66 Monza speedometer issue?

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Chiro972b
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Joined: Tue Sep 29, 2020 5:36 pm

66 Monza speedometer issue?

Post by Chiro972b »

Hey folks. I have a 1966 Monza coupe that had a strange issue this morning. I hopped on the interstate for a couple miles heading to work and the speedometer stuck at 65. Even when I got off on my exit and stopped at the bottom of the ramp, it was on 65. A mile or so down the country road, it started working again. Does this sound like a cable issue or a speedo issue? When it is working, it seems smooth and no bouncing around.
This is my first Corvair since 1976 when I was 16. I was a decent shade tree mechanic then and still have skills but no suitable garage to work in yet (in process) and I'm old but active.

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azdave
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Re: 66 Monza speedometer issue?

Post by azdave »

A cable issue will cause a bouncing needle or no movement at all from zero MPH. The indirect connection between the cable and the speedo needle is a magnetic field. If your odometer still works, your cable is still spinning. Sounds like you might have grit or dust inside the speedo head. The speedo cable on a LM comes off the left front hub of course. EM speedo cables come off the transaxle.
Dave W. from Gilbert, AZ
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5

66vairguy
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Re: 66 Monza speedometer issue?

Post by 66vairguy »

Dave said it well. You can go online and find information about the old mechanical speedometer operation. If someone has had the speedometer out (and at this point who knows what has been done) the face plate or needle may be too close and will cause the needle to stick on the face. I've seen this happen.

Some history ----- The needle is connected to a shaft that runs through a cup that a magnet rotates in. The rotating magnet, and gears for the odometer(s) are driven by the cable. The needle and cup are ONLY connected by a magnetic field interaction. The cup has a return spring (never adjust this!) that was set when it was built. The cup and needle shaft sits in very small bearings. If the speedometer is repaired it must be calibrated. Calibration is done by a device that creates a magnetic field to change the speedometers magnet strength (old speedometer shops have the device). NOTE: 65-69 speedometers are calibrated for 825 revolutons per mile (like a VW bug) NOT the standard 1000 revolutions (EM used that).

After five decades the main problem is dried out old lube. Input bushing lube dries out and causes bushing wear and the magnet shaft starts to wobble causing needle bounce. Also the Corsa has a trip odometer plus the regular odometer and the extra force required a metal intermediate gear that wears out when the lube dries out. There is a lot more, but time and space prevent me from elaborating.

In the old days folks just found another low mileage speedometer and installed it. Now good used units are scarce. It's also getting hard to find an old speedometer shop with parts and expertise, but doable. Clark's at one time sold rebuilt speedometers and the price was fair. I've rebuilt six Corsa speedometers for myself and buddies and I still had to take them to a shop with the equipment to calibrate the speed and that was nearly half the price Clark's charged for a rebuilt!

Keep in mind these speedometers were only designed to work 5-10 years depending on mileage and the environment. It's been over five decades and the fact they still work is impressive.

Some folks just give up on the speedometer and use their smart phone GPS app to show speed.

Chiro972b
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Re: 66 Monza speedometer issue?

Post by Chiro972b »

Odometer does not work, even when the speedo seems to be working fine. Speedo doesn't seem to bounce around, but it stops and I can rap on the lens and it starts working again. Only seems to hang when I go over 50 mph. Using gps on my phone, but that sucks. I may break down and put a gps speedo in, but I hate doing that, even though my car is not completely stock anyway. I ordered a new cable from Clarks. Maybe a waste, we'll see. I do have a variety of small bearings from my R/C car racing days, are the bearings replaceable without having to then calibrate?
Thanks/!
Last edited by Chiro972b on Mon Nov 09, 2020 2:24 pm, edited 1 time in total.

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azdave
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Re: 66 Monza speedometer issue?

Post by azdave »

Chiro972b wrote:
Mon Nov 09, 2020 2:19 pm
Odometer does not work, even when the speedo seems to be working fine.
Okay. Separate issue then with your odometer. Plastic gears can split after so many years.
Dave W. from Gilbert, AZ
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5

Chiro972b
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Re: 66 Monza speedometer issue?

Post by Chiro972b »

Well, after I replace the cable, if it doesn't fix things, does anyone know where to find a used unit? California Corvairs has them. It says used, untested, no guarantees, but they're $40. Clarks rebuilds are now $231+30 for core!!!

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azdave
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Re: 66 Monza speedometer issue?

Post by azdave »

You can unthread the cable housing from the back of the speedo head under the dash and then pull it back a few inches to check to see it it spins when the left front tire is lifted and turned.
Dave W. from Gilbert, AZ
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5

joelsplace
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Location: Northlake, TX

Re: 66 Monza speedometer issue?

Post by joelsplace »

If the speedo hangs it is NOT the cable. AZDave explained this.
113 Corvairs, 5 Ultravans and counting
Northlake, TX

66vairguy
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Joined: Tue Dec 21, 2010 3:44 pm

Re: 66 Monza speedometer issue?

Post by 66vairguy »

azdave wrote:
Mon Nov 09, 2020 2:23 pm
Chiro972b wrote:
Mon Nov 09, 2020 2:19 pm
Odometer does not work, even when the speedo seems to be working fine.
Okay. Separate issue then with your odometer. Plastic gears can split after so many years.
Dave - Only Monza speedometer had the plastic intermediary gear for the odometer, the Corsa speedometers all used a metal intermediary gear due to the extra force needed for the trip odometer (it has clutch pawls that require more force).

66vairguy
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Re: 66 Monza speedometer issue?

Post by 66vairguy »

Chiro972b wrote:
Mon Nov 09, 2020 2:46 pm
Well, after I replace the cable, if it doesn't fix things, does anyone know where to find a used unit? California Corvairs has them. It says used, untested, no guarantees, but they're $40. Clarks rebuilds are now $231+30 for core!!!
I haven't seen a GOOD properly working used Corsa speedometr in more than ten years, but I suppose they may exist.

ONCE AGAIN - the speedometer needle has NO direct connection to the speedometer cable. You can throw parts and money at it, or just TAKE IT OUT and check to see why the needle sticks. Could just be a simple clearance problem with the face plate (thing with numbers on it) which bends easily.

Needle bearing usually don't fail, but I had one come loose for the support bar that the face plate screws go into.

After all this time you never know what someone has done before you.

erco
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Re: 66 Monza speedometer issue?

Post by erco »

I may have to accelerate my evil plan to make a replacement electronic speedometer kit. My '67 is not on the road yet (less incentive) but I anticipate eventual speedo issues and replacing a mechanical speedo cable seems wasteful.

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