FRMULA88

After doing much searching and research I have found 2 ways to accomplish running the 3rd gens electric speedometer with older style cable driven transmissions.
If the car no longer has ECM (carb conversion) the VSS buffer box is not needed for either option.

First option:

Leave the original drive and driven gear assembly intact on the transmission
install a 4 pulse reed switch on the speedometer cable drive. This part has a treaded end to connect to the cable drive and 2 wire lead. Wire the leads; 1 to chassis ground the other directly to the instrument cluster lead wire (green with black stripe) The speedometer is calibrated for diiferent wheel tire combos by replacing the drive and driven gears in the transmission

with a turbo 400, 3.73 rear end and 26" tall tires you will need 15 tooth drive and 43 or 44 tooth driven gear.

with 4.10 gear and 28" tall tire 15 tooth drive and 40 tooth driven.

The reed switch is available from Jags that Run (AKA stealth conversions) sells for $75. There is an excellent article in June 2012 Hot Rod Magazive about this product.


2nd option for 400 trans The Turbo 400 aka 3L80 was used in late 80s-90s trucks, most of these had electric speedometers. however the VSS mechanism is different than was what used in 82-92 f-bodies. The truck tranmissionses used a 40 tooth reluctor wheel and VSS which was connected to a DRAC module. the DRAC sends the correct signal to the speedometer cluster, ecm, etc. the reluctor wheel and VSS are easy to get brand new however the DRAC modules are hard to come by, they are not made anymore.. Also any changes made to gears or tires means you have to modify the DRAC. The solution if you have the reluctor wheel VSS is to used Dakota Digitals's Frequency converter. Part # SGI-5. This replaces the VSS buffer or DRAC and sends the correct frequency to drive the factory speedometer, aftermarket speedometer.. signal for ECM etc.. this is a nice part with lots of features and fairly inexpensive, $75 thru Summit.

Option 2 is more expensive route to take for carb only application but if you need a VSS signal for stock or aftermarket ECM the other advantage is speedometer adjustments can be made thru the SGI-5 without have to play with drive or driven gears.

I hope this info helps others who want to do this swap.

Orr89RocZ

iTrader: (20)

Subscribed. Good info.

I want to switch my stock cable driven gauge and go electric aftermarket without doin the trans gears. I am efi and am converting to the lsx 411 ecm. I wonder if your info will still apply? Dont know how a 411 ecm works, need to do research but i know in the tune you set tire size and gear ratio. It may calculate speed and send signal to gauge. We shall see

FRMULA88

Starting in 1989 or 90 GM deleted the separate VSS buffer box and incorporated it into the ECM.

I think the 40 tooth reluctor works with the new LSX ecm. the 4th gens I believe come with this setup in the trans (4l60E) from the factory, I am not sure if 4th gens use a DRAC box or it's all part of the ECM.

I think what you want do is feasible, since is sounds like you are intalling complete LSx system and drivetrain into a early model car.

jmd

iTrader: (4)

Yes. The 411 can accept input from the 1990 3L80 VSS and output to speedometer.

93 is sketchy in my head but 94-up went straight from vss to PCM and then out to speedo.

Orr89RocZ

iTrader: (20)

No its my gen I sbc 400, just adding the vortec dizzy and coil packs and 24x crank ring via efi connection.
Mine is an 89 and has a separate vss buffer box i believe. If i remember right. I gotta double check. I may need a 3l80 vss then?

My speedo hasnt worked in 4 yrs so its not a bother. Well it works but its off. 40 is 60-65 and 110 was 140 or so. Lol just hoping to easily convert to higher mph speedo and electronic at that but if not thats ok, i will change gears in the trans. Good to see what options are out there.

FRMULA88

Well the speedometer works!

I wired up the Dakota digial box per the instuctions and then calibrated the cars speedometer to the chassis dyno speedometer so it is dead on !

special note TBI cars use 2000 PPM, TPI cars 4000 PPM it's all in the directions. A very nice way to run brute force trans in these cars with electric speedometers.

FRMULA88

uploaded for your reference

GrannySShifting

Does anyone have one of the 3L80 electronic VSS sensors? broke mine

tater

iTrader: (10)

Great info. Thanks!!!