Recently changed my engine,now the transmission,not changing gears or shifting properly

It sounds like you're facing a transmission issue with your MAN Diesel TGA truck. If the truck is not shifting into gear and the engine is not revving properly, there could be several potential reasons for this problem. Here are a few things you can check:

1. Transmission Fluid Level and Quality: Inspect the transmission fluid level and condition. Low fluid levels or dirty/burnt fluid could affect the transmission's performance. Ensure that the fluid is at the correct level and is not excessively contaminated.
2. Transmission Linkage: Check the linkage between the gear lever and the transmission itself. Sometimes, linkage problems can prevent the transmission from engaging properly.
3. Transmission Control Module (TCM): The TCM is responsible for controlling the shifting of gears. A malfunctioning TCM could cause issues with gear changes. Scan for any error codes using a diagnostic tool to identify TCM-related problems.
4. Solenoids: Automatic transmissions use solenoids to control the flow of transmission fluid, which in turn controls gear shifting. Malfunctioning solenoids can lead to gear engagement problems. A diagnostic scan can help identify if any solenoids are faulty.
5. Torque Converter: Issues with the torque converter can cause difficulty in shifting gears. A mechanic should inspect the torque converter to ensure it's functioning correctly.
6. Electrical Connections: Ensure all electrical connections related to the transmission system are secure and free of corrosion.
7. Vacuum Lines (if applicable): If your truck has a vacuum-controlled transmission, check for any vacuum leaks or issues with the vacuum lines.
8. Clutch System (if manual transmission): If your truck has a manual transmission, problems with the clutch system, such as a worn clutch plate or a malfunctioning clutch master or slave cylinder, could cause shifting difficulties.

Given the complexity of modern transmissions, it's recommended to have a professional mechanic or technician diagnose and address the issue. They can perform a detailed inspection, run diagnostics using specialized equipment, and provide you with an accurate diagnosis and repair plan.
If the engine is not revving properly in addition to the transmission issue, it's possible that these problems might be interconnected, and a comprehensive diagnosis is essential to resolve the overall performance issues with your truck.

There are a few possible reasons why your 2014 Fuso 515 manual transmission might not shift from neutral into gears when the engine is running but will shift when the engine is not running. The clutch is not disengaging properly: The clutch is responsible for engaging and disengaging the transmission from the engine. If the clutch is not disengaging properly, it can cause the transmission to not shift gears properly. The synchronizers are worn or damaged: The synchronizers are located in the transmission and help to match the speed of the engine and the transmission when shifting gears. If the synchronizers are worn or damaged, it can cause the transmission to not shift gears properly. The transmission fluid is low or dirty: The transmission fluid lubricates and cools the transmission. If the transmission fluid is low or dirty, it can cause the transmission to not shift gears properly. The transmission is faulty: If the transmission is faulty, it can cause the transmission to not shift gears properly. If you are experiencing this problem, it is important to have your vehicle diagnosed by a qualified mechanic to determine the root cause of the problem. Once the cause of the problem has been identified, the mechanic can recommend the necessary repairs. Here are some tips to help prevent this problem from happening in the future: Use the clutch properly: When shifting gears, use the clutch to disengage the transmission from the engine. Have your transmission serviced regularly: The transmission fluid should be changed according to the manufacturer's recommendations. Avoid shifting gears when the engine is under load: When the engine is under load, it can put stress on the transmission and cause problems.

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Did it do it under hard acceleration? or just a normal take off. I have heard of engine mounts or tranny mount bushings getting old (not mileage old but just aging) causing a thump or clunking sound in between shifting. What happens is the tranny actually hits the undercarriage of the vehicle during high torque situations such as shifting gears. I have also seen the mount retaining nut back off of the mounts and the only thing holding everything in place is gravity. Another possibility is drive shaft u-joint problems, but if it were it would probably be making the noise more often. I dont think there is actually anything wrong with the transmission itself as usually when they go bad they dont magically get better. Hope this helps. Good luck!

was the oil clean of residue ?
you might have a faulty valve that makes the shifts rough

Has the transmission flushed and the filter been changed recently? That could be the problem of it not shifting into passing gear.

I had a simular problem.
Ended up changing the themastat and the gears changed into overdrive when the temp. got to normal running.
Be carefull that you get right thermastat though. You want one that reaches the normal working Temp as soon as possable.
Hope this helps.

When was the last time the Transmission Fluid and Filter were changed? More than 35,000 miles = Fluid and Filter change.
Is there any leaks what so ever? This will affect shifting.
Have the Transmission Sensors been removed, cleaned/inspected and reinstalled? These Sensors are "magnets" and catch little metal particles that inhibit their functions, including shifting.
What is the condition and level of the Transmission Fluid. Make sure you smell the Fluid. If it smells burnt, then change it immediately. Make sure you check the level when the engine is at normal temperature and while the engine is running, with the gear in Park or Neutral (with the Parking Brake ON!).
Does this Transmission have a Solenoid (electronic shifting)? If so have you checked the electronic connections for corrosion or oxidation?
Don't spend $2,000 (or more) dollars when the rest of these combined cost less than $200 dollars!
Let me know if this helped, or if you have additional information or questions. Feel free to contact me at FixYa.com!

Sounds like the transmission needs a rebuild.

it sounds like the mechanic didn't properly adjust the inhibitor switch and transmission control cable.