Converting 89' Cable Speedometer to 90'-91' Electronic Speedo - Long Write up (Pics)

[dyeager535]

Good for the race cars they build. I like to learn new things and keep up with times. Efi for off-road is awesome so I'll be doing that next year. Thanks for the quick reply ill post my progress later.
Time to hit the junk yard for that 89 housing or 90 cluster, whichever comes first.

Even NASCAR is EFI now.

Good luck on finding those parts...there still seem to be a fair number of 'burb's out there, so either the '89 or 90-91 parts should be easy enough to find.

IMO the electric speedometers are better anyway...they probably have less mileage on them, they have less wear due to age, and they really don't seem to have many problems, where the mechanicals anymore seem to be failing, just like the distributors.

 

[Fatrat]

Great write up, lots of good info. As far as the DRAC module goes, i got two, one from a 90 sub and another from a 91 sub at the local yard. Once i got home, the connector doesn't match, is there any way to use these modules or do i have to get the other kind. The guy at the yard doesn't charge me for small stuff like this so i'm not losing anything, but i do want to get the right one. My blazer is not FI so all i need the DRAC for is the speedometer. Here is what i have, but after reading here, i need the one like yours.

 

[dyeager535]

That looks like the cruise control module to me.

 

[Fatrat]

Back to the yards I guess.

 

[dyeager535]

Astro's are a good donor too. For some reason their dashes seem to be normally torn up, and the DRAC in those is mounted in the center of the dash, I believe to one of the air conditioning ducts. Pretty easy to get to.

Stock, I can't remember how hard the DRAC is to get to on the trucks.

 

[Fatrat]

Thanks for that info, I was looking in the trucks and couldn't find it, I'll go back and check the Astros. Plenty of those there.

 

[95chevy]

dyeager535 do you know if you can take vss stuff off a drivers side drop np241 and use it to convert the passanger side drop to vss?

 

[MAX89K5]

dyeager535 do you know if you can take vss stuff off a drivers side drop np241 and use it to convert the passanger side drop to vss?

You cannot. The oil pump alignment ears are spaced differently in a driver side drop case.

 

[jeff in co]

Got some new tires and had to go back and adjust my DRAC. Noticed the link to the formula site is now automated (along with the correct chart). Anyways, here is the formula to use:

Input Ratio = [(63360)(Gear Ratio)(40)] / [(Tire Circumference)(128000)]

Website:
http://tbichips.com/?page_id=504

 

[Van88]

So I’m new to the site and want to thank you for spending the time and effort to post something so elaborate. I’m running a new wiring harness on my 85 K5 which I converted to TBI. I’m using t-case form a 89 suburban with VSS,can I run my harness and the drac out of the same vss? Can I T in to my wires from the vss to my harness with out them interfering with each other?

 

[dyeager535]

Study post #3 closely https://ck5.com/forums/threads/conv...peedo-long-write-up-pics.296187/#post-3085681

It has the pinout for the DRAC and covers combining with the VSS for cable drive setups. I'd say splicing the twisted pair (VSS to DRAC) is a no-go if it can be avoided. I generally say splicing should be avoided anyway, but take it FWIW.

As the post illustrates/explains, run the VSS wires to the DRAC, and use the DRAC output(s) for pin/wire A10 (VSS input to ECM) on the TBI harness. '85 should have the buffer/wire harness in it for optical VSS because that was cruise and TCC at that point IIRC, which covered *pretty much* every truck made. So you'll already have the ignition 12V and ground to power the DRAC.

 

[obijuank5]

Cluster ****.
I have a 91 and my cluster works great. I want to add a tach. I have parts clusters. 2 electronic speedo and several earlier tach clusters.
I am not good with wiring or anything like it. Please excuse me.
I want a tach in a vss cluster. Looks like it's not gonna happen. Look at the fuel gauge location and the printed circuit. Definitely a hard work around.
So... gonna have to use the early mechanical tach housing and just put my electric speedo in that housing. Buuuuuuuut then what do I do to my truck side? That part is melting my brain right now. I feel like I dont need to do any wiring because the speedo isnt leaving the truck but the rest is changing.
I feel like I'm seriously over complicating it or overlooking something important lol

What's the best plan of action here?
Thanks for the help guys.

 

[6872xtc]

I believe that Irish1941 did this years ago. He hasn't been on here in a long time, but maybe you can search for the thread.

 

[jeff in co]

I wouldn't think it would be too difficult. You'll want to start with the electronic cluster and then modify that housing to accept the new tach/fuel gauge. Then you can probably make manual jumper wires to the fuel gauge studs from the printed circuit board. Then manually wire up the tach studs.

The main issue would be cutting out the two sets of light housings to make room for the fuel gauge unit. Don't recall what those two lights show....?? Check engine?

 

[obijuank5]

Those two lights are seatbelt and brake lamps.

So just make room in the 91 cluster housing. And then run regular wires for the fuel gauge? How do they attach to the printed circuit?

 

[6872xtc]

Those two lights are seatbelt and brake lamps.

So just make room in the 91 cluster housing. And then run regular wires for the fuel gauge? How do they attach to the printed circuit?

You could connect to the wire at the main plug, or see if you can solder a wire to the copper trace.
Just my thoughts

 

[dyeager535]

Just to get yourself familiar, it's not a bad idea to take the older cluster, and sharpie what each trace does at the ip plug, directly on the printed circuit. Then you can work backwards, assigning each function to a terminal on the connector. Then you can go to the 91 cluster, and compare.

I can say that having gone from an earlier harness to an electronic speedo cluster, the wiring is generally simplified. Mire sharing of grounds and 12v feeds, so fewer wires at the ip connector. Ip connector is easily defined, moving one function (wire) to another terminal is easy.

 

[obijuank5]

Well proof of concept here. Here's me about to ruin a few hundred bucks.

So I lopped off the side of the cluster housing on both just to try it and see how it would work out. It was a bad idea but it could work. I think I should hog out the back of a whole cluster housing instead.
Or if I did it this way again I would just cut it a different shape so each side shares two mounting screws instead of the three and one now. It's in there and the layout of the printed circuit might not be that big of a hurdle to overcome. One thing I did notice that I didnt know what the bulb sockets are different sizes. Blue is 91 and black is 85. They don't fit through the printed circuit and the blue ones dont fit into the older housing.
Welp.

That's where I'm at today.
And they are upside down. Just gonna have to deal with that. Lol

 

[jeff in co]

Looking good so far! Might try some fiberglass or gorilla hair fiberglass to bond those two pieces together......

 

[jeff in co]

Revised. Uploaded new photos and removed the photobucket junk (the best I could). Have received requests every once in a while so tried to keep it alive.....