I did not notice that the speedo went crazy today intil I was on the highway to work.. It will go from 0-130 in first gear then lock out back at 0 in second.. Comes back down when I stop but does the same thing everytime now..

Sound like a bad speedo? or?

I know my srock 12a is not that fast....lol...

 

Speedo died probably, but check the cable and make sure its not binding and is fully seated in both the transimission and the back of the speedo before condeming it.

 

I will be checking that tonight... I noticed it the other day that at a steady 70mph it would jump every now and then... Just another thing to add to the list...lol

 

Once you're sure the cable is okay, it's also worth trying pulling the speedo out and blowing the inside of it clean with one of those aerosol "duster" cans (compressor air is too strong) before you give it last rites.

The jumpies can sometimes be caused by dirt or dust buildup in the magnetic coupler that makes the speedo work. It needs to be clean and dry to work right.

 

How hard is it to get out of the dash? I noticed the tach jumped some today also so it might be the entire cluster going bad but I will clean it first and try that..

These do not look as simple to get out as new cars...

 

Getting the whole panel out is 6 screws, two snap clips, two cable connectors, and the speedo cable. It's easier if you take the column/lock surround off, too (5 more screws, one ****, one snap-in filler), but can be done either way

Two screws in the cluster surround at the top
Pull the cluster surroud toward you gently until it unsnaps at the bottom.
Take out two screws at the top of the cluster.
Crawl under dash, take out two screws at bottom rear of cluster.
Undo speedo cable and two electical connectors
Pull panel out gently and ease out from behind steering wheel. Be careful of the screw tabs; they are fragile.

Once the cluster is out, it's six more philips screws to get the speedo out. Biggest trick is not getting the inside dirty or fingerprinted.

 

Not too bad. Lots of different screws to keep track of. Steering wheel and column cover come off first. FSM says the combo switch needs to be removed. I don't think that's necessary. FSM has good diagrams. Pages 15-21 and 15-22 from the 84 FSM attached.

 

cable might be tweaked and worn some where...Plastic gear teeth in the tranny where the speedo cable goes may be bad...or just not attached all the way properly...Just a couple of simple things you can check

 

I just put mine back in my 80 two days ago... I can attest, the steering wheel on an SA doesn't HAVE to come off. It would be easier to handle the panel that way, but its for-sure not essential... and I hate having to take my steering wheel off.

 

Well it was a bit closer this morning on the way to work... After I got here I had to run down and deliver a customers computer and it was back to normal...

Go figure that one...

 

I used to service mechanical speedometers for a living. You don't have a cable issue. The speedometer is starting to fail.

When the indicatior needle pegs out or jumps, the magnet (it is driven by the speedometer cable) is contacting the speed cup (the indicator needle is attached to the speed cup). This is due to age, wear and a lack of lubrication in the right places. It is likely not a dirt or dust issue because an RX7 instrument cluster is pretty well sealed against dust. So I doubt that blowing it out will resolve this. Also, you should not spray any lubes (WD40, etc) on the internals of the instrument.

At this point, the speedometer may have accuracy issues because it is likely that the return spring that help zero the indicator needle may have been stretched. Eventually your speedometer will lock up and distroy itself. Probably when the weather gets cold.

It may be possible to correct this issue, however you have to get into the speedometer to do this. As in remove the needle and gauge face and access the speed cup return spring and upper bearing. The issue is that when you reassemble the speedometer it will have to be recalibrated and this difficult to do without the proper equipment. So you need to contact a professional. There are still speedometer shops around the country that may be able to help you out. www.google.com

The alternative to a repair is to look for another speedometer and swap it in. A speedometer shop can assist you with moving the odometer from your speedometer to a replacement. That way your car's speedometer is still showing correct mileage.