General Motors Turbo-Hydromatic TH 400 Transmission

[Menschenstimme]

I was TOTALLY IGNORANT regarding the TH 400 banging into a low gear at fast idle when cold. I was innocently testing the gears at a cold fast idle and got a frightening big bang. I was startled and feared the worst.

Apparently, I was lucky and did no damage. I have been driving and testing the transmission while warm, including every gear and all seems well and I hear no mysterious noises.

I was also lucky in that I hear no warning sounds from the differential, rear suspension, etc.

I still think a written warning would have been an ounce of prevention.

Am I one of the rare few who has never been aware of this?

[Organfella]

Automatic transmissions are usually not happy when shifted into drive at relatively high idling engine speeds while cold or even warm. When cold, the automatic choking mechanism increases the engine revolutions to prevent stalling. If the engine could have been started while in Drive, the revolutions would be high enough to move the vehicle forward. Automatic gearboxes are designed to be engaged with a slow turning engine into the first driving gear thereafter shifting automatically upwards depending on the engine speeds. The first engagement has as pre requisite the slower engine revolutions to facilitate a softer gear engagement. Higher than normal idling revolutions will therefore cause a thumpy engagement as you have experienced and is generally not good for the transmission. The same will happen even if the engine is at normal operating temperature but with the foot slightly on the excelerator pedal thus increasing the revolutions. Better to wait a little for the engine to warm slightly and let the revolutions drop somewhat before engaging the drive gear. This might be a good test for patience if you live in a snowy or otherwise colder area.... :->

Hope this helps in explaining the cause of your unpleasant experience.

Nico

[Momboc]

It's probably the Turbo Encabulator

https://youtu.be/MXW0bx_Ooq4