3 Popular Automatic Transmissions With Common Faults
When your job is repairing faulty automatic transmissions, you get used to seeing the same offenders rolling through your door on a regular basis. Despite the popularity of the automatic transmissions we’re going to talk about in this article, they all have some fairly common issues that have seen many drivers calling for a recovery services from the side of a road, often stood next to a pretty expensive vehicle.
The push to increase driving comfort, improve efficiency, keep weight down, and lower manufacturing costs have all contributed to a number of transmissions being great to drive when they’re functioning correctly, but ultimately riddled with flaws that can cause the transmission to misbehave or worse; stop working entirely.
Here are three popular transmissions that I regularly see on my workbench with quite severe problems.
The GM 5L40-E
The 5L40-E is a five speed automatic transmission that was used predominantly between 2000 and 2007 in a number of cars, most notably BMWs, Range Rovers, and Cadillacs. Due to the high end nature of the vehicles the 5L40-E was used in, there are many still on the road today, nearly a decade after the transmission was superseded.
The 5L40-E has a number of minor problems, including some that are only just now becoming commonplace as these transmissions age, such as a complete loss of drive first thing in the morning (that is, when the vehicle is cold), but the big one for this particular transmission causes a complete loss of drive indefinitely.
- The GM 5L40-E Automatic Transmission: Common Problem...
An in-depth look at the common faults of the GM 5L40-E transmission.
The torque converter used in the GM 5L40-E is prone to failure. When this happens, the friction materials in that converter break down and contaminate the oil. The debris in the oil is then circulated throughout the transmission where, eventually, it will end up in the filter. Now, obviously the filter is designed to stop debris like this getting where it shouldn’t, but as there’s so much of it what actually happens is the filter becomes completely blocked, starving the transmission of oil. Without sufficient oil flow, the clutches in the transmission itself are unable to apply properly and begin to break down, contaminating the transmission fluid with debris which is then circulated through the transmission where it eventually blocks the filter. It’s a vicious cycle.
Unfortunately, when things progress to the point where the transmission has a partial or complete loss of drive, the damage is typically done, and there’s little for it but to get a complete overhaul. Or replace the transmission entirely.
The Mercedes-Benz 5G-Tronic 722.6
More commonly referred to as simply a “722.6” in the industry, this transmission was Mercedes-Benz’ own entry into the five speed automatic transmission market, and is still used to this day in some models of Jeep and Ssangyong—though Mercedes themselves have phased it out in favour of an updated seven speed iteration. Mercedes had a lot of confidence in the versatility of this transmission, fitting it in everything from compact roadsters to long wheelbase vans.
Without detailing every potential fault this transmission has been known to get, there are three particularly common faults that occur. The first, and least severe, is again to do with the torque converter. Wear and tear in the 722.6’s valve body can cause the converter to come in and out of lockup when it shouldn’t, resulting in a judder or rumbling sensation. There are repairs that can be carried out on the valve body to fix this issue, but if it is left to progress too far a replacement torque converter will be needed.
The next big problem for the 5G-Tronic is the failure of what is known as a “conductor plate”, or electrics pack. Essentially just a plastic board with metal contacts running through it, the conductor plate is responsible for carrying the signal to and from the 5G-Tronic’s few electrical components to the plug where the transmission is connected to the vehicle. It also houses the internal speed sensors, which are the most common point of failure. When this part fails the usual result is the vehicle going into “fault mode” (also known as “limp mode”) and will only operate in one gear.
Finally, the biggest common fault with these transmissions, and the most significant in terms of repair, is a wear and tear issue with the transmission itself. The seals within the transmission that are responsible for keeping the clutches operating properly wear down over time. This is true of all seals, of course, but in the 722.6 they wear down with almost clockwork-like precision. It is very unusual for a 5G-Tronic to manage much more than 80,000 miles without needing a complete strip down to replace the internal seals. And, given that most drivers don’t notice this kind of problem until it’s started doing damage inside the transmission, a strip down often turns into a full overhaul.
The Audi 01J Multitronic
The 01J Multitronic transmission is a 6 or 7 speed transmission that Audi used in many of their A4, A5, and A6 vehicles from 1999 onwards. The 01J is a CVT (constant variable transmission) gearbox, meaning that instead of a mess of gears or a stack of clutches, the 01J is primarily driven by a large chain around two sets of cones. These cones allow the transmission to alter the gear ratio simply by moving the cones up or down, forcing the chain in or out and thus changing the ratio at which it turns. This makes for better efficiency and a smoother driving experience.
It’s also a nightmare of a transmission.
There are different iterations of the 01J, but they’re all riddled with issues. Drivers of 01J transmissions have been known to experience a juddering sensation that is typically caused by wear in the front clutch assembly and/or wear and tear in something called an “entrainment pump”. The clutch assembly can be changed relatively easily (though the transmission will have to come out) but the entrainment pump will require a full strip down of the transmission.
In addition to this, all manner of shifting faults can be traced back to the mechatronic unit—the computer that controls the transmission. These units seemingly go faulty without warning, and need to either be repaired by a specialist or replaced entirely.
Finally, and most worryingly, the 01J can suffer a total loss of drive that is caused by the shaft attached to one of the cones snapping cleanly in two. When this happens the entire cone needs replacing at the very least, however this fault will nearly always result in a damaged chain which in turn damages the other cone. When both cones and the chain have failed, it tends to be cheaper to try and find a replacement used transmission in its entirety than to try and repair the original one.
So there you are, three very common transmissions with sadly common faults. It’s worth noting that these transmissions are common for a reason; when they work they work well, and the fact that I have seen so many of them on my workbench may be as much to do with their prevalence on the road as it is to do with their foibles.
© 2016 John Bullock