John Deere 750 crazy tach question / alternator- voltage reg possible cause?

[rmroper]

I have a JD 750 tractor and the tach has gone crazy (the tach needle is constantly moving, even at an idle). I have read previous posts about the cable being a possible cause. I am also working to troubleshoot an alternator / voltage regulator problem. My question is: Can a malfunctioning alternator or voltage regulator cause the tach to become erratic?

Thank you.

 

[JD755]

Since the tach is a mechanical drive, not much chance the electrical has anything to do with it. Also not likely to be a cable problem if the needle is always turning. The probable cause is the internal spring has broken in the damper assembly. When that happens the only fix is replacement unless you know a shop that can rebuild tachometers. There are a very few out there, mostly for motorcycles, but probably cheaper to replace it if you can find one.

I went through the problem of a constantly spinning needle until the entire assembly failed. Fix was replacement. I put pictures in another thread.
http://www.tractorbynet.com/forums/john-deere-owning-operating/279149-755-tachometer.html

 

[kebo]

Here is a copy and paste of a business here in SC that repairs tractor and farm truck gauges. I have no connection with them, and hopefully the mod's here will be ok with me posting it. If not, they can delete it.

QUOTE:

Do you have a Late Model Chevy, GM or Ford farm truck with bad gauges? ...Speedometer stuck? Odometers not working? "Jumpy" gauges? We can fix that. . . fast!

All Clusters are repaired with updated parts (we all know the original ones are JUNK).

We use only the newest, authorized, X27 Stepper motor replacement parts and offer a-

*LIFETIME WARRANTY ON ALL NEW GM/CHEVY/FORD STEPPER MOTORS*

Most repairs are completed within two hours

Premier Instruments is your local "Speedo Shop".

We are local and we're here to help.

We also repair and restore almost ANY gauge or cluster from any vehicle? Tractors too!

**Tractor Tachometers. . . Farmers save time and money by knowing your P.T.O. is accurate.

Premier Instrument's attention to detail ensures that all clusters are cleaned and the clear plastic lenses are polished before returning them to our customers.

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When you want it done right the first time, you can depend on us.

Call Premier Instruments, Your Local "Speedo Shop", we're working for you.

Premier Instruments
2514 River Road
Suite 104
Piedmont, SC 29673
864-373-9394

 

[rmroper]

I was afraid the tach was totally mechanical and I'm sure it will be expensive to replace based on other unique parts I have purchased for the tractor. I'm working out some issues with it prior to trying to sell it.

I appreciate the link to the company that repairs gauges, I will look into them.

All your help is appreciated.

 

[sshaw]

I have a JD 750 with a bad tach also. The needle jumps all over the place making it hard to determine the RPM. The needle eventually broke off and is rattling around inside the housing now. I haven't been able to find a replacement tach yet, and I've found it difficult to get behind the panel to try to service the tach. I'd be interested to see what solution you come up with.