Allison Code 2511 Output Speed Sensor/ M1078

[Lugnuts]

Hello folks:
I am having a real time navigating the Steel Soldiers site. Please, I need help. (My Daddy would agree)
My problem is a truck in limp mode stuck in 2nd gear range, has a code of 2511 Output speed sensor. I am familiar that this sensor will do just that from other vehicles I have worked on. Location of the sensor I need verification. They are generally located at the rear of the shaft but this is where you have a transfer case bolted, and it appears that the sensor is located on the transfer case lower passenger side of the case. I have read that the number on the sensor is [FONT=Segoe UI, Segoe UI Web (West European), Segoe UI, -apple-system, BlinkMacSystemFont, Roboto, Helvetica Neue, sans-serif]29505601. Are there 2 different speed sensors as in one for Transmission and one for Vehicle Speed? Is it best to service the transmission at the time of doing this sensor, that is do you need to drain the oil to get to location?
Would appreciate the assistance,
Lugnuts[/FONT]

 

[Suprman]

Output speed sensor on bottom of trans. Held on by one bolt. Over the counter allison part.

 

[Lugnuts]

Do you happen to have a picture showing placement. Thank you for responding.

 

[texfireman]

Output speed sensor on bottom of trans. Held on by one bolt. Over the counter allison part.

is this a speed sensor ?

 

[Suprman]

No. input speed sensor on bellhousing by scav pump.

 

[Lugnuts]

The photo is actually a connection for a sensor. I cannot tell quite where you are for sure. I believe Suprman said that was an Input Speed Sensor.
The Output Speed Sensor is located on the right side of the truck ie passenger side and is on the Transfer Case. The through hull is on the front of the transfer case and access to the Speed Sensor is on the rear of the Transfer Case with I believe a 10 bolt square pattern plate which has lots of oil behind it until you drain some.

 

[aaronisintexas]

Hello folks:
I am having a real time navigating the Steel Soldiers site. Please, I need help. (My Daddy would agree)
My problem is a truck in limp mode stuck in 2nd gear range, has a code of 2511 Output speed sensor. I am familiar that this sensor will do just that from other vehicles I have worked on. Location of the sensor I need verification. They are generally located at the rear of the shaft but this is where you have a transfer case bolted, and it appears that the sensor is located on the transfer case lower passenger side of the case. I have read that the number on the sensor is [FONT=Segoe UI, Segoe UI Web (West European), Segoe UI, -apple-system, BlinkMacSystemFont, Roboto, Helvetica Neue, sans-serif]29505601. Are there 2 different speed sensors as in one for Transmission and one for Vehicle Speed? Is it best to service the transmission at the time of doing this sensor, that is do you need to drain the oil to get to location?
Would appreciate the assistance,
Lugnuts[/FONT]

It is the sensor in your transfer case. On the back side of your tc there is a small square-ish shaped door held in place with about 10 bolts. there is an electrical harness in there that sometimes breaks. It is called a connector assembly, part # 29506351. Stewart & Stevenson in Houston has access to this part as it is drop sent from the manufacture . The cost for the part is about $400.00. Make sure you order the gaskets at the same time. See photos for part numbers. I just ordered this part on 6/15/2021, as soon as it comes in I will make a video on the repair. As you can see in the pictures, the wires will break free from the pins creating an open solenoid error, stopping the truck from moving out of second gear. I hope this helps someone out there... Good luck

 

[CallMeColt]

This video might help you as well. Troubleshooting codes can be a rabbit hole!

 

[Sully LMTV]

Wow Colt... just went through your troubleshooting and video - great video BTW. Thank you!

I have gotten the 2nd gear indication after putting it into Drive (expecting "7") and having to shut the truck down in the middle of the street to clear it. I was not aware of the code process until now and will check those.

No questions, just want to say a huge thanks for posting your issues and work process - it was very helpful.

 

[CallMeColt]

Wow Colt... just went through your troubleshooting and video - great video BTW. Thank you!

I have gotten the 2nd gear indication after putting it into Drive (expecting "7") and having to shut the truck down in the middle of the street to clear it. I was not aware of the code process until now and will check those.

No questions, just want to say a huge thanks for posting your issues and work process - it was very helpful.

Glad it was helpful. That is why I make the videos. Forums are great. Pictures are worth a thousand words. Videos are millions of pictures.