5.7 vortec bucks once on let off of gas.


Asked by May 18, 2015 at 07:58 PM about the 1998 GMC Sierra C/K 1500

Question type: Maintenance & Repair

I have a 98 gmc k1500 with 5.7 vortec motor. when I am cruising at a set speed (say 70) and gently let off the accelerator it bucks one time. I just replace my ujoint and the guy said the drive shaft is tweeked like its twisted. I believe it from getting hammered by this bucking when ever I let off on a set speed.. No no lights on except ABS but I did get codes C0225 C0227 C0223 C022. No one seems to h ave a clue as to what this is

15 Answers


You ring and pinion in the rear end has developed excess slack between the two gears . Backlash is occurring with the torque shifts the other direction in most cases, during slight deceleration,this also will cause a bump right after you come to a stop then release the brake to pull forward like at a stoplight. See a technician that specializing in rebuilding differentials for a living or Dealership trained Master Techs. This is a very expensive repair that require skill levels that are well over most mechanics. Time is money, diy's not recommended. Skill level scale 1- 10 . This is a 9.5 to 10, don't waste your money thinking your buddy's Granpappy can just dial it in, and it will not roar! Oh, the other thing, read the codes, you could be dealing with a faulty T.P.S! It needs to be swept with a fluke-88,to see if there is a drop out( worn out spot whee tps sends no signal back to PCM .

1 of 1 people found this helpful.

I hate spell check please excuse misspelling typos


Thank you very much . So it would only do it once on let off . Wow that makes sense why no code The codes I mentioned are for the wheel speed sensors.. the ABS is on. Im guessing eventually its going to break the gear off and ill be sitting on the side of the road. If I take this to a ring an pinon shop Im guessing they can diagnose it for me pretty quick hu?

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So I have 35 inch tires on the truck now, if I need to replace ring and pinion what gears should I go with

1 of 1 people found this helpful.

Every size above stock puts more load on the rear gears and axle bearing assemblies . Stock wears out fast enough with out the help.

1 of 1 people found this helpful.

Whatever you do on the rear has to to duplicated on the front ratio also

1 of 1 people found this helpful.

I think a better way to describe it would be, it feels like it slips and catches on deceleration. It feel like my load shifted forward. the clunk was the bad u joints getting banged by this issue. I replaced them and that got rid of the metal hitting sound. But the slip is still there.


Nope I put a new rear end in it and its still doing it. Any more ideas?


Did you get GM dealer to repair the rear end ?


Quote: Originally Posted by swartlkk C0225 - Left Front Wheel Speed Sensor Circuit Open C0226 - Left Front Wheel Speed Signal Missing C0227 - Left Front Wheel Speed Signal Erratic C0242, C0246, C0251, & C0252 - EBCM Control Valve Circuit C0265/C0266 - EBCM Motor Relay Circuit I would start by inspecting the wiring to the left wheel speed sensor and disconnecting, cleaning, and then reconnecting the electrical connection to the EBCM.


I think your dealing with more than one problem at a time which makes it very hard to diagnose


Did you scan tps for open?


Seems if it was the TPS it would do it at that point weather I was accelerating or decelerating. Also you would think it would throw a code. I know the codes are for wheel sensors, no big deal. I did not have a dealer put the axle in but I did have a off road shop do the swap. This is either mechanical or something electrical that does not throw a code. I was thinking toque converter maybe but that its a 4L60E so thats electronic, should throw a code. could be transmission thats my next check. taking it tot trans shop. no one I talk to can figure it out I must be the first one to have this problem. ;)


Still dealing with this issue. I have a new distributor in it now and tune up new rear axle. Still doing it.

1 of 1 people found this helpful.

I think I am experiencing the same issue. My issue only differs slightly. I have rebuilt the trans, rear differential, and most recently new u-joints and front drive shafts..Yet the 'bucking' is still there when letting off the pedal at steady speed. Mostly around 40-50 for me. I am now suspect of the transfer case..there's not much else I know of to replace.

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