Vibration from back pressure??

[titansarrow]

i'm no mechanic, so bear with me as i walk you through my thought process.

as i was driving home from work (10hrs) i noticed a vibration in the last 50 miles or so. nothing out of the ordinary happened, no hard stopping, pot holes or anything of that nature.

over the last few days i began investigating. with mixed driving; city, highway and everything in between. there is a vibration that can only be felt from the drivers seat (probly the rear drivers side as well). my gf said she couldn't feel it while riding shotgun, but could while driving for confirmation. it feels like it is slightly behind the seat, or at least somewhere in the rear of the truck.

it also only happens under acceleration (load?). that is, when and only when the gas is pressed. if i pop the clutch and coast- no vibration, at idle in park- no vibration. so that would eliminate something with the wheels or suspension. i would also imagine that would eliminate things like the axle or driveshaft, since although moving at a higher rate, are still moving no matter what. no have i experienced anything else noticeable with the driving (ex- loss of power).

so i was thinking maybe something with the exhaust?? back pressure difference? i haven't felt a power difference, but that's not to say that i will. as i said in another thread, my engine has a possible 300k on it and will be replaced soon.

wondering if anybody else has happened to experience this?

 

[jd4242]

U joints.put it in N wile driving and rev the motor see if it happens.when ujoints start going bad it shows up real bad under load.

 

[titansarrow]

....how hard/expensive is it to replace? and will i be ok to make another round trip do ya think?

 

[titansarrow]

narrowed it down a little bit. doesn't seem to happen in first or second. and it seems to happen under 2k rpm....or it's at least less noticeable.

 

[titansarrow]

found a shop to do it all for me. weather has been a bit too dangerous to be doing this stuff outside.

bob's auto in beavercreek,oh. $120 out the door parts and labor, both u-joints. $40 more to balance the drive shaft.

 

[Anime]

Did it solve the problem?

The driveshaft doesn't usually need to be balanced unless the factory weights were knocked off or something. If it's off balance due to age, usually brushing off the rust and scale that layers on it from being up north balances it back to normal.

A less restrictive exhaust still does wonders for the 4.0, too.

 

[jd4242]

X2 on the balancing

 

[titansarrow]

the appointment is for the morning (friday). he said it may not need to be balanced, but won't know till he can get into it. the more i drive it and think about it, it seems like the u-joints are the correct culprit. it almost seems to feel like a slight grinding.

as far as the exhaust goes- the last person put on a newer, and louder muffler, but the cats forward must be stock. it has the old duel cats in sequence. i'm sure after 20 or so years, they aren't doing much good. thankfully for me i'm in an area with no emissions testing lol. that'll just be another project for the spring.

on a side note, through picking my brain, going through options all week, i've decided to just do work on the upper end of the motor and replace the lifters, being that they are the only things i know for sure are bad. and through fixing those, i'm sure it will allow me to narrow down anything else.

i also appreciate the people on this site, there's very little if any flaming. and everybody seems to respond with a serious note

 

[jd4242]

Lifters rarely go bad and you have to take the heads of to get to them,I would say its the rockers and pushrods if your getting noise

 

[titansarrow]

i thought i've heard the 4.0's were notorious for lifter knock? but maybe i missunderstood. the mechanic said he'd take a look though. at either rate, i know the noise/shutter, what ever you want to call it, is not correct. and i have no way of knowing if anything has ever been donw to the motor. though i imagine there has been in its 300k life time lmao.

 

[jd4242]

Its the pushrods and rockers.delta cams makes a set takes all of an hour to do.you just pull the valve covers way easier than pulln heads for lifters.start there if that don't fix it have someone pull the heads but thats going to cost you more than the truck; )

 

[titansarrow]

lol. their site's not all that good, but i assume you meant the rocker arm assembly kit? $200-ish doesn't sound too bad. i'll just have to make sure i get everything i need, as well has how the hell to do it haha. if it's not too bad, i'll just do it in a few weeks on my next days off.

Its the pushrods and rockers.delta cams makes a set takes all of an hour to do.yiu ust pull te valve covers way easyer than pulln heads for lifters.start there if that don't fix it have someone pull the heads but hats going to cost you more than the truck; )

 

[jd4242]

its way easy,the drivers side you can just take the valve cover off then 3 bolts and its off and the passenger side you have to pull the coil off "3bolts" and i would pull the alternator out dont have to but way easier and the same process.i can do it under 30mins.turn the crank by hand and have someone watch the rockers and when most of the are in the closed position the pull the rocker assembly off,this will make it was easier to put back on.also when you put them back on do each bolt a little at a time,dont just crank one down could bend something.also try and push them back as you tighten the so no spring or retainer hit the rocker,sometimes i had to get them pretty snug and tap on the base to move them back.what you dont want is this to happen but then again my heads are very modified and ive heard no one else having the problem but better safe than sorry.

o and there website does suck but i use them and so does everyone else so they work and they are good people.

 

[titansarrow]

right on, thank you. just have to wait for good weather on days off and knock it out

 

[titansarrow]

got the truck back, vibration's gone. he said that one was bad for sure, he could move it all around. he also said that they might have been the stock ones (or maybe OEM?) because there was no grease access. so he put in 2 aftermarket ones with grease zerts. he said i should be able to go in and grease them from now on every now and then (probly when ever i go to re-grease the wheel bearings and such).

the guy was kind of weird, just a small shop, probly just him and another. but he seems honest and even asked me why i thought it needed u-joints. so he gets my recommendation thus far

 

[jd4242]

Glad that fixed it.