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Old 01-19-2015, 09:07 PM   #1
volvowagoon
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Default Explorer 8.8 VSS to 240 Speedo

I'm sure that there aren't many if any people on here who have thought about this, but I'm determined to keep the factory gauges in my '89 240. I think the speedometer is going to be the biggest pain in that though.

If I am not mistaking, the original gear ratio in my car was 3.31:1. I have an automatic wagon if that helps. The new Ford unit I'm guessing is a 3.73:1 because the VSS only comes on the differential if the Explorer is 2WD. A rough estimate by look spinning the rotor once and counting the pinion rotations indicate closer to this than the 3.27:1 ratio from a 5-speed.

Weren't there 240s with factory 3.73s? If so, does anybody know what speedometer was used with it and if it was electric?

Of course, there are other factors. I don't know how the Ford sensor operates other than that it's a VR. I haven't counted the reluctor wheel teeth or measured distance between wheel/sensor on either of the rear ends yet to see, but I'm hoping somebody knows enough to say "yeah it's easy" or "not worth your time" before popping the new dif cover off again.

I know that I didn't offer a lot of solid information, but I was mostly hoping to find somebody who has been through this already. Otherwise, I will attempt to be a pioneer! Thanks everybody.
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Old 01-19-2015, 09:26 PM   #2
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Dakota Digital offers an electric speedometer adapter/controller/signal manipulator thingie. Sounds like it's what you want to use.
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Old 01-19-2015, 09:41 PM   #3
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That looks nifty! Dakota digital is a pretty trusted brand too. I will have to read into it a little more.
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Old 01-19-2015, 09:47 PM   #4
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The gear ratio doesn't matter. The sensor reads the rotations of the diff carrier/axles directly. Gearing only matters when you're 'upstream'. At the diff, all the gearing is already done.

What really matters is how many triggers per rotation. If you can get the same number as the Volvo axle uses, you're good.
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Old 01-19-2015, 09:53 PM   #5
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^ Before you buy anything, pull the cover on the Ford diff and count the teeth. I seem to remember them being 40+ teeth.
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Old 01-19-2015, 10:06 PM   #6
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Ahh yeah... brain fart. The ring gear is going to spin at the same speed regardless of ratio. I didn't bring wheel size into play though. My new ones will be bigger and there is no use going through too much trouble for a wrong signal. The Dakota Digital universal signal interface is probably my best bet if I want to do it right.

How many teeth are there on the Volvo?
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Old 01-19-2015, 10:09 PM   #7
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12, what ever ABS is (24 or 48?), and I think another one. Definitely significantly less than what the Ford 8.8 used (at least the truck ones that I have been into).
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Old 01-19-2015, 10:13 PM   #8
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I found 49 and 50 tooth wheels on Summit. I guess that's the job for the signal interface. I'm reading the manual for that controller you talked about, and it seems like a really helpful piece!
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Old 01-19-2015, 10:21 PM   #9
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You could also just get a GPS speedometer. That might fit into a gauge cluster, maybe.
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Old 01-19-2015, 10:24 PM   #10
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The factory explorer ABS tone ring is 130 teeth.
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Old 01-19-2015, 10:27 PM   #11
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If you can get the speedo to read the signal coming from the diff, even if it's WAY off you could just replace the resistor that calibrates the speedo with a pot and adjust as needed. I have a 0-100 ohm installed and it is enough to wildly change the speedometer calibration.
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Old 01-19-2015, 10:36 PM   #12
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I want a factory gauge as well as the bezzel.

A pot could working too. Which resistor is it? Do you have a pic?
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Old 01-19-2015, 10:36 PM   #13
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Cut teeth if possible until there is 12
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Old 01-19-2015, 10:43 PM   #14
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lol maybe if 130, 50, 49 or whatever it is was divisible by 12 that would work. Otherwise, the needle will bounce, and that would annoy the **** out of me.
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Old 01-19-2015, 10:49 PM   #15
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Then fabricate a new ring.
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Old 01-19-2015, 11:04 PM   #16
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http://forums.turbobricks.com/showthread.php?t=239021
https://www.brickboard.com/RWD/volvo...eedometer.html

Is there I got my info to swap out the resistor for a pot. You could also temp install the pot and tweek it until your speedo is dead on with a GPS or something and then remove the pot at it's current setting and replace it with an equal value resistor.

I don't think you need to mess with the ring at all if you can bring the speedo into calibration by adjusting the value of the resistor.

Photos here also of how somebody ran the wires for the pot.
http://forums.turbobricks.com/showpo...7&postcount=23

Last edited by Andrewhans; 01-19-2015 at 11:11 PM..
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Old 01-19-2015, 11:15 PM   #17
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Good links! Thanks. This will make one part of my build easier.
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Old 01-19-2015, 11:19 PM   #18
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Just remember, I don't think this will keep your trip/odometer in check. They will continue to be off by the % that you deviated from the original resistor value. If you want the trip/odometer AND speedo to be dead on you need to fabricate a new ring like Lord_Athlon said. I have also read about cutting the ring off of a Volvo diff and welding it onto the ford 8.8" unit and then slightly adjusting with a pot. Let me see if I can find that.

This isn't about a ford unit but you may be able to do something like this.
http://www.davebarton.com/volvorearends.html

Some more info about the tone ring and peoples fixes
http://forums.turbobricks.com/showthread.php?t=204882
http://forums.turbobricks.com/showthread.php?t=280512

Here is a 108 tooth tone ring for the ford 8.8" axle. You could cut the teeth again like Lord_Athlon said to bring you down to an even 12
http://www.yukongear.com/ProductDeta...px?ProdID=1889

Last edited by Andrewhans; 01-19-2015 at 11:47 PM..
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Old 01-19-2015, 11:38 PM   #19
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I have the dakota unit in my 940. works pretty well. My car had ABS so 48 teeth was OEM.
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Old 01-20-2015, 08:48 AM   #20
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Ahh well that changes everything. I want the odometer to work too. I should have remembered that those two work semi independently. I guess I will look into tone ring mods.
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Old 01-20-2015, 09:58 AM   #21
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Quote:
Originally Posted by JohnMc View Post
The gear ratio doesn't matter. The sensor reads the rotations of the diff carrier/axles directly. Gearing only matters when you're 'upstream'. At the diff, all the gearing is already done.

What really matters is how many triggers per rotation. If you can get the same number as the Volvo axle uses, you're good.
True. That said:
Quote:
Originally Posted by volvowagoon View Post
If I am not mistaking, the original gear ratio in my car was 3.31:1. I have an automatic wagon if that helps.
3.73:1

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Originally Posted by Lord_Athlon View Post
Cut teeth if possible until there is 12
Yep. Even if one space ends up a little different, it will work.
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Old 01-20-2015, 10:48 AM   #22
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The needle doesn't react quickly enough to register a change in speed based on tooth gaps being a little uneven as the diff turns all the way around. You know, don't leave all the remaining teeth in one spot, spread them around as evenly as possible, and rely on the latency of the needle to handle the remaining slight 'theoretical' unevenness.

Or just leave the oily metal bits alone and use the Dakota unit. That actually sounds like a nice alternative.
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Old 01-20-2015, 12:28 PM   #23
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http://www.dakotadigital.com/index.c...roduct_id=126/
Thats the Dakota item- decodes input and outputs to your speedo. Its adjustable- use gps speedo app
On your phone and adjust until it matches
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Old 01-20-2015, 12:37 PM   #24
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I wonder if the stock ABS system would be happier with the removed teeth or the dakota signals? Might not matter either way, the ABS shouldn't react so quickly as to false on a very slightly uneven tooth placement.
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Old 01-20-2015, 06:10 PM   #25
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Quote:
Originally Posted by Andrewhans View Post
Just remember, I don't think this will keep your trip/odometer in check. They will continue to be off by the % that you deviated from the original resistor value. If you want the trip/odometer AND speedo to be dead on you need to fabricate a new ring like Lord_Athlon said. I have also read about cutting the ring off of a Volvo diff and welding it onto the ford 8.8" unit and then slightly adjusting with a pot. Let me see if I can find that.

This isn't about a ford unit but you may be able to do something like this.
http://www.davebarton.com/volvorearends.html

Some more info about the tone ring and peoples fixes
http://forums.turbobricks.com/showthread.php?t=204882
http://forums.turbobricks.com/showthread.php?t=280512

Here is a 108 tooth tone ring for the ford 8.8" axle. You could cut the teeth again like Lord_Athlon said to bring you down to an even 12
http://www.yukongear.com/ProductDeta...px?ProdID=1889
If they work on the input from the speed sensor in the diff then all you have to do is condition the signal before it is interpreted by the speedo/odo cluster.
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