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Author Topic: '88 K75 gauges don't work  (Read 10040 times)

Offline Bull Gear

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'88 K75 gauges don't work
« on: August 27, 2016, 06:09:01 PM »
Sorry for the onslaught of posts, but I only have a couple weeks before I try to ride this thing into Canada.
1988 K75S
I bought it from a long time owner. It ran, sorta, but he hadn't ridden it much lately so I stripped it down and performed just about every maintenance task I could come up with. It runs great now, but it's still on the operating table because the gauges don't work. Never touched 'em nor any connectors except for the fuel tank and air meter. I'm almost positive they worked when I bought it. Speedo was replaced around 10K, showing 15K now.
All the indicator lights, gear display, lights, turn signals, etc seem to be working.
At first I thought... Ah, I forgot to connect that ground wire on the master cylinder. Unfortunately, that didn't do it.
I searched and found numerous posts about gauge cluster flakiness but nothing that really matched my symptoms.

Now what?
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  • Locust, North Carolina
  • 1988 K75s

Offline Elipten

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Re: '88 K75 gauges don't work
« Reply #1 on: August 27, 2016, 06:22:34 PM »
What specifically is not working?  Odometer? Speedometer, tachometer?  And etc?


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  • San Antonio, TX
  • 1990 K75RT

Offline Bull Gear

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Re: '88 K75 gauges don't work
« Reply #2 on: August 27, 2016, 06:34:31 PM »
Gauges = Speedometer and Tachometer. Probably a safe bet that if the speedo isn't reading then the odometers aren't either but I haven't verified that.
Everything else in the instrument pod works except for the high beam indicator bulb (headlamp works fine on high and low beam).
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  • Locust, North Carolina
  • 1988 K75s

Offline Chaos

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Re: '88 K75 gauges don't work
« Reply #3 on: August 27, 2016, 06:53:04 PM »
They all do that!   (sorry, couldn't help myself :hehehe)
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  • sw ohio
1987 K75S    VIN 0231
Original owner, Original litter
200,000 miles (plus or minus) and 5 paint jobs
sold 6/23
2023 Ural 2WD sidecar (BMW's bastard step child)

Offline Martin

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Re: '88 K75 gauges don't work
« Reply #4 on: August 27, 2016, 06:55:42 PM »
Try cleaning the multi pin connector on the back of the instrument pod with a product called Deoxit.
Regards Martin
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  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Bull Gear

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Re: '88 K75 gauges don't work
« Reply #5 on: August 27, 2016, 08:29:42 PM »
I'll run down to Guitar Center and grab some Deoxit tomorrow.
What else should I look at while I have the cluster out?
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  • Locust, North Carolina
  • 1988 K75s

Offline Chaos

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Re: '88 K75 gauges don't work
« Reply #6 on: August 27, 2016, 09:11:22 PM »
Lots of into on fixing K speedos.  Scroll down to "instrument cluster" http://www.ibmwr.org/ktech.shtml

Also, if the trip and or regular odometer don't work it may be the gears, they're made of compressed applesauce and tend to lose their teeth.  Less common but very annoying is the sensor ring coming off the crown gear in the final drive, and you get no signal to the cluster. 
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  • sw ohio
1987 K75S    VIN 0231
Original owner, Original litter
200,000 miles (plus or minus) and 5 paint jobs
sold 6/23
2023 Ural 2WD sidecar (BMW's bastard step child)

Offline Bull Gear

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Re: '88 K75 gauges don't work
« Reply #7 on: August 27, 2016, 11:13:19 PM »
I'll give it a shot. Seems strange that both gauges are totally dead, though.
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  • Locust, North Carolina
  • 1988 K75s

Offline Martin

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Re: '88 K75 gauges don't work
« Reply #8 on: August 28, 2016, 12:15:21 AM »
The gears are made of cheddar cheese and they won't stop the odometer or tacho from working. I was also told once, that the lubricant used on the gears turns them to cheese, and you should only lube them with special grease. No idea whether it is true or not and have no idea what the grease is.
Regards Martin.
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  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Chaos

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Re: '88 K75 gauges don't work
« Reply #9 on: August 28, 2016, 10:15:46 AM »
Quote from: Bull Gear on August 27, 2016, 11:13:19 PM
Seems strange that both gauges are totally dead, though.

Agreed.  Usually it's the speedo.   Only time my tach stopped is when the faceplate warped and the needle stuck to it. 
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  • sw ohio
1987 K75S    VIN 0231
Original owner, Original litter
200,000 miles (plus or minus) and 5 paint jobs
sold 6/23
2023 Ural 2WD sidecar (BMW's bastard step child)

Offline Bull Gear

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Re: '88 K75 gauges don't work
« Reply #10 on: August 28, 2016, 08:36:52 PM »
Got the tach working. Thanks for the Deoxit tip.
Speedo is still dead... no gauge, odometer, or trip reading at all.
Pulled the instrument pod. The connectors look good and clean. Inside looks nice. No surprise since this bike has been mostly kept in the dry.
Cleaned both connectors and pins on the back of the cluster with Deoxit (a few times).
Checked the 12 v feeds (pins 1 & 6) and grounds (pins 13 & 18). They're good.
Cleaned the 3 pin internal connector on the back of the speedo with Deoxit (a couple times). Put a tiny bit of twist on the pins.
Pulled the speed sensor from the final drive. It was clean.
Measured resistance through the signal circuit from the cluster connector (across pins 22 and 23). Measured about 275 ohms so no open circuit in sensor, wires, or connectors.
Wiggled wires and connectors and thumped the cluster once or twice.
Nothing.

My test running is being done on the center stand in 2nd gear at high idle with an occasional throttle blip just to be sure.

I'm stumped. Don't know what else I can do. Any other suggestions?


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  • Locust, North Carolina
  • 1988 K75s

Offline Martin

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Re: '88 K75 gauges don't work
« Reply #11 on: August 28, 2016, 11:02:16 PM »
Check the sensor connection, and the sensor on the rear final drive it can get dirty.
Regards Martin.
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  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Laitch

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Re: '88 K75 gauges don't work
« Reply #12 on: August 29, 2016, 12:38:48 AM »
Quote from: Bull Gear on August 28, 2016, 08:36:52 PM
I'm stumped. Don't know what else I can do. Any other suggestions?
Well, you've done due diligence, that's for sure.

Did you read the one about the speedometer needle being seated so low on its shaft it was touching the faceplate and couldn't overcome the friction? The unit started working after the needle was raised slightly.
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline Chaos

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Re: '88 K75 gauges don't work
« Reply #13 on: August 29, 2016, 08:35:13 AM »
Also the trick of holding a cheap soldering gun close to the rear sensor out of the final drive.  The 60 cycle current simulates the sensor ring and should activate the speedo and odo, I forget what speed it reads. 
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  • sw ohio
1987 K75S    VIN 0231
Original owner, Original litter
200,000 miles (plus or minus) and 5 paint jobs
sold 6/23
2023 Ural 2WD sidecar (BMW's bastard step child)

Offline Bull Gear

  • Motobrick Curious
  • Posts: 23
Re: '88 K75 gauges don't work
« Reply #14 on: August 29, 2016, 11:12:05 AM »
Got it this time. HURRAY!!!
I pulled the speedo off the back plate so that I could remove the little circuit board on the bottom and clean the 4 pins into the board with Deoxit. Works like a champ now.

Thanks for all the help.
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  • Locust, North Carolina
  • 1988 K75s

Offline Laitch

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Re: '88 K75 gauges don't work
« Reply #15 on: August 29, 2016, 11:20:19 AM »
 :clap: Thanks for the update!
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline Elipten

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Re: '88 K75 gauges don't work
« Reply #16 on: August 29, 2016, 04:03:28 PM »
Way to go!


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  • San Antonio, TX
  • 1990 K75RT

Offline Martin

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Re: '88 K75 gauges don't work
« Reply #17 on: August 29, 2016, 04:17:46 PM »
 :clap: :2thumbup:
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  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.
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