47RE Slipping in Overdrive - Causes and Fix

A 47RE that pulls fine in the first three gears and then flares, slips or falls out of overdrive is one of the most common complaints on a 1994-2003 Cummins Ram, and it has a short list of causes. The overdrive section of this transmission is a separate unit bolted to the back of the main case, with its own clutch pack, its own apply piston, its own roller clutch and its own solenoid, and it is controlled by governor pressure and throttle valve position that the rest of the transmission does not share. That is good news: a slip that only happens in fourth is telling you where to look, and a pressure gauge will tell you which of the causes it is before you pull anything apart.

The symptom, precisely

Overdrive slip on a 47RE shows up as one or more of the following:

• RPM flares on the 3-4 upshift, then settles, and gets worse as the fluid warms.
• The truck is in overdrive at cruise but RPM climbs on a grade or under throttle without a downshift.
• Overdrive drops out around 60 mph and re-engages, or the truck cycles in and out of fourth.
• Overdrive engages but the torque converter never locks, or unlocks under load.

Note the difference between "slips in overdrive" (fourth engages and then loses grip) and "no overdrive" (never shifts to fourth). They share parts but not causes. If you have no fourth at all, start with our 47RE overdrive solenoid replacement guide.

Step 1: check the basics that mimic a slip

Diesel Hub's 47RE specification calls for ATF+4, a 14.5-16.5 quart dry fill, about 4 quarts on a service, and fluid, filter and band adjustment every 24,000 miles or 24 months, with the warning that skipping band adjustment "will ultimately reduce the life" of the unit. A low level or burnt fluid can cause a flare in fourth first because the overdrive clutch is the highest-load, lowest-capacity pack in the transmission. Check level hot, in neutral, on level ground.

Then check the throttle valve cable. On the 47RE, TV cable position sets line pressure. A stretched or misadjusted cable lowers line pressure at part throttle, and the overdrive clutch is the first thing to slip when line pressure is low. Sonnax lists "difficulty in adjusting shift timing with TV linkage," "shift timing concerns" and "poor kickdown" as throttle valve symptoms on this unit, and offers a heavy-duty throttle valve kit and an oversized throttle valve for worn bores. Adjust the cable per our 47RE TV cable adjustment guide before spending anything.

Step 2: put a gauge on it

This is the step that separates a seal from a valve body from a clutch pack. The 47RE has pressure test ports on the case; Mopar1973Man's port testing guide places ports 1-4 on the passenger side and port 5 (the overdrive port) on the driver's side above the rear cooler line. Their published expectations for a stock unit: accumulator port 54-60 psi at idle rising to 90-96 psi at wide-open throttle in manual 1, manual 2 and drive with overdrive off; front servo within 3 psi of accumulator in drive; reverse 145-175 psi at idle rising to 230-260 psi; and governor pressure 0 psi at 0 mph rising roughly 1 psi per mph. Pressures below spec indicate pump wear or regulation failure; pressures above spec point to a stuck valve. Our own 47RE/48RE line pressure test procedure walks through the same ports.

For the overdrive port specifically, the forum consensus among Cummins owners who test these units is consistent: with a 0-200 psi gauge on the port above the rear cooler line on the driver's side, you see light pressure in drive at all times, then a jump into the 80-130 psi range (depending on valve body setup) when the 3-4 shift is commanded at roughly 35-40 mph. The reading tells you the cause:

• Pressure rises and holds at spec, but the truck still slips: the hydraulics are delivering; the problem is the overdrive clutch pack, its clearance, or the overrunning (roller) clutch.
• Pressure ticks up briefly and then bleeds off: the overdrive piston seal is leaking. Forum testers describe this as one of the most frequent overdrive failures on the 47RE.
• Pressure never rises when the shift is commanded: the shift is not being commanded or the valve body is not delivering it. That is the overdrive solenoid, its wiring, governor pressure, or the overdrive spool valve.

Cause 1: governor pressure and the solenoid circuit

On the RE unit, Diesel Hub notes, governor pressure is electronically controlled rather than hydraulic as on the 47RH. The PCM drives a governor pressure solenoid and reads a governor pressure transducer to decide when fourth is allowed. Next Gen Diesel describes both as poor-longevity parts that respond badly to raised line pressure. A drifting transducer or lazy solenoid produces late, hunting or dropping overdrive that feels like a slip. Sonnax's 47RE catalog lists a governor bore plug kit for 1-2 shuttle, oversensitive 2-3 and 3-2, early upshifts and shift timing problems, which is the worn-bore version of the same fault. The fix is a new 47RE governor pressure solenoid 52118652 with the transducer, and a governor bore repair kit if the bore is worn. Our solenoids collection has the overdrive and lockup solenoids that share the case connector.

Cause 2: the valve body is not delivering fourth

Sonnax lists a long set of 47RE valve body symptoms that cause slip: "leakage of 4th and TCC oil pressure" and "slipping gears" from the boost valve spring retainer; "TCC slip under load," "no line rise during TCC apply in 4th" and "no lockup" from a worn lockup boost valve bore (1994-later with the boost oil delivery tube); "lockup shudder," "low cooler flow" and "build-up of release pressure during lockup" from the 4-spool switch valve; and "poor line pressure control," "reverse slip" and "soft reverse" from the line pressure plug and sleeve. Forum diagnosis also points out that the overdrive spool valve has a tiny bleed hole that a splinter of debris can block, which is easy to miss. If the gauge shows no pressure rise on a commanded shift with a good solenoid, the valve body is the fix. A Sonnax-updated, dyno-tested 47RE valve body is the clean answer; browse the valve bodies collection for the 1996-1999 and 2002-up versions.

Cause 3: the overdrive piston seal, clutch clearance or roller clutch

When the gauge says pressure is arriving but bleeding off, or arriving and holding while the truck still slips, the problem is in the overdrive unit itself. Three things go wrong there:

• Piston seal. A cracked or rolled overdrive piston seal lets apply pressure escape, which is the "brief tick then nothing" gauge signature. Forum testers also note that excess clearance in the direct or overdrive clutch lets the piston overextend and damage the seal, so a seal failure after a rebuild often means clearance was never set.
• Overdrive direct clutch and snap ring. Next Gen Diesel identifies low-quality overdrive direct frictions and the factory snap ring that holds the backing plate as a catastrophic failure: the ring breaks, the plate releases, and debris scatters through the unit. Its fix is a thickened updated snap ring and better frictions. Insufficient clutch capacity in the overdrive brake is a second cause of upper-gear burnout.
• Overrunning clutch and bearings. Sonnax lists an oversized overdrive sprag pilot bushing for "OD roller clutch failure" and an inner overdrive bearing and internal bearing and plate kit for bearing noise and failure. A Mopar1973Man teardown of a 47RE that failed five days after a rebuild found the overdrive thrust bearing had come apart and taken the clutch pack with it; replies stressed that the Torrington bearings and the preload spring for the roller clutch are easy to install backwards. If the roller clutch is reversed, the 1-3 load runs through the overdrive direct clutch, which holds until it wears and then slips.

The fix at this level is an overdrive rebuild: frictions, steels, piston seal, snap ring, bearings, and clearance set to spec. A 47RE master rebuild kit 1998-2002 with filter supplies the overdrive and main-case soft parts together; see the rebuild kits collection for other year ranges and our master kit vs stock replacement kit guide to pick the right one.

Replace while you're in there

• Overdrive piston seal and updated thick snap ring, even if the old ring looks fine
• Overdrive direct and brake frictions and steels, with clearance set
• Overdrive thrust bearings and sprag pilot bushing
• Governor pressure solenoid and transducer
• Overdrive and lockup solenoids (they share the harness and the case connector)
• Filter, pan gasket and fresh ATF+4
• Band adjustment on the main case while the pan is off
• TV cable adjustment after reassembly, before the road test

Cost and effort framing

The diagnosis is cheap: a pressure gauge, an afternoon and the TV cable adjustment cover step 1 and step 2 for almost nothing. Governor solenoid and transducer replacement is a pan-off job in the truck. A valve body swap is also done in the truck, a few hours with the pan and filter off. The overdrive unit can be removed and rebuilt separately from the main case, which is why forum members rebuild it on the bench; it needs a press or a shop to compress the overdrive hub spring and careful attention to bearing and roller clutch orientation. That is still far less work than a full rebuild, provided the gauge said the main case is healthy. If the fluid is burnt and metal is in the pan, the slip has already cost you the rest of the transmission and a full rebuild is the honest answer.

Frequently Asked Questions

Why does my 47RE only slip in overdrive?

Because the overdrive is a separate unit with its own clutch pack, apply piston, roller clutch and solenoid, controlled by governor pressure and TV position. Low line pressure from a bad TV cable, a leaking overdrive piston seal, a worn valve body bore, or a failing overdrive clutch pack all show up in fourth before anywhere else.

How do I tell a piston seal from a valve body problem?

Put a 0-200 psi gauge on the overdrive port on the driver's side above the rear cooler line and drive it. A brief pressure tick that bleeds off on the 3-4 shift is the piston seal; no pressure rise at all is the solenoid, governor circuit or valve body; full pressure with a slip is the clutch pack or roller clutch.

Can I drive a 47RE that slips in overdrive?

Lock out overdrive with the O/D off switch and drive in third until it is fixed. Every slipping shift burns friction material and heats the fluid, and the debris from a failed overdrive snap ring or bearing spreads through the whole transmission.

Sources

• Sonnax Chrysler 47RE Transmission Parts Catalog
• Diesel Hub: Chrysler 47RH and 47RE Transmission Specs
• Mopar1973Man: 47RE Transmission Line Pressure Port Testing Guide
• Mopar1973Man: Just Rebuilt 47RE and It Went Out 5 Days Later (overdrive teardown)
• Next Gen Diesel: 47RE/48RE Transmission Problems, Solutions and Upgrades
• Cummins Forum: Overdrive Testing 47RE