Common Issues With The 1000/M74 Transmission
Posted by Regis on Tuesday, March 5th, 2013
The 1000/M74 is a very heavy duty automatic overdrive transmission built by Allison Transmission. It is primarily used behind the powerful Duramax diesel engine found in many later model GMC and Chevy trucks. It can also be found on GM chassis under custom motor homes, buses and other heavy duty vehicles. While this is a very heavy duty transmission, it is not without faults and problems. Let’s take a look at the 1000/M74 transmission.
Electrical: The 1000/M74 transmission is loaded with electrical components. It incorporates multiple electrical solenoids and sensors, not to mention a fairly complex wire harness. All electrical transmissions suffer from similar problems. Solenoids often fail. They either develop an internal short, or end up with a break in the internal wiring that makes up the electrical magnet in the solenoid. Sensors can go bad for a number of reasons. Excessive heat or vibration can destroy them. Improper grounding can also cause them to malfunction. Excessive heat, driving conditions and age can destroy the wire harnesses.
Overheating: By far the biggest problem with this transmission is overheating. This is not the manufacturers fault. Overheating is usually caused by the vehicle owner. They tow loads way heavier than the maximum recommended limit. The also load their vehicle with more payload than is recommended. Doing either will put tremendous strain and stress on the transmission. Clutches and bands will sometime slip in server instances, creating excessive heat. Keep in mind that these transmissions are designed to run at a maximum temperature of 200 degrees. Every 20 degree about this temperature will cut the life span of the transmission by a factor of two.
Lack of maintenance: All vehicles come with recommended maintenance intervals. The problem is that most owners pay no attention to them. Filters get clogged over time and restrict the flow of transmission fluid. Transmission fluid breaks down over time and the result is a fluid that loses its hydraulic properties and ability to lubricate the transmission correctly.
Want to make your transmission last longer? Who doesn’t? Here are a few recommended upgrades:
Fluid upgrade: Your transmission comes from the factory with an organically derived transmission fluid. It is specifically designed to meet strict requirements. Over time it will break down from the many heating and cooling cycles it endures on a daily basis. Therefore, I recommend you upgrade to a synthetic fluid. Synthetic fluids are designed not to break down like organic fluids. Just be sure to replace your organic fluid with a synthetic fluid that has the same properties as the original OEM fluid.
Deep pan: Install a deep pan. The extra fluid will help keep the fluid a little cooler. The fluid will also last a little longer before it needs to be replaced.
Oil Cooler: Buy an aftermarket transmission cooler. A good rule is the bigger the better. Excessive heat is by far the number one killer of all automatic transmissions, and this transmission is no exception. Additionally, you can buy an aftermarket cooler that comes equipped with its own electrical fan. This will provide addition protect from overheating the transmission.
The 1000/M74 transmission is a great transmission. You should get years of trouble free service and reliability from it as long as you adhere to the information we provide.
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