L3400 Tach Quit Working

KJNDIVER

New member

Equipment
L3400
Sep 14, 2022
3
0
1
Lake Charles, LA
2007 L3400 430hrs today all of a sudden the tach quit working. Upon startup it just barely moves but doesnt even get up into the markings on the readout. I disconnected the engine end of cable, appears to be fine. Cranked engine while disconnected and looked down into the hole, the mechanism is spinning. Connected to a cordless drill, it did register on the dial, but not much, only a few hundred rpms (stands to reason the drill wont turn as fast as engine). Disconnected the instrument, appears fine. Started engine while disconnected, cable spins. Reconnected, started engine, still nothing. So everything appears to be working, but no read out on the dial. Could the cable still be damaged/broken and have the indications i mentioned here? Seems to reason if it was broken then it would be broken, but i dunno. Any other ideas on what it could be? Cant be too terribly complicated. Or i wouldnt think so.
 

GreensvilleJay

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Equipment
BX23-S,57 A-C D-14,58 A-C D-14, 57 A-C D-14,tiller,cults,Millcreek 25G spreader,
Apr 2, 2019
11,414
4,905
113
Greensville,Ontario,Canada
you should be able to slide the 'core' out of the casing, one end usually swaged square, the other has a 'ferrule' swaged on it. If the ferrule isn't tight on the core, that could be the reason.
 
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KJNDIVER

New member

Equipment
L3400
Sep 14, 2022
3
0
1
Lake Charles, LA
So i used the tractor this weekend to do some mowing/discing for food plots. The hours do advance while running. At the beginning the needle would barely move even if wide open. The more i ran it the needle did creep up ever so slightly, but never more than about 7-800 rpms on the gauge. Does this mean there is something wrong internally with the gauge? Im assuming plastic gears that may have stripped? something else? Inquiring minds want to know. Could there possible be something electrical in nature that could cause issue? Reason I ask is I noticed that my fuel gauge is acting funny as well. Gauge showed empty. I filled it to the brim for weekend work at the lease. Yet the gauge only indicated between 3/4 and full. Never done that before. Then while running for several hours with high rpms for bush hog the fuel gauge never moved. When key is off, it does not go to empty (always has before). Could there be a corroded connector to the panel that could be causing these issues? Had this tractor for about 10 yrs now, no issues that werent self induced, and now both of these issues occur at the same time. Just thinking they may be related to some common issue. Dunno, which brings me here. Any thoughts?
 

Dave_eng

Well-known member
Lifetime Member

Equipment
M7040, Nuffield 465
Oct 6, 2012
5,235
1,017
113
Williamstown Ontario Canada
So i used the tractor this weekend to do some mowing/discing for food plots. The hours do advance while running. At the beginning the needle would barely move even if wide open. The more i ran it the needle did creep up ever so slightly, but never more than about 7-800 rpms on the gauge. Does this mean there is something wrong internally with the gauge? Im assuming plastic gears that may have stripped? something else? Inquiring minds want to know. Could there possible be something electrical in nature that could cause issue? Reason I ask is I noticed that my fuel gauge is acting funny as well. Gauge showed empty. I filled it to the brim for weekend work at the lease. Yet the gauge only indicated between 3/4 and full. Never done that before. Then while running for several hours with high rpms for bush hog the fuel gauge never moved. When key is off, it does not go to empty (always has before). Could there be a corroded connector to the panel that could be causing these issues? Had this tractor for about 10 yrs now, no issues that werent self induced, and now both of these issues occur at the same time. Just thinking they may be related to some common issue. Dunno, which brings me here. Any thoughts?
Here is what forum member asbug said in 2011;
I used to test speedos for internal damage by chucking up a chainsaw blade file backwards into a drill and inserting the square part into the back of the speedo. I think that you have to drill in reverse, but with a cordless drill you could rule out the tach head.

Personally I have had that style of tach quit because of small spyders getting inside and interferring with the magnetic coupling. Months sitting in the sun dried them out and suddenly the tach was working again.

The tach itself is replaced as part of a $500 dash panel.
There are companies around the country which repair that style of old instrument as an alternative to replacement.

forum L3400 tach.jpg



Dave
 
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GreensvilleJay

Well-known member

Equipment
BX23-S,57 A-C D-14,58 A-C D-14, 57 A-C D-14,tiller,cults,Millcreek 25G spreader,
Apr 2, 2019
11,414
4,905
113
Greensville,Ontario,Canada
It sounds like the needle is loose from the shaft, Since the hrs does work, cable is fine and internals of the meter are working. The needle is just probably just a 'press' fit ,same as 'old style' clocks with hands.
The big problem is how to carefully open up the case and reclose it. Opening is the easy part, closing... well not many have the proper 'rim roller' device in their garage....
 
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