The GM5L40e is a rather inept gearbox for the L322, it saw light in the E36 328i Bmw's IIRC and even then it was made of cheese.
As with LR they never bothered CHECK!! the torque limit for this particular 'box or it's known isses as there were failures already documented at it's time of introduction in the L322 and the de-tuned M57 is putting this box right on the limit..
The TQ is also rather weak in it's design aswell as the Valvebody that has funky solenoids that will cause unintentional clutch slip which destroys the box..
The 'box is a five-speed that saw common use between 1999 and 2006ish It features five forward gears and one reverse, with 4th gear being a 1:1 ratio and 5th gear being “overdrive.”.
So essentially it's a 4spd with overdrive
Problems include but aren't limited to...
Juddering/ leaking from behind the gearbox pump.
Though it’s possible for a pump seal to wear down on its own, in 5L40 like to leak because of a more serious problem, behind the pump seal is a bush that is responsible for keeping the torque converter steady and central as it spins. In this particular case they like to wear down relatively quickly, allowing the torque converter to “wobble” slightly. In addition to certain driving issues such as a juddering sensation, this “wobble” squashes the seal out to the point that it begins letting transmission fluid through.
Which causes low fluid pressure and in turn clutch slip which just eats the box..
You can catch the issue early but you need to remove the gearbox, remove the front end of the transmission dismantle the pump assembly and replace the bush and seal. However in most cases this issue will cause damage to the torque converter neck and even the pump itself, and replacing those parts is sure to be expensive, at that point you might aswell have the entire unit replaced.
Symptoms are
Juddering when driving
and a leak toward the front of the gearbox..
Another issue is Output shaft pline wear..
the output has been known to wear down to the point of no longer functioning the entire drive of the vehicle passes through this shaft so when note the "WHEN" it wears down the vehicle will no longer drive at all and tends to make a horrible noise when it's tried
Next...
When an auto box changes gear, oil is fed into a sealed chamber forcing a piston to push against a stack of friction clutch discs/plates. If the oil was just shot into that chamber all at once the clutch pack will apply with a harsh thump and make for a
very unpleasant shift. The 5L40 gets around this problem with the use of a number of fluid accumulators which allow the oil to be fed in gradually until the pressure is sufficient.
The accumulators work by sitting a small sealed piston on top of a spring so that when the oil is fed into the chamber, it pushes the piston against the spring. These springs, however, have a nasty tendency to break. luckily, repairing this problem is easy. You don’t need to remove the gearbox, just the valve body which is found inside the sump at the bottom of the gearbox..
Symptoms..
Harsh gear shifting and "Trans Failsafe".
Now the Main issue with this 'box is the torque converter..
The most common reason for a vehicle running a GM tranny to the ****ter is torque converter failure For a number of reasons torque converter solenoid, worn valves, worn converter the TQ fails and begins contaminating the oil with debris. The debris circulates throughout the transmission and begins blocking the filter. Once the filter is filled with crap, the clutch packs are starved of oil and begin to slip. The slipping clutches begin to burn up, further contaminating the oil with crap and you get the gist.
If you were very lucky and caught this problem
very early, you might get away with an oil flush and a new converter/filter though It would be advisable to get it rebuilt. For most people nothing less than a full rebuild and replacement converter will fix the problem. The easiest way to check for this problem is to remove the sump and check for metal and general debris in the sump. If the converter has failed in this fashion, the sump will be full of metallic debris.
Run the old oil through coffee strainers to catch an debris, this will give a good indication of the trannys heath, if it is currently behaving..
