I have a 1993 940 Red Turbo Wagon that is my “Truck with 7 seats”
I use this car for everything from hauling grandchildren to pulling a utility trailer full of firewood.
It really bummed me out when the Diff lost a bearing after some really bad snow driving here in Norther Colorado.
So, off to the junkyard I go where I get a rear end out of an earlier 760.
Now for the problem, Everything works, but the VSS reads EXACTLY DOUBLE the vehicle speed.
I saw that the VSS units on the two diffs were different in size, connectors and exact location but hoped for the match to work.
So has anybody done any work with differentials and noticed what is different?
I have not pulled the covers yet but wonder if the easier fix might be with the older speedometer head.
Will the older speedometer unit fit in the model with 900 (curved) dash?
Any brilliant ideas would be great.
And, oh yeah, the ABS and Cruise work great.
So my car will now bury the needle in record time, but my wife doesn't like looking at the speedometer reading 140+ on the interstate.
Waiting for any ideas. Thanks,
Flying low in Colorado

Early ABS equipped 700 series used a 96 tooth tone ring in the differential. You have installed one of those in your car which uses a 48 tooth tone ring. The ABS will not work as your front hubs are still 48 tooth count.

You need to install the correct count tone ring, or change the differential again.

Dakota Digital makes a speedometer signal converter. I don't know if one of those will work, or not. See http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/category_id=287/home_id=59/mode=prod/prd126.htm. They are $80 plus shipping. Dakota Digital has a disclaimer about using the speedometer signal converter to interface with an ABS system.

Good luck. Let us know what you do.

--
john

Thanks John,
I like the look of the unit and it's potential to solve the problem.
Yesterday for the first time the ABS light came on for a while but was off after the next start up.
I say the ABS works because I hear it engaging on ice, but question what true effect it would have in a crisis.
Killing a diff was a bad experience, I had hoped that a unit I already had at the junkyard would work, and I am trying to keep from buying a used one and doing another install.
I am still recovering from a broken back after rolling a truck down a mountain 325 feet in the fall of '08 so hard work is HARD!
What year models will fit the 93 940TA if I go that route?
I will keep you posted.
JPGurley

All 1989 and later 700 and 900 turbo cars, with automatic, use the 3.73 ratio and have 48 tooth tone ring.
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john

A little tape over the speedo and a GPS that displays your speed. Just a cheap thought from a nut that would put this malady low my priority list.

To add to Spook's mention of a speedo shop, I had very good service from Palo Alto Speedometer in (of course) Palo Alto, CA. May be worth contacting them for a quote - assuming they can help.

www.paspeedo.com

Dear jpgurley,

May this find you well. The rear-end unit from a 760 is a type 1031. The sensor ring is Part #1209835. The rear-end unit from a 940 (1993) is a type 1041. The sensor ring is Part #6814113. Both parts cost about $70.00.

These parts are not gears. Rather they are wheels with openings, like the "tone ring" on the flywheel, openings in which are read by the crank sensor.

According to the Volvo VADIS diagram, the 760 sensor ring has half as many openings, as does the sensor ring in 940 rear end. Thus, there would seem no easy way to modify the 760 ring - to add openings - to produce a correct speedometer reading.

Equally, changing the ring would involve dismantling the rear end. This would surely be costly, if one could find someone competent. There have been few posts reporting rear end failure. That means few have had to work inside of one of these units.

Note that there are several rear-end variants for 940s - all designated Type 1041. The final gearing ratios differ.

A better alternative: contact APT Instruments (Bloomington, MN). They are instrument specialists. They might be able to change your speedometer's internal setting(s), so that it reads correctly, despite an incorrect input.

You can contact APT at: 9632 Humboldt Ave S, Bloomington MN 55431
877-856-7103 or 952-881-7095 (www.gaugeguys.com). Their prices are reasonable: they charged about $60 to re-set a salvage yard speedometer to my car's actual mileage.

If APT can't help, then the only choice is to find a Type 1041 rear end with the correct final drive ratio, and install it. That's a lot of work.

Hope this helps.

Yours faithfully,

Spook

I suspect that the sensor wheel in the rear has twice the teeth as the old one. I think you're going to find it impossible to use the earlier speedo in the 940 panel without modification due to different connectors.
--
See the 700/900 FAQ at the drop-down menu above right.

Is it possible to open the inspection plate and grind every other tooth off of the sensor ring?

I took the cover off the old one, thinking the same thing. However, I don't like the loss of structural integrity to the "ring" as well as the metal filings I would be introducing into the diff.
I am talking with an electronic guy to find a way to electronically divide the signal in half.
That is way above my skill level, but have hopes the solution will be simple.
Someone else suggested a speedometer shop to change the reading, but would just as soon add an external device if possible.
I will post the solution when I have it.
I'm, Still flying low in Colorado.
PS (I'm getting twice the mileage now though:)

Dear jpgurley,

May this find you well. If the Volvo VADIS parts diagrams are correct, you would have to weld into place, a "bar", to divide into two sections, each tone-ring opening. Thus, there would be no metal filings.

What I don't know is whether small variations in the size of each opening would matter to the sensor. I think it would be hard to hold in place, very small pieces of metal, while welding was done. Thus, there might be small variations in the size of the openings.

I think a call to APT Instruments is worthwhile. They'll tell you whether or not there's a "fix", and - if so - what it will cost.

Hope this helps.

Yours faithfully,

Spook

This situation has been discussed on this board before. I remember, because if it was a 240, whose speedometer's inner workings I'm familiar with, I know it would be a simple trick to add a front end divider. Volvo made one for the '91 240's when equipped with ABS, before standardizing in '92.

But for the 940, I can only guess, so I noted someone's post of this device made for just this sort of problem. At $80, it would be a hard swallow for me, and maybe for your electronic enthusiast friend who could whip up something for very little cost in parts. But sometimes it is the round tuit that is hardest to get, where this is already whipped up. I doubt you can get a speedo shop to even look at it for that money, but don't let my doubts stop you from checking.

What I can't understand is how the 940's ABS was able to adapt to the doubled output. I'm guessing it just ignores it, or front and rear work independently.
--
Art Benstein near Baltimore

The man who fell into an upholstery machine is fully recovered.

Well. I did what I should have, put the right diff in the car from a 940.