Lockup surge in Allison 1000s

Have you ever found yourself chasing a “phantom” TCC driveability problem in a GM vehicle that uses the Allison 1000/2000/2400 series of transmissions?

If you have, there’s a good chance that the root of your problem turned out to be the torque converter. No earth shattering news there, but what is unique is that the problem was likely on the outside of the converter, not the inside. Here’s a case in point. A 2001 2WD Chevrolet 1500 with a 6.6L diesel engine and an Allison 1000 transmission was returned to a transmission shop. The transmission had been overhauled recently and the customer’s complaint was a cycling TCC, or what he described as a lockup surge. A scan check of the vehicle found no codes. The PCM would command the TCC solenoid off at regular intervals. The vehicle’s tachometer remained steady, but the live data on the scan tool showed a small repeating spike in the engine rpm. The pickup for the engine rpm sensor is the input speed sensor located in the bell housing of the transmission and is excited by the row of dimples on the torque converter closest to the engine.

To read the rest of this Technical Article on the Sonnax Website click here.

Article No.: TCTIP-04-07
Author: Ed Lee
Total Pages: 2

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