E type tach drive

My tachometer has stopped working. I think the problem is in the tach drive mounted at the rear of the right side cam cover. Has any one ever taken one of these apart? Should I attept to repair it or, look for a replacement? Any info would be greatly appreciated.

Thanks JW
66 E Type 4.2 FHC

JW, before tearing your Tach sender apart, do a few things:
1. Check that the Sender is turning (the drive dog is engaging the slot in the Cam Shaft). You should be able to feel the thing spinning with your hand placed on the back cover. Also, there should be THREE allen head screws holding the sender firmly in place on the back of the cam cover.

2. Take a volt meter (available at Radio Shack), set it on AC, and measure the voltage "across" the sender terminals. The voltage should increase as RPM increases (about 1 volt per 100 RPM). If not, then the sender is bad (or not engaging per step 1 above). To determine if its really bad, or just not engaging, you can remove the sender and spin it with a bitless drill (lightly engage the drill on the sender drive dog so as not to damage the drive dog). This may take two people...one to hold the sender and drill and a second person to measure the output across the terminals. If it is definitely not putting out you might be able to have it repaired (I would not try it myself)

2. IF the sender unit is putting out voltage per the test above, then check the continuity of the wires between the sender and the tack. Use the meter set on "ohms" (x 1000 or 1k is a good setting). You will notice when the meter is set on Ohms, and you touch the leads together, the needle deflects fully. Well, it should deflect fully (0 ohms or very very small ohms) when you place one lead in the wire connector on the tach sender and the other lead in the wire on the Tach itself. If the needle does not deflect fully, there is an open. You must check BOTH wires this way.

3. If the sender is good and the wiring is ok, make sure the connections are good (clean, solid connection, etc). If it still doesn't work, then suspect a bad Tach. The Tach can be rebuilt. Once place that does it is "Nosingers" (See their link in our "Vendor Links" section). Other places such as Classic Jaguar, Terry's etc can probably rebuild either the Tach, the sender, or both if needed.

Hope this helps. Let us know what you find out!

Basil

[ 01-01-2002: Message edited by: Basil ]</p>

The tach on my 64 E type stopped working some time ago also.
Everything checked out OK when I spun the sender
in a drill press (good voltage)but it still would not show on the tach face inside the car.
I applied a small AC voltage to the leads using a Variac (be very carefull). This showed the tach meter to be working OK.(good response).
I then used a mirror to look up into the opening where the sender had been removed from. I did this to inspect the small plastic "drive dog" that connects the cam to the sender center shaft. It was in good shape (sometimes these will break and must be replaced)but still no output from the sender.

What I finally found was the bushing (bearing)around the center shaft of the sender unit had lost its press fit on the housing and slipped back into the unit just far enough to prevent the end of the shaft from engaging the plastic "drive dog" in the end of the cam shaft.
I was able to fix the problem by driving back the indents on the back of the sender case to remove the cover plate and the internal rotor magnet along with the bushing. This is an oil impregnated sintured bushing which is pressed into the housing. Using a sharp punch I made a number of small indentions in the wall of the housing around its diameter. This raised the metal just enough to allow the bushing to be pressed back in place giving a tight fit. You have to be careful to press the bushing only in to its original position. Not too much, not too little. Discoloration on the bushing can be used as a guide. (I think it is designed to be flush with the inside of the housing).
Check the orientation of the slot in the end of the cam shaft, orient the sender shaft to fit and reinstall using all three screws.
Hope this helps.

Wow! Great info from both of you. Thank you Basil and Jim. I feel very confident now after reading your posts. I plan on inspecting and diagnosing the problem this weekend. I'll be sure and let you know the results. Thanks again.
JW

You can also place a penny behind the driver dog inside the back of the cam shaft and that will lift the dog enough to engage with the tach generator.