700 hall sensor replacement

[BillB]

This report covers the steps needed to fit a new hall sensor to the pre-RPM sensor 700 series distributor (up to 88/9 I think). Having removed the distributor, firstly you have to remove the pin securing the drive dog – this can be VERY tight. I started it with a centre punch and drove it out using a dulled masonry nail (you need something hard for this). You must support the drive dog well – I rested it in the vice jaws.



With pin removed the distributor can be dis-assembled carefully. Take note of the sequence of the washers. Some are fibre and will break easily!



Note that the shaft bearing in the centre of the distributor body contains an oil seal that should be replaced. It’s not a Volvo part but the 700/900 FAQ gives details of a suitable substitute. I didn’t change it as I was rushing. Next, you need to remove the hall sensor by drilling out the rivets which retain it. This is done from the underside and needs a drill press. They should be CAREFULLY centre-punched first. Lack of care here can result in a ruined distributor base as it is much softer than the rivets. On no account try to punch the rivets out – you will wreck the dist. base.



If successful you now have a stripped base with two correct size holes:



Next the difficult part! You install the new hall sensor which comes with new rivets ready to preen over. This is almost impossible as the rivets are hard steel and the dist. base isn’t. You have to be very accurate with a suitable punch whilst at the same time supporting the top of the rivets (on the hall side and out of sight) using a suitable round metal bar clamped in the vice. The danger is that the hall moves a little and you damage the plastic housing whilst striking a rivet. This I did but not too badly. I found that the rivets were not crushing easily so I decided to use “metal” araldite instead.




The following shows the new hall in place (sourced from PFV for £35- ScanTech).



You can see traces of araldite around the hall. The connector on the right is obtainable from Volvo quite cheaply. Next the shaft assembly is replaced and the drive dog re-fitted. THIS CAN BE DONE 180 DEGREES OUT – TAKE CARE. The pin is driven back in using the vice:






Note the green seals which are obtainable from Volvo very cheaply. You can also see a bent nail on the table tennis bat which I’d tried before the masonry nail when removing the pin. You should now have a serviceable distributor at a lower cost than a complete new unit. There may be a risk, in my case, that the araldite lets go, but I doubt it. Hope this is of use to someone. Note that there is further info. on this procedure in the FAQ. Regards.