Why does my automatic transmission slip or shift hard?

If your automatic car revs up without accelerating to match, slams into gear or bangs into Drive, or jerks when you accelerate, something is wrong with the transmission… or the engine. This article covers how to tell whether it's slipping, shifting hard or jerking, why each one happens, why it sometimes only fails cold or hot, the known problems of the most common transmissions and which parts get replaced.

Slipping, hard shifts or jerking? How to tell

• Slipping: the engine revs up but the car doesn't accelerate to match, or a shift takes too long and flares. Sometimes it smells burnt.
• Hard shifts: the gear slams in. It can happen when you put it in Drive or Reverse, on the 1-2 shift, on downshifts or while braking.
• Neutral flare: during a shift, the revs jump for a moment as if it were in neutral, because one clutch released before the next one applied.
• Jerking or shudder: jolts when accelerating or at steady speed. It's often the engine, not the transmission, from failing spark plugs or coils, so rule that out first.

First: the fluid level and condition

Before buying parts, check the fluid. With low fluid there isn't enough pressure: according to Ford's workshop manual, the transmission engages poorly or slips, and the 5R55W, for example, drops into neutral in corners. With too much, the fluid foams and pressure turns erratic. The wrong fluid matters too: Chrysler warns that on the 41TE another fluid can make shifts worse and cause converter shudder, and in 2015 it fixed harsh shifts on 62TE minivans just by correcting the level.

Many modern transmissions have no dipstick, and the level is checked at a plug at an exact temperature: 95 to 113 °F on the 09G and 01M, and 175 to 185 °F on the 6R80, according to their makers. If the fluid is burnt or has metal in it, there's already internal damage. Sun Transmissions lists the signs of a slipping transmission.

Why does an automatic transmission slip?

An automatic transmission changes gears by applying clutches, which are packs of friction and steel plates, and on many units, bands too. It slips when one of them doesn't hold hard enough. These are the typical causes:

• Worn or burnt clutches and bands. On the 4L60E, if it slips in 2nd and 4th but 3rd is fine, GM suspects the 2-4 band; on the 4R70W, if it won't shift into 4th or drops into neutral in overdrive, the overdrive band.
• Leaking seals and pistons, so the clutch doesn't get full pressure. On the 41TE, the underdrive piston seal leaks when cold and the transmission is slow to move; on the 4R70W, a blown 2-3 accumulator piston burns the direct clutch and it slips in 3rd.
• A worn valve body: the valve bores wear, pressure leaks and the transmission slips, especially when hot. Transmission Digest documents it on the 4R70W, and Sonnax on the 6R80 and the Nissan CVT, where low pressure makes the belt slip.
• Worn case bores: on the 5R55W and 5R55S, worn servo bores let the bands slip, worse when hot.
• The pressure control solenoid or its circuit. Note: on the 4R70W, replacing only the EPC solenoid doesn't fix a worn valve body.
• On a CVT the belt slips, and on a PowerShift, the dry clutch slips when it's contaminated by oil from leaking seals.

Sun Transmissions explains how automatic transmission bands work and how to measure clutch wear.

Why does it slip when cold or when hot?

If it only slips when cold and gets better once warm, suspect seals that leak while they're cold: that's the case with the 41TE underdrive piston, which according to TransGo makes the transmission slow to move when cold. If it slips when hot, after driving a while, the usual cause is wear in the valve body or case bores, which leak more with hot fluid: that's how Transmission Digest describes it on the 4R70W, and specialists on the 5R55W and 5R55S. On the Nissan CVT, losing power on the highway or uphill can be the temperature protection, which limits power to protect the transmission.

Slips on the 2-3 shift or in 3rd

If the problem shows up on one particular shift, that shift tells you which clutch or band to check. On the 4R70W, slipping in 3rd points to the direct clutch and its accumulator; on the 4L60E, no 3rd or 4th points to the 3-4 clutch; on the 5R55W and 5R55S, to the band servos. On the 2002 Explorer with the 5R55W, Ford issued bulletins for a slipping 2-3 shift, depending on the build date.

Why does it shift hard?

A hard shift is almost always too much pressure, or pressure at the wrong moment. These are the causes manufacturers document most:

• Limp mode: when the computer detects a fault, it raises line pressure to maximum to protect the transmission, and shifts come in hard. GM describes it that way for the 4L60E, and Ford for the 6R80.
• Something slips and the computer compensates: on the 4L60E, code P1870 (P0894 on newer models) means something is slipping; the computer raises pressure and the 1-2 shift feels harsh. It's one reason a 4L60E Silverado slams the first shift.
• The accumulators and their dampers, which cushion each shift: when they wear, the shift comes in harsh. Sonnax and TransGo mention it on the 6R80, and Sun Transmissions explains how the accumulator relates to gear changes.
• A worn valve body and solenoids: on the 09G they cause bangs into Drive or Reverse and harsh shifts, especially when cold; on the 6R80, harsh downshifts.
• The computer hasn't finished learning: after a battery disconnect or a repair, shifts can feel firm for a few days, according to Ford. On the 09G the adaptations must be cleared and relearned, and on the 41TE and 62TE, a Quick Learn is done with a scan tool.
• A missing update: Chrysler fixed several 41TE and 62TE harsh shifts with reprogramming. Ask a dealer with your VIN.
• It isn't the transmission: loose or broken engine or transmission mounts, or the driveshaft. Ford found that the clunk shifting from Reverse to Drive on some 2015 to 2017 Mustangs came from the driveshaft.

Sun Transmissions covers common shifting problems and fixes and why a transmission needs to learn after a repair.

Bangs into Drive or Reverse

If the bang comes when you move the shifter with the car stopped, also check the engine and transmission mounts. On the 09G it's one of the most common complaints, from valve body and solenoid wear; on the 2004 and 2005 5R55S, Ford documented delayed or harsh Reverse; and on the 62TE, GEARS recommends relearning the engagements with the fluid warm, around 90 °F, when the normal relearn doesn't fix it.

Is the jerking from the transmission or the engine?

Jerking on acceleration often comes from the engine, from misfires. A clue we explain in the 4L60E guide: if it shudders right when the converter locks up, suspect the converter or its circuit; if it shudders once it's already locked, the cause is usually elsewhere, such as the engine, and a misfire can even keep the converter from locking up. On the Nissan CVT, the jerking when pulling away slowly has a name, judder, and Nissan diagnoses it with codes P17F0 (belt slip) and P17F1 (valve body). On the PowerShift, the shudder when pulling away comes from the clutch. Sun Transmissions explains why a car jerks when stopped at a light.

Known problems by transmission

Each transmission has its typical problems. These are the most common ones, each with its full guide:

Not sure which transmission your car has? Look it up in our guides for Nissan, Chevrolet, Ford and Volkswagen.

What happens if I add an additive to an automatic transmission?

An additive doesn't repair worn plates, leaking seals or a worn valve body. Ford's fluid chart says not to use supplemental additives, treatments or cleaning agents in its transmissions, and Nissan asks for only the fluid in the owner's manual. If the transmission slips, the right fluid at the right level is the first step; the rest is diagnosis.

How it's diagnosed and repaired

• Check the fluid level and condition as the manual says, at the right temperature.
• Scan it with a tool that reads the transmission: incorrect-ratio codes (P0730 to P0735), low-pressure codes (P0868) or slip codes (P0894) tell you where to start.
• Ask a dealer about software updates for your VIN. If the battery was disconnected or something was repaired, let the computer relearn or run the relearn with a scan tool.
• Rule out the engine, the mounts and the driveshaft.
• Test line pressure before replacing solenoids: a worn valve body gives the same symptoms. Sun Transmissions has a pressure testing guide.
• Don't keep driving it while it slips: every slip heats and wears the plates, and a small repair can turn into a rebuild.

Sun Transmissions has articles on codes P0730 and P0868.

See TSS plates, bands and pistons

TSS parts for a transmission that slips or shifts hard

These are the parts most often replaced when a transmission slips or shifts hard, and the TSS catalog has them for the most common transmissions:

• Overhaul kits: Rojo, the economy line, and Dorado, the premium line, with the seals for a full rebuild. We explain the difference in TSS Rojo vs Dorado overhaul kits.
• Friction plates and steel plates, such as the 4L60E 3-4 steels, among TSS's best sellers.
• Bands, such as the 4R70W overdrive band and the A4LD and 5R55E intermediate band.
• Bonded and accumulator pistons, and piston kits such as the 09G's.
• Filters, solenoids and valve bodies.

Before ordering, confirm your transmission by year, engine and VIN.

TSS is an aftermarket brand with OEM-comparable quality and quality control on every product. You can buy it from our authorized distributors: in the United States from Sun Transmissions, and in Mexico the full TSS catalog at Transmisiones Veinte 07.

TSS products

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• Disco Acero 3ra y 4ta 106" 1993/UP 4L60E 4L65E
• Banda Flexible Intermedia Overdrive C3 A4LD 4R44E 5R55E
• Banda Sobremarcha TSS AODE 4R70W 4R75W OEM F2TZ Ford
• PISTON VULCANIZADO 3RA-4TA TH700-R4, 4L60E, 4L65E, 4L70E
• Juego de Pistones 09G (AQ250) 09K (TF-61SN) con Sellos
• Piston Acumulador 1ra-2da & 3ra-4ta TH700-R4 4L60E 4L65E 4L70E TH200-4R TH325-4L
• Juego de Empaques TSS Dorado 4L60E 1993/03
• Filtro 6.3" Altura Total, 1.30" Altura del Espaciador GM 6L50 6L80 6L90

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