1982 Avanti Transmission Speed Sensor.

[Stuart Boblett]

Hell folks, I have another difficult problem that I need your help on. On the side of the Automatic OD transmission there is a "device" that installs into the transmission and the speedometer cable and a couple wires connect to it. I thought initially that it was a cruise control sensor but have been advised that it is a "Speed Sensor" that connects to the computer. I was told that these were specifically made for Avanti and are hard to come by. Mine is leaking transmission fluid and supposedly that is a symptom for failure in the near future throwing a check engine light. The cost of these is about $500. dollars which really crazy. Is anyone familiar with these devices, had problems and have any suggestions? Thanks a bunch, this has got me flabbergasted and I can find no reference to it elsewhere in this forum. 

[Avanti83]

Interesting as yours is a year older than my 83 and, I believe, you have the TH 350/400 3-speed auto. The 700R4 from my 83 only has a mechanical speedo cable connector in the tail shaft so if your part exists NOS it must be real rare part. Mine must pickup speed from the timing/tach setup. 

IAC, when I bought mine it ran kinda OK but was a dog and had acceleration issues. I just replaced the ECM setup with a carb and eventually a performance engine with EFI. 

I'm surprised any part you would need is not available as Avanti used SBC's as they were already smog legal so I would think they would use basically GM electronics also to keep the smog certs.

Post a picture of what you have if possible and IIWM, I'd Google for a lot of info on the GM setups for 81/82 for reference.

One last comment. The computer harness and controls in your car are essentially a stand alone harness as I found out when I eliminated my stock ECM setup so I just pulled the whole set up out. Yielded a lot of good wiring for other projects. I don't recommend this approach if you don't like to do auto wiring, however.

[Stuart Boblett]

Back to the transducer / speed sensor or whatever it is, here are some pictures. I am not sure if this is a part just on the 82 with the electronic carb or cruise control or what. Help guys, any ideas.

[Avanti83]

The spiral blue/??? colored wire pair in the pictures are usually the speed sensor wires to an aftermarket (Dana/Rostra) cruise control. They appear to be cut off in one picture above but IAC my opinion is that the box in the speedo cable assembly is a wave generator for the cruise control and not part of the engine control system. 

The way to check is to remove it, reconnect the speedo cable and see if it creates issues. My money is on no issues.

[JavierB]

STUART!

I know this thread is 2 years old but do you have updates on what that unit was and what it does?

My 81 has the same unit, and I was in midst of a plan to change my mechanical speedo to an electric one when I discovered this thing in my way.  I can't really do my conversion with that in the way.  As a matter of fact it looks almost exactly like the Hall Effect unit I was going to install for my speedo.

The manual for the Dana Cruise says something about a magnetic pickup on the driveshaft and nothing at all about speedo pickup, but maybe its an updated system and not in the manual?    I've never actually used the cruise yet, but don't want to permanently disable it if I can help it.  can I rewire this signal to use the same electric pulse as the speedo?

Any advice here helpful.  Ugh, always questions.