740 instrument cluster repair (and, likely, fuel level sender)

I've finally gotten to the point where I decided I need to do something about my instrument cluster on my '89 744t.

About 2 months ago, my fuel level gauge never returned to full after a fill up. For some time before this incident, it would often stick around at the old fuel level and make its way to full or near full during the drive home.

Does that sound like a stuck fuel level sender? I am thinking if it were wiring, it would be stuck at dead empty rather than a quarter tank it's been stuck at. Is it easy to r&r a fuel level sender on these cars, and from where is it accessed?

In addition to this problem, both the odometer and trip meter don't work. Just great for knowing when to fill up. However, my speedo does work just fine. Do the odo. + trip meter work off of the speedo input, meaning it may be a gear break or something of the like?

Oh, also the gauges suffer from needing the old Volvo-gauge-flick, but that doesn't bother me..

So, what should I look into doing? I likely need a replacement fuel level sender for one, but I have no idea what to do about the odometer and trip meter. Send it for repair, try to do it myself, or replace it altogether?

Thanks.

The odometer not working will be a broken plastic gear. See www.davebarton.com

As for the fuel gauge, you need to find out if the fault is in the gauge or the fuel tank sending unit. If you earth the wiring connector at the sender, and the gauge goes to full you know the gauge works.

Your instrument cluster is so old at this point that it needs all the solder joints reflowed so all of your gauges will work properly. There use to be some places that fix 7/9 clusters but I don't know of any currently.

DNA Speedometers in Florida will do it, just have to ask. It's not listed on their website anymore. About $300 to reflow, replace caps, etc.

Thinking about replacing the whole thing for that price. That will not, however, guarantee me a good cluster that works and will continue working as it should. I'll think about sending it over to them, until then I should probably get to diagnosing the fuel level issue.

Any untested unrebuilt cluster for a 740 is almost guaranteed to need some repair.

daniels740 said:

Is it easy to r&r a fuel level sender on these cars, and from where is it accessed?

Click to expand...

http://cleanflametrap.com/ReginaFuelPump/ (Should be similar in your Turbo).

In the trunk, under the liner.
Unscrew the access cover, and there it is.



Looks like fun. doesn't it? Well, it isn't.



Once you get the b!tch out (without breaking anything )



The sender's float slides up and down in the big plastic tube, making contact with a pair of resistor wires. It can stick, sink, lose contact, do the Cha-Cha, etc.

In addition to this problem, both the odometer and trip meter don't work. Just great for knowing when to fill up. However, my speedo does work just fine. Do the odo. + trip meter work off of the speedo input, meaning it may be a gear break or something of the like?

Click to expand...

Mine's doing the same thing (again), the odo sometimes works fine, sometimes totally stuck, sometimes I go 50km and it stutters along only registering 5-10. I thought I fixed it a few months back, but it's acting up again, so I'll be doing a different fix this weekend.

Depending on what style you have (VDO or Yazaki), different things can go wrong.
Check for dividers between the trip meter numbers.



One style (VDO?) has freaky plastic "epicyclic" gears that can lose a tooth or 3 and stop working...



Mine is a Yazaki, and so is the 1989 turbo speedo I'll be swiping parts from.
This version has a normal-looking electric stepper motor with a worm gear on the shaft.
(My crappy pic from 2 minutes ago)



It turns 2 "spur" gears that simultaneously turn the Odo gearset and the Trip gearset. The maintenance light gearset is driven by the main Odo gearset.

(Someone else's better pic from his fix-it site)



On his, the ancient grease had dried up on the black spur gear shafts, and they were both totally seized. He had to drill them off and make new custom mounting posts for the replacement gears.

My gears all spun freely on their shafts, so that wan't the problem. The stepper motor did seem a little stiff, so I put a tiny drop of oil on either end of the shaft. Seemed to fix it at the time. I guess not.

I'll be disassembling both speedos and swapping over the odo stepper motor from the lower-mileage turbo (260k vs 517k). If *that* doesn't work, I'll try swapping the turbo's circuit board over too, after double-swapping the main driver IC (BA6140A). Why? All components between the two boards are identical, and the IC is the only one listed as "The BA6140A is a member of Atmels family of 4-bit single-chip microcontrollers." That must be where the counting circuits are for the speed sensor (48-slot Turbo, 12-slot N/A). Us the wrong chip, the speedo and Odo will be either 4 times too fast, or 4 times too slow.



I guess we shall see what happens.
Maybe I'll even take some better pics. I LOOOOOOVE pics.

^ Wow. Thanks a bunch! Right now, the Volvo has found itself to be my daily, so I think I'll check the fuel level sender once I get my Nissan up and running. Looks like a whole lotta fun .

I'll also have to order a fuel sock and the rubber seal for the whole unit for when I tackle it. Anything else I'm missing?

Also, I have a Yazaki unit. Small, delicate electronics intimidate me. I think I'll send it to repair after fixing my fuel level issue. I'll be lucky to get all this done by next year.

740 clusters are year specific, which makes them pretty hard to find the correct one. Mine was a 91 Turbo, one year only, though it bled over to early 92. I couldn't find a used cluster to save my life, hunted for a while. I used my phone with a GPS speedo app in the meantime. Had to drive around with nothing but the hole where the cluster was with my phone propped up in there.

Lol. Good to know it'll run without the cluster. I think I'm good enough at knowing speed by feel, although I will definitely not be testing that supposed skill.

What I am thinking about doing is buying an $80 cluster such as the following: https://www.ebay.com/itm/1747951092...eYW9W1ZaXNCrr08zZW_hVx8bhtNQnM-AaAtWFEALw_wcB from eBay, and work out shipping it straight to a repair shop like DNA Speedometers that will then send it to me. Not sure how much it'll cost me or if it's even a good idea, I will look into it when I have the time (and self-motivation).

It won't run for long without the cluster. Just as the 240 does, the 7-9 gets the alternator exciter circuit signal through the cluster. For whatever reason, the alternators used on the 7-9 do a better job charging without the exciter circuit than 240s do. If you are doing a lot of in town, slow speed driving you will soon have a dead battery without the exciter circuit hooked up.

A stuck fuel sending unit is common on the 7/9 series. The barrel the float slides up and down in may have popped off the upper section of the sending unit. That causes the float to stick. Another possibility is the contact on the float may have worn through causing a sharp edge that catches on the wire wrapped rods the float slides on. That is also a common problem.

2turbotoys said:

DNA Speedometers in Florida will do it, just have to ask. It's not listed on their website anymore. About $300 to reflow, replace caps, etc.

Click to expand...

Thanks for this, I'm looking to have my 760 cluster sent out.

2manyturbos said:

It won't run for long without the cluster. Just as the 240 does, the 7-9 gets the alternator exciter circuit signal through the cluster. For whatever reason, the alternators used on the 7-9 do a better job charging without the exciter circuit than 240s do. If you are doing a lot of in town, slow speed driving you will soon have a dead battery without the exciter circuit hooked up.

Click to expand...

This was my next question, as I ran into this exact situation in my 240. Maybe I can jumper the circuit, or temporarily throw a bulb in it.

I drove for 3 weeks with no cluster, everyday. But I had a large Optima battery that probably helped. It could start the car when it was at 11.9 volts.

leecatd8209 said:

Maybe I can jumper the circuit, or temporarily throw a bulb in it.

Click to expand...

That's all I did with a customer's 1989 740 Turbo. He said I could "take anything I wanted" before he took it to the scrapper, so I snagged the whole cluster. I didn't want it dying on the way, so I stuck a 194 bulb between the Power and Alternator terminals on plugs C and D. Worked fine. His only complaint was that he was afraid of getting a speeding ticket (no speedo, you see ). If you're going to drive it that way for a while, you may want to "re-bulbify" your oil light circuit too . Of course, that still won't tell you if you're out of gas, or overheating, or.......

daniels740 said:

Lol. Good to know it'll run without the cluster. I think I'm good enough at knowing speed by feel, although I will definitely not be testing that supposed skill.

What I am thinking about doing is buying an $80 cluster such as the following: https://www.ebay.com/itm/1747951092...eYW9W1ZaXNCrr08zZW_hVx8bhtNQnM-AaAtWFEALw_wcB from eBay, and work out shipping it straight to a repair shop like DNA Speedometers that will then send it to me. Not sure how much it'll cost me or if it's even a good idea, I will look into it when I have the time (and self-motivation).

Click to expand...

I have one from an 89 740t if you want a cheap cluster to send off. $30 plus shipping

MasterBlaster said:

If you're going to drive it that way for a while, you may want to "re-bulbify" your oil light circuit too . Of course, that still won't tell you if you're out of gas, or overheating, or.......

Click to expand...

AYY! Thank you! My cluster doesn't perform most of those functions right now anyway.

Update:
The other day, I replaced my fuel level sender which fixed my fuel level issue. Huge thanks to MasterBlaster for the pics.

Anyway, today, 2 days later, I smelled a fuel leak which I quickly found out was coming from the pressurized fuel hose. I must've nicked it during reinstallation or it must've cracked. In any case, it didn't leak at first and developed into quite the 'spray.'

I was able to fix it by cutting the affected area near the end of the hose and pulling it forward, as soon I discovered the issue. That's for the night but I must soon replace the hose (only about 8" long). Does anybody know its diameter + pressure rating?

Here's a pic of the hose in question (circled in red):


Thanks in advance.

PS: I am working on my cluster right now, too, so thanks to all those who helped regarding that as well.

That is usually 12mm id hose. Rated for fuel injection it will be something like a 95psi rated hose. But that only has to be rated for low pressure fuel as it's not a high pressure pump in the tank if you have the two pump setup.

white855T said:

Your instrument cluster is so old at this point that it needs all the solder joints reflowed so all of your gauges will work properly. There use to be some places that fix 7/9 clusters but I don't know of any currently.

Click to expand...

Late to this party, but I used Overseas Speedometer probably 20 years ago to fix the flickering speedometer on my '86 745T. It's still working fine. IIRC, they reflowed the solder joints. Can't remember how much it was and what difference would that make 20 years later anyway.

Looks like they may still be in business.
http://www.speedometer.com/index.html

Thanks. I just used fuel hose from the auto parts store. Think it's rated for 50psi. It will do. In fact, when I removed the old hose, I discovered I could practically break it apart with an acute bend. That tells me there wasn't too much pressure on that hose -- otherwise it would have blown up prior to now.

Also, I was able to get my odometer repaired. Turns out, the 'ancient grease' had in fact dried up causing one of the gears to completely seize. This blog page, from which MasterBlaster borrowed a photo, was extraordinarily helpful. Now I have about 13 miles and another 300,000 ahead of me. I think I felt more joy than a child on Christmas morning seeing the trip meter move 1/10 of a mile at a time. Surprised I even made it back home with my eyes glued to the cluster.

I'll end with this - It's truly magical to see the first mile roll over in a 32 year old car. Not many people will experience it (even if it's not exactly true.) I owe many thanks to those who made it possible by taking the time to impart their knowledge.