Truck runs and idles great but knocks when decelerating

Tiny
WILLIAMHINDMAN
  • MEMBER
  • 1993 CHEVROLET SUBURBAN
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 235,000 MILES
My SUV is a k1500 with 235,000 miles on the original engine. Mine makes a knocking noise only when I decelerate and the knocking gets slower the slower I go and only starts at like 20 mph. I have replaced the CV axles, u joints, plugs and wires, rebuilt the transmission, just rebuilt the transfer case because my chain was loose and changed the transmission filter, and put a new rear and on it. I regularly change my oil and even dropped the oil pan the last time and there is no metal in it. I am at a loss as to what it could be. I can grab the hook ups for my CV axles at my front differential and they have no up, down, side to side play. But I can turn each one back and forth about a half inch in each direction with the truck on the ground and the tires not moving. Any idea what it could be? It is loud enough for people to hear in a parking lot over my straight pipe exhaust. (3" pipe 5" tips with no catalytic converters or mufflers) which is embarrassing as hell. Sometimes it is worse than other times. I do all my own mechanic work myself and can do it all easily. I am just tired of playing process of elimination.
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Saturday, October 29th, 2016 AT 12:37 AM

12 Replies

Tiny
HMAC300
  • EXPERT
It kind of sounds like you have too much wear in front differential. It should not move 1/2" in each direction. Does it do it in two wheel drive as well?
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Saturday, October 29th, 2016 AT 7:02 AM
Tiny
WILLIAMHINDMAN
  • MEMBER
Yes, that is why I try not to use the four wheel as much as possible. The actuator was bad in it when I got is and supposedly they never used the four wheel. I replaced the actuator and it worked fine for a while but then got to where you had to try a couple times for it to actually engage and the last two times I used it, it would not disengage. I changed the differential fluid before using four wheel and it was black. It has been like a year and just checked yesterday and it is a gray/black. Not as bad as before though. I thought about changing the hub and bearing assembly and the differential bearings and seals, but that is a lot of money to throw at it for it to not be the problem.
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Saturday, October 29th, 2016 AT 7:12 AM
Tiny
HMAC300
  • EXPERT
I think if you disconnect axles and try to move it back and forth if you get the same result then something is worn out in front axle and probably your noise as well.
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Saturday, October 29th, 2016 AT 8:59 AM
Tiny
WILLIAMHINDMAN
  • MEMBER
I guess I will just tear into it and slide the axle shafts out and look. I got my torsion keys cranked but that is because my uncle who owns a tire and alignment shop pointed out my CV boots were rubbing. I am having trouble finding extended sway bar links for the front for a decent price so I am probably going to make my own. I planned on lifting it about three inches soon anyways and would need to put in a differential drop. So might as well go ahead and crack it open to see what I am working with. If it is a total loss, (like the rear end was that I had to replace where the pinion ring broke teeth and they locked it up and snapped my drive shaft) do you think it would be cheaper to rebuild this front end or to convert it to a straight shaft? And if I open it up to look, would ATF be okay to run in it for maybe a week until I can get gear oil?
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Saturday, October 29th, 2016 AT 9:12 AM
Tiny
HMAC300
  • EXPERT
I would put motor oil in instead of ATF.
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Saturday, October 29th, 2016 AT 10:01 AM
Tiny
WILLIAMHINDMAN
  • MEMBER
What kind of oil? Like 10w30? Synthetic or not?
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Saturday, October 29th, 2016 AT 11:56 AM
Tiny
HMAC300
  • EXPERT
Well if you are going to tear it apart in less than 1000 miles then put the cheapest oil you can find in it. Do not bother with synthetic until you fix it then use synthetic gear oil.
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Saturday, October 29th, 2016 AT 12:22 PM
Tiny
WILLIAMHINDMAN
  • MEMBER
I have not gotten around to tearing it apart yet, I'm ordering a rebuild kit for the front on payday this week. It comes with all new bearings, seals, gaskets, and some other stuff. However I did notice yesterday when I was putting my shock extenders on the front that my driver side cv axles middle section is loose as hell and makes a noise when I shake it. These axles ain't even 2 months old with no tears in the boots or anything so no reason for it to be worn out or broken. Could the front diff being messed up like it is cause the cv axle to wear out/break like that? I mean my guess would be "well no shit" I just need a second opinion for when the ole lady starts complaining about what I have to do and that I just replaced the axles lol. I love when stuff breaks on my truck because then I get to upgrade and add on and she has no clue what I'm talking about or what parts are actually needed lol
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Monday, October 31st, 2016 AT 11:01 PM
Tiny
HMAC300
  • EXPERT
Shock extenders? Is this truck lifted by chance? If it is with no front end kit then that may be the problem for premature axle wear because every thing is screwed up. Check your axles kind of sounds like they aren't any good they may be warrantied as well.
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Tuesday, November 1st, 2016 AT 5:35 AM
Tiny
WILLIAMHINDMAN
  • MEMBER
Just the torsion keys are cranked up because my cv boots were rubbing on the bottom
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Tuesday, November 1st, 2016 AT 5:38 AM
Tiny
HMAC300
  • EXPERT
What size tires did you put on as well? If larger that may be the problem and how far did you lift with torsion bars.
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Tuesday, November 1st, 2016 AT 5:40 AM
Tiny
WILLIAMHINDMAN
  • MEMBER
A couple inches. The middle of my fender is 37.5" off the ground but I'm only running 265/70r 16s
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Tuesday, November 1st, 2016 AT 5:42 AM

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