744 Speed sensor wiring.

[Offgrid]

I seem to be on the home straight with the brakes and the exhaust, but I have a problem with the speedo. Whilst under the car, I noticed a couple of wires hanging down. I've been ignoring these, as I thought that reconnecting them would be a simple job. I should have known better. They appear to be off the speed sensor, which is in the differential cover. I started to look at reconnecting them, and it seems to be non-trivial.

It doesn't look as if it is a simple plug in option, so I decided to rove the speed sensor for further investigation. Haynes tells me to remove the Panhard rod, and the retaining screw in the sensor. So I removed one bolt retaing the rod, and I hoped to be able to swing it down. No such luck, as I can't pull it over the inner bar. I can't get to the other bolt, as it is hard up against the boot well. The boot is full of rubbish, but I could remove that under suffrance, however, I can't see how to romve the well, as it seems to be welded to the chassis. It is also coated with some sort of tar covering. So my next idea is to disconnect the hand brake cable, and remove the differential cover. Am I going to get into trouble with this if I drain the oil, and replace it with new oil? My fear is that I won't be able to get the cover off with removing the boot tray.

The sensor looks to be in bad shape. So if I replace that, will I have problems checking the gap on the hall reader. Haynes tells me to use a feeler gauge through the filler hole, but it is too far away for that to be a possibility. Did they change the diff cover on 1988 models?

[Offgrid]

OK - I've managed to disconnect one end of the Panhard bar, which is a great relief as I don't have to remove the diff cover. Now I have to work out how to remove the bolt. It's in a real mess with bits sticking to the side of it. I may have to cut away the plastic surround to get it off. I'm also having problems in sourcing the sensor. The ones I find don't look like the fitted part, and those that do seem to be for ABS systems. I'm not sure what ABS has got to do with things, unless there is an extra wire for the ABS unit.

Does anyone know the part number for the original speed sensor. It;s a 1988 744 which originally had a B200E engine.

[bob12]

Not quite sure I fully understand your problem. Maybe a couple or so pics might help.

However, removal of sender in the rear diff (assuming non-abs) should not be a big problem once you have loosened the ring. Haynes do tend to go overboard at times but, it can be difficult.

These sensors are normally bullet proof and, as you suggest the problem is the wiring/connection rather than the sensor itself.

Maybe a replacement section of plug in wiring to the sensor might fix the problem .... see: https://www.skandix.de/en/spare-part...meter/1029612/ or, elswhere might be a cheaper option.

Bob

[Offgrid]

Thanks for the reply, but that doesn't look as if it is the correct part. I'm starting to think that I have ABS on this car. It is a 1988 740SE, and it had a B200E engine originally. I found one that looks like the correct part, but they want 128 Euros for it. Does an ABS/speedo sensor only have 2 wires connecting it? I need to look up the method of checking to see if I have ABS.

The parts I've found have the wiring fixed in the sensor. I think I'm going to try to remove the old one, and see if I can connect a couple of wires with spade connectors on them. The speedo was working, so I suspect that the only fault is the ripped out wiring. It's a bit of a mystery as to what ripped it out. There is a retaining mounting for the cable, and that is twisted, but it is well out of the way of anything passing under the car. The wire has a rubber grommet, and that has been pulled out of the retaining ring.

I'll try to make a short video a bit later when the car park has dried out.

[john.wigley]

Good morning, 'Offgrid'.

If I remember correctly, none of our 740s, and we had four over the years, had ABS. That is not to say that it wasn't available as an option, of course. I believe that late GLTs may have had it as standard.

My first Volvo to have ABS was my '91H 940, which I think was a standard fitment by then.

If you do have ABS fitted, that should be apparent from the distribution block under the bonnet.

Regards, John.

[Offgrid]

Oh! The joys of playing with classic cars.

I don't have an ABS light on the dash. I believe it is position 3, and that seems to be blank. The sensor doesn't look like any of the ones recommended for my vehicle. It doesn't have a retaining ring, but it looks like an ABS one with a small bolt to keep it in place. I've looked at the master cylinder, and it had 4 pipes into it. 2 look as if they are going to the offside front wheel, and two are going to the rear. I can't see any signs of an ABS control box or wiring near to the master cylinder.

When I have worked up the enthusiasm, I'll try to remove the old sensor, and I'll see if I can find a part number.

[john.wigley]

It sounds as though you have the standard triangular split dual circuit braking system, 'offgrid'. In the event of one system failing, both front and one rear brake, or 80% braking effort, remain. The only exception would be in the unlikely event of the master cylinder itself failing internally. You couldn't miss the distribution block if the car has ABS.

Regards, John.

[NI_Volvo_Nut]

Mine is an 88MY 740 SE and no ABS.

£ wires to the diff sensor from memory and they come inside the spare wheel well and connect to a plug on the floor roughly below the boot lid hinge (saloon). Black box from memory has the junction point.