740 speedometer needle setting after fix

Hell Driver · Mar 24th, 2019, 13:43

Hi, I've just replaced the broken cog to repair the odometer in my 740. Foolishly didn't note the exact position before removing needle to access the cogs

. Does it sit exactly on the zero position marker (just noticed the lowest position relates to 10mph not zero!) or slightly below as some cars do at rest? I don't want it to over read if I get it wrong. Many thanks in advance, a photo would be great.

PS. It's the 25 tooth VDO speedo from a 1988-9 F reg

Laird Scooby · Mar 24th, 2019, 15:02

I'm guessing you have a smartphone as well? Download a GPS speedo app and set the phone up in your car. Now take it for a drive and compare the readings. As long as your car speedo shows the same as the GPS with up to 10% more but nothing less (in other words, if the GPS says 30mph, your speedo can read anywhere between 30-33mph but no lower, like wise at 60 on the GPS app it can read 60-66mph but not 59 or lower) then you're ok.

I think there's a pin to stop the needle at 10mph so it won't read until you reach 10mph so this is how i would do it.

Granted if you need to reposition it, it will be a faff stripping it all out again but nothing else for it sadly.

Hell Driver · Mar 24th, 2019, 19:43

Thanks for that, yes I was going to use a dashcam with a gps speed readout to calibrate but then I found this https://www.240turbo.com/740-odometer-repair.html which happens to have the same speedo. Set at 10mph and needle begins to lift above 10mph. All back together now but odometer still not working, it was a broken cog which I've replaced but I've either put something back wrong or it had got another problem as well. Got to take it all apart again! Was working OK so likely something related to cog. Apparently the broken tooth can jam in the mechanism. I wound it on a bit to allow for missing miles so as far as I can tell it should be free to move.

bob12 · Mar 24th, 2019, 20:23

Fret not ... in my humble opinion the best guide for the VDO is on Dave Barton's website as said ^^^ at: https://www.240turbo.com/740-odometer-repair.html , although it is a bit long winded!

You will find that once the needle is back on the spindle again that with care you can still 'adjust' it by holding the hub and turning it ever so slightly backward or forwards .... be careful!! Backwards is easiest as you are turning it against the inbuilt stop. If you put the needle on just above zero you can then adjust it downwards to zero. In this position you will find that it is likely to read about +/- 2mph above zero. Give it a few gentle flicks to make sure where the needle settles.

Then, as said above you can test accuracy with a satnav or an app.

bob12 · Mar 24th, 2019, 20:28

Quote:

Originally Posted by Hell Driver

Thanks for that, yes I was going to use a dashcam with a gps speed readout to calibrate but then I found this https://www.240turbo.com/740-odometer-repair.html which happens to have the same speedo. Set at 10mph and needle begins to lift above 10mph. All back together now but odometer still not working, it was a broken cog which I've replaced but I've either put something back wrong or it had got another problem as well. Got to take it all apart again! Was working OK so likely something related to cog. Apparently the broken tooth can jam in the mechanism. I wound it on a bit to allow for missing miles so as far as I can tell it should be free to move.

So, the speedo needle is working and the mileometer, but not the trip odo?

NI_Volvo_Nut · Mar 25th, 2019, 12:30

There are 2 different sized cog's, did you get the right one?

Clan · Mar 25th, 2019, 13:04

Quote:

Originally Posted by Hell Driver

Hi, I've just replaced the broken cog to repair the odometer in my 740. Foolishly didn't note the exact position before removing needle to access the cogs

. Does it sit exactly on the zero position marker (just noticed the lowest position relates to 10mph not zero!) or slightly below as some cars do at rest? I don't want it to over read if I get it wrong. Many thanks in advance, a photo would be great.

PS. It's the 25 tooth VDO speedo from a 1988-9 F reg

you should find a hidden white mark on the face which lays just below the needle stop , that is the place to fit the pointer to .

Hell Driver · Mar 25th, 2019, 14:18

Thanks for the replies, now an update. Yes, I've got the 25 tooth one which is what the old one was, (I counted the teeth and missing tooth on the old one). Speedo needle now the least of the problems! Got it all back together (including needle!) and odometer (miles) still not working. Took apart and found that tiny 25 tooth cog has different sides (on has a collar) so turned it over. (On the bench, it works both ways to move digits so can't see it matters which way up it goes). I've now rebuilt it in stripped down form (no dial cover and no needle, no housing etc. for ease of stripping down again). It works for a few clicks (sometimes nearly a mile) then jams up. Can release with finger on digits as suggested in the link and get it going again. Got about 80 clicks out of it before jamming again Stepper motor working ok. Sometimes I can hear it trying when jammed. I've recovered the broken tooth so not that causing problems. Maybe lubrication needed.

bob12 · Mar 25th, 2019, 14:37

Yes, 25 toothed cog is the norm in the UK. I think it's in the US and other world markets where the 26 are prevalent.

I suspect that your problem might be that the pcb is screwed down too tight preventing the stepping motor from running freely, but that's no guarantee.

I seem to recall that the little collar faces upwards. I see if I can find a picture ... found!!

Hell Driver · Mar 25th, 2019, 14:57

Hopefully final update! Looks like friction was the problem. Yes, the collar should be upwards as per diagram. I've returned it to that position (in which it wasn't working when I first reassembled) and added a tiny amount of oil to every moving cog/friction surface. (But not the digits!) I wondered about the screwing down of the PCB but the motor centre has a clever spring loaded friction surface to avoid that problem. I've jacked the car up and gone through a few miles and all seams OK. By the way, the odometer works as normal in reverse so no easy clocking of mileage that way! (Although it's dead easy when the stepper motor is off). I added a few missing miles from while it's been not working. 99,050 miles so still a low mileage example in Volvo terms.

Mar 24th, 2019, 13:43	#1
Hell Driver Junior Member Last Online: Yesterday 14:42 Join Date: May 2009 Location: Doncaster	740 speedometer needle setting after fix Hi, I've just replaced the broken cog to repair the odometer in my 740. Foolishly didn't note the exact position before removing needle to access the cogs . Does it sit exactly on the zero position marker (just noticed the lowest position relates to 10mph not zero!) or slightly below as some cars do at rest? I don't want it to over read if I get it wrong. Many thanks in advance, a photo would be great. PS. It's the 25 tooth VDO speedo from a 1988-9 F reg Last edited by Hell Driver; Mar 24th, 2019 at 13:58.

Mar 24th, 2019, 15:02	#2
Laird Scooby Premier Member Last Online: Yesterday 21:06 Join Date: May 2012 Location: Lakenheath	I'm guessing you have a smartphone as well? Download a GPS speedo app and set the phone up in your car. Now take it for a drive and compare the readings. As long as your car speedo shows the same as the GPS with up to 10% more but nothing less (in other words, if the GPS says 30mph, your speedo can read anywhere between 30-33mph but no lower, like wise at 60 on the GPS app it can read 60-66mph but not 59 or lower) then you're ok. I think there's a pin to stop the needle at 10mph so it won't read until you reach 10mph so this is how i would do it. Granted if you need to reposition it, it will be a faff stripping it all out again but nothing else for it sadly. __________________ Cheers Dave Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........

Mar 24th, 2019, 19:43	#3
Hell Driver Junior Member Last Online: Yesterday 14:42 Join Date: May 2009 Location: Doncaster	Thanks for that, yes I was going to use a dashcam with a gps speed readout to calibrate but then I found this https://www.240turbo.com/740-odometer-repair.html which happens to have the same speedo. Set at 10mph and needle begins to lift above 10mph. All back together now but odometer still not working, it was a broken cog which I've replaced but I've either put something back wrong or it had got another problem as well. Got to take it all apart again! Was working OK so likely something related to cog. Apparently the broken tooth can jam in the mechanism. I wound it on a bit to allow for missing miles so as far as I can tell it should be free to move. Last edited by Hell Driver; Mar 24th, 2019 at 19:46.

Mar 24th, 2019, 20:23	#4
bob12 bob12 Last Online: Apr 17th, 2024 22:05 Join Date: Aug 2006 Location: Woking	Fret not ... in my humble opinion the best guide for the VDO is on Dave Barton's website as said ^^^ at: https://www.240turbo.com/740-odometer-repair.html , although it is a bit long winded! You will find that once the needle is back on the spindle again that with care you can still 'adjust' it by holding the hub and turning it ever so slightly backward or forwards .... be careful!! Backwards is easiest as you are turning it against the inbuilt stop. If you put the needle on just above zero you can then adjust it downwards to zero. In this position you will find that it is likely to read about +/- 2mph above zero. Give it a few gentle flicks to make sure where the needle settles. Then, as said above you can test accuracy with a satnav or an app. Last edited by bob12; Mar 24th, 2019 at 20:50.

Mar 25th, 2019, 12:30	#6
NI_Volvo_Nut Volvologist Last Online: Dec 6th, 2023 11:13 Join Date: Aug 2008 Location: Bangor - Norn Iron View Photos By: NI_Volvo_Nut	There are 2 different sized cog's, did you get the right one? __________________ What's the matter with the car I'm driving? Can't you tell that it's out of style? Should I get a set of white wall tires? Are you gonna cruise the miracle mile?

Mar 25th, 2019, 14:18	#8
Hell Driver Junior Member Last Online: Yesterday 14:42 Join Date: May 2009 Location: Doncaster	Thanks for the replies, now an update. Yes, I've got the 25 tooth one which is what the old one was, (I counted the teeth and missing tooth on the old one). Speedo needle now the least of the problems! Got it all back together (including needle!) and odometer (miles) still not working. Took apart and found that tiny 25 tooth cog has different sides (on has a collar) so turned it over. (On the bench, it works both ways to move digits so can't see it matters which way up it goes). I've now rebuilt it in stripped down form (no dial cover and no needle, no housing etc. for ease of stripping down again). It works for a few clicks (sometimes nearly a mile) then jams up. Can release with finger on digits as suggested in the link and get it going again. Got about 80 clicks out of it before jamming again Stepper motor working ok. Sometimes I can hear it trying when jammed. I've recovered the broken tooth so not that causing problems. Maybe lubrication needed.

Mar 25th, 2019, 14:57	#10
Hell Driver Junior Member Last Online: Yesterday 14:42 Join Date: May 2009 Location: Doncaster	Hopefully final update! Looks like friction was the problem. Yes, the collar should be upwards as per diagram. I've returned it to that position (in which it wasn't working when I first reassembled) and added a tiny amount of oil to every moving cog/friction surface. (But not the digits!) I wondered about the screwing down of the PCB but the motor centre has a clever spring loaded friction surface to avoid that problem. I've jacked the car up and gone through a few miles and all seams OK. By the way, the odometer works as normal in reverse so no easy clocking of mileage that way! (Although it's dead easy when the stepper motor is off). I added a few missing miles from while it's been not working. 99,050 miles so still a low mileage example in Volvo terms.

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