I took my truck out of town for the first time last night. Just got my liscense two weeks ago.

It is a 99' Sierra 4.8 RCSB with a few mods already installed when I bought it.
It has 104,000 miles on it. It has 3.42's with one wheel peel.
My truck is supposed to get 16 mpg in the city & 21 mpg on the highway.

The rearend has been vibrating for the past week and I have noticed that my truck was sucking gas bad, real bad.

So last night I filled my truck up with gas and drove 17 miles to another town. Ate at Sonic and then drove staight back and filled up again. The TOTAL trip was 38.4 miles (about 4 miles of this was driven in town, the rest on the highway driving 65). I did not speed the entire time, I drove easy.
I then filled the tank all the way again. It took 8.2 gallons!!! That's only 5 miles per gallon.

And the rearend was sounding awful, like it was about to die. It was vibrating and moaning and groaning like crazy when I was driving in town. I could not hear it on the way home on the highway, but that was driving 65 mph with the windows up and the stereo on. When I pulled up to my drive way it felt like I was pressing the brake but I wasen't, and the rear was squealing pretty bad.

So it has been parked ever since. The truck was kind of fixed up when I bought it. I bet the previous owner drove the sh*t out of it. I'm sure it needs the rearend to be rebuilt, and that's fine because I want to get some 4.10's and Eaton anyways. But the 5 mpg is what scares me, what do y'all think is the problem? I'm begging for some kind of an explanation!

Thanks,
Nick

 

Man that sucks. Check the rear brakes too. Jack it up and try to turn the tires by hand with the truck in N. It may be easier to pin point the problem. Good luck

 

Are you sure that one of your rear wheel brake calipers are not locking up?
Take a look at rotor at rear. If your brakes look fine...... The rear differential will be the problem.
First check your diff fluid. Remove the rear diff cover and look for metal shavings. If something is wrong in there, there should be lots of metal from what you described.
If everything looks fine, it may not be as bad as you think.
You may have a bad rear wheel bearing. One of them may have froze up.
If so, you need to replace both rear wheel bearings. Each rear axle shaft should be inspected for wear marks caused by the bad bearing.
That axle shaft should be replaced.
You should find something with all of this said.
If you descide to change out the rear gears, go with "ONLY" GM gears!
Whoever does the gear swap, make sure you tell them that!
I promise you it will save you head-akes later down the road. The GM gears are one of the truest set of gears you can purchase.

Jim

 

do ya'll think the gas problem is because of the wheels being harder to turn from the brakes or rearend screwing up, or do ya'll think the bad gas miledge is from something else. It had to be, because the guy who I bought it from said he was very pleased with the mpg. and the brakes/rearend seemed fine when I bought it. I have only been driving it for 3 weeks.

Please, any advice would help!

Thanks,
Nick

 

You need to re-check everything. Anything could happen at any given time.
I think your gas miliage problem is from the rear end problem you have.
Do you have any mechanical skills?

Jim

 

That could deffinatly cause the MPG problem, but you need to find out what it is. I would lean toward the brakes simpally because if you have that much friction in the rear, I doubt you could have driven 30 miles. But it is still a possibility.

 

Sounds like a pinion bearing, trust me I know lol, well Im just throwing that out there.

Alex

 

My dad knows alot. I think it is the brakes personally, but I don't know much.
Alot more than before I found ls1tech.com. My dad said he will try to look at it tomorrow. It use to make noises only when I pressed the brakes, but now all the time.

Thanks,
Nick

 

hopefully it's just a sticky caliper....very sticky. lol

if so, i would strongly recommend changing BOTH calipers even if only one seems bad. usually if one is bad, the other one is on its way out.

as for brakes i recommend factory AC Delco pads. or get ceramic AC delcos if you dont mind forking over a little more money.

you also probly need new rotors by now. stick with the good brands. dont go to advance or autozone. lol trust me. i know this.

 

NAPA has some good brake pads, paid $55 for my mid grade ceramics and had them double check how true the rotors were before i took them home. After thats all said and done if it is the brakes screwin up, you should be alright.

My ceramics and rotors from napa have help up very well the past 4000miles.

Dave