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G80 speedo issues.

ZVOLV

ZVOLV

<Master Tech>
Joined
Nov 19, 2002
Location
California
I installed a G80 into my 1990 240 without ABS. I trimmed the ring down from 48 window to 12 window as members here suggested. I used the original differential cover and I got NO Speedo operation. Just a little flicker here and there.




TODAY, I installed an aluminum G80 diff cover. Now my speedometer reads 60mph by the end of first gear!!!

What are my options here?



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Nah, that's just pointing out the obvious.

Seriously though, you're always coming on here as the prophecy of expert advanced electrical engineering diagnostics with professional tools and what not. This one single issue you're having is a place where a scope would come in handy to see what's going on.

What am I missing here?
 
There's a speedo calibrations thread floating around here, use a potentiometer to replace a single resistor on the speedo motor board and you can adjust the speed up and down.
 
My guess would be that it's reading the G80 body as extra pulses. Try shimming the sensor further out?

If you can look at the signal in the scope and you have clean, evenly spaced pulses - you can get gadgets to resample those pulses at a fixed ratio and make the speedo read whatever you need it to.
 
Uncleknucklez said:
There's a speedo calibrations thread floating around here, use a potentiometer to replace a single resistor on the speedo motor board and you can adjust the speed up and down.
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This should be that thread: http://www.forums.turbobricks.com/showthread.php?p=5624342#post5624342

I actually did connect a portable snap on labscope to it after the G80 install on the stock 1990 240 non ABS diff cover and got NOTHING! I was hoping the airgap was wrong and the aluminum diff cover would space it out properly, but it reads wayyy too fast.

Solutions that have been suggested to me have been to play with the gap, reverse polarity or the wires, try a different sensor, to possibly messing with calibration of the gauge.
 
The earlier 90-91 type sensor that's a single blade instead of 2 works with 12teeth and and the aluminum cover. They used a similar, but slightly different aluminum cover 90-91. Sensor (different) mounts the same in either cover, 92+ cover has the magnet and oil filter built into it....


...




Labscobe

*squirrel*
 
When I installed a g80 in my 91 240 without abs, did exactly as you did and cut the teeth down to 12 but I had to space my sensor out with a washer. Everything has been working flawlessly since.
 
I noticed this sensor had two blades. Year/model is unknown but it had that filter/baffle thing in it.

Which model can I get this sensor from? G80 in a 90-91 may be hard to come by....
 
I still wonder if the G80 body is getting picked up by the sensor. I would try the spacing first, then the sensor type change. I bet if you scope it right now you'll see a very dense, very messy pulse train.
 
I scoped the sensor before pulling it apart, just as practice, over a year ago on this car. I was able to capture a clean sine wave with increasing voltage and frequency with speed. It's the same as any ABS sensor that is NOT a hall effect.

I may just do some tests with a multimeter set to AC voltage or frequency.

I really hope I can find a sensor that will work with my new alum cover!
 
ZVOLV said:
I really hope I can find a sensor that will work with my new alum cover!
Click to expand...

I really hope you do as well, I have an 86+ cluster in my 80, and have the 940 sensor in the aluminum cover, with a G80, and the tone ring cut the same as yours. I can't figure out why this wouldn't work, but it won't.

I still haven't tried to space it, I guess that should be my next stop. I just really need the signal for the mildly annoying high idle on occasion. I've really grown to like my digital speedo on my phone.
 
ZVOLV said:
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propav8r said:
Why did you grind all the teeth off the G80 and weld on a ring rather than just grind off the unnecessary teeth and use the aluminum cover and stock sensor? Seems silly.
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I'm confused, there is another way to get all of these parts to work with a 240 speedo? I was firmly under the impression that a 940 sensor, on a 12 tooth ring (cut down G80 ring) and the 86+ 240 speedo would all play nice together?
 
I removed the 48 tooth tone ring from the G80 and cut it down to 12 windows. I didn't grind the diff or weld anything. I just knocked the ring back in place.

The high idle is annoying and my MPG may be suffering too so I want to get this figured out.
 
Uncleknucklez said:
I'm confused, there is another way to get all of these parts to work with a 240 speedo? I was firmly under the impression that a 940 sensor, on a 12 tooth ring (cut down G80 ring) and the 86+ 240 speedo would all play nice together?
Click to expand...

I remembered incorrectly. I was thinking about the time I had to put an ABS open diff in a non-ABS 240. On that car, the tone ring is cast into the diff itself. There's not cage/ring to swap.

I thought he had ground off ALL the teeth, then welded a 12-tooth ring over top.
 
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