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JD 650 tachometer troubles

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Angelo B.
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2002-09-09          42198

We recently bought a JD 650 and have experienced problems with the tachometer needle going beyond the numbers on the tach face. Sometimes the tach works properly other times it almost spins around to the tach-stop. One dealer said its the cable another said it's the tach-head. Before I start taking it apart, anyone out there run into this condition before? It's my understanding that the 650 uses a mechanical tach. Thanks

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JD 650 tachometer troubles

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2002-09-10          42230

I suspect it's the head. However, you might try taking the cable off and greasing it with white grease. The cable on my Ford 1710 was bent during a dealer repair and broke not long after I got the tractor back. I installed a new cable. As part of the installation, I pulled the cable apart and lubricated the entire length of the centre wire. Small chance but it might do the trick.

There is a however. There would be a small chance in some drive designs that if a drive was broken, pulling the cable end out could release a part that would drop into the oil pan. Its probably not much of a chance but something to be aware of.
....

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JD 650 tachometer troubles

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Angelo B.
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2002-09-10          42235

Thanks for the suggestion. I was going to try as you suggested taking the cable out from the tach head. I'm going to see my dealer first to make sure if the cable's hanging on by a thread that the connection to the engine is not in danger of dropping any gear or drive mechanism into the engine. ....

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JD 650 tachometer troubles

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Mrwurm
Join Date: Feb 2002
Posts: 184 South East Michigan
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2002-09-12          42303

My John Deere 650 (now gone) needed to have the tach head and the cable replaced. Mine did not behave like yours. Mine would work some days and not on other days. I pulled my cable out many times to investigate the problem. I replaced the tach head myself and I can't quite see how any part of it would fall out.
Jerry ....

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JD 650 tachometer troubles

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TomG
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Posts: 5406 Upper Ottawa Valley
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2002-09-12          42307

Jerry: It's a bit theoretical, but the drive end rather than the head end (Hope we've got the terminology straight) is the cable with a length of more or less square wire extending from it and a fitting. The wire extends into the tach drive. The drive on many tractors is taken off one of the gears under the timing-gear cover. In theory a broken drive part could remain on the tach cable end wire, and pulling out the drive end of the cable could allow the part to drop to the bottom of the timing gear cover, which is pretty much the same as in the crankcase.

Anyway, without knowing the particular drive design, I didn't want to recommend just pulling off the drive end of the cable without noting that there might be a small risk.
....

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JD 650 tachometer troubles

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Mrwurm
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Posts: 184 South East Michigan
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2002-09-12          42314

Hey Tom, I see what you mean. I wonder if all drive heads are similiar. The drive head on my 650 was a right angle drive. The flat piece of cable went into a gear that turned another gear that was 90 degrees to the first. The second gear had a small shaft that went into the block just below the water pump. It's possible that this small shaft could break off and fall in the engine, but the gear it was pressed on was too big to fit in the hole. Just my random thoughts and observations.
Jerry ....

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JD 650 tachometer troubles

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Angelo B.
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2002-09-16          42493

I checked the cable and the tachometer and it appears the tachometer is the problem. Any suggestion where I can get a tach at reasonable price? the dealer wants $144 for it which is more than i'm willing spend. any suggestions? ....

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JD 650 tachometer troubles

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MRETHICS
Join Date: Jul 2003
Posts: 190 Star City, Indiana
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2002-09-16          42497

I'm not being sarcastic here, but the problem still seems like a drive problem to me. We haven't seen a failed tach with those symptoms......yet anyway, who knows what tommorow will bring?

Ive seen cables that would only bind when bent excactly like they were installed on the tractor. I have also seen drive coplers that were loose enough they would cause the tach to jump.

Might want to double check. ....

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JD 650 tachometer troubles

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Angelo B.
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2002-09-18          42590

No sarcasm taken. Any insight you can offer is helpful. I notice the lower cable connection was loose when I first checked it but tightening it didn't seem to make a difference. The cable's spinning fine at the top (where it connects to the tach head) and there doesn't appear to be any cable damage. One thing I notice was apparently the cable had been lubricated with oil and there was oil on the light bulb in the tach housing. Any other suggestions?

One thing I'm thinking of doing is seeing if I can find someone who deals in old or used JD parts to see if I can pick up an inexpensive tach head. Any thoughts? ....

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JD 650 tachometer troubles

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MRETHICS
Join Date: Jul 2003
Posts: 190 Star City, Indiana
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2002-09-18          42594

ok.......

That oil in the tach head bothers me some..It could cause the head to malfunction.

But also, it's hard to look at a spinning tach cable and see any rpm spikes wich would cause the tach to jump off the scale.

I don't know of any salvage yards that handle compacts...in my area anyway, but maybe soemone else knows of one. ....

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JD 650 tachometer troubles

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mack 2k
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2002-09-18          42596

why not connect the tach.to a cordless drill and run at a steady speed and see what it does...mack ....

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TomG
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2002-09-19          42624

Mack's idea is interesting. A variable speed or geared down drill would be needed since direct drive from AC would be off most tach scales.

Yes, I believe that cables are supposed to be lubed with white grease rather than oil. Mr.E's comment about oil in the tach head is a possibility.

I guess excessive play in the drive gears might be a cause. An experienced mechanic might be able to turn the drive wire back and forth by hand and know how much play to expect.
....

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MRETHICS
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Posts: 190 Star City, Indiana
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2002-09-19          42652

Just had a few more thoughts on the subject..

The most logical way to attack this problem is to follow the flow of power......

start with the drive...The end that hooks to the motor.
Check for worn gears, drive couplers etc.....

Next, spin the cable by hand...on the tractor...does it feel free? Spin it with a varibale speed drill while hooked to the tach head...does it function properly??

Last, if the first two items check out..yup...it's the tach head. But just for the heck of it, try spraying some kind of solvent inside the light socket in the tach head. I would try Stoddard Solvent. Maybe that will clean things up enough to get things working again...

Besides...if it is the head..what have you got to lose?? ....

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