DRAC/VSSB Questions...

**DavidBraley** · 12-09-2016

Dave,

I am embarrassed to say I have no idea what I need. I need what will work with a 4L80e and a 7427 PCM. The only thing I do know is the VSS at the rear of the 4L80e outputs a 40 pulse per driveshaft revolution. I will go back and read some of the DRAC articles I have collected... I think they mention what kind of signal is needed for the PCM.

Worse case, I can use and microprocessor to do this all for me. But I would like to avoid that...

**DavidBraley** · 12-09-2016

Thanks for the help. I'm going to reach out to some of the sellers and see if I can get them to open up the plastic case these things come in and let me know if the unit they have for sale is the 7 pin (DRAC) or 14 pin (VSSB). I could even send them some images so they are sure.

Thanks again and take care.

David

**dave w** · 12-09-2016

I've attached some better schematic pictures. I have successfully used both the 7 pin and the 14 pin to convert a 40 pulses per drive shaft revolution signal into 2000 pulses per mile signal. The 16197427 requires the 2000 pulses per mile signal to operate either a 4l60E or 4L80E. I have never used a DRAC (sometimes known as the 7 pin) or VSSB (sometimes know as the 14 pin) to supply signals to a speedometer, cruise control or an anti-lock brake system. Rear Wheel Anti-Lock = (RWAL) in the schematics. dave w

**DavidBraley** · 12-10-2016

Thanks for that information Dave!

I managed to find a 14 pin VSSB this morning from a 95 C1500.

Turns out, I will need to do something with a microprocessor for my speedometer signal anyway. The truck as an Eaton 2-Speed rear axle. The idea kicking around at the moment is to use some known signal from the DRAC/VSSB (probably the 40 pulses per rev), and then come up with a way in software to send the correct count going to the speedometer when the rear differential is in low or high.

I'm trying to collect "two" of everything for this project. The hope is to create some kind of bench testing area with the second set of parts. I'm hoping it helps me learn more about the way these systems work, how to get TunerPro talking to the 7427, and a way to sniff some of these signals.

Of course I will share everything I learn!

David

**myburb** · 12-10-2016

Originally Posted by DavidBraley

Thanks for that information Dave!I managed to find a 14 pin VSSB this morning from a 95 C1500.Turns out, I will need to do something with a microprocessor for my speedometer signal anyway. The truck as an Eaton 2-Speed rear axle. The idea kicking around at the moment is to use some known signal from the DRAC/VSSB (probably the 40 pulses per rev), and then come up with a way in software to send the correct count going to the speedometer when the rear differential is in low or high.I'm trying to collect "two" of everything for this project. The hope is to create some kind of bench testing area with the second set of parts. I'm hoping it helps me learn more about the way these systems work, how to get TunerPro talking to the 7427, and a way to sniff some of these signals.Of course I will share everything I learn!David

Might be possible to use 4low ability of 7427 and drac/vssb to use when 2 speed in low..

**Six_Shooter** · 12-10-2016

Setting up different divisors in something like an Arduino to show correct vehicle speed regardless of which rear gear would be pretty easy.

I'm currently using an Arduino based speedo in my car, just driving an LCD currently, but plan to have it drive a motor to drive the original speedo eventually. It wouldn't be that difficult to have the code check a digital input to swap between two divisors used in the speed calc to get proper vehicle speed.

**DavidBraley** · 12-10-2016

Originally Posted by Six_Shooter

Setting up different divisors in something like an Arduino to show correct vehicle speed regardless of which rear gear would be pretty easy.

I'm currently using an Arduino based speedo in my car, just driving an LCD currently, but plan to have it drive a motor to drive the original speedo eventually. It wouldn't be that difficult to have the code check a digital input to swap between two divisors used in the speed calc to get proper vehicle speed.

I agree. I'm thinking it would really fun to try and retrofit the steppers they use in modern clusters. Keep the outside look and feel of the original gauges, but modern steppers behind them. Easy for something like an Arduino or Microchip Pic...

**DavidBraley** · 12-10-2016

Originally Posted by myburb

Might be possible to use 4low ability of 7427 and drac/vssb to use when 2 speed in low..

Interesting. I'll have to look into this. It's my impression from the reading I've done so far the 4x4's with the 4L60e/4L80e have the driveshaft VSS moved to the transfer case so what the PCM and speedometer sees is revolutions of the drive shaft. The ratio change in a 2-speed rear happens after this sensor. I will try and understand more about this "4low" setting.

Originally Posted by lionelhutz

I've never seen a DRAC/VSSB connector layout with a 40ppm output shown. I think you're looking at 2 different 2000ppm configurations depending on the module and/or the mask.

I would agree with Dave, you can't use a DRAC in a newer truck because the DRAC is missing the correct output for the anti-lock.

With a 2-speed rear-end you could use 2 different DRAC modules and switch between them.

My plan is to adapt the entire non-anti-lock braking system from the Ford F550 for this project (similar class 4 vehicle). No anti-lock for this truck means that kind of output from the DRAC/VSSB wouldn't be needed. Your idea to use two DRAC/VSSB's for the ratio change is also interesting. I'm imagining though it might take a fair bit of steering logic to do this. Might be easier to make a device out of a microprocessor that emulates a DRAC/VSSB instead. Then in software I could change the divisor by simply changing the state on an input pin when I make the gear change.

All worth looking at!

David