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2nd Gen Non-Engine/Transmission Why is truck "squirming"?

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My '96, 2500, 4wd, Cummins, 317k miles, is occasionally "squirming" when I start to move forward or backward. It is apparent enough that even non-mechanical passengers ask, "What was that?"



It seems to quickly correct, but something is wrong and I don't want it to get worse.



I'm thinking it feels like a driveshaft that is running out of true for a few feet and then it centers again.



What do you think it is? How can I check it out? Etc.



Appreciate your input, folks.



DrJC

Michigan
 
Check the shackles and and spring bolts on the rear, also check the U-bolts that secure the springs to the rear axle. Could also be the front suspensio as it is 4X4. bg
 
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We have a 96 12v 3500 at work that the driver was complaining about similarily. Turned out to be one of the u-bolts holding the spring pack to the rear axle had broken. Thank goodness he said something (most of our drivers dont let me know there is an issue until whatever it is is so bad that it cant be driven and the repair bill quadruples due to other incidental damage) and didnt just let it go could have been a bad at the office for him had the other one on that side let go.
 
Barry,



I'm going to check the rear axle, as you suggest. I'm glad I asked for help via the TDR. Thank you for taking the time to give me guidance.



DrJC
 
Greg,



I've checked out the spring bolts, etc. as suggested by others and all are in good shape. The center driveshaft bearing is not loose, and I can't find any drive line U-joints worn excessively. Yet, the "squirm" continues occasionally--usually after I've changed direction from forward/reverse.



I'll double-check the 4WD, as you suggest. Thank you.
 
Long shot here... . does your truck have a posi or no spin rear end. Back in the day when I was young and foolish, I had a Mustang with a posi rear end. After one too many stoplight races, the car started doing what you descibe, what I also would call squirming when taking off from a stop. I killed the posi clutches evidently as it left me dead at a light finally, beaten by a Camaro. I was disgraced... ..... :{



Sam
 
Long shot here... . does your truck have a posi or no spin rear end. Back in the day when I was young and foolish, I had a Mustang with a posi rear end. After one too many stoplight races, the car started doing what you descibe, what I also would call squirming when taking off from a stop. I killed the posi clutches evidently as it left me dead at a light finally, beaten by a Camaro. I was disgraced... ..... :{



Sam



You could be on to something. If the rear axle has a factory Limited Slip Differential (LSD), and if the gear oil has not been changed in a while, it could be getting a stick-slip condition. The stick-slip condition is best felt in an old Jeep Quadra-Trac transfer case, but it can also show up--in my experience, I am not a mechanic--in a fairly high mile LSD. This happened to me with a 1976 Jeep Cherokee 4 speed with conventional transfer case, but with LSD. It was a weird feeling.



1. If the differential oil has not been changed in 50,000 or more miles, change them both now. Regardless of the brand you put in, buy a small bottle of LSD additive from the dealer or someone reputable and add it. If your truck has an oversize differential cover, add two. If the bottle of 80W-90 or 85W-140 says that it works on LSDs, add it anyway. (Do not ask how I know this. ) That might solve the problem.



2. If it does not solve the problem, try this. You may need to do this anyway to get the new oil into the LSD clutch packs. (A LSD is very weird inside compared to a regular differential. ) Find an empty parking lot. Paved is best, but dirt or gravel will do. Drive in fairly tight figure eights for about ten minutes. That will get the oil circulating. And it should solve the problem, if that is actually what the problem was.



3. If you bought the truck used, or if you otherwise know that it was used as a grocery-getter, try step 2 first.



4. If it is an automatic, you may be getting internal slippage that starts to go away as it warms up.



5. Double check the spring shackles again, anyway. While doing so, check the rubber "eyes" that the bolts go through, front and rear. The shackles and the front track bar (especially) can look OK, but the rubber can be shot and in need of replacement. They can make the truck feel squirmy, but it should squirm all the time.



6. With the parking brake firmly set, and the auto transmission in Park (if it's automatic), with the engine on and with you lying on the ground, have a trusted friend turn the steering wheel about 45 degrees each way while you watch the front end parts. If the diagonal track bar acts "funny" where it attached to the frame, it is shot. Replace it. If the right front tire, and only the right front tire, seems to be wearing on the outside, it is an indication that the track bar is going south.



Apart from that, I am clueless.
 
Check the bushing in the front four-link. If the control arms are loose or the bushings are out the front axle can move front and back. If it's just one side, the axle can move backwards on one side, making it drive that way, then bounce back forward and steer the other way. Very not good. Look for wear marks on the brackets where they attach, too. The bolts can be loose sometimes.
 
Is it a front end squirm or back end squirm?

Check all suspension parts (ca, trackbar, leafs and hangers, etc)

LSD additive is not needed with full synthetic fluids like Royal Purple, redline, amsoil , etc .
 
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