Volvo Car Forums


Reply
Thread Tools Display Modes

740 Speedometer Sending Unit Question

 
Jamie
Guest
Posts: n/a
 
      12-06-2006
Howdy folks,
Yesterday I tried to find the cause of my speedometer issue. It has a
mind of its own. Usually only kicks in after driving down the highway
at speed for a short while.

I pulled the dash first and disconnected and reconnected everything. I
reinstalled it and no change. Next, I removed the pan hard rod from
the rear and unplugged the electrical connector from the sending unit
on the differential. The ends of both wires were exposed, so I cleaned
them and the connector with throttle body cleaner. From there I applied
liquid electrical tape, plus electrical tape over the bare wiring. The
wires did not appear to be broken.

I reconnected the unit and still it does not work. I am thinking my
next step is to remove the unit from the differential, but I do not
know what I will be looking for.

Any suggestions?

Thanks!
Jamie

1987 740 GLE

 
Reply With Quote
 
 
 
 
Jamie
Guest
Posts: n/a
 
      12-06-2006
I didn't take apart the speedo or any components on the cluster, I just
unplugged the wires and reconnected them in case they were loose.

I wonder which end should I dig into the guts first - behind the dash,
or at the chunk? BTW- where exactly are the wires to the speedo on the
dash?

Can ya'll help me out from memory?

As I recall, from the drivers side going left to right are:

1) a multi pin connector on the lower left.

2) A yellow wire going high center with a plastic lock cover.

3) A brown/white wire going low, just right of center onto 1 of 2 pins.
I use the lower pin.

4) A multi-pin connector to the low right

5) A multi pin connector off to the high right.

6) There is also a 3 wire set (3 or 4 - can't remember), in a weird,
hard to disconnect plastic housing. It looks like you open the plastic
connector downward and back the wires out. I could not get this off and
did not want to break it. It was just to the lower right of the speedo
on the rear.

Can ya'll tell me what any or all of these wires do and which are for
my speedo?

Thanks

 
Reply With Quote
 
 
 
 
zencraps@comcast.net
Guest
Posts: n/a
 
      12-06-2006

this might help

http://www.brickboard.com/FAQ/700-90...eterFluctuates

 
Reply With Quote
 
Jamie
Guest
Posts: n/a
 
      12-06-2006
Thanks. I've read through all of these and while very informative, I
was hoping someone could give me a more descriptive answer on what I
should see when I remove the sending unit from the differential.

This gives a good detail of the wiring, but not much about the inner
workings at the 'chunk'. Haynes talks about using a feeler gauge to
determine the correct distance when installing a new unit.

I wasn't sure if there were any tell-tale signs of problems once you
remove the sending unit.


(E-Mail Removed) wrote:
> this might help
>
> http://www.brickboard.com/FAQ/700-90...eterFluctuates


 
Reply With Quote
 
User
Guest
Posts: n/a
 
      13-06-2006
In article <(E-Mail Removed) .com>,
(E-Mail Removed) says...
> Thanks. I've read through all of these and while very informative, I
> was hoping someone could give me a more descriptive answer on what I
> should see when I remove the sending unit from the differential.
>
> This gives a good detail of the wiring, but not much about the inner
> workings at the 'chunk'. Haynes talks about using a feeler gauge to
> determine the correct distance when installing a new unit.
>
> I wasn't sure if there were any tell-tale signs of problems once you
> remove the sending unit.
>
>
> (E-Mail Removed) wrote:
> > this might help
> >
> > http://www.brickboard.com/FAQ/700-90...eterFluctuates

>
>

There is a tone ring, or shutter wheel fixed to the ring gear carrier.
The pick up is a simple coil wrapped around a permanent magnetplaced in
a brass can and molded shut with plastic to form a seal and a plug
connector. The sensor is shimmed from below and held in place by a
threaded cap while it is sealed with an oil ring. The sensors only go
bad when the car is hit from behind driving the panhard rod into the
molded plastic and breaking it or the diff cover or both. Or if
something inside differential literally blows up. If you had to name one
piece on a Volvo that is absolutely bulletproof you have found it.

Now if you have ABS on the car the signal from the vehicle speed sensor
goes to a divider/multiplier circuit where the AC signal from the speed
sensor is split. One portion is converted to a square wave for use by
the ABS controller and the frequency adjusted for that use, IIRC the
tone ring for the hubs is 72 teeth and the ring on the differential is
48, the other half goes directly to the speedo head. The 4 pin plug that
connects to the speedo is the other end of the speed sensor wires, the
Gn/W, Bn wire twisted pair plus a R/Bl switched B+ and a SB-.

If you jack up the rear of the car enough that the rear wheels can spin
free you should be able to read a good AC signal from the sensor wires
with the cluster removed. There should be very little amplitude change
but some increase from wheels turning at idle, but a substantial
increase in frequency with each increasing change in rear wheel speed.
If the signal is there and reliable then the speedo needs to be repaired
or replaced.

Bob

--
The goal when driving is to miss the maximum number of objects.
 
Reply With Quote
 
Jamie
Guest
Posts: n/a
 
      13-06-2006
Well, lots done and still no speedometer:

1) Removed and inspected the sending unit. Reinstalled - did not know
how to test it.

2) Cut off two-wire connector to sending unit, removed each wire-end
from the connector and rebuilt the wiring using a butt connector
installed in each hole with replacement 12 gauge wiring. I reinstalled
connector with new wires and re-wired wiring.

3) Removed the dash and inspected all connectors

4) Checked ground wires around left foot side of driver's floor. There
was an assembly that had dismounted from the chassis, so I remounted
it.

5) Checked fuses.

Everything else on the dash works - the odometer, tach, fuel -
everything but the speedo.

(sigh).


Jamie wrote:
> Thanks. I've read through all of these and while very informative, I
> was hoping someone could give me a more descriptive answer on what I
> should see when I remove the sending unit from the differential.
>
> This gives a good detail of the wiring, but not much about the inner
> workings at the 'chunk'. Haynes talks about using a feeler gauge to
> determine the correct distance when installing a new unit.
>
> I wasn't sure if there were any tell-tale signs of problems once you
> remove the sending unit.
>
>
> (E-Mail Removed) wrote:
> > this might help
> >
> > http://www.brickboard.com/FAQ/700-90...eterFluctuates


 
Reply With Quote
 
James Sweet
Guest
Posts: n/a
 
      13-06-2006
Jamie wrote:
> Well, lots done and still no speedometer:
>
> 1) Removed and inspected the sending unit. Reinstalled - did not know
> how to test it.
>


Measure it with an ohm meter, unless it's open circuit then it's
probably fine. As someone else mentioned, all it is is a coil.

> 2) Cut off two-wire connector to sending unit, removed each wire-end
> from the connector and rebuilt the wiring using a butt connector
> installed in each hole with replacement 12 gauge wiring. I reinstalled
> connector with new wires and re-wired wiring.
>
> 3) Removed the dash and inspected all connectors
>
> 4) Checked ground wires around left foot side of driver's floor. There
> was an assembly that had dismounted from the chassis, so I remounted
> it.
>
> 5) Checked fuses.
>
> Everything else on the dash works - the odometer, tach, fuel -
> everything but the speedo.
>
> (sigh).
>


And the odometer and cruise control don't work either I assume?
 
Reply With Quote
 
Jamie
Guest
Posts: n/a
 
      13-06-2006
The odometer is fine, works well. The cruise works if/when the speedo
kicks in.

Everything works fine, only the speedo doesn't work.


James Sweet wrote:
> Jamie wrote:
> > Well, lots done and still no speedometer:
> >
> > 1) Removed and inspected the sending unit. Reinstalled - did not know
> > how to test it.
> >

>
> Measure it with an ohm meter, unless it's open circuit then it's
> probably fine. As someone else mentioned, all it is is a coil.
>
> > 2) Cut off two-wire connector to sending unit, removed each wire-end
> > from the connector and rebuilt the wiring using a butt connector
> > installed in each hole with replacement 12 gauge wiring. I reinstalled
> > connector with new wires and re-wired wiring.
> >
> > 3) Removed the dash and inspected all connectors
> >
> > 4) Checked ground wires around left foot side of driver's floor. There
> > was an assembly that had dismounted from the chassis, so I remounted
> > it.
> >
> > 5) Checked fuses.
> >
> > Everything else on the dash works - the odometer, tach, fuel -
> > everything but the speedo.
> >
> > (sigh).
> >

>
> And the odometer and cruise control don't work either I assume?


 
Reply With Quote
 
zencraps@comcast.net
Guest
Posts: n/a
 
      13-06-2006

Go to a U Pull It and yank out another cluster, if all else fails.

 
Reply With Quote
 
Jamie
Guest
Posts: n/a
 
      13-06-2006
What is giving me fits is the yellow wire is on pretty tight and I
didn't remove it out of fear of breaking it.

The only other set I cannot remove is I think the speedo set, a small
cluster of wires in a cube (not like the parallel snap-ons), that are
on the lower corner of the speedo. I can't see how these are clipped
in. I want to pull the cluster and inspect the back side, but I mainly
fear I will break this one cluster of wires.

Can anyone tell me how these are removed?

Thanks.

Jamie


Jamie wrote:
> The odometer is fine, works well. The cruise works if/when the speedo
> kicks in.
>
> Everything works fine, only the speedo doesn't work.
>
>
> James Sweet wrote:
> > Jamie wrote:
> > > Well, lots done and still no speedometer:
> > >
> > > 1) Removed and inspected the sending unit. Reinstalled - did not know
> > > how to test it.
> > >

> >
> > Measure it with an ohm meter, unless it's open circuit then it's
> > probably fine. As someone else mentioned, all it is is a coil.
> >
> > > 2) Cut off two-wire connector to sending unit, removed each wire-end
> > > from the connector and rebuilt the wiring using a butt connector
> > > installed in each hole with replacement 12 gauge wiring. I reinstalled
> > > connector with new wires and re-wired wiring.
> > >
> > > 3) Removed the dash and inspected all connectors
> > >
> > > 4) Checked ground wires around left foot side of driver's floor. There
> > > was an assembly that had dismounted from the chassis, so I remounted
> > > it.
> > >
> > > 5) Checked fuses.
> > >
> > > Everything else on the dash works - the odometer, tach, fuel -
> > > everything but the speedo.
> > >
> > > (sigh).
> > >

> >
> > And the odometer and cruise control don't work either I assume?


 
Reply With Quote
 
 
 
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
fuel gauge or sending unit in '91 w/Regina? James B. General Motoring 1 02-01-2006 02:08 AM
Where is Oil Sending Unit on '94 850 caaron Volvo 850 1 04-10-2004 02:32 AM
89-740 fuel sending unit R Zych Volvo 740 1 24-04-2004 09:19 AM
Re: 89 740 fuel sending unit Mike F Volvo 740 1 23-07-2003 04:10 PM
Re: 89 740 fuel sending unit Peter Milnes Volvo 740 0 30-06-2003 11:55 PM


All times are GMT. The time now is 12:50 AM.