Anybody have a wiring diagram or manual for this speedometer tachometer?

[Mex-Busnut]

Dear Friends,

This is my current speedometer-tachometer unit, which shows about 60% of the actual speed you are going, and the tach does not work. Does somebody have any manuals or files for this unit?

Thanks in advance!

[John316]

Dr. Steve,

I do not have any info on that exact speedo. However, I do have another idea for you. For the speed part of it, you might try to adjust it. Look to see if there is an innocent looking screw (for adjusting it, but it might look like a regular screw) in the back. If there is, get a GPS unit, another car on cruise, or whatever. Take your bus out for a drive, while you have somebody else adjust the screw until you are accurate.

That is what we did, and worked pretty well.

Sorry no help on the tach part.

God bless,

John

[RJ]

Dr Steve -

Hmmm. . . a "tattletale" unit, looks to be of 1974 vintage.

Did you Google search the name on the back?

Argo Tachograph used to be the common brand name for a similar style here in the States.

You might give Luke a call, he might have some sources. 

Being that it's in German, it's possible that Jeremy might be able to scarf up one from a truck boneyard in England out of a German lorry.

BK might recognize it - I think they used a similar unit in the Setra S215s.

More pics would be helpful, front & back plus the one you've shared.

FWIW & HTH. . .

[zubzub]

60% (50%?) of speed would make me think it is missing a magnet on the wheel sensor....just a guess...mine (which is a more modern model) has a sensor (really a winding) that gets a magnetic pulse from magnets attached to the hub, if one magnet was missing I would expect 50% of speed  to show up.  Tach who knows.  Are you sure it is getting a signal from the alt/wherever your engine sends a signal from?

[bevans6]

I would adjust the wheel sensor if it has one as a first try.  Mine doesn't use magnets, nothing more sophisticated than 1/4" bolts screwed into the rim of the brake drum.  Sensor had to be 3/16" from the bolt heads to work properly, mine was too close and when I got to 50 mph it jumped straight to 80 mph.  Previous owner said he could cruise all day at 80 - what a doofus.

Brian

[Oonrahnjay]

    Steve, is what you're holding the actual unit with the dials on it (it looks like the dials are facing down so we can't see them)?  If it's a unit that has dials built in to the face, you need to find out exactly how the unit works.  Are there any spec sheets or circuit diagrams on the Innerweb?  I'm thinking that you have two separate drive systems:

1)  Speedos usually work in one of two ways, you can have a "sensor unit" (on my bus it's a cam off the transmission, the cam trips a little switch so that as the cam turns the electrical signal goes "on-off-on-off") on something like a gear or cable drive, sometimes off the transmission and sometimes off the rear axle; or you can have a signal system that counts the wheel revs, this often uses a magnetic coil mounted near the wheel.  As people have said, it sometimes reads magnets or sometimes the magnet is fixed and it reads off a steel or iron (metal that a magnet will stick to) trigger mechanism.

2)  Tachos usually read the pulses from the alternator.  Is there an electrical input on this unit?  If so, you should check to see if there's a "pulse" at that point.  If the pulse is there, it's probably a bad unit or a bad ground.  Speaking of grounds, have you checked the grounds on the unit?  It is kind of odd that both the readouts should be wrong at the same time.

(Brian said "Previous owner said he could cruise all day at 80 - what a doofus."  Yeah, he had to drive at 80 all the time -- it must have been terrible to have all the trucks pass him doing 95!)