C-1 Tachometer Repair

[Frank B.]

I am orig. owner of body off 57 restoration in 2011. My tachometer just died a horrible death, first needle jumped all over then it screeched and the needle fell off. When I disassembled it the hairspring was in a knot and the needle shaft solder joint to the speed drum was broken. When I restored it in 2011 I cleaned cable and sleeve with WD-40 and lubed with I think too much graphite lube The lube congealed with the WD-40 and made a puddle in the bottom of the Tach case. Some of this hardened goo must have gotten between speed drum and magnet and caused the damage after 3 years and 1000 miles. My investigation of many sources indicate that probably all C-1 and C-2 Tachs and Speedos share the same basic mechanism with the only logical difference being calibration adjustment and strength of the hairspring. Calculations for my 57 show that 70 mph (straight up) gives cable rpm of 2841 and mid range (straight up) on Tach is 3000 rpm and is I think within calibration range.

I would really be happy if anyone could confirm my suppositions on this and or tell me where I can get a good speed drum and hairspring assy so I can make repair

[Terry D.]

Re: C-1 Tachometer Repair

I would google Corvette Tachometer repair or look in the driveline and find the people that do this, contact them and see if they will sell you the parts.

[Richard M.]

Re: C-1 Tachometer Repair

Frank, I agree with Terry to investigate and research parts, but it may be tough to find just a speed cup. I recommend that you send it off to a shop because they have the needed calibration equipment to get it right, and have a supply of parts, new and used. Even if you find a speed cup/spring assy, the unit must be calibrated using the cup housing adjuster. Also, chances are that the bushing in the main case may be worn and marginal after all these years. Noisy tachs are the result of worn bushings.

Ironically, I just got a call from Bill Harrison http://harrisonspeedometer.com/ yesterday that a '61 tach that he repaired for me is all set. It needed a new bushing, magnet/shaft assy and re-calibration. He's done several for me over the last few years and his work is excellent.

BTW, the amount of magnetism determines the calibration, not the speed cup spring. The spring is just to return the needle to zero it and to tension it steadily due to the the centrifugal force of the rotating magnet. 1x vs 2x cable speed is done at time of magnetizing the mainshaft gear/magnet assy during the calibration.

Rich

[Dan P.]

Re: C-1 Tachometer Repair

Stay away from D&M . I used Ricks restoration (800) 651-1270 after D&M almost ruined my Gauges .

[Ken A.]

Re: C-1 Tachometer Repair

Rich, early tachs & speedos did not have bushings just a removable oil plug.

[Richard M.]

Re: C-1 Tachometer Repair

Rich, early tachs & speedos did not have bushings just a removable oil plug.

Right, thanks for clarifying that Ken. I was wrong. The frame itself is the bushing and can't be serviced. Bill told me if the frame is worn the 1st worm/magnet shaft will be loose and be noisy. He has to replace the frame if that's the case.

Were the later years post '67 bushed? I've not had the fun of taking a C3+ gauge apart......yet.

Rich

[Ken A.]

Re: C-1 Tachometer Repair

The c-2's were bushes as were the c-3's.

[Richard M.]

Re: C-1 Tachometer Repair

Ah, then I must've been thinking of the '67 I worked on a few years ago.

This must be the bushing? Bronze?
P3130036.jpg

That's when I also learned that reproduction magnets.....aren't magnetized! Bill Harrison bailed me out of that sinking ship. I called him and told him the needle isn't moving after I put in a new 1st worm/magnet shaft. He laughed...."Rich, take a ride over.....I'll magnetize it for you." I said, "Huhhhh? My magnet isn't a magnet?" He laughed again.

He fixed it, calibrated it, reassembled it, and it was perfect.

...some pics for future reference.
P3130035.jpgP3130037.jpgP3130038.jpgP3130051.jpgP3130052.jpgP3130056.jpg

I used your new speedo face and tach face on that cluster. Nice pieces.

P3130058.jpgP3130059.jpgP3160013.jpg

[Stephen G.]

karlburl@gmail.com

He has done clusters & wiper motors & washer pumps for me. 100% fast and reasonable.

Steve