Question on Gas Guage - The 1947 - Present Chevrolet & GMC Truck Message Board Network

kilomanjaro · 04-18-2002, 12:49 PM

Does anyone have any info on making these work. I have about 10 of them and they all have the needle at different places on the guage. Are they all broken? I try and align the needle at zero before i put them in, but they never indicate correctly. any help would be greatly appreciated. thanks
john

bigvinnie · 04-18-2002, 02:20 PM

first of all, how did you come to have 10 gas guages...??? Anyway, I doubt all of em are shot, so you probably need to look at the tank sender and the wiring running to your dash... pull the seat forward and check that the brown wire is connected, and follow it along the floor to make sure it's in good shape... if it checks out ok, you probably have a bad sending unit... good luck.

------------------
'72 short step, 350, 700R4, tilt, ps, pdb, a/c, lowered coils, etc., other work in progress... San Diego, CA
http://www.ixpres.com/vlusardi/chevtrk.htm

kilomanjaro · 04-18-2002, 04:17 PM

sender is new, i guess i kind of just ended up with all the guages from all the trucks i have parted out.
john

*Fast68Chevy* · 04-18-2002, 04:18 PM

kilomanjaro-
they are not suppoosed ot return to E, the needles are free floating not connecte dot anything, they react to energy waves pulling on them there are pole piece type of deals on the needle inside the gause assembly, that variable energy(controllled by sending unit) pulls or pushes on which moves the needle, if you take one apart you will see how it works, you have enough around to take one apart and learn on. thats the only way to learn, and who doesnt have a bunch of gauges laying around ? i thought everyone did ?? and plus dashes from all kinds of other makes and models and years..

good luck!

------------------
Randy- Lincoln, IL
r68c30@hotmail.com
-71 C-10 350/CH465/3.07
-84 Z28 Camaro 5.0L 700R4, 3.73
-84 Firebird SE 2.8L T-5
-82 Firebird 350 4bolt (TBL)/TH350
buy/sell/hoard/trade most any GM vehicle parts of any kind
-parting out: '81 Cutlass Supreme Brougham
*Paint is overrated
© RSS Enterprises 2000

Longhorn Man · 04-18-2002, 04:18 PM

You are not getting power to the back of the guage. If there is no 12V, it won't move at all regardless of the sending unit.

------------------
'69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man
I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite.
If you need a pic posted, E-mail me at longhornmail@yahoo.com
Andy, in Columbus Ohio

67Blacksheep · 04-18-2002, 08:29 PM

Kila-
I have similiar probs. Only mine works when it feels like it!! I used to think if it was registering at all, I had some fuel. I ran out of gas 2 weeks ago using this theory!! I have another guage, but haven't tried switching it out. I fear it's the sender!

------------------
67 Chevy C20 LB Stepside,
350 4-bolt with goodies.

DANGF · 04-18-2002, 09:38 PM

I just replaced my sending unit and checked my fuel gage. It is not a hard task. If you are getting readings sometimes and not continuosly then there is either a connection failure or a bad sending unit. the gage reads when there is a signal. I would bet on the sending unit. You can test the gage by doing a continuity check across the leads on the back of the unit. This will flow current and force the needle to move. The gage is bad if it does not move with this test. The sending unit has a copper or brass contact that swings across a linear resistor and this causes metal wear. As old as these trucks are this is a very common failure point. You can also check it with an ohm meter. You should read from 90 ohms to zero accross the resistor. DO THIS CHECK WITH THE SENDING OUT AND AWAY FROM THE GAS TANK. Make sure that both of your crimp lugs on the sending unit wire is solid.
If these things all check out then you should be reading fuel accurately. Good luck.

TC70C10 · 04-19-2002, 07:51 AM

You may also have a ground problem. I had to run a ground to one of the posts on the gauge itself. I've never had a problem since. That metal backplate has a tendency to rust and after several times on and off, will not fit tightly.

------------------
1970 Chevy C-10 350,3 spd
1998 Pontiac Firebird
1999 GMC Envoy

Harvest,AL 35749

JimKshortstep4x4 · 04-19-2002, 08:07 AM

John,

It sounds like you just need to adjust the needle to zero. We have adjusted them a couple of ways. The method that I feel works best is to hook the gauge up and feed the gauge with a known 90 ohm signal. This should have the gauge reading at full. Install the needle at full and then ground the tank wire. When the wire is grounded
the gauge should be reading at empty.

If you don't have an ohm calibration unit you can test your tank sender with an ohm meter to make sure it reads 90 ohms and use it for the reference.

Jim

04-18-2002, 12:49 PM	#1
kilomanjaro Senior Member Join Date: Mar 2001 Location: From Kansas now in Palmer, Alaska Posts: 807	Question on Gas Guage Does anyone have any info on making these work. I have about 10 of them and they all have the needle at different places on the guage. Are they all broken? I try and align the needle at zero before i put them in, but they never indicate correctly. any help would be greatly appreciated. thanks john __________________ 63 Buick Wildcat 425 72 Chevy Blazer CST 72 Chevy C10 Cheyenne 00 Ford F-350 Super Duty 7.3L 09 Dodge Challenger SRT-8 10 Ford Expedition Limited

04-18-2002, 02:20 PM	#2
bigvinnie Registered User Join Date: Aug 2001 Location: escondido, ca 92026 Posts: 1,222	first of all, how did you come to have 10 gas guages...??? Anyway, I doubt all of em are shot, so you probably need to look at the tank sender and the wiring running to your dash... pull the seat forward and check that the brown wire is connected, and follow it along the floor to make sure it's in good shape... if it checks out ok, you probably have a bad sending unit... good luck. ------------------ '72 short step, 350, 700R4, tilt, ps, pdb, a/c, lowered coils, etc., other work in progress... San Diego, CA http://www.ixpres.com/vlusardi/chevtrk.htm __________________ '72 short step, 350, 700R4, tilt, ps, pdb, a/c, lowered coils, etc., other work in progress... San Diego, CA 72 Stepside Project

04-18-2002, 04:17 PM	#3
kilomanjaro Senior Member Join Date: Mar 2001 Location: From Kansas now in Palmer, Alaska Posts: 807	sender is new, i guess i kind of just ended up with all the guages from all the trucks i have parted out. john __________________ 63 Buick Wildcat 425 72 Chevy Blazer CST 72 Chevy C10 Cheyenne 00 Ford F-350 Super Duty 7.3L 09 Dodge Challenger SRT-8 10 Ford Expedition Limited

04-18-2002, 08:29 PM	#6
67Blacksheep Registered User Join Date: Mar 2002 Location: Ohio Posts: 135	Kila- I have similiar probs. Only mine works when it feels like it!! I used to think if it was registering at all, I had some fuel. I ran out of gas 2 weeks ago using this theory!! I have another guage, but haven't tried switching it out. I fear it's the sender! ------------------ 67 Chevy C20 LB Stepside, 350 4-bolt with goodies. __________________ '94 GMC Seirra Ext. Cab '67 Formula Firebird '89 GSX-R 750

04-19-2002, 07:51 AM	#8
TC70C10 Registered User Join Date: Nov 2001 Location: Harvest, AL 35749 Posts: 337	You may also have a ground problem. I had to run a ground to one of the posts on the gauge itself. I've never had a problem since. That metal backplate has a tendency to rust and after several times on and off, will not fit tightly. ------------------ 1970 Chevy C-10 350,3 spd 1998 Pontiac Firebird 1999 GMC Envoy Harvest,AL 35749 __________________ 1981 K5 Blazer 305, 4spd, 4x4, 4" Lift, custom bumpers, Warn 9.5 Ti Winch 1995 T10 Blazer 4.3L 4x4 (Son's) 2004 GMC Envoy 4.2L 2WD 2005 GMC Sierra Crew Cab Z71 4x4 5.3L 240 Fun Finder Travel Trailer Harvest, AL 35749

04-18-2002, 04:18 PM	#4
Fast68Chevy Account Suspended Join Date: May 2000 Location: IL Posts: 0	kilomanjaro- they are not suppoosed ot return to E, the needles are free floating not connecte dot anything, they react to energy waves pulling on them there are pole piece type of deals on the needle inside the gause assembly, that variable energy(controllled by sending unit) pulls or pushes on which moves the needle, if you take one apart you will see how it works, you have enough around to take one apart and learn on. thats the only way to learn, and who doesnt have a bunch of gauges laying around ? i thought everyone did ?? and plus dashes from all kinds of other makes and models and years.. good luck! ------------------ Randy- Lincoln, IL r68c30@hotmail.com -71 C-10 350/CH465/3.07 -84 Z28 Camaro 5.0L 700R4, 3.73 -84 Firebird SE 2.8L T-5 -82 Firebird 350 4bolt (TBL)/TH350 buy/sell/hoard/trade most any GM vehicle parts of any kind -parting out: '81 Cutlass Supreme Brougham *Paint is overrated © RSS Enterprises 2000

04-18-2002, 04:18 PM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	You are not getting power to the back of the guage. If there is no 12V, it won't move at all regardless of the sending unit. ------------------ '69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it. FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite. If you need a pic posted, E-mail me at longhornmail@yahoo.com Andy, in Columbus Ohio

04-18-2002, 09:38 PM	#7
DANGF Registered User Join Date: Mar 2002 Location: Florence,SC,USA Posts: 6	I just replaced my sending unit and checked my fuel gage. It is not a hard task. If you are getting readings sometimes and not continuosly then there is either a connection failure or a bad sending unit. the gage reads when there is a signal. I would bet on the sending unit. You can test the gage by doing a continuity check across the leads on the back of the unit. This will flow current and force the needle to move. The gage is bad if it does not move with this test. The sending unit has a copper or brass contact that swings across a linear resistor and this causes metal wear. As old as these trucks are this is a very common failure point. You can also check it with an ohm meter. You should read from 90 ohms to zero accross the resistor. DO THIS CHECK WITH THE SENDING OUT AND AWAY FROM THE GAS TANK. Make sure that both of your crimp lugs on the sending unit wire is solid. If these things all check out then you should be reading fuel accurately. Good luck.

04-19-2002, 08:07 AM	#9
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	John, It sounds like you just need to adjust the needle to zero. We have adjusted them a couple of ways. The method that I feel works best is to hook the gauge up and feed the gauge with a known 90 ohm signal. This should have the gauge reading at full. Install the needle at full and then ground the tank wire. When the wire is grounded the gauge should be reading at empty. If you don't have an ohm calibration unit you can test your tank sender with an ohm meter to make sure it reads 90 ohms and use it for the reference. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC



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