Gas gauge not working???

74Runneer · Jun 17, 2013

Hi, im new to this forum. I have a 1974 Roadrunner with a 318 in it. Ill do a post on my car later, but what i need help with is figuring out how to get my gas gauge to work right. It reads completely empty and doesn't move at all when the car is turned on. I checked the sending unit in the tank and that was good and the float was working. Also my gauge next to it (i forgot maybe temp, oil pressure or battery) isnt working either). Im thinking that this is a dash gauge issue but im not sure. I checked the fuses under the dash and all 8 looked good. The wiring looks like a rat nest under there but i dont want to spend the time and money to rewire everything. There appears to be a wire or two that arent attached to anything but that may be because there are 3 more gauges added (oil pressure, battery, and temp). Anyways how can i test my gauges and/or tell if the wire is just not hooked up. Does anyone know the symptoms of a bad voltage limiter and/or if they can be easily replaced? What do you guys think?

Also my speedo gauge is off. When it reads 50 im actually going 40 when it reads 70 im going 50. The wheels and tires arent stock but the rims measure the same diameter as the stock rims. Im not sure if the rear end is stock. Im unsure of the gearing. Sorry for the lack of information but id like to fix it.

Mopar-Charger · Jun 17, 2013

"There appears to be a wire or two that arent attached to anything but that may be because there are 3 more gauges added (oil pressure, battery, and temp). Anyways how can i test my gauges and/or tell if the wire is just not hooked up. Does anyone know the symptoms of a bad voltage limiter and/or if they can be easily replaced? What do you guys think?

Also my speedo gauge is off. When it reads 50 im actually going 40 when it reads 70 im going 50. The wheels and tires arent stock but the rims measure the same diameter as the stock rims. Im not sure if the rear end is stock. Im unsure of the gearing."

Every old car has wires that have no use in them. What it sounds like is that you need a ground or your ground loosened up and fell off. I'm sure you can just pop your dash out and look. For the speedo, what type of tranny you have? You can follow the spedo cable down to the tranny. There should be a outlet into the back of the tranny. You may have to find a book for your tranny or google and see how it's supposed to be turned. It may have just wiggled loose while you where driving. Mine has done that before.

74Runneer · Jun 17, 2013

Mopar-Charger said:
Every old car has wires that have no use in them. What it sounds like is that you need a ground or your ground loosened up and fell off. I'm sure you can just pop your dash out and look. For the speedo, what type of tranny you have? You can follow the spedo cable down to the tranny. There should be a outlet into the back of the tranny. You may have to find a book for your tranny or google and see how it's supposed to be turned. It may have just wiggled loose while you where driving. Mine has done that before.

So just look for loose wires behind the dash? does the steering column need to come off?
Would a loose speedo cable throw off the speedometer? I think its the stock tranny. Ill have to look that up

- - - Updated - - -

Mopar-Charger · Jun 17, 2013

There are two prongs that come out of the dash. On those prongs should be a positive and a negative. The negative cable should be connected across the dash to all the gauges to ground them all together. Find where the ground cable leds and ground it.

That might be a problem with the spedo, reach up behind the dash and push the lever on the end of the speedo cable and push it on the dash. If that's all the way in then it is wrong down on the tranny. The cable should go to something on the tailshaft of the tranny.

Bruzilla · Jun 18, 2013

Welcome to the site. I had a problem with my fuel gauge that was similar except it would work fine about once every two or three months, so I suspected it was the sender unit. My first question to you would be did you check the voltage at the sender unit, or did you just pull it and make sure the float moved? Also, since there's more than one gauge involved, I would suspect a grounding issue too. The ground is just a printed circuit board on a plastic sheet and these can cause continuity faults. I would suggest you pull the rally cluster out rather than try to fish around behind it.

As for the speedo, I've found a loose cable at the speedo will make the needle read erratically and you'll hear a clicking sound. Your issue sounds more like the gear in the tranny that drives the speedo is the incorrect one for your car. This is a pretty common thing in our cars since trannys get swapped over the years and if the drive gears aren't swapped out, and the new car has a different rear gearing, the speedo will read too high or too low. You probably need to find out what ratio your rear is and order the correct drive gear for the tranny.

74Runneer · Jun 18, 2013

My gas gauge hasnt worked since i bought it a year ago. I check the sending unit by measuring the volts when the float is up and down. I think it read 10v-60v or something similar to that. Do you know i have a rally cluster? If so how? Ill probably pull the cluster out today. Do i need to take the steering column out? What all do i have to do, and what should i look for?

Yeah im thinking its probably the tranny gear because the speedo reads very steady and consistant but it just reads high. Ill check the gears (i think i did this and found that they were 3.23), and find out what tranny i have. How difficult is it to change the tranny gear?

UKPlymouth · Jun 19, 2013

I just did this job. Be patient as it is tricky. You will have to drop the steering column and also remove the steering wheel. Do the wheel first and you will need to make a puller.
Once wheel is off/column lowered undo the half dozen or so screw that hold the dash front panel/bezel to the dash. This will allow you to gently pull the dash cluster towards you.
Now the tricky part. If it is a Rally gauge there are six screws that have to be removed that hold the cluster to the bezel. The heads are facing away from you ie towards the front of the var so you can't ee them easily.
Use a short stubby screwdriver and remove them. Six along the top and two at the bottom. Be patient, you can't afford to mess up the screw heads.
After that you can release the the bezel/front panel away from the dash cluster.
Helps to also remove the headlamp and wiper switches too to get good access to the cluster.
Get a workshop manual from Rock auto. Priceless! It has a very good full size picture of the rear of the dash cluster and what each part does and how it is wired.
Good luck, I'm still struggling to get parts of mine to work a week later!

dodge41969 · Jun 19, 2013

I do this for a living having worked at RedLine Gauge Works and Currently North Hollywood Speedmeter, feel free to message me if you have any questions regarding your gauges...maybe I can help.

UKPlymouth said:
I just did this job. Be patient as it is tricky. You will have to drop the steering column and also remove the steering wheel. Do the wheel first and you will need to make a puller.
Once wheel is off/column lowered undo the half dozen or so screw that hold the dash front panel/bezel to the dash. This will allow you to gently pull the dash cluster towards you.
Now the tricky part. If it is a Rally gauge there are six screws that have to be removed that hold the cluster to the bezel. The heads are facing away from you ie towards the front of the var so you can't ee them easily.
Use a short stubby screwdriver and remove them. Six along the top and two at the bottom. Be patient, you can't afford to mess up the screw heads.
After that you can release the the bezel/front panel away from the dash cluster.
Helps to also remove the headlamp and wiper switches too to get good access to the cluster.
Get a workshop manual from Rock auto. Priceless! It has a very good full size picture of the rear of the dash cluster and what each part does and how it is wired.
Good luck, I'm still struggling to get parts of mine to work a week later!

UKPlymouth · Jun 20, 2013

Thanks Dodge, appreciate the offer. I'll keep plugging away and see what I can sort first.

rsd859 · Jun 20, 2013

Not trying to hijack but...my spedo doesnt work at all. Where does one start on that fix?

UKPlymouth · Jun 20, 2013

Check the cable. I unclipped mine from behind the dash which is tricky and then cable tied it under the dash and drove down the road. Cable was spinning fine. Next up, fill the speedo aperture with grease or put grease around the cable when youmre plug it behind the dash and see if it works.
If that fails you are at the messy end where it plugs into the transmission. You need to jack the car or trams from the rear so that when you pull the speedo cable from its location in the trans it don't leak all over you (probably still will!) and check that it is connecting properly into the tran aparture.

74Runneer · Jun 28, 2013

If I have 3.23 gears and the car originally had a 2.73 gears with that tranny gear, would that throw the speedo off the amount im seeing?

UKPlymouth · Jul 1, 2013

Yes, sounds right. Just changing to bigger/smaller tyres ail do that. 2.73 to 3.23 is a big jump. You need to change the speedo drive where it fits into the transmission. If you do, make sure you jack the car up from the rear so the trans is tilted or you will get covered in trans oil as you release the piece that retains the speedo cable to the transmission.
Done that!

74Runneer · Dec 22, 2013

Hey I finally ordered my new speedo gear, a 33 tooth yellow one and I also ordered the gaskets (o-ring and small rubber ring). My old one was a 27 tooth gear, after some calculations i found that it was way off. The o ring is way too big and I'm not sure how the other small rubber piece goes on. Does anyone know how this goes on?

Also I'm in minnesota so Im not going to be drive it around in the snow to test it. Can I just keep the rear end jacked up and run the car to see if the speedo needle moves. I don't have a posi. Can it run if all the fluid is in the front of the tranny?

- - - Updated - - -

Here is a pic of my gaskets.

b_body_hopeful · Dec 23, 2013

This is how the pinion gear and gaskets fit:

74Runneer · Dec 23, 2013

Great thanks that really helpful. Another question. My gear I ordered was supposed to be a 33 tooth long sharft and I just got it and it has the number 55 stamped on the plastic end. I thought that this number meant the amount of teeth it has. Anyone know about this?

74Runneer · Dec 23, 2013

Okay I found out that its the right gear. Should my speedometer read anything if my car is jacked up at the rear end and I'm just giving it gas? I notice only 1 tire spins but still it should work right?

73runner · Dec 23, 2013

74Runneer said:
Okay I found out that its the right gear. Should my speedometer read anything if my car is jacked up at the rear end and I'm just giving it gas? I notice only 1 tire spins but still it should work right?

Should still work with you open (one wheel turning) rear end.

Gas gauge not working???

74Runneer

Well-Known Member

Mopar-Charger

Well-Known Member

74Runneer

Well-Known Member

Mopar-Charger

Well-Known Member

Bruzilla

Well-Known Member

74Runneer

Well-Known Member

UKPlymouth

Well-Known Member

dodge41969

Well-Known Member

UKPlymouth

Well-Known Member

rsd859

Well-Known Member

UKPlymouth

Well-Known Member

74Runneer

Well-Known Member

UKPlymouth

Well-Known Member

74Runneer

Well-Known Member

Attachments

b_body_hopeful

Well-Known Member

74Runneer

Well-Known Member

74Runneer

Well-Known Member

73runner

Well-Known Member

Similar threads