hello all,
i am freshly back in a volvo after a couple years driving little hatches. I got my hands on a sweet 1984 with what I was told was a 1987 volvo 5 speed transmission conversion. when I picked the car up the owner and performer of the swap informed me that when he made the swap he lost the ability to use a cable speedometer, so he installed an aftermarket unit that is really just cobbed together and now inoperative. he alluded to the fact that in order to us a 1987 gauge cluster the whole rear end would need to be swapped? is that the case?

what did I get myself into? do I need to swap the rear diff in order to get an electric speedo sender to work for me?

what options are there in terms of alternate speedometer options?

the one he installed was an old vdo gauge that seems to work like the ones you put onto a bicycle (magnet on the drive shaft, readed mounted to take that signal and translate it to speed).

is it possible to simply remove the speedometer unit from the gauges and replace it with another unit?

thanks for reading my ramblings!

Early cars had mechanical speedos, driven by a flexible cable from a special gear on the back of the gearbox tapping the output shaft.
Later cars omitted this mechanical take off and instead used a special diff crown wheel with I think holes (like on the flywheel for the Crank Position Sensor) and a magnetic sensor. This was linked electrically to a special speedo head.

Your problem is you have a later gearbox with no cable take off provision.

I have heard that it is possible to dismantle the gearbox and substitute the rear end from a model that does have the take off. I don't know whether that is true.

Alternatively you need to put in a later type axle, and wire it up to a later type speedo. I don't know whether you can swap the internal crown wheel and use a later cover with the sensor mounting, or whether you need an entire new axle.
That would be easier, if you have one.

I have read warnings that all sensors are not necessarily compatible with all (electronic) speedos. So it would be safest to get both from the same car.


Finally, I have myself recently discovered that the wiring and sensor connector pins are not consistently wired the same way. I swapped in a known good sensor from another car and it didn't work. Close inspection showed the wiring orientation was reversed, so the sensor was trying to read backwards. I had to cut and rejoin the wires, ignoring the colour code.

They went to the electrical speedometer in '87, more or less, and those spedometers were built to expect a cretain number of holes in the tone ring in the diff. Later on, when ABS was added to the cars, they changed the number of holes in the tone ring, to better suit the ABS function, and changed the speedometers accordingly.

Changing the rear axle and doing all that wiring is a pretty big PITA if the axle is in otherwise fine condition. I'd try seeing if you could get that VDO gauge working properly. Or failing that, perhaps one of those fancy GPS speedometers?
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'63 PV544 rat rod, '93 Classic #1141 245 +t

I beg to differ John. My '86 has an electronic speedo. It escapes me right now what the '85's used... ABS was added in '91 on the 240SE models and all 240s in '92.
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854 - 244 - Mini

thanks for the responses guys. that is the unfortunate state I find myself. is there any way that I might swap in an early tone ring(NON ABS) into the diff as well as a new cover with provisions for mounting an electric speed sensors? I really can't picture where the speed sensor mounts to the newer diff? am i right in the assumption that it is on the diff cover?

the reason I am asking asking is I came a cross a converter box that will I think translate an electric speed sender to a cable driven speedometer allowing the stock gauges to function. solving the entire conundrum.

Yes, the electric speedo sensor is mounted in the rear cover of the diff. The tone ring would be the tricky part I imagine. I don't know if one could be mounted without taking apart the diff.

The speedos can be removed/replaced independant of the rest of the cluster. I don't see why an ABS sensor/tone ring wouldn't work as long as it was paired with the corresponding speedo. An automatic speedo will have a number "10042" on the face, an manual car would have "9800".

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854 - 244 - Mini

The speedo head # has nothing to do with the trans. They differ because the 200 series sedans and wagons use different tire sizes. The 10042 is for sedans and the 9800 is for wagons. Mike

thanks again guys,
I am curious if anyone had any experience with installing the tone ring in an older diff to run an electric sender? it looks like the whole diff would need to be taken apart. I might be in for too much of a headache.

I came across an article about installing a LSD in a 240 diff, it mentioned that what he did was to use a die grinder to make 12 grooves in the face of the true tack lsd, and the speed sender read those just like the tone ring. sounds like it could be a 2 birds one stone sort of thing.

parts:

true track LSD
85+ diff cover and sending unit
85+ speedometer head

modify the true track per the article, drop the car off to the local 4x4 shop with the new diff cover. pick up car, pull instrument cluster, mount new speedometer head, run wires form sender in the rear up to the gauge cluster?

I think the last part is the part that is troubling me the most. what sort of wiring is on the rear of the speedo head? does it just take the two wires and a ground from the sender?