Can't run a speed sensor, now what?

[moparman76_69]

Not sure where this should go, but here it is.

So I just pulled apart the PTU from the 93 AWD van. The early (91 only?) AWD vans to my knowledge still had a provision for a speed sensor to drive off the shaft that runs the ptu ring gear. On the 93 PTU the provision for the sensor is still there, but not machined out. I had hoped that the shaft would still have the teeth cut for the gear drive on the sensor. It doesn't. This leaves me with no way to run a factory style speed sensor.

What I do know:

The output of the PTU runs at the same speed as the transmission output, which is what I need to reference.

There are ABS rings on the AWD CVs

The 41AE auto trans uses a sensor in the transmission to reference vehicle speed, I don't have that option with the 523.


What I don't know:

What does the SMEC use vehicle speed for?

[ShelGame]

What does the SMEC use vehicle speed for?

It uses it to know when to take over idle control on coast down, for boost control (which can be negated easily), and for (obviously) cruise control.

[zin]

Off the top of my head, the SMEC will use that info for Cruise Control, Idle speed, pretty much all the same stuff the SDS in any other car would use it for.

In short, I think you could get away without it, though there would be some driveability issues, high idle at a stop, etc. But nothing particularly dangerous.

I have a thought as to how to "fix" the problem, just replace the shaft with an earlier version that has the teeth to drive the sensor... I know too easy, but where to find just a shaft, or a suitable "core" to cannibalize...

I'm wondering if the sensor from the latter transmissions could be retrofitted to work on yours...

Am I thinking correctly in that the SDS is a hall-effect device? If so, it might be possible to add a shutter wheel in the form of a sheet metal plate to the diff gear and install the sensor in the cover?

Really though, I don't know if it would be worth the effort, and I certainly wouldn't let it derail the project, it just shouldn't that big of a problem.

Mike

[moparman76_69]

The biggest issues is no speedo, but that isn't too much of an issue. I planned on going all aftermarket gauges at some point, so I'll just go ahead and get a tach for now and then do it NASCAR style to figure out my speed. Either that or use a GPS speedo app.

I am wanting to use computer controlled boost, is that still possible?

[ShelGame]

I am wanting to use computer controlled boost, is that still possible?

Yes, just set the boost vs speed targets to the max and it will ignore the SDS.