Hi,
Im in the middle of a v8 tpi speed density with th350 swap in my 86 camaro which originally had a 2.8. Do i need to get a vss for the th350 or not. Ive heard both yes and no.
It has the mechanical speedo
Thanks

 

TH350s have mechanical speedometer drive (uses a cable with gears) HOWEVER my guess is you will want to change the speedometer in the dash to something that reads higher than 85 MPH.

That being said you will want to find a Mechanical 120 or 140 MPH Speedometer for the Camaro. which should be OK since they were mechanical units until 1987 in the Camaro. If you use an aftermarket electronic speedometer or a OEM unit newer than 1987 you will need to retrofit a VSS unit on the 350 trans.

 

im going to keep the original speedo for now but my main question is do I need the vss signal to the ecm or not?

thanks

 

I posted this 2 years ago..

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 different wheel/tire/rear end 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 Magazine 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.

 

Thanks for the info. ive been looking at the 4pac from JagsThatRun.com but I was told I don't need one but the site says I need one because it sends a signal to the ecm to let it know when decelerating etc..

 

Bump... do i need the speed sensor?

 

yes, you need to convert the mechanical drive to an electric signal.. for the ECM to function.