Problem With the Back End

I'm new to the area so get me if i'm doing something wrong.

A while back i installed the Revtech 3 inch lift and 33 inch tires and love it. however sometime after the install i started getting a knocking feeling coming from the back end. it only happens when i start off with normal throttle. its a little worse when i hammer it and a little better to non existent when i baby it. it almost feels like i'm getting hit softly by another vehicle. has anyone had this problem? Could it be the blocks are a little off, the differential, CV joints? I've had it on a lift and shook things around but didn't get anywhere. i can't tell if its serious and don't want it to become serious. any help would be great.

 

It could be many different things - please pardon, this is all off the top of my head.

Get it in the garage (or where-ever) and check the blocks & u-bolts again. After you did the install - did you make sure the centering pin was inside the hole on the spring perch? Check these again.... Check your u-bolts and make sure they're tight (they can and will loosen). Check the bolts on your main spring eye hanger and the shackle bolts. Not too tight but not too loose. I'd torque them to about 50ft lbs to start.

That knocking feeling could also be driveline slop - which may (or may not) be more noticable due to the larger tires/current gearing. Chock the front wheels, Jack up the rear-end, put the truck in neutral and grab the driveshaft and turn it by hand. Is there a certain amount of play before it 'hits' the gears (so to speak)?

And I would also (while tires are off the ground) - grab each wheel and shake it side to side and back-n-forth (checking bearings, balljoints, etc).

In general, go around and make sure everything is tight...paticularly the areas that were removed/changed during the install.

 

maybe a u-joint also....while under truck try to push up or down on driveshaft see if it has play in the joints....also did you add longer shocks? axle wrap can cause a too short shock to hit and give you a thunking noise....

 

yeah most everything you've suggested i've thought (except the driveline slop) about but theres definately some different ways i could go about troubleshooting that i didn't think about. i definately changed out the shocks since the old ones were too short and completely blown. though i did only install the lower performance ranchos, maybe a higher grade would work better.

 

I'm willing to put money on a loose U bolt. Whenever I lift or lower a truck with a block I drive for 500 miles or so and then re-torque the u bolts again. 9 times out of 10 they require a little more love. U bolts stretch a bit when they are brand new.


~Brian

 

well, you seemed to be right brian. i got the truck up on a lift the other day and checked the torque on my u-bolts. the were about 15 pounds off. i got them tightened up and checked the center bearing and the front driveshaft just to make sure i covered everything i screwed with when i installed my lift. so far no problems.

 

Glad to hear you worked it out. I hate it when I have a problem that is boggling my mind. Drives me nuts until I finger it out.


~Brian