Vss & tach

[jking78]

Just need a little help I'm installing these aftermarket gauges I have a 6.0 with a th400 and was wondering if I can use the VSS & Tach wire from the stand alone harness to run the gauges



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[LHanded Lead Foot]

I see that is has been a month since the post was made...with no answer Sorry!
As a rule, the LS series engine uses a high resolution VSS signal as a direct input into the PCM. The PCM uses this info a provide signals to the ABS, IPC and the infotainment system. The radio gets louder as you drive. The ABS is 3 channel, meaning no speed sensor at both rear axles. The VSS signal to operate the speedo goes into the PCM (which can be programmed for you speedo as per manufactures specs / Some can be calibrated by actual mile maker during a program button). I don't know the brand of gauges and would expect this why no one has responded.
The tach signal come from the PCM via a dedicated wire or perhaps some newer vehicle will use Class2 serial data.

I have a official CD of GM eSI installed on a stand-a-lone laptop, but only goes to 2004. Depending on the year of your donor engine, it may change.

Getting your high-resolution VSS signal:
There are several ways to get a TH400 from memory. The 700r4, in the mid 90's started using a powered metal 40 tooth gear that is a very tight fit onto the tail shaft of the tranny. It should be heated gently with a torch, then driven straight onto the shaft using a tube shaped driver that is flat on the drive end. The gear will crack if not done right. The pick-up of sensor is electronic. It used a soft iron core that has wraps of fine cooper wire around it and provides a two wire A/C voltage. It goes directly into the PCM where one terminal is marked "Signal High" & "Signal Low". It makes no difference which wire is used.
Now the TH400. It has a plastic drive gear for the speedo driven gear. The plastic gear is held in place with a spring clip and can be changed with the tranny in the vehicle. I do not know if the 40 tooth metal gear will fit, but I think the I. D. is the same.

Here is the problem. The sensor has to fit the tail shaft housing and be inline and air gap correct for it to work. I believe there are some tail shaft housings that will bolt on your TH400 to make the mid 90's "F" body 2 wire PM generator sensor to work. I would provide one wire that is dedicated for shielding, a simple ground-to-ground wire, then wrap in foil tape found in the HVAC area of your local big box home improvement stores.
I would ask you to research youtube for VSS sensors from Monster transmission and others. Give them a call, but have your info ready. The other way to provide a VSS signal is GPS signal generator from Dakota Digital. It is not too complicated and does require some wiring skills and understanding of how it works. It comes with instruction that are NOT vague. IT NOT CHEAP!

My wallet could not take the hit, but I had to retired due to multiple joint failures that cause severe chronic pain all of the time. So it sucks to be me! Who cares. So I am stuck after years of fixing thousands of other peoples vehicles as an ASE Master Tech since 1978.

I do not know your bank account, but be prepared to drop $700 to get a GPS speedo signal generator.

The tach signal from the PCM is a dedicated wire to the instrument cluster (Engine Speed) on the donor vehicle. (Depending on the year of vehicle / could be serial data / No info).

The only problem is the signal from the OEM "LS" engines PCM is usually 4 cylinder. That may be changed on the tach by a switch...if not, it can be changed by reprogramming the PCM. Also, depending the internal resistance to the tach, it may require a resistor wired one end to the tach wire and the other to fused B+. This is a common "Pull-Up" circuit. This increases signal strength so the tach will work.

Best of luck. Retired ASE Master Tech. I have a lot of electronics experience as well.