electronic speedo in early dash, any advice please?

[Bugjam1999]

Ok, I had a speedo on the workbench today. If you bridge the two pins as detailed in the guide, then connect 12v ac to the sensor wire and ground, then a 12v Dc supply to the power input and the same ground as the ac supply the speedo will show 20mph or so.

So you can test the speedo works before installing and or jacking one wheel up to test that way etc.

Cheers

[heckflosse]

The plot thickens..
The link shows a test for the sensor, 2.7K ohms approx.
My sensor is 1.2 K Ohms. tried another late type alloy diff cover sensor on our other car and that too was 1.2.
So, there are early and late sensors.
Ive tried my 3 pin speedo (86 model) in a running 1988 240 spares car we have, wired up just using the link wire and the L connector only.
It works fine.That car has a steel diff cover.
When swapped to the 265 (with late sensor in the alloy diff cover) nothing.
Live and Earth are good.
It looks like a diff cover swap is next.

Is there a knack to pulling the speedo needle off without wrecking the mechanism behind it?

As an aside, what Diff ratio is best for a 240 Turbo?
The axle in it is a 3.9 which might be a bit "urgent". Its M46 on 195/65/15s.
Our other 240 we own is a 230F 93 with a 3.5 which is too tall in 5th for most roads round here. Which leaves a 3.7. I want to get the car running and usable first then toy around with fitting the G80 etc so that can wait.
Thanks,
Jim

[heckflosse]

Just popped the diff covers off, the alloy one has a cast ring, like an ABS pickup, with loads of teeth, the steel one a steel "cage" with a few large windows.
Cant mix and match.
So, back to square one.

[Bugjam1999]

Interesting- I thought there was just one kind of sensor, then either 12 or 48 teeth inside the cover to read, sounds like there’s an early and late sensor as you say.

Speedo needle can be removed by gently turning the needle anti-clockwise past ‘0’ to break the glue and then keep turning it whilst gently pulling up.

This page is worth a read:

https://www.prancingmoose.com/240-odometer-repair.html

Cheers

[heckflosse]

Lots of good stuff on there, thanks.

[Laird Scooby]

A little bit of extra info that i don't think you've found yet. There are two different instrument manufacturers on the 7xx series and i suspect on the 240 series as well - VDO and Yazaki.

For some reason, the Yazaki and VDO clusters aren't interchangeable so check that whoever made your original cluster and whoever made the replacement speedo head are the same people.

Also there are three different reluctor rings available in the 7xx, 12 tooth for early non-ABS cars, 96 tooth for 88-91 ish cars and then 48 tooth for post 91/92 time.

I know for certain that my 1988 760 originally had 96 tooth reluctor rings not only in the back axle but on the front stub axles for the ABS. The speedo ahd a divider between the ABS wiring and the speedo to divide the number of pulses by 8 (96/8=12) to register correctly. Later cars had a 48 tooth system and a direct wire speedo but needed a different ABS ECU (i currently have a 1991 240 ABS ECU in mine) and later cars still (92 on) had a 48 tooth system with Bosch ABS-2E system which isn't a plug'n'play compatible ECU for the earlier ABS.

Because of all this you need to find out if the donor vehicle of your speedo had ABS or not. Likewise with the back axle and also how many teeth on the reluctor ring (12, 48 or 96)
If the donor vehicle for the speedo had ABS with a 96 tooth ring and the speedo converter, it should work fine with a 12 tooth reluctor ring in the back axle. However if it had a 48 tooth back axle and the speedo is a 12 tooth animal, it will read 4 times the speed - conversely if the speedo is a 48 tooth animal being fed from a 12 tooth back axle, you'll need to be doing 120mph to register 30mph on the speedo.

Be careful if you try a diff cover swap, often the sensors are in different places and not compatible with being fitted to a diff with the sensor/reluctor ring in a different position. Note the senor must not touch the reluctor ring but have a clearance of ~0.030"/0.75mm between the tip of the sensor and the highest point of the ring.

When i changed my back axle for a later one with a 48 tooth ring i had to do several other mods, change the reluctor rings on the front hubs, the ABS ECU for a slightly later one and rewire the speedo converter to only divide by 4 instead of 8 but it's all sorted now.

If you can find out exactly what you've got there, you should be able to get something working, let us know and between us we should be able to sort you out.

[heckflosse]

Thanks,
It wasnt an ABS donor but it was a late one.
I'm trusting my instincts and doing an earlier axle swap-that way speedo and pickup are compatible.
Sounds drastic but it needed doing anyway.
Will update when done,
Jim

[heckflosse]

Groundhog day strikes again.
Axle duly swapped, with nice new support bushes lovingly fitted.
This TLC was rewarded by-still no speedo!
So, retrace steps.
Speedo head works fine in a spares car on just the L shape connector and the two lower pins bridged.
Checked live from ign on spares car, it is batt voltage.
continuity and resistance readings on both cars same for the other two wires to the diff.
Checked AC voltage on spares car in gear with engine running across the 2 terminal in the L connector (speedo removed), it increases with revs. Same on the 265. What am I missing.
How can a circuit with 3 wires be so baffling?
Getting suggestions that a bit of household DIY is a more fruitful use of time, so enough Volvo for today.
Jim.

[Laird Scooby]

Originally Posted by heckflosse

Groundhog day strikes again.
Axle duly swapped, with nice new support bushes lovingly fitted.
This TLC was rewarded by-still no speedo!
So, retrace steps.
Speedo head works fine in a spares car on just the L shape connector and the two lower pins bridged.
Checked live from ign on spares car, it is batt voltage.
continuity and resistance readings on both cars same for the other two wires to the diff.
Checked AC voltage on spares car in gear with engine running across the 2 terminal in the L connector (speedo removed), it increases with revs. Same on the 265. What am I missing.
How can a circuit with 3 wires be so baffling?
Getting suggestions that a bit of household DIY is a more fruitful use of time, so enough Volvo for today.
Jim.

Silly thought Jim, swap the two wires coming from the axle sensor - it shouldn't in theory make any difference but it might be something as silly as that. Some speedos of that era were designed to trigger in a certain way and as such were configured to only give an output when going forwards.

Even if it doesn't work, it's a step forward as you will eliminate that as a possible cause.

[Clifford Pope]

Originally Posted by Laird Scooby

Silly thought Jim, swap the two wires coming from the axle sensor - it shouldn't in theory make any difference but it might be something as silly as that. Some speedos of that era were designed to trigger in a certain way and as such were configured to only give an output when going forwards.

.

I suggested that ages ago in this thread.
I had that very thing - a tested set up in another car failed to work in mine, but did work backwards. I just swapped the sensor wires over under the back seat.