Tach sending unit for 6V92

[chuckdrum]

On a trip to MT last week my tach started acting erratically and then one morning it stopped working altogether.  I suspect the first place to look would be the sending unit, eh?  And, where would that be located on a 6V92 (in my MCI-5C)?  What does it look like?  I'm not much of a mechanic but if I can locate and get access to a part, I can generally remove & replace. 

Thanks for your advice and assistance.

Chuck

[luvrbus]

If it has a pulse generator looking at the front of the engine it will be on the left side with 2 wires ,the other would be a signal feed from the R terminal on the alternator,and if a DDEC electronic engine it gets the signals from the ECM

[MC8Mike]

My 92 has the tach sender on the back of the blower.

[luvrbus]

My 92 has the tach sender on the back of the blower.

They do that on the 8v92 and 8v71 but not enough space for the tach drive on the blower on the 6V's

[chuckdrum]

Ok, I took my rig into the local DD shop as there were a couple of items besides the tach that needed attention so I figured I'd just pay for them to fix the tach problem, too.  After 2 1/2 weeks, they still haven't come up with a solution for the tach (my previous feelings about this particular shop have been further reinforced here, but they are very convenient to my home and do good work, once they get around to it).  They say the gauge is obsolete and they don't seem willing or able to come up with a bid to replace the gauge and/or the sending unit.

So, all you ever-so-knowledgeable bus nuts, I need some VERY SPECIFIC advice and info on what to do next, if you please.  I still don't know what the sending unit for the tach looks like on my 6V92 or where, EXACTLY, it is located.  Besides the gauge itself and a sending unit, what other parts are there to a tachometer system that might be causing the gauge to not read RPMs at all?  My gauge is an ISSPRO, if that is helpful.  My bus is a '79 MCI-5C with a 6V92.

Any suggestions, even including a service place you'd recommend in the Seattle area, would be appreciated!!  Thanks!

Chuck

[chessie4905]

You can go to Isspro site if it requires a new sender or tach. Did they check the drive end for broken drive pin or depth setting or dirt if it is inductive? They may be not interested in spending time researching for a replacement unit you may or may not purchase. Maybe Isspro has schematics and troubleshooting info, or you could Google Isspro forum or Isspro tach issues or something similiar. Could be as simple as a bad connection. There is a way to read the output of the sender while you rotate the input. Some require a scope to check the signal. Maybe it is possible to contact them for basic diagnostic info.

[Geoff]

Isspro sells a two magnet pick-up sensor.  Call them, they are very helpfull:

Instrument Sales and service  Customer service
800-333-7976

Or the big guys:

ISSPRO Inc.
2515 NE Riverside Way
Portland, OR 97211

Phone
1-800-888-8065      503-528-3400     

[luvrbus]

Don't the ISSPRO use glued on sensors or the sender that pickups the signal from the flywheel with a sensor screwed into the bellhousing ?

[richard5933]

Aren't there tachometers out there that can be fed from a terminal on the alternator?

[chessie4905]

Probably, but he would like his to work if it won't be costly

[richard5933]

I guess my point was more to say that there are other ways to get a signal to one of these things. Possibly the current tach is adjustable and can be made to work with another signal feed.

[chuckdrum]

Thanks, all, for your thoughts and suggestions.  I finally got to speak on site with the shop foreman and took this pic of the sensor.  I think a couple of you had it right on this system.  I won't have the bus back in my possession until later today, but it looks like the sensor is triggered by points on the wheel that are brazed on? glued on? not really sure there but they are badly worn.  And/or the sensor itself is shot.  Or there's a wiring problem. The foreman suggested that it's likely the only option is an entire new system which, apparently, they weren't willing to bid out.

As I just discovered all of this yesterday, I haven't had time to see if anyone might have that ancient part; used, even.  Or had time to trace the wiring to see if there's anything obvious there.  The saga continues...

[richard5933]

Looks like all you need is one of these kits:

http://isspro.mybigcommerce.com/r8906/

Clean the end of the pulley wheel, then stick on the little bits with the adhesive in the kit. If your wire ends up not being good, then hopefully you can find a spare one in your harness or run another somehow.

If the kit doesn't work, give these guys a call. https://www.robinair.com/fuel-systems-inc

They are pretty good about getting oddball things like this running.

[chessie4905]

I had something very similar to that in my Audiovox/Rostra cruise control kit, I installed on the cycle. You glued on little magnets on the rear wheel and that sensor, which looks almost identical, transferred the signal to the control box.

[luvrbus]

Thanks, all, for your thoughts and suggestions.  I finally got to speak on site with the shop foreman and took this pic of the sensor.  I think a couple of you had it right on this system.  I won't have the bus back in my possession until later today, but it looks like the sensor is triggered by points on the wheel that are brazed on? glued on? not really sure there but they are badly worn.  And/or the sensor itself is shot.  Or there's a wiring problem. The foreman suggested that it's likely the only option is an entire new system which, apparently, they weren't willing to bid out.

As I just discovered all of this yesterday, I haven't had time to see if anyone might have that ancient part; used, even.  Or had time to trace the wiring to see if there's anything obvious there.  The saga continues...

LOL that is some engineering call the guys at Precision Speed in Phoenix he can help you out www.precisionspeed.com I would check and see if there is a tach drive installed on the other cam side you could get lucky