Odometer works but Speedometer doesn’t??

[Muddy1966Bronco]

My speedometer flops around randomly, but doesn’t usually move too much. I have another gage cluster so I wired that in and it does the same thing. Then I thought maybe the cable wasn’t engaging enough so I tried pulling it out some (gently, not even with much pressure). It came out of the casing a good foot with ease! I thought for sure it was just a cable replacement issue after that. Worked the cable back in, screwed it back in place, then I noticed on the last drive that the odometer is clicking over just like it should. Is it still just a cable issue still? Or do I need to pull apart the gage cluster too?

 

[DirtDonk]

Strange only that two clusters do the same thing, but not uncommon for this to happen in general. Since the odometer and speedometer are on different mechanisms, they can do completely different things.

I would have said it's simply a speedo issue, since the cable is obviously turning the odometer, which is mechanically connected. The speedometer needle is not connected to the cable directly. The cable spins a disc shaped magnet that in turn spins a hollow disc shaped metallic "cup" that is attached to the needle.

Sounds initially to me like the mechanism between the cup and needle is wonky. They do wear out, but I wonder at the chances that you have two of them?
You can re-check the cable action by disconnecting it and letting it hang through the now-open hole where the cluster used to be (because you're going to be removing it again anyway) and watch it as you drive. If it seems to turn consistently (which is sounds to be doing) then it's on to the next phase.

Three ways to proceed then as I see it:

1. Easy to take things apart yourself and see what's going on. If it's fixable on the work bench, go for it.

2. Have it fixed, and/or the whole cluster re-furbed by Kevin at Klassy Chassis Restoratoins (member fallingdown here and you can see his thread over in the Vendor section). Or...

3. Buy a new cluster. They are readily available brand new these days (here's a sampling: https://www.wildhorses4x4.com/category/dashgauges) in either just the speedo, or the full cluster with gauges. Also all the usual electronic suspects are available too, if you want to go big.

Lots of fun ahead, but I usually start my money spending spree with the hope of fixing it myself, so I take things apart still.;D

Good luck.

Paul

 

[blubuckaroo]

If the odometer is clocking, the cable is working.
The odometer runs directly off the cable, but the speedo uses a magnetic drum affair to get the pointer to follow the magnet.
You can carefully open the housing for a look, but most of these are old enough for some service.
There's a tech page on this site that is sure to help.
Many here have used this outfit to service and repair their gauge cluster.
http://www.classygauges.com/

Here's the tech article.
https://classicbroncos.com/tech/speedometer-rebuild-101

Oh, and it's a lot easier to remove the speedo cluster through the floor vent. I can't tell you how many times I've done it from under the dash.

 

[Muddy1966Bronco]

Thank you both immensely. This explains a lot. I also like to tinker with something first and see if I can fix it. I’ve saved thousands on rebuilding the Bronco this way. I will be checking out that tech article soon, but probably not until after Roundup at this point.

And blubuckaroo, you remove through the floor vent? I’ve always pulled it from under the dash with no problem. But I’m also smaller and can fit under and reach everything no problem. My husband won’t touch under the dash type work, haha.

 

[DirtDonk]

Me too neither anymore! Well, not if I can help it at least.;D
But if you're finding it easy enough, then I'd keep doing it that way because it's quicker with no new surprises thrown in front of you.

But don't forget the trick of removing the (I call it a cowl vent) driver's side vent because it really does open up a new world of viewing angles for that part of the dash.
I've never had to use it on any of mine, but the few times I've messed about with that open spot on other's rigs, it was a real eye-opener.

I don't like to remove something like that if I don't have to, because it fits so nicely and does not leak. But if I needed to, I'd do it.

Have fun!

Paul

 

[blubuckaroo]

Thank you both immensely. This explains a lot. I also like to tinker with something first and see if I can fix it. I’ve saved thousands on rebuilding the Bronco this way. I will be checking out that tech article soon, but probably not until after Roundup at this point.

And blubuckaroo, you remove through the floor vent? I’ve always pulled it from under the dash with no problem. But I’m also smaller and can fit under and reach everything no problem. My husband won’t touch under the dash type work, haha.

Wow! I'll have to keep that in mind. I sort of like the idea of watching my sweetie while she's working under the dash!
I've worked on it quite a few times from below. I removed my gauges and put in a spare while getting them refurbished. Then the refurbished one didn't work. I switched gauges quite a few times before getting things to work. I have a small folding painter's work platform that I put in the doorway to lay on.
The hardest part is reconnecting all the gauge and light terminals. I've got wire markers on all the terminals, and a drawing showing their device.

 

[R1bit]

Me too neither anymore! Well, not if I can help it at least.;D
But if you're finding it easy enough, then I'd keep doing it that way because it's quicker with no new surprises thrown in front of you.

But don't forget the trick of removing the (I call it a cowl vent) driver's side vent because it really does open up a new world of viewing angles for that part of the dash.
I've never had to use it on any of mine, but the few times I've messed about with that open spot on other's rigs, it was a real eye-opener.

I don't like to remove something like that if I don't have to, because it fits so nicely and does not leak. But if I needed to, I'd do it.

Have fun!

Paul

My cowl vent is glued down… When I remove it do I have to re glue?

 

[DirtDonk]

Well I would certainly use something. It’s not so much for gluing it in place as much as for sealing it against water intrusion into the cabin.

Maybe silicone would be a little harsh because it would make it hard to be removed the next time. I know that new units come with a gasket, so check yours to see if there’s a gasket in place as well.
Maybe it’s just some form of non-hardening putty? In your case maybe the old putty finally hardened up.