Tachometer

[Norm Ahlheim]

I have a CD30 with a Volvo MD7A . The tach hasn't worked in a few years and I believe Volvo's prices to repalce it are absurd. Has anyone replace their tach with and auto parts tach. If so what type? I can get along without it but it is nice to have. Thanks



Grayrocks@aol.com

[wayne grenier]

I have a CD30 with a Volvo MD7A . The tach hasn't worked in a few years and I believe Volvo's prices to repalce it are absurd. Has anyone replace their tach with and auto parts tach. If so what type? I can get along without it but it is nice to have. Thanks

I have the same problem-with a volvo md11-I paid a guy $70 and he replaced the "sending unit" in the alternator-I was told that is how these tachs work-but guess what-ain't no such thing-I bought a replacement tachometer-that did not work-so I assume its the sending unit-which is located near the rear of the motor-I assume its some kind of magenitic pickup-but is been one problem I've never been able to solve-despite spending a couple of hundred bucks-any tekie's out there? how do you test a tach? what to they run off of? do the sending units go bad? it looks just like an oil or water temp sending unit-I wouldlike to isolate the problem before I replace it cause it won't be cheap-any help would be appreciated-thanks



grenier@ma.ultranet.com

[Ken Cave]

Hey guys, be sure to check the electrical wires that go to the unit attached to the engine, and see that they are in place. The unit in question is just above the oil filter, and it is easy to pull one of the wires off the unit, especially when trying to remove the filter!

I replaced my unit (about $70.00) and found out that I had one of the two wires disconnected which caused the tachometer to not register.

Hope this helps!

Ken Cave



bcave@whidbey.net

[Geoff]

Norm,
In my CD30 the original MD7 has been replaced with a Volvo 2002 (18hp). I'm not sure how the tach works in the MD7 but in the 2002 the alternator has a tach output circuit (W teminal). When my tach failed, to determine if the failure was in the alternator or tach, I put an oscillocope on the alternator output. I found a nice square wave whose pulse width varied with the engine speed. Based on that, I bit the bullet and paid the absurd Volvo price for a new tach. It's actually a nice unit with a built in digital hour meter and universal for all Volvo diesels.
Good luck,
Geoff



k4nkc@aol.com

[Jerry Hammernik]

I may have to do this project myself. Do you mind telling us how bad the absurd Volvo price was? Thanks.

Jerry Hammernik
Lion's Paw CD28 #341

Norm,
In my CD30 the original MD7 has been replaced with a Volvo 2002 (18hp). I'm not sure how the tach works in the MD7 but in the 2002 the alternator has a tach output circuit (W teminal). When my tach failed, to determine if the failure was in the alternator or tach, I put an oscillocope on the alternator output. I found a nice square wave whose pulse width varied with the engine speed. Based on that, I bit the bullet and paid the absurd Volvo price for a new tach. It's actually a nice unit with a built in digital hour meter and universal for all Volvo diesels.
Good luck,
Geoff

dauntles@execpc.com

[Geoff]

Jerry,
The new tach was $229...Ouch. But again, it works great and has a little LCD screen for the engine hour display. It comes with instructions on how to electronically configure it for all Volvo's.
An option may be to try Continental Imports in Gainesville, FL for repair (continentalimports.com). They charge a $27.50 bench fee for VDO instrument estimates. I haven't tried them.
Good luck.
Geoff.
s/v Wings of Morning

I may have to do this project myself. Do you mind telling us how bad the absurd Volvo price was? Thanks.

Jerry Hammernik
Lion's Paw CD28 #341

Norm,
In my CD30 the original MD7 has been replaced with a Volvo 2002 (18hp). I'm not sure how the tach works in the MD7 but in the 2002 the alternator has a tach output circuit (W teminal). When my tach failed, to determine if the failure was in the alternator or tach, I put an oscillocope on the alternator output. I found a nice square wave whose pulse width varied with the engine speed. Based on that, I bit the bullet and paid the absurd Volvo price for a new tach. It's actually a nice unit with a built in digital hour meter and universal for all Volvo diesels.
Good luck,
Geoff

k4nkc@aol.com

[Scott Sirgo]

I have a CD30 with a Volvo MD7A . The tach hasn't worked in a few years and I believe Volvo's prices to repalce it are absurd. Has anyone replace their tach with and auto parts tach. If so what type? I can get along without it but it is nice to have. Thanks

I had a problem with my tach. I determined it was the sending unit using an ohm meter (open). We disassembled the sending unit by trimming the terminal end of the sender on a lathe,heated the housing with a tourch and pushed out the guts. Only heat the unit enough to remove the internals because there is a nylon bobin inside. Next we respun the bobin with #40 magnet wire with a machanical crimp to # 22 ga. wire. this was sealed with WEST SYSTEM and the leads attached to the wire harness. It works just fine and I did not spend the $125. This is not an easy solution but is do-able. My 28'is back in action.