Want a VSS signal from your 5 DS-25?

[Lynn Larsen]

click image for auction

Seller Says:

This is a new motorcraft vss - vehicle speed sensor - that installs between the right angle speedo cable adapter and the speedo cable. It is a totally adapter-free installation for the zf 5-ds-25 transaxles used in many gt40 kit cars. Threads are exactly the same as the adapter-speedo cable threads. This is a hall effect, pulse generating vss. As such, it should* provide the input necessary for efi and cruise control applications.

* my emphasis - this should be researched to determine if the pulses per mile are in the range expected by your EMS and/or speedo. Many speedos have the ability to adjust to the signal provided; however, your EMS systems might not. But, there are standalone boxes that will modify speed signals IF it is needed. I would also make sure the drive cable profiles are the same.

Lynn

 

[Dave Wood]

Most Ford VSS units pulse at 8000 pulses per mile. Just programmed the speedo in my rod.

 

[Lynn Larsen]

WDZ,

Pulses are controlled by transaxle, so depends on the gearing and how the transaxle was setup for the mechanical speedo (as in, say, a Pantera.) This is not necessarily the same as the tranny out of a Mustang or other domestic Ford product that is designed to provide a VSS signal.

Lynn

 

[Dave Wood]

WDZ,

Pulses are controlled by transaxle, so depends on the gearing and how the transaxle was setup for the mechanical speedo (as in, say, a Pantera.) This is not necessarily the same as the tranny out of a Mustang or other domestic Ford product that is designed to provide a VSS signal.

Lynn

It would seem that since the gearing in any car controls the rotation of the VSS, it would have the same effect on pulse rate. I noticed that it has the speedo through drive so the VSS on that unit looks to only control the cruise or other equipment that requires the pulse. I'm curious, and you make a point, if Ford specifies that their VSS( and according to their manuals they are) have an 8000 pulse rate per mile...how does that get determined in the varying cars and gear ratio?? Although I programmed the VDO electronic speedo with the VSS pulse rate, and it is accurate when checked with mile markers, how would that be changed if another gear ratio was installed? The VDO has a programmable feature, but the stock Fords don't, at least I don't think so. Since the drive gear is removable as on a regular speedo drive, it is unlikely that they would make multiple parts, especially when the manuals state the 8000ppm figure.

 

[Lynn Larsen]

WDZ,

Usually the pulse is taken off of the ouput shaft of an inline transmission, so that only the diff or tire diameter would have an effect on the VSS output. On a transaxle, if the signal is taken off of the ring gear (on the '87 - '90 something Porsche it is taken off the bolt heads of the ring gear. Later models use the toothed wheel that is used by the anti lock braking system) then only tire diameter will change the output.

On my car, I used a Dakota Digital signal modifier that not only modifies the pulse rate (via dip switch settings) it also has the ability to put out two different wave forms. Additionally, I also used the box as a signal boost for the Ford EEC-IV EMS system. One of the cool things that is done with the signal by some EMSs is turning off the electric radiator fans once a speed of around 45mph is reached.

On the 5 DS-25 it is possible that changing the drive gears on the speedo output would be adequate to obtain the 8000 ppm (this is what I meant when I said "it depends on the gearing.") Otherwise, and in the case of changing the diff ratio or changing tire size, to do it right, you'd use a box like the one I described. They are readily available and made by several different vendors and have a very wide range of adjustability.

 

[Dave Wood]

Lynn,
Thanks for elaborating. The rod was the first usage I have had of a VSS that wasn't in a production car. Fortunately I grafted the '40 Desoto onto the '87 T-bird chassis, so all the hardware is still the stock 'bird stuff. The VSS was also part of the same.

 

[Phil]

WDZ
Is that figure of 8000 pulses per mile correct? the GM units use 1000 or 2000 pulses per mile..8000 pulses per mile would mean a pulse approx every .66 feet or every 7.92 inches of vehicle travel. I don't know exactly how the speedo drive is geared internally in a ZF, but it seems awfully fast....just thinking out loud.
cheers
Phil

 

[Dave Wood]

Phil,
The VSS units used through the 80s-90s was 8000, the later units may have changed. The VDO speedo instructions mentioned as many as 199,999 (or maybe more) pppm's that the speedo could be set up with.With as high a # as the instructions stated I thought the 8000 was too low,LOL, but when I programmed it it worked out right. So,while 8000 seems high compared to the ones you listed, there are others with an even higher one. I would think that the higher the pulse rate the more accurate it would be, but that's me thinking out loud.

 

[Phil]

WDZ
Sorry if I sounded doubtful. just had not seen a pulse rate that high on a speedo sensor. I guess the resolution must be awfully good as I have seen some of the lower pulse rate units create a flutter in the speedo at very low speeds (lets say below 10 mph.) I guess I learned something new today. Thanks for posting the info on that unit, as I was getting around to figuring out how to set the drive up anyway, and sure didn't want to run a cable!. I once drove an original Forty and the speedo was all over the place at elevated speeds...I guess the cable and housing were in need of attention, and I remember a 40 mph swing in the reading from min to max.....didn't bother me much, I was driving an original, and a little thing like an inaccurate speedo didn't much matter.
Cheers
Phil