A518 / 46RH No Overdrive and Burned OD Clutch: Diagnosis and the Real Fix

August 10, 2026

A518 / 46RH No Overdrive and Burned OD Clutch: Diagnosis and the Real Fix

You press the overdrive button, the light goes out, and nothing happens. Or 4th engages for a few miles, slips under load, then quits. Pull the pan and the fluid is dark with the overdrive clutch material gone. Most A518 and 46RH owners replace the burned clutch pack and burn the new one within a season.

The clutch is the casualty, not the cause. On these Chrysler four-speeds the overdrive section is fed by a small group of valve body circuits and held in position by a bushing and a stack of selective washers. When any of those lose control, the OD clutch pays for it. Here is how to find the root cause before you buy frictions twice.

What you are working on

The A518 arrived in 1990 as a stronger, medium-rated overdrive unit built on the A727, with an extension housing bolted to the rear of the case carrying the overdrive gearset. The code name tells you how it shifts: in "46RH," the 4 is four forward gears, the 6 is torque strength on a 1-to-9 scale, the R is rear-wheel drive, and the H means hydromechanical control with a governor. On an RH unit the first three shifts are governed hydraulically, while overdrive and converter lockup are switched on and off by their solenoids. A518 ratios run 2.45, 1.45, 1.00 and 0.69 with a 2.35 reverse, rated to roughly 400 lb-ft of input torque in stock form; the A618 is rated to about 450 lb-ft (HGM Electronics).

So 4th gear is a bolt-on section at the back of the transmission, and a "no overdrive" complaint splits into three buckets: the solenoid circuit that commands OD, the valve body circuits that fill and time the OD clutch, and the mechanical parts inside the OD housing.

Diagnosis, in order

1. Confirm the command before you condemn the clutch. Because OD engagement on an RH unit is a straight on/off solenoid function, verify the dash switch, the OD solenoid circuit and its ground first. A unit that never receives the command feels identical to one with a destroyed clutch pack, and this is the cheapest test you will run.

2. Read the fluid and the pan. Black, burnt-smelling fluid with friction material says the OD clutch has been slipping. Bright metal flake or bearing debris points elsewhere in the housing, which changes the parts list.

3. Vacuum test the valve body. This is the step most rebuilds skip, and the one that decides whether your new clutch survives. Sonnax publishes a vacuum test guide for the 46RE, 46RH, 47RE and 47RH valve bodies that maps each critical wear area to the complaints it produces. Test OE valves in rest position unless instructions say otherwise; a low reading indicates wear at that bore (Sonnax Chrysler 46RE, 46RH, 47RE, 47RH Vacuum Test Guide). Three locations in that guide bear directly on a no-overdrive or burned-clutch complaint:

3-4 quick fill valve. Wear symptoms listed as OD clutch burned, no 4th, and gear ratio codes. A worn bore here means the OD clutch never fills cleanly and slips every time it applies.
3-4 timing valve. Listed symptoms: no 4th and gear ratio codes.
Lockup boost valve area. Listed symptoms include no line rise during TCC apply in 4th, and loss of lube oil.

4. Check the boost valve retainer. The U-shaped bracket at the top of the valve body holding the boost valve and spring is prone to cracking, letting both fall out of position. Sonnax lists the result as leakage of 4th gear and TCC oil pressure plus slipping gears, and sells a steel replacement, 22990-01, covering 42RE through 48RE plus the A727 and A904 (Sonnax 22990-01). A broken retainer burns OD clutches and leaves no evidence once the pieces move.

5. Measure the overdrive sprag pilot bushing bore in the output shaft, covered next.

The fix: stop the leak, then set the clearance

If the vacuum test found worn bores, seal the circuits rather than chasing individual valves. Sonnax's Zip Kit 46-47RHE-ZIP seals critical pressure losses in the main line, converter and throttle circuits of 46RE, 46RH, 47RE and 47RH valve bodies with drop-in parts and no special tools. It replaced the discontinued Sure Cure kit SC-46/47RHE, and most contents also service a 48RE, the exceptions being the line pressure plug and sleeve kit and the endplay shims (Sonnax 46-47RHE-ZIP).

Mechanically, Sonnax states that on '88-later units the sprag pilot bushing bore can vary in diameter by as much as .011", leaving replacement bushings loose and showing up as OD roller clutch failure. The correction is to machine the output shaft bushing housing I.D. and install oversized precision bushing 12509-01, a steel-backed bimetal bushing .710" wide with a 2.140" shaft diameter and 2.301" housing bore. That machining requirement makes this a machine shop step, not a parts swap (Sonnax 12509-01).

Then set endplay properly. OE overdrive washers are selective, which is why so many builds end up with whatever thickness was in the box. Sonnax shim kit 12783-01K supplies one .175" primary washer plus three .010" shims so end clearance can be set instead of approximated (Sonnax 12783-01K).

With the circuits sealed and clearances correct, friction material is the last piece. For a 1990-1997 A518, a complete kit beats a bare clutch pack so the seals, rings and gaskets go in at the same time.

A518 Master Transmission Rebuild Kit 1990-1997 with frictions, steels, seals and gaskets — A518 Master Transmission Rebuild Kit 1990-1997 - frictions, steels, seals and gaskets.

If the OD clutch is the only burned element and the rest measured clean, an A518 Friction Clutch Kit 1990-Up covers the friction side alone. For a truck that tows or makes more than stock power, build the A518 High-Performance Deluxe Rebuild Kit 1998-Up with Alto Red Eagle frictions, since the stock unit is only rated to roughly 400 lb-ft. Compare rebuild kits and clutch packs.

Replace these while you are in there

The overdrive housing is bolted to the back of the case, so once it is open these parts cost you nothing extra in labor:

Overdrive bearings. Sonnax lists bearing noise and bearing failure as symptoms here, and offers bearing and plate kit 12860-01K for the O.D. sungear-to-planet location plus inner overdrive bearing 12738 (Sonnax 12860-01K, Sonnax 46RH unit listing).
Boost valve spring retainer 22990-01, which prevents a repeat 4th-gear pressure leak.
TCC apply limit valve kit 22771A-44K if a converter is going in anyway. Sonnax notes 46-47RH/RE and 48RE units lack a valve controlling apply-side converter pressure, so full line pressure hits the converter clutch when it locks; in worn or performance-built units that can reach 150 psi or higher and balloon the converter (Sonnax 22771A-44K).
Overdrive shim kit 12783-01K, so endplay is set with correct pieces rather than reused selectives.

Effort and cost framing

This job splits into two levels of difficulty. The overdrive section and valve body are the approachable half: the OD unit is a separate housing bolted to the rear of the case, and the Zip Kit parts are drop-in with no special tools, so a careful DIY builder can handle the clutch pack, seals, bearings and valve body work. The pilot bushing repair is not DIY, because 12509-01 requires the output shaft bore to be machined oversized. Budget for that machine shop step and the time to set endplay; skipping it is how a rebuilt overdrive comes back apart.

FAQ

The overdrive light works and the solenoid clicks, so why is there still no 4th gear? Command and apply are two different things. Vacuum test the 3-4 quick fill and 3-4 timing valves: Sonnax lists no 4th and burned OD clutch as the wear symptoms for those bores, and a worn bore will not fill the clutch properly no matter how good the solenoid is.

Can I just replace the overdrive clutch pack and leave the valve body alone? You can, and it is the most common reason these units fail a second time. If a worn 3-4 circuit or a broken boost valve retainer caused the original burn, the new frictions see the same conditions the old ones did.

Is an A618 or 47RH overdrive the same repair? The circuits and most parts overlap: Sonnax lists the Zip Kit, the 12509-01 bushing and the 12783-01K shim kit across 46RE, 46RH, 47RE and 47RH, and the boost valve retainer covers 48RE too. Confirm your year and variant before ordering.

Electronically controlled unit rather than an RH? See our 46RE and 47RE complete guide, or 42RE and 44RE erratic shifts and no overdrive.