| Subject: Re: 78FC Tachometer |
Author:
Jeff Miller
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Date Posted: 03/ 17/ 02, 1:14pm
In reply to:
Bud Leffel
's message, "78FC Tachometer" on 03/ 15/ 02, 10:52pm
Bud:
When I bought my '77, I was told that a lot of people don't bother to repair the tachometer when/if it fails, even though it might be a cheap repair, as the engine is governed anyway. I wanted to watch it, especially on the downhills, so I repaired mine. Holland Motorhomes had a replacement in stock, fortunately I didn't need it.
There are several failure items in the circuit. First there is the tach., and the tach. drive/sending unit ($250 when I bought my tach. drive). There is also an Angle-Drive, about $120 when I bought mine, and two short pieces of cable/adapter. The more common failure is either the adapter from the injector pump (about 2" long), the short speedometer cable from the angle drive to the tach-drive (about 2" long), or the angle drive itself. All of these can be found at a truck junkyard, and cheap. Just remove them all CAREFULLY from the front of the engine by removing the speedometer-type threaded ring holding the angle-drive to the "Adapter Plate" (Caterpillar part, cast aluminum on front of engine, held in by two bolts like a small thermostat housing, around $40, yup I broke one of these also) and removing the wire from the sending unit. Soak liberally with penetrating oil before attempting removal/dissasembly as the aluminum/steel connections are trouble and breaking the Adapter Plate on the engine is easier than you think, and could also damage the Drive Pin inside the Adapter Plate which is screwed into the nose of the Injection Pump drive (did that too).
The whole thing is best accessed by removing the radiator, and the radiator fan assembly. My mistake was trying to loosen the whole thing from below with the radiator in place, bad move.
If you don't have a swing radiator, you can remove the tach drive/sending unit (about the size of a "D" cell battery) if you are lucky and the penetrating oil works well, this is how I broke mine. If you are so lucky, you can look at the condition of the short cable, see how freely the sending unit turns, and check for stripping in the angle-drive and adapter by attempting to turn the output cable with the engine off. If it doesn't loosen easily, my opinion is you're best off aborting until you have the radiator open, hopefully you have a swing radiator.
Best of luck,
- Jeff Miller
'77FC in Holland, MI
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