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Tech Tips

Tach Drives

By Jim Riff & Dyke W. Ridgley

FML Tech Tip
No. 1.11.150

Printed in FML Volume 9 Number 7

On Ferraris with non-electric cable driven tachometers, some periodic maintenance is required.

A jumpy tach needle may be caused by one of three major areas: The right angle drive at the rear of the engine, the cable, or the tach itself. Let's examine each, and go over the service.

First, the right angle drive. It was originally packed with that typical thick soap-based brown grease. This material dries out and soon the gears are lapping themselves together until they bind up. At this point, the drive destroys itself and must be replaced. They are very expensive-if you can find one! A good spring cleaning task would be to remove the unit and re-lube it. Remove the cable and completely remove the 6 mm pinch bolt that runs a right angles to the mounting. You will notice a grease fitting on the casting. Pump a good quality high temp grease into it until it comes out the end caps. Do not use high pressure, but slowly allow the grease to flow through. Turn the drive with your fingers and check for any binding or roughness. If this occurs, disassemble the drive by removing the end cap cotter pins (note: some late zinc units are staked in and cannot be removed. Wash all of the grease and shavings out and inspect the unit.

If the gear teeth are pointed or sharp, rather than gear shaped, and early death is near. In these cases a replacement should be located. Carefully reassemble and pack with grease. If a low temp chassis grease is used it may melt and run out of the drive. A good choice is the high temp, disk brake rated, wheel bearing grease. Install a new "O" ring and reinstall in the engine. Be sure the drive tang engages in the engine-but do not force this.
The tach cable is the next wear item. Pull the center out from the tach end and wash it in solvent. Inspect it for broken or frayed wired. Next, pack the cable with a good light grease as you slide it back into the sheath. Check the sheath for breaks or kinks, if it is damaged a replacement is needed. If the center cable only is broken, this is a common replacement part from most Ferrari parts houses.

If the tach itself is broken, it should be repaired by a competent instrument shop. In order to isolate the areas of the tach system (drive, cable, tach) that are faulty, it may be necessary to do steps 1 and 2 in order to confirm the trouble spot.

NOTE: These tips are presented for your information and guidance only, and no guarantee of their applicability is expressed or implied by the authors of the Ferrari Market Letter.

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