Rotmilky

I'm trying to get my 84 speedometer/odometer working. Neither one does a thing. I don't think it has since I bought the car...although I've only had it maybe a month or two and it's been running for maybe a week tops.

Here is where I am with it: I did quite a lot of searching of Rennlist and have tried many of the suggestions so far:
1) Tested resistance between T1/T2 as the rear wheel is rotated slowly. I see it go open/closed several times per tire rotation.
2) Yanked pod. Cleaned all connectors with Deoxit. Soldered the rivets. I did not, however, fully pull the speedo and check the backside of it's circuit. I did check the rivets to make sure I had continuity between the rivet and the connector point by tracing the conductive channel back.
3) Reinstalled the pod. No change in Odo/Speedo. As a side note, the voltmeter is working much better. It no longer bounces all over the place and no longer seems to slowly decrease in registered voltage as the car gets hot. Now it's a pretty rock solid 13.5-14V. So I call that at least a partial victory.
4) Checked the voltage at H1 with ignition on--4.8ish volts. I would have thought it would be 12V? But in the prior threads I've seen on H1, it says to check for voltage. So, I'm guessing that's what it should be.
5) Checked continuity between H1 and H2 with ignition off. I see open/closed condition as I slowly rotate the rear wheel.
6) Just for giggles, I used Deoxit on the connectors in the rear spare tire area. Also used Deoxit on the H-connector and T-connectors in the CEB. No change...although I could swear I at least saw the needle on speedo bump when I started the car. Maybe just seeing things I want to see.

At this point, I've pulled the instrument cluster again and am going to yoink the speedo to check it. Does anyone have any suggested problem points on the speedo itself? Any other suggestions?

Edit: I've now pulled the speedo. I see nothing on the circuit board that indicates de-soldered joints nor anything that looks burnt. Outside of spraying deoxit on the 4 pins that insert into the speedo circuit board, I'm pretty much stuck. Is there a way to test the speed itself to make sure it has some life in it?

SeanR

At the rivets, make sure you have continuity between the rivets and the posts on the back of the circuit board. If so, then follow the traces from the posts back to the connections for the wiring harness. If good there and you know you have the pulses at L2 and R13 from the speed sender, then you most likely have a failed speedo.

Rotmilky

Thanks for the suggestion to test all the way back to the posts that insert into the speedo, Sean.

I checked all the rivet connections from the connector point (where the big white plug clamps onto) to the posts that plug into the speedo (there are 4 rivets related to the 4 posts on my 84). I figured if I could get conductivity from the plug to the post, I could at least ensure the PCB was doing it's job. I found that the point that corresponds to the axle pulses showed no continuity. Oddly, I had forgotten to solder that rivet on the bottom side. I then soldered it and still couldn't measure conductivity. I tried several times and could swear I had what looked like a good solder joint. But the circuit stayed open. So, I got ticked and went to Radio Shack and bought some conductive paint. I had used it in grad school to do some pcb repairs on thin plastic circuit boards that I accidently snapped in half. I figured I could smoosh it up under the rivet better. I applied that all the way around the rivet with a toothpick and 'presto', I was getting continuity between the speedo pin and the connector point.

I can't attest to the longevity of the conductive paint...but seemed to work better than soldering. The product I used was called electric paint by Bare Conductive.

I cleaned all the exposed metal again, this time with a fiberglass brush, reapplied deoxit to plugs. Put the pod back in and took the car for a test drive. Both the speedo and odo worked great. Now that I can see how fast I'm going, I've suddenly realized I've been speeding all over town. What I thought was about 40 mph was more like 60. Oops.

MainePorsche

Nice job.
I'll be there soon with my occasional 'dancing' speedometer. Didn't know exactly where to go, but now I do. Thanks.

Tim Noce

I too just started having a "dancing speedo" and was about to post a thread about it. I just drove back from a SW Missouri float trip and once I hit the awful pot holes of Chicago the speedo started moving strangely and not responding as well (still works for the most part.) I downloaded a speedometer iphone app (uses gps) and it looks like I'm about 5mph off at 50-60mph. Might this be the same issue that requires a dash pullout or something else?

Wisconsin Joe

Dwayne's Garage has an excellent writeup on it.

You have to pull the pod and get the instrument cluster out.

Dwayne covers it very well.

Rotmilky

Given the age of the electronics in these cars, I think wonky connections could certainly be a culprit. At least in my case that was the problem. I think the challenge for you is that your connectivity is intermittent, so you may or may not discover the problem when you first look for it if it's in the working state.

If I had to go through it again (I should probably say 'when'), here's what I'd do: Before doing anything, I'd clean the connectors in the spare tire area. Easy to do and might fix your problem before you do anything more. If not, then:
1) Test connectivity between T1/T2 when rotating the rear wheel (requires jacking up the rear tire and putting car in neutral).
2) Turn on ignition, check for voltage on H1
3) Check H1/H2 for open/closed as wheel is rotated.
4) If that's OK, pull pod and clean connector board (any of the shiny metal contacts) with a cleaner for electric circuits and a good eraser scrubbing. I got my Deoxit at Radio Shack. I think auto parts stores usually carry some sort of circuitry cleaner.
5) Solder rivets on BOTH sides. Make sure you get them all unlike me. That missed rivet is why I had to pull the pod a 2nd time.
6) Check conductivity between the plug end of the circuit board and the pins that insert into the speedo. If you get this condition, I think you can eliminate the PCB as a problem.
7) Inspect the circuit board of the speedo to make sure nothing looks crispy.
8) Spray all the connector plugs with cleaner as you reassemble.
9) Hope you killed the electrical gremlin. That's largely what I did, although I had to do it twice.

If clarification is needed for any of the above, just ask. Dwaynes writeup is what I used to pull my pod. Great writeup.

Tim Noce

Thanks for the follow-up, the last thing I would want to do is to pull the dash and not have it be the problem. I'll start with the spare tire area and see what happens.

-Tim

Rotmilky

Yea, I kinda went at my speedo repair the same way. I worked my way up to pulling the pod. I sorta reached a point where I ahd no choice. Note that you don't pull the whole dash. Only the section that gets raised and lowered by the steering adjuster. First time I pulled it, it took maybe an hour becaue I was going carefully and documenting everything. Second time it took maybe 10 minutes. If I recall correctly, there is one 27mm nut to remove (steering column), two 10mm bolts, three phillips screws and two 5mm allens. If you have the tools ready and know where to look, it's quite fast. Probably the hardest part is removing the 27mm steering nut. With a ratchet/breaker bar, you have to hold the steering wheel steady. I had a Dewalt battery powered impact wrench that made it a one handed 2 second job. A decent impact wrench is worth it's weight in gold.

Good luck on your electrical gremlins.

Dads928

If your speedo and tach are not working then you need to look elsewhere. I lost my instruments many times as a result of an intermittent short in my interior lights. Loose wires in the unprotected lens housing in the rear hatch would contact the body shell briefly over hard bumps and I would lose instruments. Sometimes they would come back on restart, sometimes not. I would blow the fuse from time to time as well. I don't have my chart with me so off hand I cant remember which one. Took me years to trace the problem because the symptoms varied so much. I also get a pulse on the tach about a second after shut off...

Dads928

Sorry read it wrong, I thought your tach was out as well/

yaskota

Just saw this and as another '84 owner, I thought I'd chime in as they problem I had with my speedo & odo & trip odo might be similar- and the solution? A fuse... or two.

Not discounting actions taken- which all seem good and quite worthy of doing- I was headed down a similar path until I decided- for the near term- to ignore it and troubleshoot more low hanging fruit...

When I picked up my car back in February, all three of the above were erratic as hell in operability and when working, sometimes speedo seemed shakey. I only drove it once back then though and not again until recently- and straight home at that- as I had bigger fish to fry so I didn't dwell on it.

Recently, in the past two weeks (as of today, in fact!) I have been using my car almost daily so the need for a consistent speedo/odo/trip odo moved up on my priority list.

Observable Behavior:
Sometimes it would work, sometimes not. Sometimes turning on my lights (or moving light switch!), pressing trip odo reset switch, raising/lowering window or opening/closing sunroof seemed to have an impact. Sometimes not. THE ONLY gauge affected though? Speedo, odo & trip odo. Everything else on dash & center console fine- except a few lights. (All pod switch lights new & haven't pulled pod yet for refresh- but will... sometime soon).

I'll admit, I replaced two or three fuses related to other issues (& overall refresh)- two of which covered dash lights, cigarette light & lighter, AT indicator light, Climate Control lights, etc. As soon as these two fuses were replaced, speedo, odo & trip odo have been rock solid. Again, rock solid.

TANGENT: Sure, I wonder about my speedos accuracy as sometimes it says 60 and people are passing me (I'm in Hawaii were "slow" is kinda normal lol)- but when I'm at 80- I'm passing most others- so maybe it's just fine...

My source for which fuses? My cars manual! I have since performed a CE Panel refresh (an awesome source available elsewhere here, I think- with my post & images coming soon too) and switched all fuses to ceramic- but that's another topic for another time... ;-)

-tom

PS: In addition to speedo/odo/trip odo- yes, a whole bunch of dash & console lights work more reliably and more brightly now too!

UPDATE: Did I say rock solid? I think I meant to say "rock solid until now"... Got in Eleonore this morning, nada: no speedo, odo or trip odo. Curious- is there an "open mouth, insert foot" icon???

SeanR

Going to sound weird, but after trying to solder or conductive paint those stupid rivets, we started using this.




Snap tool that can compress the rivets a bit more. I use Deoxit, wiping it down real well then give the rivets a bit more of a crimp and good to go.