Buick Century
Transmission Problems

The W-body Century shares its platform and drivetrain with the Regal, Grand Prix, Impala and Monte Carlo of the same years. That is good news for owners: every transmission shop has seen hundreds of these, parts are cheap, and used units are easy to find. The bad news is that most Centurys were bought by people who never thought about the transmission until it started slipping, and by then the fluid has often been cooked for years.

Behind the 3.1L sits GM's electronically controlled four-speed front-drive automatic. Earlier cars use the 4T60-E family, and later cars moved to the 4T65-E family. The two look alike on the car, but they are not the same transmission inside.

Century Drivetrain at a Glance

Do not guess from the model year. Read the RPO code on the Service Parts Identification label, usually in the trunk near the spare tire or in the glovebox, or read the ID tag on the transmission case. Solenoids, filters, drums and rebuild kits are not all interchangeable between the 4T60-E and 4T65-E, and ordering the wrong one is the most common parts mistake we see on these cars. Our 4T60-E problems and cost guide and 4T65-E problems guide go deeper on each unit.

Common Century Transmission Problems

1. Flare or slip on the 1-2 and 2-3 shifts

This is the classic Century complaint. You accelerate, the rpm jumps between first and second or second and third, then the gear finally grabs. Early on it only happens when the car is hot or under heavier throttle. On these units it usually traces back to a worn second clutch, a worn 2-1 band, or low apply pressure feeding them. Check the fluid level hot and scan for codes before anything else. If the fluid is full and the flare keeps getting worse, the friction material is going and no additive will bring it back. A 4T60-E shift kit installed during a rebuild firms up apply pressure, but it is not a fix for clutches that are already burned.

2. Harsh shifts and the pressure control solenoid

A Century that bangs into second or slams into drive from park is often telling you the pressure control solenoid has worn out. That solenoid sets line pressure, and when it sticks or drifts, shifts go from soft to violent or bounce between the two. It may or may not set a code. Do not ignore it: erratic pressure is what wears the clutches that cause problem number one. On 4T60-E cars a 4T60-E solenoid kit covers the common electrical parts; on 4T65-E cars use the 4T65-E pressure control solenoid.

3. TCC shudder at highway speed

A shudder like driving over rumble strips at 40 to 55 mph, usually at light throttle, is the torque converter clutch applying and slipping. Old, worn-out fluid is the first suspect. A failing TCC solenoid can cause shudder, a converter that never locks, or a stall when coming to a stop. Change the fluid and filter, and if a TCC code is present or the shudder comes right back, replace the 4T60-E TCC solenoid. If it still shudders on fresh fluid with a new solenoid, the converter itself is the problem.

4. No reverse

Forward gears work fine but nothing happens in reverse, or reverse engages late and slips. On these transmissions that points to the reverse band or its servo. Confirm the fluid is full first, because low fluid shows up in reverse before the forward gears. If the level is right and reverse is gone, it is an internal repair. Our 4T65-E no reverse fix walks through the diagnosis, and most of it applies to the earlier unit too.

5. Dead speedometer and erratic shifts

When the speedometer drops to zero and the transmission starts shifting at odd times or hangs in one gear, the vehicle speed sensor or its wiring is the usual cause. The controller cannot pick shift points without a speed signal. A sensor is cheap and easy compared with anything else on this page, so scan for a speed sensor code and check the connector for corrosion before anyone mentions a rebuild.

6. A burnt-up unit that never saw a fluid change

The most common way a Century transmission dies is simple neglect. A car at 150,000 miles or more on factory fluid, dark brown and smelling burnt, with slipping in several gears, is worn out inside. Changing the fluid at this stage sometimes makes it worse because the fresh fluid has different friction properties than the varnished stuff that was holding it together. The lesson is to service it before 100,000 miles.

How to Tell a Cheap Fix From a Rebuild

• Speed sensor code, dead speedometer: sensor or wiring. Under a couple hundred dollars.
• Harsh shifts, fluid looks good: pressure control solenoid. Side cover or valve body work, not a rebuild.
• Shudder only, clean fluid: fluid service and TCC solenoid before a converter.
• Flare getting worse week by week: clutch or band wear. Rebuild or replace.
• No reverse with full fluid: reverse band or servo. Internal.
• Black, burnt fluid with debris in the pan: the transmission is done. Plan accordingly.

Fluid: Dexron III Then, Dexron VI Now

The Century was filled with Dexron III at the factory. Dexron III is no longer licensed, and Dexron VI is the backward-compatible replacement GM specifies today. It is fine to service an older Century with Dexron VI; our Dexron III to Dexron VI compatibility guide explains why. Drop the pan and replace the filter with a 4T60-E/4T65-E filter and pan gasket kit, then refill with ACDelco Dexron VI. On a high-mileage car with original fluid, do a pan drop rather than a pressure flush.

Real Repair Costs

Rebuild or Replace?

Be honest about the car. Most Centurys on the road today are worth less than a shop rebuild costs. If yours needs a solenoid, a speed sensor or a fluid service, fix it without a second thought. If it needs a full rebuild, a warrantied used transmission is usually the smarter money, as long as it matches your RPO code. A rebuild makes sense when the car is unusually clean, low-mileage, or you are doing the work yourself with a 4T60-E master rebuild kit or the parts in our 4T65-E rebuild parts guide. Rebuild kits for both units are also available at Core Transmission Parts.

FAQ

What transmission is in a 1997-2005 Buick Century?

A GM front-drive four-speed automatic behind the 3.1L V6. Earlier cars use the 4T60-E family and later cars use the 4T65-E family. Check the RPO code on the Service Parts Identification label or the ID tag on the transmission before you order parts, because the two units do not share every part.

Why does my Century flare between first and second?

A flare on the 1-2 shift usually means the second clutch is worn or not getting enough apply pressure. Low fluid and a worn pressure control solenoid can cause it too, so check the level and scan for codes first. A flare that gets worse every week is clutch wear, and that means a rebuild.

Why will my Buick Century not go into reverse?

On these transmissions no reverse with good forward gears usually points to the reverse band or its servo. Low fluid can cause it as well. If the fluid is full and clean and reverse is still gone, the transmission has to come apart.

What fluid does a Buick Century transmission take?

The car was filled with Dexron III from the factory. Dexron VI replaces Dexron III and is the correct fluid to use today.

Is it worth rebuilding the transmission in a Buick Century?

Solenoid, sensor and fluid repairs are worth doing on almost any Century. A full shop rebuild usually costs more than the car is worth, so unless the car is unusually clean or you are doing the work yourself, a used transmission with a warranty is usually the better call.