Minor Electrical Gremlin?
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Cargo Master
Joined: Dec 2004
Posts: 3,362
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From: Florence, SC
Minor Electrical Gremlin?
When I turn on my vents (from the HVAC panel), my tachometer jumps a second. When I turn them off again, same thing happens. Otherwise, it works fine. I never noticed this happening before; is this normal?
Also, my speedometer cable is "shaky" until about 30 MPH.
My cab was removed for painting a few months ago, so something could be loose. Any ideas?
Also, my speedometer cable is "shaky" until about 30 MPH.
My cab was removed for painting a few months ago, so something could be loose. Any ideas?
Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
Moat likely, the speedometer cable needs lubrication. I cannot think why the tachometer would jump, since the vents are vacuum controlled. Does the engine momentarily change sound or speed when you do this or is it just the tachometer?
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Cargo Master
Joined: Dec 2004
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From: Florence, SC
When I move the lever over to turn on or off the vents, the tachometer jumps for a second but the engine doesn't change at all.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
The tach issue may be a poor ground in the cab. Try the cigar lighter and see if it does it. The HVAC fan and the lighter are the two highest current draw items in the cab, and if their ground isn't good the current will go back another way, like via the tach's ground.
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Cargo Master
Joined: Dec 2004
Posts: 3,362
Likes: 22
From: Florence, SC
The tach issue may be a poor ground in the cab. Try the cigar lighter and see if it does it. The HVAC fan and the lighter are the two highest current draw items in the cab, and if their ground isn't good the current will go back another way, like via the tach's ground.
Do you know where the grounds are in the cab?
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
Lead Driver
Joined: Nov 2013
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The tach issue may be a poor ground in the cab. Try the cigar lighter and see if it does it. The HVAC fan and the lighter are the two highest current draw items in the cab, and if their ground isn't good the current will go back another way, like via the tach's ground.
Does your truck have the AC positions on the selector panel? When you select VENT, are you switching directly from the OFF position? What about when you move the lever to VENT from the other direction (HEAT or DEF)? The reason I'm asking is to see if you are also turning on the fan in the process.
If the fan ground (G701) is suspect, you can easily rig up a test jumper to a good ground via the case of the cigar lighter. Both components are grounded through G701, so if it has worked loose, you can test it by grounding the cigar lighter case.
Gary provided a link in post #6 with more details about G701.
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Moderator
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From: Denver Metro Area, CO
David was suggesting lubricating the speedometer cable, not the speedometer itself.
Ford had special lube for that, I think I've used white lithium grease or maybe some sort of graphite thing, don't remember.
Ford had special lube for that, I think I've used white lithium grease or maybe some sort of graphite thing, don't remember.
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Cargo Master
Joined: Dec 2004
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Likes: 22
From: Florence, SC
Yes.
Yes.
No. The tachometer does not "jump" if I do this. I suppose this means it is the fan ground, right?
Thanks to you and Gary's garagemahal! By looking at Gary's diagram, it appears that the ground wire is bolted behind the instrument panel near right hand side of the radio. Is that right?
Of course! Where do gain access to the speedometer cable in order to lube it?
If the fan ground (G701) is suspect, you can easily rig up a test jumper to a good ground via the case of the cigar lighter. Both components are grounded through G701, so if it has worked loose, you can test it by grounding the cigar lighter case.
Gary provided a link in post #6 with more details about G701.
Gary provided a link in post #6 with more details about G701.
Originally Posted by ctubutis
David was suggesting lubricating the speedometer cable, not the speedometer itself.
More Turbo
Joined: May 2008
Posts: 585
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Yep, white lithium grease works well. Don't use regular wheel bearing or gun grease...its too thick and sticky in cold weather. To lube the cable you'll need to remove the instrument cluster. Once the cable housing is disconnected from the cluster, grab the cable end inside the housing and pull it out. Give it a good coating of grease and slide it back into the housing.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
There is also a graphite-based lube that the parts stores used to carry for speedo cables. That is what I've always used. And, Dad taught me to only lube the bottom half of the cable. Otherwise you might get too much lube and it can get into the speedo itself. But, as you slide the cable back in the lube on the bottom half lubes the top of the housing so everything gets lubed.
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Cargo Master
Joined: Dec 2004
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From: Florence, SC
There is also a graphite-based lube that the parts stores used to carry for speedo cables. That is what I've always used. And, Dad taught me to only lube the bottom half of the cable. Otherwise you might get too much lube and it can get into the speedo itself. But, as you slide the cable back in the lube on the bottom half lubes the top of the housing so everything gets lubed.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
Now, it is remotely possible that Ford did us a favor by allowing both the upper and lower cables to come out at the transducer. So, I would pull them off there loooooong before I pulled the speedo out, and see if the inner cables will come out from there as it would be a lot easier.
Hotshot
Joined: Mar 2013
Posts: 14,255
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From: Phoenix, Az.
I just ran across Ford's PTFE lubricant for driveshaft slip yoke splines is also recommended by them to lube speedo cables. It's still available from your local Ford Dealer.
Ford Motorcraft part number XG8A is a 1 lb. container.
Ford Motorcraft part number XG8 is a 3 oz. tube.
Ford Motorcraft part number XG8A is a 1 lb. container.
Ford Motorcraft part number XG8 is a 3 oz. tube.
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