smacota1

Having an interesting speedometer issue, under acceleration the speedometer needle seems to just stick in place , as I let off the gas and start to shift it will riseup to speed until I start accelerating again after shifting to the next gear.

To better explain...
I ease from dead stop and about 10MPH (speedo works perfect) accelerate quickly, the needle will stay at 10mph, let off gas and the needle will release and climb to 35, accelerate hard in second and needle sticks at 35, let off gas and the needle climbs to 45. Go strong in to 3rd and needle sticks at 45 until I go to shift to 4th and needle shoots up to 55,

The speedo seems to work if I just really ease into the the gears, but that is not a normal driving situation.

The speedo seems to be accurate, just wierd that it sticks then reads again as you left off the gas.....

Don't think there is a broken motor mount that could be putting the cable in a bind.

Do you remove the cable to lube from the speedo head or the tranny case?

Thanks for any trouble shooting suggestions...

One more thing...the odometer and trip meter did not work when I bought the car, but I am pretty sure the speedo worked correctly.

Bluestripe67

First idea is....if you are talented and have patience, remove the cable housing from the back of the cluster (it's a tight fit, but can be done) and clean it and the cable. Be careful when you pull the cable, there should be a very small (size of an eraser head) retainer washer on the end of the cable. Use a semi-stiff wire with a small piece of rag pinched in the end, saturate it with a cleaner (WD-40, Breekleen) run it up and down until it's lean, wipe the cable also. Get some Cable-Ez or equal and lube the cable, but stay away from the head end by about 4 inches. Reassemble and see if things are fixed. If this is not your choice of effort, you may well need to have the speedo assembly repaired and that means pulling the cluster. NOW you may be at a point of restoring the entire cluster. Proceed carefully! Dennis

smacota1

Dennis,

Thanks very much for the suggestion. I hope to tackle this over the weekend if possible. Will keep a post going on what I find out. I really need to pull the cluster to address the odometer issue but weather is getting so nice I hate to put her down for such a long period...but might just have to do it.

C.W.C.

Hello, just a thought but could it be that inside the transmission there is a round "drive" gear mounted on the main shaft that turns the transmission "driven" speedometer gear. It COULD be that your transmission was rebuilt at some time and they replaced that internal metal drive gear with a plastic gear and used a "spring clip" style of retainer that has a tendency to slip off allowing the gear to no longer be mechanically bonded to the main shaft. You may also want to check if the "driven gear has started to disintegrate allowing it to skip while on load.

smacota1

Was hoping to look at this this weekend but got called out of town. Will post some updates when I get a chance to dig into this deeper.
Thanks for the suggestions.

65GGvert

I doubt that lubing the cable will affect your issue. I have no explanation why rapid acceleration would make it happen, but the only thing that should make the needle stop where it is would be that it is binding or rubbing on something. It is not directly or physically attached to the cable. Try speeding up and if it stops, tap lightly on the front and see if it twitches up more.

A thought: How tight is the speedometer cable stretched between the transmission and the dash? Maybe the engine is rotating and pulling the cable moving the internals of the speedo enough to touch the needle or movement to something in the housing or glass.

Frankie the Fink

It sounds to me like the cable is binding or 'wrapping up' in its housing when its asked to move swiftly. I would do the lube trick and see what happens...

65GGvert

It seems like if that happened the needle would drop or at least twitch and make a noise. Stopping the cable completely won't make the needle stick, it drops down if the magnet stops spinning as fast as the needle shows.

solidaxel

My bet is at the transmission end, easier to eliminate
Remove cable and test with a drill motor and look at the gears while you are there

DansYellow66

Most likely if the speedo needle is hanging still at a speed above 0 mph at any time, it's probably hitting the lenses or the dial face. There's no direct connection between the needle and the cable assembly so I would suspect there is a problem in the speedo head or the needle clearance. Possibly accelerating is displacing the magnet cup attached to the needle so that it or the needle is hanging on something. When you let off or accelerate slowly it relaxes to normal position and works. This might be a very small amount of axial movement.

smacota1

OK,

So I grabbed a few minutes tonight before heading out of town tomorrow. Pulled the cable out of the trans and removed the speedo gear. Best I can tell tail shaft gear is metal and does not seems to out of place and tight on the shaft. Very hard to take a pic of it. The plastic gear seems to mesh with the cable ok but the button on the other end seems to have some slight age cracks. The teeth that mesh with the tail shaft gear seems to be in good shape. Might make sense to go ahead and replace the gear. My issue is it is hard to tell the color of the gear. Looks like it might be purple but also seems to have some age to it.
My rear end code is AM which denotes 3:36. Another thing I did notice is it seems there is a lot of thick grease on that end of the speedo cable.

That's it for now until I get a little more time and get the new parts in. Gonna order the parts from NAPA so hopefully they will be in by the weekend.

65GGvert

You can change the gears, cable, transmission for that matter and it won't stop a needle from sticking. As mentioned several times, the needle floats freely from the cable. If the cable stops completely the needle drops to zero, if it binds or changes speed so will the needle. Your needle is sticking.

smacota1

I am pretty sure I am gonna have to break down and pull the cluster. Need to do that also to get the odometer and trip meter fixed. I have to decide whether it is something I want to do now that weather is getting nice or just live with it for a while and pull it a a later date. Kinda lucky as the majority of the cluster is in super shape so project creep will be at a minimum.
Decisions decisions......


But thanks for all the helpful responses.

smacota1

I did check the cable and it has some slack. One thing I am gonna try is to remove the right side ignition shielding and see if that makes a difference. Sees this issue might have started around the time when I put it back on.

65GGvert

The problem will be in the speedometer. If it were me, I'd drive it until I decided to fix all three issues. It's not like the speedometer isn't working at all. But, it may stick and stay after a while. Still be fun to drive though.

Frankie the Fink

I couldn't drive more than 20 miles with all that broken stuff - but that's me; some of the instrument repair guys can do a quick turnaround so your car won't be down that long. Check with Corvette Specialties (West), Bill Harrison or Joe Ray...

smacota1

smacota1

FTF,

Seems I am just as "AUTATTAR" (anally unable to accept things that aren't right)

smacota1

Drove the car today and took a go-pro video of the speedo issue. You can see it really good around the 1:50 minute time line though the video is abut 12 minutes long.Was just enjoying the drive.

You can see the video here:

Plan is to drive it a while and pull the cluster to have speedo as well as tach worked on.

Thanks for all the suggestions and help.

DansYellow66

Not exactly sure what is going on but when you are holding steady speed the speedometer is reading very steadily which to me sort of discounts a cable or gear drive issue. Actually it's so steady I would like to have your cable. But something is hanging in the needle cup area at times. The tach is pretty jumpy too so an eventual rebuild is probably the ultimate solution.