Redog

My new set-up has an early model TH-400 tranny so I need a speedo drive unit.

Can I get one to hook up to my 1985 Delta's axle and can I hook it up to the rear axle?

How do they work? Tire size a factor?

joe_padavano

What do you mean by "speedometer drive unit"? If you're talking about the pulse generator used on late model cars with computers and electric speedometers, you don't need one. The 200-4R is a cable drive speedo with the electronic vehicle speed sensor in the speedo head. Your existing speedo cable should attach directly to the speedo cable fitting in the TH400. If you have a TH400 out of a 60s Olds full size that used the front wheel to drive the speedo cable, you're S.O.L. Get a correct trans. If your TH400 housing has a knockout plug in place of the speedo drive adapter, you can remove that plug, install a speedo drive gear on the output shaft, and install a speedo drive adapter and driven gear in the opening.

If you're talking about one of the motorized speedo drive units that allow you to use a cable drive speedo on an electronic trans, you're also S.O.L. These are designed to work with fully electronic transmissions like the 4L80E and require a trans that already has an internal speed sensor and a VSS output plug. The TH400 has neither.

Yes, both tire diameter and rear axle gearing will effect the speedo drive gear requirements.

Redog

That's what I got it's either from 65, 67, 70

Redog

Is this plug a cup looking thing on the pass side of the tranny?

Redog

No it wasn't it. What else is there to do?