All,

This is going to probably seem like a weird question...please bare with me. I've got a 92 F250 diesel. Right now it has the computerized/digital speedometer. I'm in the process of re-wiring the truck with the intention of making the wiring as bare-bones as possible. I would like to switch to the mechanical-style speedometer used in the pre-91 trucks. I have already found just the speedometer I can order to swap out with the one I have, but what I don't know is if the rear ends are different. Is it possible for me to purchase the mechanical speedometer and associated cable and sensor for the rear end? I know it might seem like a silly request but I'd like to cut wiring and go back to mechanical systems wherever I can. Thanks for any advice on if this is at all possible!

 

Mechanical speedo's usually plug into the transmission or TC via a cable. The trans or TC needs a port and a gear inside to work.

Are you talking about an electronic speedo with an analog display?

Or an old style cable operated job?

 

By switching the speedometer you might be complicating things. Do you have a manual transmission or the E4OD?

 

Thanks for the replys folks.

85e150: I was under the impression that pre-1991 speedometers used an old-fashioned cable style speedometer from my google searches and youtube video watching. If that's not accurate then that would probably put a damper on my plans. Here's an example of the kind of gauge I'd swap to.

Olds64: I've got the 5 speed manual.

Thanks!

 

You are on the right track, but as mentioned, need the transmission or transfer case to have the port for the cable to plug into. If you don't have that port, you'll need to swap the transmission (2wd) or transfer case (4x4) to have a place for the cable to go.
The sensor in the rear end I believe is for ABS for mechanical speedo models, and should be the same sensor so nothing to worry about there.

 

Thanks for the reply. I was under the impression that the port was in the rear end.

Where is the port located on the transmission? I don't have 4x4. Just a standard ZF-5.

 

Oh you're possibly in big trouble then. The VSS port is in the tail of the trans, so you'll need a tail housing that has that provision. Then inside there would be a plastic gear that drives the VSS, and obviously the transmissions output shaft needs to be capable of accepting said gear. Your truck being a 92 could still have all these things in place and just the port of capped off. I've also seen transfer cases where the boss for the VSS is cast but not actually drilled, and the shaft is machined for drivev gear but gear itself was never installed cause it ain't needed - no idea of these things happened with the 2wd transmissions as well. Crawl under your truck and look on the left side of the transmission tail housing and see what's going on there, may wanna snap a few pics and post here for us to ID things for you too.

 

Ok. I think I found it. There is what feels like a plastic insert where I'm guessing it would plug in. See attached image. Any help appreciated. Just really frustrating that the current speedometer requires 6 wires to work...

 

6 wires is an improvement over the mechanical speedo cable. I'd suggest you stick with it.

That port doesn't have the hole drilled to hold the cable in.

Is it a blind hole? There should be a smaller threaded hole next to it to hold the cable in.

Is there a gear on the output shaft?

 

+1 on keeping the electronic speedometer. It's generally more accurate and reliable, I've had to go thru several mechanical speedometer heads till I get one that doesn't drift off as the speed increases.

The other issue is physically bolting the mechanical speedometer into your cluster, a while ago I looked into going the opposite direction and they appeared close enough to where they can be made to interchange with some work, but it's still a hassle.

Finally the 1st time you need to pull the mechanical speedometer cluster out of the dash you'll wish you had stayed with the factory setup - that drive cable is a pretty unyielding beast and just amps up the frustration.

 

you will have to remove that trans and disassemble it to drill the case to fit the speedometer cable in, than drill and tap the hole for the clamp bolt. plus you will have to fit the drive gear inside the case...if it even has the parts to accept the drive gear.
than you will have to mount the cable, drill a hole in firewall to get it into the cab, and fit it to the dash. than modify the cluster to accept a mechanical speedometer head.
way more effort than it is worth.

 

I'm not much for electrical parts either (see sig line), so take it from me that you wanna keep the stock speedometer. It's not a critical part, you can still drive your truck if the speedometer stops working, so the whole "mechanical everything makes the truck more durable" angle doesn't really come into play.

You asked, so here are my random thoughts on how you could accomplish this project:

On 4x4 and 1.5-ton applications, many of the transfer cases and parking brakes that will fit have a VSS kadingus that uses a mechanical speedometer gear to make the sensor work, and you could simply swap that for a real gear and cable. You could swap in a 4x4 trans then simply not connect the front to anything. In your case though, your best bet would be a tachometer gauge face overlaid with road speeds for each gear, like 1970's iH tractors had. But, the stock tachometer is electric too, so you'd have to rig up something that works off the back of the camshaft or something like an old-school JD 4.5/6.8 used. In case you're wondering, International Truck applications used an electric tachometer too, it's not just a Ford thing. Another avenue you could look into- in the 1950's through 2000, many automotive engines that were converted to industrial use had a belt-driven governor, some of which had provisions for a mechanical tachometer. If your username is any indication, you've probably seen a combine or an irrigation pump with one and know where to get it. You could attach one of these to the belt system for the sole purpose of running the tachometer. Or, get really crazy and sandwich a V-belt pulley into the driveline somewhere, and then have a true speedometer.

That said, my $0.03 (used to be $0.02 but inflation and all) is that you should keep the existing speedometer for a total cost of $0 and no time invested. If it makes ya feel better, think of it this way- as far as critical parts that actually make the truck run, either electric vs. mechanical speedometer leaves you in exactly the same place. BUT, the electric speedometer option results in one fewer potential oil leak and one less mechanical part that can get stuck in the driveline and cause damage. As an added bonus, you won't have to hack up your dash.