Fuel gauge question? 1985 Chevy C30

[Todd68Chevy]

In our repair shop we checked out an 85 C30 that the fuel gauge would read different everytime the truck was turned on. Tested and found the fuel gauge was testing bad. Removed and replace the fuel gauge with a new gauge. Now the gauge reads the same everytime the truck is started but moves around while driving. It acts like it is just reacting to the sloshing of the fuel-- starting, stopping, cornering, if you park on an incline. Should the gauge have a slosh module to help with this? Could it be a problem in the new gauge? I was hoping someone has been through this already and knows the answer to the problem. Thanks for your time and knowledge.

[speedmachine]

others may disagree but the squarebodies ive had in the past were the same, truck needs to be on level surface to read the gas right.. may have more to do with the sending unit design then the gauge.

just my 2 cents

[beamn7]

Originally Posted by speedmachine

others may disagree but the squarebodies ive had in the past were the same, truck needs to be on level surface to read the gas right.. may have more to do with the sending unit design then the gauge.

just my 2 cents

Correct, both mine do it too as only the fuel injected trucks had baffled tanks....
I can be cruising at 1/2 tank and come to a stop sign, she jumps to E and then back up to 1/2

[Todd68Chevy]

Originally Posted by speedmachine

others may disagree but the squarebodies ive had in the past were the same, truck needs to be on level surface to read the gas right.. may have more to do with the sending unit design then the gauge.

just my 2 cents

Originally Posted by beamn7

Correct, both mine do it too as only the fuel injected trucks had baffled tanks....
I can be cruising at 1/2 tank and come to a stop sign, she jumps to E and then back up to 1/2

Thanks guys, I was hoping that was right but I really have not drove one of that body style much.

[tucsonjwt]

In my experience, it is a sending unit issue. Aftermarket sending uints like Spectra brand, will move around whenever the vehicle is in motion, or stops quickly. Others will disagree. Delco sending uints are about $14+, Spectras are about $40 - I have bouncing Spectra sending units in my truck.

[motornut]

i just replaced the tank and sender in my 79
both Spectra brand (no bouncing issues before or after)
i had a bouncer in the 78 tho
Spectra brand again but
changed the cluster from idiot to tach/gauge
added some grounds behind it and the bounce went away

when i first looked into the bounce ,adding a ground was suggested here
not sure why it didn't help me when i test grounded it
and why it stopped when i added the diff cluster
i can only suggest there must be feed back disrupting the path to ground
seeing they all go to one wire
and it can't hurt to add one...
when I ordered this one my parts guy said he never heard of this issue and he sells a lot of the Spectra brand
and tank is not baffled