89 240 Wagon...

I just replaced the clock in my speedo cluster with the tachometer. Attached the red & white wire to the single male spade on the back of the tach and, voila!

Now the questions...

On the top of the back of the tachometer, there is a plug-in that has 3 wires. One says positive, one negative, and one of them has a little light bulb attached. I'm assuming the light bulb is for the "shift up" indicator. But what about the positive & negative wires? What do they do?

Also, the tachometer reads Zero rpm when the engine is at idle. Obviously the engine does not idle at zero rpm. When I accelerate the engine, the tach responds - only about 700-800 rpm slower than the engine is actually running.

Is there any way to adjust the tachometer?


Thanks so much!

 

From what I have read, and thus assume with the info you have given, the negative and positive wires supply power to a little clock that goes hand in hand with the big tach, it's a kit (or was an optional kit). You know the little plastic covers to the right of your instrument cluster (assuming it is a left-hand drive) that's where the little clock goes. Someone else should come on here who know more about them, but I'm sure that is where the positive and negative cables go at least.

 

yeah, the clock fits in the square closest to the steering wheel. nice little analog quartz clock. our 1987 240GL came with the tach and clock from the factory.

 

Yeah, must be standard on the Grand Luxe. I have heard about problems with those small clocks not working due to poor contacts in the back. Have you had any problems?

 

ours has been fine. no electrical problems at all on that 25 year old car with 400K miles. ok, flaky tail lights, hahahaahah. i had to replace them a couple years ago because they'd suffered plastic rot and were letting rain water get into the trunk. and the 'bulb out' indicator has been on pretty much full time for the last 10 or 12 years. but other than that.... no electrical problems.

 

Thanks for the info guys!

I'll just assume - when looking at the tach - that I'm actually running 700-800 rpm higher than it registers. Even so, it really doesn't matter much, as I have an auto transmission.

Thanks again.

 

one thing I'd check is if the tach is getting the proper power. I'm looking at the schematic for the instrument panel on a 92 740/940 (because my book just HAPPENED to be on that page) and the power to the panel is on the blue/red wire to pin 4 on connector D(the 4 pin in the middle), that wire comes from the 15R pin on the ignition key. I'd measure this and ensure its 12-14V relative to the dashboard ground terminal .... *wait a minute*, you have a 240. argh, I don't have a decent set of schematics for a 240....

anyways, I'd find the power to the instrument panel and make sure its a clean 12 to 14V relative to the ground to the instrument panel. The tach itself has three wires into it, ground, power, and the pulse signal from the ignition. on a 740, that pulse signal is on a brown-white wire, and it pulses to ground.

the tach itself is, more or less, an 'integrator' circuit that produces a higher voltage when the ignition pulses are faster, and a volt meter that displays that voltage. inside, there's *probably* an adjustment screw on the spring that sets the zero point. I've never taken one apart, and I know from past experience with meters in general, they are pretty darn delicate inside. This also could be an electronics problem inside the tach, perhaps a bad capacitor or something in that 'integrator' circuit that converts the pulse timing to a voltage.

hey! Volvo 240 Tach and Small Clock
(that clock appears to be missing the square bezel to fit on a later model 240's dash)

 

LOL, you're in the same boat as me. I just *have* to know what I'm turning or it drives me insane. Wasn't too pleased to find out that 80mph turns 3K...but expected it...kinda...my mind and ears are used to hearing pissed off Chevy LS motors that don't turn nearly what this car does.

Thankful that my tach worked great, first try. Had the ENTIRE interior out of my 240 today, ran the carpet cleaner, took out everything I could for cleaning, and have just started to put it all back together. Hazard lights don't work all the time...but other than that, I'm pretty stoked on my $800 Volvo. Oh, and Burn...my 7 year old shattered the passenger side door pocket. Smashed the hell outta it.

Numerous fragments...some large, some small! (points for whoever can tell me what movie that line is from)

 

those door pockets are really fragile on 240s'. highly recommend the IPD reinforcers for them. or just leave them out, kids seem to think they HAVE to use their feet to open the door and its a really hard habit to break.

re; the Chevy LS, sure, twice as many cylinders, 3 times the displacement, and it turns over slower. yeah, well, whadjaexpect?? 80-90mph is about as fast as you wanna cruise in a 240 anyways... they typically top out flat out somewhere just north of 100MPH. My old Jetta GLI turned over 3000 rpm at 62mph, close to 4000 RPM at 80MPH, and liked to go 110mph all day long, eeek. whadda ticket trap that one was, heh.

 

I would suspect the tach itself; sounds like you did everything right. We already know that Volvo speedos are unreliable..

Just curious - how do you know that the engine is turning 700-800 rpm slower if you don't have a tach?

 

Yeah, I took my passenger door pocket off right away. I'm thinking on buying some PVC or similar plastic and doing my own reinforcing job. I'll do a write up on that for sure. Heck, I might take my pocket to a smitty and tell them to make me and indestructible replica and tell the kids to jump on that...

 

^^I didn't do a photo write up, but I reinforced my set by fiber glassing the interior w/ fiberglass mat...not the fabric. Has held up through one teenage daughter and a wagon of cohorts!

 

Woah! I like that idea, sounds easy. How did you do that?

 

It's really easy. Take the map pocket off and do all the work on the back side.
They always seem to break where there is no bracing, so lay down a good coat of fiberglass resin with a cheap paint brush....

Before you mix the resin, cut a correctly sized patch of fiberglass mat...this stuff...

Notice how the fibers run in every direction? Much stronger than fiberglass cloth...the cloth is prettier but we want strength...here's cloth for comparison.

After you lay the mat on the wet resin, paint another coat on top. The trick is to completely saturate the mat. It won't look professionally perfect, but it is strong as anything!!

 

Sweet, thanks, nice mini write-up mid thread that is way off topic...
I would think after you paint the fiber glass and trim up the edges, it would look like a job well done that no one else is going to notice.

 

Yes, I generally hand sand with 50 grit and paint w/ SEM black trim paint.

 

SEM Black Trim Paint *rocks* ... I used that to touch up a peeled spot of the black on the tailgate window strip on my 92 745T, and dang, wish I'd stripped the whole piece and painted it, and not just hte part that was peeled, heh. from 10' away, looks new. from 4' away, you can see where i touched up vs the rest of the 19 yr old original trim.

 

Well... When the car is idling, the tachometer shows Zero RPM. I assume the engine idles at roughly 700-800 rpm. That's all I mean.

 

well, if you know an electronics engineer or technician who has an oscilloscope, you could probably get him to hook his scope up to the signal into the tach and see what it looks like. should be clean evenly spaced pulses 0 - +V - 0 - +V ... from the ignition module. of course, it would be just about as easy to hook up a spare tach (it just needs that pulse signal, plus ground and power.)