46RE Towing Upgrades and Cooling

The 46RE is the RE-family unit behind the gas V8 Rams: the half-ton and light-duty trucks that end up pulling a camper, a boat or a car hauler on weekends. It shares a case, a valve body layout and a lot of hard parts with the 47RE and 48RE — all three are built around the same front and rear clutch packs, kickdown and low/reverse bands, overrun roller clutch and overdrive unit, per ATSG's own technical description of the family — but it is not a 47RE. The 2001 factory spec table gives the 46RE three front clutch discs where the 47RE gets four, and the band settings are different. So the towing plan for a 46RE is not "do what the Cummins guys do." It is heat control first, a few targeted holding-power parts second, and honest expectations: if the trailer is over the truck's rating, the transmission will tell you with heat, and no cooler or servo fixes that.

This is the order we work in on a 46RE that tows. Factory numbers come from Chrysler's 2001 Dodge Ram Truck (BR/BE) service manual, 46RE section. Upgrade parts and what they fix come from Sonnax. Sources are listed at the end.

Recommended 46RE towing parts

A 46RE cooler, a finned deep cooling pan that lists the 46RE, and a heavy-duty band strut and anchor for the A518/46RE front band. Secure checkout.

46RE Transmission Cooler

$331.23View part

Derale 14210 Transmission Cooling Pan Dodge 47RE 48RE 46RE

$375.99View part

PW518AC Band Anchor & 22717HD Heavy-Duty Band Strut for 47RE 48RE A518 A618 A727

$57.99View part

Start With What the 46RE Does When It Overheats

Before buying anything, know the factory heat logic, because it tells you when you already have a problem. The 2001 manual (page 21-606) says the transmission fluid temperature thermistor is built into the governor pressure sensor, stays immersed in fluid, and reads about 1000 ohms at room temperature. The PCM uses it to control the overdrive clutch, the converter clutch and governor pressure:

• Below about 10°C (50°F): no converter clutch and no overdrive.
• Above 126°C (260°F): the PCM forces a 4-3 downshift, applies the converter clutch on the third-gear lockup schedule, and lights the overdrive OFF lamp.
• Fourth gear stays locked out until fluid drops to about 110°C (230°F).

If the O/D OFF lamp comes on by itself halfway up a grade with a trailer behind you, that is not an electrical glitch. The transmission hit 260°F. Treat it as a warning that the cooling system is not keeping up, and do not keep towing on it until you know why.

The same logic tells you how to drive a loaded 46RE. Because of the third-gear lockup schedule, holding third with the overdrive switch on a long pull keeps the converter clutch applied. An unlocked, slipping converter is what makes the heat, and a 46RE hunting 3-4 on a grade unlocks on every downshift.

The PCM already tries to stop gear hunting

The manual (page 21-541) also describes "grade hunting prevention": the PCM delays an upshift on a grade if the engine cannot hold speed in the higher gear. That helps, but it cannot fix a trailer that is too heavy for fourth. If the truck keeps shifting in and out of overdrive on the highway, lock out overdrive and stop making heat.

Upgrade 1: A Temperature Gauge, Then a Cooler Flow Test

The first money on a towing 46RE goes to a transmission temperature gauge. The factory already decided 260°F is an emergency. You want to see 220°F and climbing, not find out at 260°F when the lamp comes on.

The second thing is flow, and it is free. Sonnax's bulletin on 46-47RH/RE cooler and converter flow calls cooler restriction "by far the most common issue" in this family, and lists the likely spots as the drainback fitting, auxiliary or radiator-mounted coolers, and the lines. With the converter clutch released, that back pressure pushes the switch valve into a mid-circuit position that restricts converter and cooler flow even more, and Sonnax says it can become a problem as head pressure nears 80 psi or more. Their check is simple: temporarily bypass the cooler circuit and re-test. If the complaint goes away, the problem is outside the transmission.

The drainback valve

The part people forget on the 46RE is the converter drainback check valve. Per the 2001 manual (page 21-606), it sits in the cooler outlet (pressure) line near the radiator tank and keeps the converter from draining back when the truck sits. The check ball is spring loaded and opens at about 2 psi. The manual's rules for it are strict:

• It is serviced only as an assembly. Do not clean it if it is restricted or has sludge or debris in it.
• Replace it if it fails, or after any transmission failure that made significant sludge, clutch material or metal.
• Remove it whenever the cooler and lines are reverse flushed.
• It must go in the pressure line, pointing the right way. Restricted, backwards, or in the wrong line, it blocks flow and causes overheating and eventual transmission failure.

Adding an auxiliary cooler means cutting into these lines, which is exactly when the drainback valve gets flipped or left in the return line. Check its direction before you close the hood. Our cooler flush guide covers flow testing a cooler, and the manual says to test the drainback valve the same way.

Upgrade 2: Add Cooling Capacity to a Healthy Circuit

Once flow is confirmed good, add capacity:

• An auxiliary cooler. Plumb it in series with the factory cooler. The drainback valve still has to sit in the pressure line going to the radiator, pointing the right way. Size the cooler for the trailer you actually pull. Our cooler types and sizing guide goes through plate, tube-and-fin and stacked-plate designs.
• A deep, finned cooling pan. It adds fluid volume and case surface area. One catch on the 46RE: the rear band adjusting screw is inside the pan (manual page 21-540), and so are the filter and valve body. A pan with a drain plug makes the band and filter service below much easier.

Neither one fixes a restriction. Both help a clean, flowing circuit hold temperature on a long grade.

Upgrade 3: Keep the Bands Adjusted to 46RE Spec

Towing loads the 1-2 and 2-3 shifts hardest, and second gear on the RE family depends on the kickdown (front) band. The manual describes it as holding the common sun gear by applying and holding the front clutch retainer, applied by the servo through an apply lever and link bar. The low/reverse (rear) band holds the rear planet carrier. A loose band slips under load no matter what else you do.

These are the 46RE numbers from the 2001 manual (pages 21-539 and 21-540), and Chrysler's 1998 Ram Truck service manual (pages 21-308 and 21-309) prints the identical procedure and the same 46RE-versus-47RE back-off table. They are not the 47RE numbers, so do not work off a Cummins tag sheet:

• Front band: loosen the locknut and back it off 3-5 turns, make sure the screw turns freely, torque the adjusting screw to 8 N·m (72 in-lb), back it off 2-7/8 turns, hold it, and torque the locknut to 41 N·m (30 ft-lb). If you need adapter C-3705 to reach the screw, torque it to only 5 N·m (47-50 in-lb).
• Rear band: pan off, loosen the locknut 5-6 turns, torque the screw to 8 N·m (72 in-lb), back it off 2 turns, and torque the locknut to 34 N·m (25 ft-lb). Pan bolts go to 17 N·m (13 ft-lb), and the refill is Mopar ATF+4, Type 9602.

The 47RE backs off 1-7/8 turns front and 3 turns rear, so setting a 46RE to 47RE numbers is an easy way to get a flared second gear. With an aftermarket higher-ratio apply lever, use the lever maker's back-off instead.

Holding-power parts for second gear

Sonnax lists several servo and band parts for the 46RE. These are the ones that matter for towing:

• 2nd Gear Super Hold Servo Kit (22301B-01K). Sonnax calls it the largest and most leak-free servo available for the 46RH/RE, 47RH/RE, 48RE and A727. Its stated gains are 16% more apply area and 15% less leakage than other designs, with improved 1-2 and 2-3 shifts. Sonnax says it reduces the need for aggressive lever ratios and excessively high line pressure to get firmer shifts. That is the right way to add holding power: more area, not more pressure everywhere else.
• Heavy Duty Kickdown Band Strut (22825-01). Sonnax says stock struts in these units often bend or break, and describes its strut as solid, heat-treated steel with an extra-thick cross-section.

Upgrade 4: Protect the Converter Clutch

A converter clutch that slips under load makes heat, burns its lining, and sends that material into the cooler. Two things matter here.

Enough apply pressure. Sonnax's 46RE listing includes an Oversized Lockup Boost Valve Kit (22771-19K) for TCC slip under load, no line rise during TCC apply in fourth, and overheated converters, plus 4-spool switch valves (22771A-01 and oversized 22771A-13) for lockup shudder, low cooler flow and soft TCC apply. A worn boost valve or switch valve bore is a valve body repair, and it is the usual reason a tired 46RE unlocks every time it sees a hill. Our 46RE converter shudder guide covers that diagnosis.

Not too much apply pressure. This is the part people get wrong with shift kits. In a 2024 Sonnax article, Jim Dial explains that the RH/RE TCC apply valve feeds line pressure straight to the converter clutch when it applies. Stock max pressure in Drive is near 130 psi in TCC or fourth gear, and performance kits raise it to 150 psi and higher, which can balloon the converter. His fix is Sonnax's drop-in TCC Apply Limit Valve Kit (22771A-44K), which limits apply pressure to about 130 psi, depending on the maximum line pressure set point. If you are putting a firm-shift kit in a towing 46RE, this valve keeps the converter from being the part that pays for it.

Get Baseline Pressures Before and After

Never raise pressure on a towing unit without gauges on it first. A low reading means a leak somewhere, and more pressure just hides it until the next trip. The 46RE pressure test specs from the 2001 manual (pages 21-488 and 21-489), which match the Test One through Test Four ranges in Chrysler's 1998 Ram Truck service manual (pages 21-217 and 21-218):

• Line pressure at the accumulator port (manual low and 2 range, 1000 rpm): 54-60 psi with the throttle lever forward, rising to 90-96 psi with the lever fully rearward. Rear servo pressure in manual low should match line pressure within 3 psi.
• D range, third gear (1600 rpm): line pressure 54-60 psi at closed throttle and rising; front servo pressure within 3 psi of line pressure up to the kickdown point.
• Reverse (1600 rpm, rear servo port): 145-175 psi with the lever forward, rising to 230-280 psi as the lever moves rearward.
• Governor: no more than 3 psi at curb idle with the wheels stopped, rising about 1 psi per mph and dropping back to 3 psi or less when you stop.
• Overdrive clutch, fourth gear: 68-72 psi at closed throttle, 90-120 psi at 1/2 to 3/4 throttle, and around 130 psi at full throttle.

A front servo reading more than 3 psi below line points to a leak in the servo circuit, which is exactly what the super hold servo's tighter sealing fixes. Line pressure that is low in every range sends you to the filter, pump and regulator valve before anything else.

The Input Shaft: Only If the Unit Is Coming Apart

Dodge diesel input shaft failures get most of the attention, but the Sonnax Heavy Duty Input Shaft (22121B-01) is listed for the 46RE too, 1994 and later with the 1.245 in. sealing ring. Sonnax describes it as a one-piece shaft that combines the input shaft and forward clutch hub, replacing the OE two-piece shaft and hub and removing the weak joint between them. It is made from 300M steel and works with OE seals. On a gas 46RE that only tows occasionally, it is not a reason to pull the transmission. If the unit is already apart for a rebuild and the truck tows regularly, add it to the build. The same goes for Sonnax's Heavy Duty Forward (Rear) Clutch Retainer (22554-HD), also on the 46RE list.

Fluid and Service for a Towing 46RE

The 2001 manual specifies Mopar ATF+4, Type 9602, for the 46RE. The maintenance section puts trailer towing on the list of conditions for Schedule "B." On that schedule, the transmission service is "change automatic transmission fluid, filter and adjust the bands," at 30,000 and 60,000 miles. That band adjustment is part of the factory service, not an extra. Check fluid color and smell at every oil change on a truck that tows. Dark, burnt-smelling fluid is the warning to find the cause before the next trip. Our 46RE fluid type and capacity guide has the fill amounts.

A Sensible Upgrade Order

1. Every towing 46RE: a temperature gauge, a cooler flow test, a new drainback valve installed in the pressure line and pointing the right way, correct ATF+4, and bands set to the 46RE spec (2-7/8 turns front, 2 turns rear).
2. Regular towing: an auxiliary cooler and a deep pan with a drain plug once flow is confirmed. A 2nd gear super hold servo and a heavy-duty kickdown band strut at the next pan-off service.
3. At the next rebuild: lockup boost valve and switch valve repairs, the TCC apply limit valve if any firm-shift calibration goes in, and the heavy-duty input shaft if the truck tows often.

Do it in that order and each step fixes a real failure mode instead of hiding one.

Frequently Asked Questions

Should I tow with overdrive off in a 46RE?

On long grades or with a heavy trailer, yes. The 46RE has a third-gear converter clutch schedule, so holding third keeps the converter locked instead of hunting 3-4 and unlocking on every downshift, which is where most of the heat comes from. On flat highway with a light trailer, fourth with the converter locked is fine.

Why does my 46RE O/D OFF light come on while towing?

Per the 2001 Chrysler service manual, when fluid temperature passes 126C (260F) the PCM forces a 4-3 downshift, applies the converter clutch on the third-gear schedule and lights the overdrive OFF lamp. Fourth gear returns once fluid cools to about 110C (230F). It means the transmission overheated, so check cooler flow and the drainback valve before towing again.

What are the 46RE band adjustment specs?

From the 2001 service manual: torque the front band adjusting screw to 72 in-lb, back it off 2-7/8 turns and torque the locknut to 30 ft-lb (47-50 in-lb on the screw if adapter C-3705 is needed). The rear band is torqued to 72 in-lb, backed off 2 turns, and the locknut torqued to 25 ft-lb. These differ from the 47RE, which backs off 1-7/8 and 3 turns.

Where does the 46RE drainback valve go?

In the cooler outlet (pressure) line near the radiator tank, oriented in the direction of flow. The manual says a drainback valve that is restricted, installed backwards or in the wrong line blocks flow and causes overheating and eventual transmission failure. Replace it after any failure that made sludge or metal, and remove it when reverse flushing the cooler.

Is a shift kit a good towing upgrade for a 46RE?

Only with care. Sonnax notes that the RE TCC apply circuit sends line pressure straight to the converter clutch, stock max near 130 psi, and kits that raise it to 150 psi or more can balloon the converter. If you add a firm-shift calibration, pair it with a TCC apply limit valve, and prefer adding holding power with a larger servo instead of more line pressure.