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240 electronic speedometer calibration (1986+)

Would it be possible to upload the pics this week?

My car currently shows 40mph when I'm going 48. I would love to have this live!

I did this on a previous 240, as I recall it?s as simple as finding the 50 ohm resistor, and replacing it with a 100 ohm micro potentiometer set to 50 ohms, then adjusting it so the speedo matched my GOS app.

I glued the pot behind the plug for the clock adjust stalk hole, and can adjust mine without removing the cluster.

I used something like this, multi turn trim pot.

Old thread -- perhaps we can revive. Is there a late model 120 mph electric speedo that I can transplant into my '82 cluster to replace the cable driven unit?

JW240 - a few things; go slow with me and talk like I'm a second grader. :oops: The unit in the first 2 pictures above looks entirely different from the unit you actually worked on. What am I missing there? Which one is an electronic speedo for a 240? Also, in your written comments you say you hooked up 2 resistors in series; but from the picture (with the 'screw terminal thingie') 2 resistors appear to be hooked up in parallel. Do my eyes deceive me? Last - is there another resistor that can be used to adjust the odometer accuracy? Is there a way to alter the odometer reading? I need to ADD miles to mine; when the 85 mph speedo it came with was swapped with a 120 mph unit -- the new speedo had about 48,000 fewer miles than the original. Us Volvo owners are proud of our high miles....

The good news about this is if it will work, I can hook the whole thing up temporarily in the car while I'm driving, calibrating, checking against GPS, etc. And once I get it right - then I can transplant into the cluster.

Michael- did you ever get the late model speedo in the old cluster? I am facing this with my ?81 240.
The other choice would be to swap the whole cluster from a late model. Has anyone done this?
I’ve got an ‘87 cluster in my 242GT with ‘81 dash. Got sick of the cable speedo actuation after 3 different cables all failed to be the right length (Supra 5spd conversion). It works using a Toyota mechanical-to-pulse adapter which came off something Japanese & obscure, and an aftermarket adjustable pulse-counting-and-conversion kit (speedo “tuned” off ‘phone & SatNav GPS :)).

With the ‘81 cluster it works fine, with the ‘87 cluster there’s some cross-wiring which I haven’t been arsed hunting-down. The “Acc” setting for the (new) switch (replaced the switch with brand-new one before it occurred to me the problem could be incompatibility between clusters) has the effect of the “On” setting, so I basically don’t have an Accessories setting.

Apart from that, the majority of it just plugged in, including at least the two big whacky-shaped plugs. Speedo plug is obviously custom though, that won’t be plug-and-play. The car drives fine, and everything works as expected for the “On” ignition-switch setting.
I still have them, need to re-host.

But wont have acces to the pics this week. Maybe Art's site can help you with the chip pinout, you can trace it. In a few weeks i can have the pics up again.

Would be very interested in seeing these pics. Thanks so much for doing this write-up!
I have basically unlimited hosting space if there are some photos that could be used for this topic. If they're sent to me I can load them and send the link which could be edited into the article and, MAGIC, the all important photos will appear !!
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I have basically unlimited hosting space if there are some photos that could be used for this topic. If there are sent to me I can load them and send the link which could be edited into the article and, MAGIC, the all important photos will appear !!

Great, yes, seen the PM, will get the pics soon! (not on my laptop anymore, need to dig)
Thanks for the offer and will send them ASAP!
Bump, fixed!

I have basically unlimited hosting space if there are some photos that could be used for this topic. If they're sent to me I can load them and send the link which could be edited into the article and, MAGIC, the all important photos will appear !!

Ended up finding hosting myself! Thanks for the offer though.

Life has been very busy and stuff.

As far as speedometer work, replaced the odo gear last month. 240 is sporting the aluminium cover now with a homemade tone ring wrapped around a TrueTrack diff. Works great, still. 225/45/17 tires and calibration is good with the aforementioned resistance values.
Hi all,

Yet another thread revival...

So we're working on a friends car at the moment, 1978 with a cable driven speedo. The B21A is out and a B230FK is in. Hybrid speedo being made, with a late speedo within the early case (has been done a few times now and someone on here was offering a conversion kit just last week)

My question then - we're tracking down a late axle to transplant in to provide the speed signal for both the speedo and so 2.4lh plays nicely. Would an alternative be to mount a standard diff housing sensor pointing at the 4 bolts of the diff input flange, or the thee bolts of the gearbox output flange, then recalibrate the speedo using an adjustable resistor?

Does anyone know if the range of adjustment would be great enough?

Thanks all,

I looked at the datasheet for the speedo chip and it should have plenty of adjustment range.

The original setup is 12 pulses per axle (or tire) rev. If you have a 3.73 differential ring/pinion and use the 4 diff flange bolts, you'll get 3.73 * 4 = 14.9 pulses per tire rev, or ~25% higher. Using 3 bolts, 3.73 * 3 = 11.2 pulses/rev, or ~7% lower. Either one should be easily within the adjustment range, and either one is close enough to the 12 pulses/rev to keep LH2.4 happy.

The biggest difficulty may be mounting a sensor, and aligning the bolt heads (or add-on metal flags?), to get a good signal.

[Note: changing the resistor affects the speedo only, the odometer will still be fast or slow depending on the 3 or 4 bolts.]
Great! Thanks for looking that up and replying. Annoyingly the engine and gearbox are in the car now, which makes adding something a little more difficult. The gearbox has a conversion bracket like this bolted to the back of it to allow it to bolt to the M47 cross member, it would have been relatively easy to weld a bracket to it whilst it was out of the car as it?s made of steel. Still considering options, might put a complete axle in it.

Can the odometer accuracy be adjusted in a similar fashion?


The odometer can't be adjusted in a similar fashion. It relies on an exact count of pulses per mile from the differential sensor.
Ah, fair enough.

Well, we?re going with the ?swap the whole axle? approach as one came up locallyish and cheapish. Since the axle needs new bushes and brakes, refurbishing the ?new? ones and installing it seemed like the best approach this time.

Thanks for the advice,

Looks like you're sorted … but had I seen the more recent posts last week, I'd have pointed to something like this:


… which was only available in kit form when I bought one for my car, but which allowed me to convert the Toyota-branded pulses from the 90's Sprinter sensor on the 80's Supra 'box into Volvo branded pulses for the '87 cluster I fitted into the '81 dash (and which isn't actually a perfect fit electrically - despite all looms just plugging in, something is wrong with the ACC setting but ONLY with the '87 cluster fitted - but I don't care as I don't sit there listening to music with the car off).

Something like that might be helpful if there's another thread-dig by someone else. :)
Ok, moving on with this - have contacted petiww to see about one of his conversion plates.

Am I correct in thinking the speedo will read correctly for all speeds, once calibrated?

The pictures from earlier in the thread would be useful... does anyone have a copy?

I didn't want to wait for a potentiometer to come in so I just tried a few different resistors. I found that about 1.5 ohm of added resistance would decrease the speedo reading about 5%. My original resistor in a '90 240 wagon measured 51.6 ohm. The speedo was reading 5% fast initiallly, even though the odometer was spot on, so it was nice to get it calibrated.