64vert

I currently have my dash cluster apart fixing a few problems. My odometer is stuck, and after searching the archives I found a lot of information on this very common problem. My second worm gear is worn, so I know how to fix that. My other problem is a noisy tachometer. I have taken it apart and found that it is very similar to the speedometer. It looks like the noise is coming from the drive hub that connects to the spinning magnet. I have not removed the magnet or drive hub yet, is there a bushing in there that needs replaced? I can't find anything about this in the archives.

Thanks,
Brian

Pilot Dan

Many years ago (back in the 80's) you could purchase a new speedo or tach mechanism and install it yourself for about $80. Apparently, they no longer sell them to individual do it yourselfers anymore and the only way I know of to get one is through a repair shop when THEY install it.
I have never seen any individual tach replacement parts available.
After all the work involved in pulling the dash and taking the cluster apart, I think you would be better off sending the tach out for a proper servicing. You would not be happy having to do that job over just to save a few bucks now. JMO Pilot Dan

Dennis Beck

x0000rgw

Go to Lowes. They have 1/4 inch bronze bushings that will fit.
I just re-built my 61 tach with one of these. It's about 3/4 inch long.
You can cut to fit.

Ray

1snake

If you have a speedo repair shop locally, they can fix both your problems. There is no need to send your stuff to a Corvette "specialist". There is nothing special about Corvette gauges and those that repair them all get their parts from the same places.

Jim

GCD1962

Check Dr Rebuild. They used to have the tach heads

64vert

Thanks for all of the advice. If it is something as simple as replacing a bronze bushing I can do it myself, but would that require it to be calibrated? I will check to see if there are any local speedo shops, or I can take it to Corvette Expo this weekend and have someone do it for me.

Pilot Dan

Ray, how did you calibrate it at home ??? Can you give us some details of how you rebuilt your tach, I would be interested in how you went about it and what problem you had originally. Pilot Dan

x0000rgw

Dan,
Adjusting the tach is very easy. Get a short (8 inch) section of the
inner cable (from an old one). Chuck it up in a variable speed drill and
stick it in the end of the tach magnet shaft. My drill runs at 825 rpm
at full speed. adjust the tach hair spring so that the tach shows 1650
rpm. If it is a generator driven tach then it should show 825 rpm.
Generator driven show actual rpm of the cable. Distributor driven
show twice the cable rpm. The tach must be out of the case to get
to the small lever that adjusts the hair spring. Do it very carefully so
that no damage is done. A small thin screw driver will work.

Do not try to make a distributor drive tach work on a generator
drive. The hair spring is weaker and will not adjust. You will need
the cup and hair spring from a generator drive tach.

Ray

You can also calibrate the speedometer the same way. 1000 rpm should
show 60 mph on the speedometer. 825 rpm from the drill should show 49.5 mph.
I calibrated mine this way and it is dead on at 70 mph with my GPS unit.
I did the speedometer first to make sure the drill was running at 825 RPM.

THe problem with the tach was loud chattering on cold mornings. Once it warmed
up it was OK. Be sure to use white lithium grease on the magnet shaft (not too much).

Ray

64vert

Ray,

How is the tach magnet and shaft removed from the bushing?

Brian

x0000rgw

You will have to take the tach or speedometer completely apart.
Nothing but the magnet shaft and housing. The shaft is held by a
3/16 wide brass ring on the end of the shaft. The bushing, a steel
washer (thin) and the 3/16 ring. The brass ring is pressed on, so
be very careful in removing. I heated mine a little with a Weller
soldering iron and used a pair of pliers to twist it loose. Hold the magnet with your hand while twisting. It should pull off.
I used some locktite blue to re-assemble the ring.
When you re-assemble, be sure you don't bind the ring too tight. The shaft will be hard to turn if you do. If you get it too tight, insert a
small nail into the cable hole in the shaft and give it a light tap to
free it up.

You may can insert a nail into the end of the magnet shaft and remove the
ring by heating the ring lightly and tapping on the nail. Make sure that the nail
fits loose in the shaft and grind a flat end on the nail.

I was telling you before, how I did it with the pliers.

Ray

x0000rgw

Just remember when working on these old cars, they are not
very complicated. Just use your head and don't force anything.
I added power steering, power windows, power brakes and A/C to
mine so that the 61 is more comfortable to drive. The 13 inch
steering wheel gives a lot more room inside to get in and out. My
daughter can drive it and park it as easy as I can.
Good Luck.....

Ray

Pilot Dan

I have an old tach laying around, I think I will take it apart and see if I can put it back together (without breaking it) before I try it on my real one. Good info Ray.

mike coletta

Ray,
I'm very interested in all of what you posted, but can you give a little more detail on adjusting the "small lever". Do you bend the little tang that is protruding from the cross bracket? (this is where the spring is attached). I assume that it is a very small adjustment, up or down. There usually a colored paint daub in the location that I'm talking about. This is good information. Thank you for posting.!!

Mike Coletta

x0000rgw

You do NOT bend the tang..... It slides from side to side, to tighten
or loosen the spring. More tension or less tension on the spring.
Slide the tang back and forth around the rim that it is resting on.


( use your head )

Ray

Pilot Dan

Ok, that makes sense. It is similar to the way the clock is adjusted (fast/slow) Thanks for clarifying that.

mike coletta

Ahhhhhh.....It makes sense now!!!! Thank you. I never thought that that was a "lever". Somehow, I was under the impression that it was welded/soldered. Thank you for sharing.

Mike Coletta

x0000rgw

I forgot to tell you, the drill must be reversable. Cable
must turn counter-clockwise. Hope this helps.

Ray

64vert

Ray,

I replaced my bushing as you describe and the chatter is gone, at least while I am turning it with my drill. I still need to calibrate it, my drill speed is supposed to be 1200 RPM which would mean my tach needs to show 2400. I can't adjust it to get it that high, my next step is to verify that my drill is actually turning 1200, we have some industrial tachometers at work that I can use to do that.

Does this same ratio hold true for midyears?

Thanks,
Brian

JohnZ

Yes, it does. 1000 rpm = 60 mph is the standard calibration for GM speedometers.