Hey guys,


I recently did a T5 manual swap into my 89 Formula.

The WC T5 I used was set up for a cable-driven speedo at the tailshaft (drive gear mounted on the tailshaft instead of a reluctor for a VSS but my speedo is electric so to solve it, I installed one of these a 89-95 Firebird large-can speedo sensor VSS units (p/n 10456087):
https://www.ebay.com/itm/176658035778



However, the gear on this VSS unit now causes the speedo to read about 10% low - I've confirmed this with GPS. It makes sense since a factory car with one of those sensors in it would've had a 3.08 rear, but my car has a 2.73.

Does anyone know if the gear that is present on this VSS can be had in a different tooth count? The drive shape is a D, whereas a drive shape for a cable-driven speedo gear is square (and these are readily available online).

I've spent the last hour or so scouring the internet and can't seem to find one of these D-shaped driven gears... I presume I'll need to go the route of an electronic ratio adaptor if these gears don't exist in different tooth counts

Thanks in advance for any help!

 

Yes of course. That's how the factory set them all up.

Problem of course is finding one, as you've discovered. Some tooth counts are easier to come up with than others. Butt I know of no place anymore that pretends to "stock" those, they've been out of production for too long, and there are vanishingly few used ones running around.

An electronic ratio adapter sorta works; problem with those in this application is, the VSS only outputs 4 pulses per rev, and since you need something like 4.4, it'll be terribly inaccurate and bouncy at low speeds. Those work ALOT better with transmissions that put out LOTS of pulses, like the T-56 for example, at 17 per rev.

PM me.

 

Swap a 3.08 geared limited slip drum brake rearend into the car.

 

GM did make a 19 (14090592), a 20 (14090593) a 21 (14090594) and a 22 (14090595) tooth T5 gear for electric Speedos,.. don't know if they made any others.

In any case; this is what you need :



https://www.summitracing.com/parts/DAK-SGI-5E

This will allow you to set your speedo correctly with the sensor and rear end that you have in the car now,.. as well as the replacement rear end your going to be replacing in the future.

Just My Opinion here, but I'm fairly certain that you are NOT going to enjoy driving around with 2.73 gearing and a T5.

 

To the best of my knowledge, for the years of 3rd gens that I'm into which is 87 to 92, I don't think GM ever put a rear gear that was numerically lower than a 3.08 behind a LG4, L03, or LB9 V8 M39 T5 combo. That is a lug fest combo too. I'm sure GM would have loved to have stuffed a 2.73 gear in those cars for C.A.F.E. reasons but realized even they couldn't do that to people with a straight face.

No matter which version of 5.0L V8 engine or M39/MK6 version of the T5 I'd want no less than a 3.23 gear.

 

Yes, noted, and I can confirm it does feel a bit slow. One step at a time though, my budget is limited. 3.23 or 3.42 will happen down the road. For now I'm just happy to have the T5 in place.