So I drove my 86 fc to the post office today and the speedo was working fine. shut the car off and went in. when I started driving her again, the speedo is doubling the speed? it starts at zero and always goes back down according to speed but when I do 20mph, it reads 40mph. 30mph reads 60mph. what the hell happened? It's not dead but doubling my speed? all the other gauges work fine, I didn't hit any big bumps or anything, nothing at all happened. something just got loose or broke or something? help me out guys, I have no idea what this could be.

 

speedo is cable controlled from a gear in the trans. does your speedo bounce at all? if not then check connections on the cable at the cluster and trans. if they are good then id assume the weights in the gauge have relocated themselves.

 

If the cable was loose anywhere, wouldn't the speedo just stop working? the weights seem like a more likely idea. the needle is bobbing slightly, almost not at all though. how would I check the weights?

 

easiest way to fix this problem would to be just go to the junk yard and bring home a new instrument cluster. spend 4 hours trying to figure what it is.. 20 min to replace it.

 

my brother has an extra cluster and 2 speedo cables. if it is the cable, theres no way it could break the cluster is there? I'll check the connection on the cluster and see if thats loose first and then replace it if that doesn't do anything thanks for the help.

 

if you replace the clutster and cable, then obviously it's your tranny, at which point, i would make a couple of videos of you doing 260MPH!!! :-D

 

I'm pretty sure that since our speedo's only go to 160mph, I would break the needle at 260mph.lol.

I wiggled the speedo cable on the cluster and drove to a store and it was back to normal. got back in the car and drove and it was doubling again. I'm going to my parents house to get my bro's cluster to see if that does anything. then its on to the cable which looks like will be a PITA. I have a T2 tranny here, might have to run that on my N/A if its the tranny. my T2 needs $600 worth of seals and parts.

grrrrrrrr, might be time to break out the impreza again. I hate automatics though.

 

well, I noticed that it alternates when I turn the car on and off. It will be normal then I turn the car off and later when I turn it on, it does the double speed thing again. so I did that a couple times, accelerated really hard and went fast when it was normal and now it seems to be fine. Just needed its regular speed run I guess.lol.

I'm going to keep the spare cluster in the car for now to see if its going to stay fixed. I'm thinking it was some sort of magnetic problem seeming how it was alternating between start ups. thanks for the help guys.

 

did you go UNDER the car to check the connection ofthe cable at the transmission?
it is Unlikely that the cable dislodges from the Inside Cluster(maybe if somebody took the instrument cluster out at one point).
the cable AT the transmission however can get loose and not contact the Speedometer gear on the inside of the trans,and that would make the Speedo go all wonky.
It could also destroy the Plastic gears on it too.They are easy to source though(auto parts stores) as people often change that gear out to offset the speedometer when running a Bigger set of tires.(they get the gear so the speedo will read correctly),.

 

well, the car needs a lot of work. mainly the rockers and side frame are toast, I'm going to see if I can salvage it this winter. also getting T2 swapped next year so I think I am just going to get my subie out and start working on the 7 in the garage. since the tranny's getting swapped, I don't really see a reason for looking around down there right now. I've put this project off long enough, It's time for me to get her to the condition she should be in. I hope the side frame will only require sections of bracing and some POR-15. thats the part that is going to decide whether I sell her off as a major project car (or demo car) OR try and fix it but I don't have the skills or money to do any major restore work.

I think I will just replace the speedo cable when I do the swap just to be on the safe side though.