fun and games with diesel 80 instrument clusters

[John Young]

So we are racing to get the Omani diesel 80 to the shipper by 23 NOV. Down to the wire. And as I've posted in the WDYDWYDT thread I've had a problem with the tach reading about half what it should, or a little less, after we did a bunch of work and removed some of the clutter from the engine.

The Omani diesel 80 has an engine from an HDJ81. The 1HD-FT came with EGR which I always hated. For some dumb reason I decided to do the EGR delete before shipping and it turned out to be an interesting but very time-consuming exercise. And inexplicably the tach, which had been working fine, started acting up after this EGR work. I still don't see the connection. One important factor is that in our ignorance we did not transplant the HDJ81 instrument cluster or any other electronic bits (to the extent there are any) while swapping it into the Omani 80--which was, from the factory, an HZJ80 with an ordinary 1HZ. So there was were some unknowns when it came to exactly what the wiring was. You live, you learn...

So anyways, with the shipping date looming I decided to try to fix the tach issue. Went down a huge rabbit hole with the diesel pump sensor, first installing a new Chinese pump, then even buying a new Toyota sensor and installing it on the new Chinese pump, then putting the original Toyota sensor on the Chinese pump, then sending the original pump to Bosch to have it rebult, then reinstalling the rebuilt pump (which did have a crack in the housing so it was a good move to have it rebuilt) with the original Toyota sensor, all with no change.

I also had a couple of spare diesel 80 clusters kicking around and I tried them, but no joy.

Faced with these continuing failures I got kinda mad. And it so happened that our own @logicbyondreaso had DM'd me asking about instrument clusters for his diesel 80 project. I had sent him to the one supplier I know who has clean JDM clusters (with a price tag reflecting same). But this got me thinking. And I decided to brute force the problem. I knew where in Sharjah a place where they have very rough clusters in large quantities. I got in Mr. Blue the 105 two nights ago and drove through truly horrendous traffic for over 2 hours to get there and then I spent the next hour and a half sorting clusters. Thankfully they close at 8pm in these places.

And I came home with a Sack o' Clusters:

Yes that is a 70 series cluster in there, but I have been burning out oil pressure gauges through ignorance and spotted a 70 with the tach mechanical speedometer and picked it up.

You may think I was crazy to get all these, but the other reason I bought some of them was to get the MPH dials so I could put them on two other 80s in the US.

 

[John Young]

These clusters were pretty rough and very, very dirty. First thing to do was to give them bit of a scrubbing.

The dial faces were not too bad

I used to be apprehensive about just washing these things but hot water and dish soap has not seemed to cause issues.

 

[John Young]

By midnight yesterday I had 4 clusters more or less cleaned up and drying out. (The other two clusters had mechanical speedometers from the early 80 Series. The Omani 80 is a '97.) So this morning I went in optimistic that one of these four had to work.

It was not to be.

The tach did not even twitch on any of the four when they were installed. Now I know that there are a lot of cluster configurations but I figured that late 80 core functions should have worked and I could have dealt with misplaced indicators. I was about to give up when the Ancient Swede (the senior mechanic at the garage) suggested I simply swap a tach from one of my spare clusters into the cluster whose tach was sort of working albeit reading only a fraction of what it should have.

Doing this swap is not a drama. There are 4 to 6 screws that serve both mechanical attachment and electrical connection functions, so no big deal really.
Incidentally, this is the cluster that was partly working:

And of course I figured as long as I was going to try to swap the tach module I might as well change the speedometer face at the same time and try to make the best cluster I could out of these salvage units.

 

[John Young]

Shockingly, the first tach swap I tried, from a mechanical speedo unit as it happens, actually fixed the problem! I now had a working tach again, and that is something I really use on a manual 80 with a turbocharged diesel. Victory!

So I cleaned everything up and made it all pretty. Got out my plastic polish and picked the best front piece and largely got rid of the scratches, and I even put some vinyl restorer on the dial faces to make them look really nice and new.

Turned out surprisingly well, I think. BTW, this is not the final tach. The final one only had a timing belt light.

Incidentally, by changing the speedo face I may end up with the MPH slightly off, but it won't be by much.

 

[John Young]

So I'm happy. I have a functional tach and cluster. I put it in and the timing belt light is on. I tried resetting by poking the hole. No joy. Turns out you can disable that light just by removing one of the mounting screws that also provide the signal from the speedo to light the T-Belt LED and initially I did just that. But then I paused before putting it back in. Maybe I should take a closer look and maybe I could get the alert light to function properly.

And now I am finally coming to the real point of this whole thread. I saw something that other 80 diesel guys may find useful, and something I wanted to post here so others with T-Belt LED issues might save some time.

I pulled off the speedometer from the working cluster and looked closely at the momentary switch for resetting the T-Belt light:

I initially figured, ok, this is some kind of momentary switch that I have not come across before and the intent is that a probe will cause a momentary connection. But then I noticed that it was just broken.

Then I looked at the other clusters:

Here is a close up view of the switch:

Of the four clusters with electronic speedo's only one was intact. The rest were either had the hat missing or were broken but just held in place by the wires, but still definitely non-functional.

AI misidentified this as a Matsushita momentary single pole, double throw switch. It is not. It is a latching single pole, double throw switch. I verified this on the one intact cluster.

It so happened that I had the older mechanical speedo clusters at the shop as well so I pulled those out to look at the differences. The earlier 80 speedo had a much higher quality, metal body switch, and with a multimeter I verified that it also was a latching single throw, double switch. I could have swapped in the one intact plastic body switch, but that seemed like a bad idea considering that the 75% failure rate demonstrated by my collection of clusters.

 

[John Young]

What I did was take the metal switch from the mechanical speedo and put it on the electronic speedo.

The hole and the distance from the face are different for the two types of switches but it still worked well enough.

I put the cluster back together again (adding the MPH dial at the same time) and tried it out.

 

[John Young]

We did some more fooling around and the light came on again, but we reset it again with the engine on and that seems to have sorted it.

 

[VADUS]

It might helps:
1HD-FT WITH EGR Tachometer working through Emission control computer. The sensor on pump sending signal to ECU, and ECU sending different signal to the dashboard tacho - it is a circuit with +.
1HD-FT WITHOUT EGR Tachometr working directly from the pump sensor to the dashbord, as all other 1H series motors 1HZ, 1HD-T etc. It is just a pulse of ground signal.

 

[TheBussman]

Good work, yea you have to wait for the light to turn on before you can reset it. Those MPH speedos that don't say "unleaded fuel only" would be valuable here in the US i would think. You should have done the temp gauge mod too I just did another one today.