I think the actual speedometer in my car is hosed, can anyone confirm that it is?


The Facts:
1) Odometer works correctly, ALL the time.
2) Speedometer usually spools to 200 km/h at about 1-15km/h.
3) Sometimes, the speedometer shows actual speed.
4) 84 GSL-SE, with original dash & speedo, to the best of my knowledge (making it a semi-fact, I guess

My Reasoning:
1) Since the odometer ALWAYS works correctly, the connection at the transmission is fine, as is the cable
2) Problem must therefore be that the cable is not the original, and perhaps the centre piece goes too far into the speedo, and touches a second gear it shouldn't touch, or
3) speedo itself is hosed (2 gears sticking together, perhaps?

Anyone have a crap speedo sitting around they want to conduct a science experiment upon to help me out? I don't want to cut back the tab on the cable, only to find that my Odo no longer works!

 

perhaps the speedometer itself is just going bad. they do go bad.

 

Probably hosed.

I haven't played with a Mazda speedo, but generally speedos work by generating a current and then the needle moves around based on that. (But it's been a while and not on a Mazda) Anyway it'd be possible for things to go bad in such a way that the speedo goes screaming off the deep end so to speak.

They read about 10% high from the factory anyway.

 

I had the same problem-- My speedo was just dead.

I've heard (last time one of these threads came around) that with a little work they can be made to live again, but I can't verify that personally...

 

I did a search before posting this thread, but couldn't see anything in the forum. Can you remember any details about what had to be done to bring it back from the dead? Total disassembly, or as simple as a squirt of WD-40

 

You won't know til you take it out of the gauge cluster. It's completely mechanical on the FB, so its likely that somthing is just sticking.

 

My speedo goes right to full speed as soon as I start moving forward.

After picking up an 85 gsl-se and getting it running...new injectors, new front calipers, new battery she seemed to run pretty good (idles a little rough), everything in the car works great in the garage. So with thoughts of going to get it safetied right away I took it for a spin down the back lane and discovered the speedo was wacky. As soon as I started moving forward the speedo would pin itself. All the other guages seem to be working perfectly except the oil pressure guage which I'm not too worried about.

Any simple fixes? Any speedo repair shops in Edmonton, Alberta...Canada?? lol

can the speedo be replaced by an autometer guage easily. Just wondering what the best and speediest fix is to get it on the road for the summer.

Thanks and all info is much appreciated.

Rug

 

IIRC, speedos in first gens are magnetically coupled; cable spins magnetic rotor inside a coil-wound cage that's attached to the needle & balanced on very low-friction supports; magnetic "drag" (eddy current) between the spinning rotor and the cage causes the needle to rise higher the faster the rotor spins. The needle is opposed by a hairspring, so the actual reading is based on the balance between the magnetic force pushing the needle upscale, and the spring pushing the needle downscale.

With age and wear, a lot of different things can go wrong; the spring can break or weaken, the pivot points can bind or fail, the rotor can collect dirt or crud which drags on the cage, parts can become magnetized...

They're surprisingly delicate. I can easily see why repairing & calibrating them would be a specialty

 

These speedos are delicate instruments. I tried to R&R mine on my SA with marginal success but it still had issues.

Unless you can or want to send it to a speedo repair place your better off getting one from a parts car and throwing it in.

 

DIVIN DRIVER is right. There's nothing electronic in our 1st gen speedos.

I've replaced several and there are a lot of mechanical factors that could go wrong.

The way I see it, you can try a couple of things.

First, pull the instrument cluster and remove the speedo. Once you get the cluster out, remove the speedo from the cluster by taking out the 2 screws in the back on either side of the cable input shaft.

To better gain access to the interior mechanical components, you can remove the face if you gently pop off the needle and remove the two retaining screws on the front. That will make it a lot easier to see the mechanical parts.

Make sure you don't have a lot of old grease and grime building up and then give it a good cleaning and re-lube. For me, I use a silicone spray lubicant.

Check the gear interface and make sure nothing is slipping. Reassemble as before.

When you reinstall the cluster, make sure the speedo cable is firmly engaged and not backing out through the firewall.

Give it a go and see if it works properly. If not, you may have to try swapping it out with another.

Someone in this forum may have one that works and can sell it to you. If you've already gone this far, replacing the speedo is a piece of cake.