48RE service manual:

• Gear ratios: 2.45:1 first, 1.45:1 second, 1.00:1 third, 0.69:1 fourth, 2.20:1 reverse.
• Front clutch: 5 discs.
• Rear clutch: 4 discs.
• Overdrive clutch: 5 discs standard, 6 on the Diesel HO.
• Direct clutch: 23 single-sided discs.
• Fluid: Mopar ATF+4. Chrysler's 2006 Ram Body Builder fluid chart lists a 3.8 L (8 pint) service fill and 14-16 L (29-33 pints) after overhaul.

The forward ratios match the rest of the heavy-duty RE family, so ratios alone will not name a 48RE. The clutch content and the overdrive clutch count are more telling. A six-disc overdrive pack points to a Diesel HO build; a five-disc pack in a unit sold to you as a Diesel HO 48RE deserves a second look at the stamping and the build history.

Band hardware is shared family design, and it is a useful sanity check that you are at least holding an RE unit and not something else entirely. The manual puts the front (kickdown) band adjusting screw on the left side of the case above the manual valve and throttle valve levers, and the rear band adjuster inside, reachable only with the pan removed. Front band spec is 72 in-lb then back off 1-3/4 turns with the locknut at 30 ft-lb; rear is 72 in-lb, back off 3 turns, locknut 25 ft-lb. If there is no external band adjuster on the left side of the case, you are not looking at an RE unit. See our 48RE vs 68RFE comparison if the core came from a later truck.

Watch for Modified Units

Diesel owners modify these transmissions, and a modified 48RE can defeat a parts lookup even when the stamping is correct. The most common one that changes what you order is the input shaft. Sonnax's Smart-Tech big input shaft kit uses a 35-spline shaft and requires a converter fitted with a 35-spline turbine hub; Sonnax rates it 35% stronger than even the best heavy-duty 23- or 29-spline shafts. If you pull the converter and the hub spline count does not match what a stock converter would have, stop and count before you order a replacement converter or shaft.

Other things to note on a used core: an aftermarket deep pan, a billet flexplate, a reinforced overdrive housing or an aftermarket valve body. None of these change the identification, but each one changes the parts list. Write them on the ticket at teardown, not after the customer's kit shows up wrong.

One more thing worth checking before you reassemble: the manual shaft and rooster comb. Sonnax's write-up on 48RE manual shaft issues explains that the shaft controls the manual valve, the reverse light, and Park/Neutral safety, and that spring tension in the Park/Neutral safety switch pushes the shaft sideways. That sideways load wears the case bore where the shaft seal rides from round to oval, which tilts the shaft so the rooster comb no longer sits centered on the detent ball — producing a sticky or binding shifter, a stretched shift cable, and worn shift detent hardware in the valve body. Check for play by rocking the shaft like a teeter-totter with the detent ball and spring removed; any play means the shaft or its bore is worn. Sonnax notes that filing or grinding the rooster comb is a common aftermarket workaround for Park binding, but that masks the real wear rather than fixing it — if you find a modified comb on a core, expect the shaft and bore to need attention too.

A Quick ID Checklist

1. Read and photograph the part number, build date and serial number on the left side of the case above the pan rail.
2. Confirm the application: 5.9L Cummins, Ram 2500/3500, 2003-up. On an '03, trust the build date over the model year.
3. Look at the throttle input: TTVA means a 2005-later diesel 48RE; a cable means 2003-2004 48RE or 47RE.
4. Pan off: check the valve body casting, the large separator plate ID (27 on the CHR135 '03-later unit) and the channel plate number (52854129AA).
5. On teardown, confirm the clutch counts and note any aftermarket input shaft, converter hub or overdrive hardware.

Once you know exactly what you have, the parts decisions get easy. Our 48RE rebuild cost guide breaks down what goes into the bill, and the 48RE fluid guide covers the fill.

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Frequently Asked Questions

Where is the 48RE transmission ID number?

Per the Chrysler service manual, the identification numbers are stamped on the left side of the case just above the oil pan gasket surface. The pad carries the part number, build date and serial number. Clean it with a plastic scraper and solvent rather than a wire wheel so you do not erase the stampings.

How can I tell a 47RE from a 48RE?

Read the part number and build date on the case first. On the truck, a 2005-later diesel 48RE uses an electric throttle valve actuator instead of a TV cable; a cable means a 2003-2004 48RE or a 47RE. With the pan off, Sonnax's valve body ID checks (closed casting, separator plate ID 27, channel plate 52854129AA on the '03-later unit) settle it.

Can I use a 47RE valve body in a 48RE?

No. Sonnax documents that the 48RE raises line pressure about 22-28 psi in lockup and fourth versus about 10-15 psi on the 46/47RE, and feeds the TC solenoid from the manual valve. A 46/47RE valve body seems to work at first, but the truck comes back with a failed converter clutch or overdrive clutch.

What are the 48RE gear ratios?

The service manual lists 2.45:1 first, 1.45:1 second, 1.00:1 third, 0.69:1 fourth and 2.20:1 reverse. The forward ratios match other heavy-duty RE units, so use the case stamping and valve body to identify a 48RE rather than the ratios alone.

Does a 2003 Dodge Ram 2500 Cummins have a 47RE or 48RE?

It can have either, because the 48RE went into production during 2003 and changeovers do not line up with model years. The stamped build date on the left side of the case is the reliable answer, and it outranks the model year on the registration.