SPEEDOMETER PROBLEMS---HELP!!!!

I have a 78 F150 that originally came with a Kilometer speedometer gauge (truck must have been built in Canada) and I purchased an entire used instrument cluster that had the MPH speedometer gauge.

When I installed it and took it for a drive, once I hit 30-35 mph, the speedometer suddenly made an extremely loud (I mean loud!!) buzzing sound and the speedometer needle instantly wound clear around past 80 mph and bounced around at the bottom of the speedometer gauge (down by the odometer). When I slowed down to less than 30-35 mph, it quit making the loud buzzing noise and the needle went back to functioning normal.

The noise almost sounded electrical (kind of), but not sure. The gauge is operated by a cable, so I didn't think it was an electrical problem or a problem with the printed circuit board, but who knows....I'm not sure.

I took the cluster out of the truck and took the speedometer gauge out of the cluster and visually inspected it for any obvious broken or worn components, but everything looked brand new; was in really good shape with no sign of wear whatsoever. Since I'm at a loss, I decided to ask you guys for help....

Questions....

1) Has anyone ever had this happen to them?
2) If so, what was the problem and what did you do to fix it?
3) Could this be a problem with the printed circuit board?
4) Is this an electrical problem or mechanical?

Thanks in advance for your advice....

I would pull the end out of the transmission and check the plastic gear for worn teeth. No it is not electrical.

Pull the cable out of the housing and grease it and put it back in.

Mechanical. Sounds like the cable is frayed. Like what has been said,pull it out of the tranny ,check the gear,replace whats necessary.  

Make sure you didn't put any kind of kink or stress point in the cable housing when you changed the dash unit, that happens sometimes and you don't even realize it's happened. Make sure you didn't pull the inside cable out of the housing when you replaced the thing, or what Supervel said may bear looking into. I think you may have pulled it out of the housing a little, only goes into that plastic gear in the tranny about 3/4 of an inch, give or take, doesn't go into the speedo very far either. It's a round cable, but it has ends that have been pressed "square" in both ends. You may not have seated it in the tranny gear before you put the speedometer on it, or you may not have gotten it into the speedometer end correctly, and it bound things up in the housing a bit... Easy fix is to just pull the housing retainer off at the tranny and make sure the inside cable goes into the tranny gear (Turn the cable [Not the housing] until it goes into the gear, you'll feel it when it does [If it's not right to start with]). Both ends have to go into the square hole for it to work correctly (Yeah, I know, I didn't say that very well). Lube the cable while you've got it out.
If the unit you bought to replace the other is at fault, that's another thing. You may want to return it, or not. It's a mechanical speedo, and if it went to full scale fairly quickly, then there may be a piece of trash/shrapnel between the driving insert and the driven cup. Works like a magnetic slip clutch, faster the insert turns, the more it pulls the cup along with the speedo pointer attached to that. You can check that by pulling the housing/cable off the speedo, turn the speedo with your thumb & forefinger, the speedo should go to somewhere between 20 and 40 or more depending on how fast you can turn it. It should do that smoothly, though, not erratically.
I've got an 80 mph speedo for a '78 in my junk pile somewhere if you need it, but it may be 2 or 3 months before I get back where it's located now... I put one of the 100 mph ones into my truck years ago, another eBay "find".
Hope I've helped.
Glenn M.

Glenn M. wrote:Make sure you didn't put any kind of kink or stress point in the cable housing when you changed the dash unit, that happens sometimes and you don't even realize it's happened. Make sure you didn't pull the inside cable out of the housing when you replaced the thing, or what Supervel said may bear looking into. I think you may have pulled it out of the housing a little, only goes into that plastic gear in the tranny about 3/4 of an inch, give or take, doesn't go into the speedo very far either. It's a round cable, but it has ends that have been pressed "square" in both ends. You may not have seated it in the tranny gear before you put the speedometer on it, or you may not have gotten it into the speedometer end correctly, and it bound things up in the housing a bit... Easy fix is to just pull the housing retainer off at the tranny and make sure the inside cable goes into the tranny gear (Turn the cable [Not the housing] until it goes into the gear, you'll feel it when it does [If it's not right to start with]). Both ends have to go into the square hole for it to work correctly (Yeah, I know, I didn't say that very well). Lube the cable while you've got it out.
If the unit you bought to replace the other is at fault, that's another thing. You may want to return it, or not. It's a mechanical speedo, and if it went to full scale fairly quickly, then there may be a piece of trash/shrapnel between the driving insert and the driven cup. Works like a magnetic slip clutch, faster the insert turns, the more it pulls the cup along with the speedo pointer attached to that. You can check that by pulling the housing/cable off the speedo, turn the speedo with your thumb & forefinger, the speedo should go to somewhere between 20 and 40 or more depending on how fast you can turn it. It should do that smoothly, though, not erratically.
I've got an 80 mph speedo for a '78 in my junk pile somewhere if you need it, but it may be 2 or 3 months before I get back where it's located now... I put one of the 100 mph ones into my truck years ago, another eBay "find".
Hope I've helped.
Glenn M.

Thanks Glenn (and everyone else) for your advice....

Just a side note...My original instrument cluster with the kilometer speedometer did not have this issue. It worked perfect. That's why I'm wondering if it's a gauge issue or a printed circuit board electrical issue. I guess I can swap the mph speedometer into the original instrument cluster (with the original circuit board) and maybe that would answer some questions, but I was hoping someone on here could answer my questions before I went that route....

With that said, I have a few more questions regarding your advice....

1) if the cable came out of the speedometer gear (at the tranny) when I pulled the original instrument cluster out, then why does the mph speedometer work fine until it reaches a certain MPH?
2) Wouldn't the speedometer have this problem from the very start and not after it reached a certain speed? (If the cable isn't seated in the tranny gear, then it wouldn't turn at all, right???)
3) just for curiosity (and a possible future purchase), how much for your 80 mph speedo gauge?
4) Are there any issues with your 80 mph speedo gauge? Does it work flawlessly?

Not sure I can help with why it works fine until it hits a certain speed. Maybe for kicks, pull that speedo gear out of the tranny and have a look at it, my guess is that it'll be fine, but, hey, it's only one little retainer bolt and out it comes.
One other very remote possibility is that the odometer or odometer gearing in your new unit isn't working right or bound up a bit - check and see that it adds the right number of miles on it when you drive the truck. I'm kind of running out of ideas about now, hopefully someone else will chime in to help. But, if your old unit was working, and your new unit works until a certain speed, pull the cable all the way out of the housing, (From the speedometer end should be the easiest) and make sure both ends are still good and square, and check the entire length of the cable for any bright shiny wear marks or broken strands. If it all looks good, then lube the inner (rotating) cable, and put it all back. Use a light weight grease, wheel bearing grease ain't gonna work good unless you use a very small amount or "cut it" with a little motor oil, LOL... Make sure it goes into the tranny gear like it should (Rotate it until it does). Then put the housing/cable back on the speedo, making sure it goes in easily and "all the way". Sometimes, you have to rotate the speedo end to make sure the cable goes in right since the tranny gear is holding the cable in one position - as I'm sure you've done a few times by now.
If it's doing the same thing after installing everything correctly (And no kinks in the housing), then I sorta have to cast an evil eye to your new speedo. And, unless you've fooled with them before, it's kind of a pain in the butt to pull the speedo out of the dash unit, take it apart far enough to clean it out, put it back, etc.
A very long time ago, I used to work on mechanical speedometers, used a Stewart Warner speedometer machine when checking them out, calibrating them, etc. - so, I feel your pain, brother!!   
My speedo was working fine when I changed it out, but that was some time back, and I'd probably pull my present dash unit out and put the old one in just to check that it's still working properly. It may be 2 or 3 months until I get back to where that dash is though, and then I gotta find it amongst all the other junk that I have...      
Somehow, I've got this feeling that the loud "pop" you heard early on was the cable wasn't quite into one or the other end (Tranny gear or probably the speedo), and it snapped into place when you started driving it... Might have kinked the inner cable... Or not... Wish I were closer by, I'd be glad to help... I'm fairly confident that you're going to find your problem, though.
Glenn M.

Glenn M. wrote:Not sure I can help with why it works fine until it hits a certain speed. Maybe for kicks, pull that speedo gear out of the tranny and have a look at it, my guess is that it'll be fine, but, hey, it's only one little retainer bolt and out it comes.
One other very remote possibility is that the odometer or odometer gearing in your new unit isn't working right or bound up a bit - check and see that it adds the right number of miles on it when you drive the truck. I'm kind of running out of ideas about now, hopefully someone else will chime in to help. But, if your old unit was working, and your new unit works until a certain speed, pull the cable all the way out of the housing, (From the speedometer end should be the easiest) and make sure both ends are still good and square, and check the entire length of the cable for any bright shiny wear marks or broken strands. If it all looks good, then lube the inner (rotating) cable, and put it all back. Use a light weight grease, wheel bearing grease ain't gonna work good unless you use a very small amount or "cut it" with a little motor oil, LOL... Make sure it goes into the tranny gear like it should (Rotate it until it does). Then put the housing/cable back on the speedo, making sure it goes in easily and "all the way". Sometimes, you have to rotate the speedo end to make sure the cable goes in right since the tranny gear is holding the cable in one position - as I'm sure you've done a few times by now.
If it's doing the same thing after installing everything correctly (And no kinks in the housing), then I sorta have to cast an evil eye to your new speedo. And, unless you've fooled with them before, it's kind of a pain in the butt to pull the speedo out of the dash unit, take it apart far enough to clean it out, put it back, etc.
A very long time ago, I used to work on mechanical speedometers, used a Stewart Warner speedometer machine when checking them out, calibrating them, etc. - so, I feel your pain, brother!!   
My speedo was working fine when I changed it out, but that was some time back, and I'd probably pull my present dash unit out and put the old one in just to check that it's still working properly. It may be 2 or 3 months until I get back to where that dash is though, and then I gotta find it amongst all the other junk that I have...      
Somehow, I've got this feeling that the loud "pop" you heard early on was the cable wasn't quite into one or the other end (Tranny gear or probably the speedo), and it snapped into place when you started driving it... Might have kinked the inner cable... Or not... Wish I were closer by, I'd be glad to help... I'm fairly confident that you're going to find your problem, though.
Glenn M.

Thanks Glenn for the wisdom. Looks like I need to pull the cable out and inspect it and make sure it's seated properly in the gear and speedo and put it back in and see what happens. Will work on that this Sunday if the weather allows. It's cold right now and I'm not too crazy about working in the cold weather. When I was much younger I'd work on my vehicles no matter how cold it was, but now that I'm older I'm a little less ambitious to suffer the cold weather. Thankfully, this isn't my only vehicle to drive. If it was, I'd have to get a second job just to afford the gas....LOL

I have had this samething happen to me on my 69 F100 when I replace the speedometer cable the on it. I know you said you replace the speedometer but what happen to me when I put cable on the back of the speedometer it look like it had enough to make but it rub the back and not engage into the speedometer so I had to put the cable on the speedo then pull the trans gear back off and push the cable into the speedo you can feel it engage into the speedo and it will slide in some.more then I put the gear back on and it worked right. I think my was touching but when I would get over about 40 the needle would start jumping around then just stop working until I would just about get stop and it would jump back up. Just something you might want to.try when you put it back together.
Jim

69F100 wrote:I have had this samething happen to me on my 69 F100 when I replace the speedometer cable the on it. I know you said you replace the speedometer but what happen to me when I put cable on the back of the speedometer it look like it had enough to make but it rub the back and not engage into the speedometer so I had to put the cable on the speedo then pull the trans gear back off and push the cable into the speedo you can feel it engage into the speedo and it will slide in some.more then I put the gear back on and it worked right. I think my was touching but when I would get over about 40 the needle would start jumping around then just stop working until I would just about get stop and it would jump back up. Just something you might want to.try when you put it back together.
Jim

Excellent Idea!!! I will definitely try that. I think what will be the easiest way to make sure it's seated in the speedo. I'll work on that Sunday, if the weather is ok....

Here's an update on my speedometer issue....I pulled the instrument cluster back out today and inspected the cable end and checked to see if there was any dirt in the back side of the speedometer where the cable is inserted, but everything looked good. So I put the cable back on the speedometer and made sure it was secure and the clip "clicked" into the groove. Then I crawled under the truck and pulled out the speedometer cable out of the transmission. I took off the gear and spun the cable itself and pushed on it to make sure it was seated in the back of the speedometer, then I put the gear back on and put it back in the transmission. I didn't notice anything wrong with this end of the cable either. I took the truck for a drive and it worked flawlessly with no noise. Not sure what the problem was but it seems to have been resolved. Thank you every for your help....

Good deal! I knew you'd get it!

Glad you got it fixed.
But them old cables need to be lubed. Take the cable all they out of the housing and lube it and put it back in. They will brake if not lubed.
Pull it from the trans end.

Well, maybe the problem isn't resolved afterall. I drove the truck to work this morning (25 miles) and the speedometer went crazy twice; making a loud buzzing noise and the needle pegged out and bounced around at the bottom of the gauge (by the odometer). Eventually it stopped, but did it again and then stopped. So I have no clue where the problem is, if it's the speedometer gauge itself or the cable. I can definitely pull the cable out and lube it, not a problem. So what kind of lube do I use? Oil? Lithium grease???

78 F150 wrote:Well, maybe the problem isn't resolved afterall. I drove the truck to work this morning (25 miles) and the speedometer went crazy twice; making a loud buzzing noise and the needle pegged out and bounced around at the bottom of the gauge (by the odometer). Eventually it stopped, but did it again and then stopped. So I have no clue where the problem is, if it's the speedometer gauge itself or the cable. I can definitely pull the cable out and lube it, not a problem. So what kind of lube do I use? Oil? Lithium grease???

Lithium grease???
You could have a bad gauge.

That's what I wa afraid of. Is this something that can be repaired or is the gauge ready for the trash can?

78 F150 wrote:That's what I wa afraid of. Is this something that can be repaired or is the gauge ready for the trash can?

I sure wouldn't trash the gauge. Not yet. I can probably clean it out for you when I get back to VA if that is indeed what the problem is. Or trade gauges with you if I can find mine and get it all checked out for good operation.

If you don't have any speedo cable lube - stop-gap grease = regular chassis grease cut with a little 30 weight or whatever little bit of oil you've got around including some wipe-down off the engine oil dip stick... It ain't all that critical, just needs to be enough to coat the cable, not "gobbed on", just heavy enough to stick to the cable, and not so thick as to try and be a problem, not so thin that it won't stay on the cable. Clean the cable first with a clean rag before you put new lube on it. Real world - that cable is "driven" by a gear, you have to have some pretty good amount of binding to just "break" one, the biggest problem is usually just 35 or 40 years of wear that ends up breaking some strands, a kinked housing, or a speedo problem...
Have you pulled the cable out and checked it for any broken strands or shiny spots where it's rubbing hard on the housing? If you do, then watch how you pulled the cable out, check how far from whichever end it's bright & shiny, and look at the housing at about the same length from the same end. If the cable comes out real easily, I'm betting it's not the problem, usually one that's rubbing the housing gives a little resistance to coming out and especially going back in whenever it hits the kink... If the cable's good to go, then it's the speedo...

Hmm, looks like I'll have to pull the cable out and inspect it. However, intuition and common sense tells me that since I never had this issue with the kilometer gauge I had in it (or the cable) then the issue is probably with the mph gauge when are you heading back to VA?

78 F150 wrote:.....(when are you heading back to VA?

When it warms up!!!       
Sorry....  

Sent you an email, been a busy weekend with the music and all...