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Banging under feet when reqaching 100-120 km/h

twisted_ed

twisted_ed

NAXJA Forum User
Location
Courtenay, British Columbia, Canada
I have recently found that I am getting a banging sound under my seat when I reach anywhere 100 kmh, it happens at that speed, and I dont know why. I have a SYE and have the front ds in the rear which was rebuilt a year ago... so mabe at the angles I have (6" lift) its worn out already. I know its not the front ds cause its not there, and just by quickly looking at the ds (in park) there is no noticable slop... Im going to take it out tomorrow and look at it closely... I was just wondering what poeple thought it might be.. I hope its not the tc, but I would think if it was it would be banging at all speeds.... its pretty specific... at 100 km/h it starts, not before. I would thing at 95 if it was the tc it would do it but nope, gotta be 100 to start banging.
 
describe the banging? rythmic? random? proportionate to speed? bumps?
 
I havent actally driven it in a few months... but if I recall its not proportionate to speed, it starts at 100 km/h and thumps/bangs the same speed up to 120. it used to only happen at 120 but started happening sooner at 100. thats about all I can tell you. its almost like mabe ive lost a weight and its out of balance?
 
Rythmic, same thump every time... it might get faster which would be indicitive of driveline noise but never went fast enough to find out, between 100-120 isnt much of a change to notice I dont think but defently rythmic, its a thump-thump-thump
 
interesting... I will defently try it.. could you explain why that might make a diffrence... wouldnt it just still be there?
 
Well, without driving your rig, its impossible for me to imagine what the thump feels or sounds like, but see if it moves or changes (like say, to the rear).

The next thing to check out would be the condition of your trackbar and lca bushings - but those wouldnt likely be rythmic.
 
true. the front end it pretty much brand new, everything replaced with curried hd front tie rod/ etc etc. and the track bar it tight cause right before this happened I got mad shake up front (i think death wobble) and I noticed the bollts were loosed on it, tightened em up good and it went away so that shouldnt be it, but Ill check again.... Im hoping that its the driveshaft, that the non greasable joints I had put on packed it in... and I just cant tell without taking the thing off... my s10 pickup daily driver was like that... had vibration and stuff and it turned out to be a ujoint that was so toast im surprised it didnt break off yet couldn;t feel it when I crawled under there to look. Could be my centering ball too, thou that was rebuilt as well.
 
Trans and motor mounts would be possibilities and easy to check.

Do you ever get a noise on accelleration or shut down?
 
come to think of it occasionaly I beleive there was the odd noise... how would notor mounts be the problem upon reaching 100 thou and how can I check them they were all replaces 4 or 5 years ago so they could be worn now
 
twisted_ed said:
come to think of it occasionaly I beleive there was the odd noise... how would notor mounts be the problem upon reaching 100 thou and how can I check them they were all replaces 4 or 5 years ago so they could be worn now
Click to expand...

Who knows but the location you gave us indicates a t-case smacking the floor pan and that tells me bad trans mount or motor mounts.

The stock motor mounts are great if you have a stock setup and don't leverage the drivetrain offroad much. But add a diet of offroad use, a leaking RMS and all of a sudden those mounts deteriorate quickly. Anything over 24 months is lucky for the guys I wheel with.

Throw that thing in gear and go back and forth from forward to reverse and have someone look at the drivetrain to see if it's flopping around.
 
Hard to say if it would be motor mounts or not. The fact that it comes in at a certain speed and is rythmic would imply its something that is moving.

I suppose rear driveshaft could be it. The front driveshaft IMHO isn't really beefy enough to work in the rear. The
slip joints don't hold up to it and they are usually pretty worn out before they make it there even with a rebuild.

See if you can borrow someone elses front shaft for a few hours?
 
All righty, ill check into that, I guess I may just redo the ujoints in the ds just to be sure... im sure they are just about ready to be replaced at best.... and ill check the mounts...
 
no one around here goes with the front ds in the rear so.... thats out...
 
tighten your wheel lugs? I had the same thing last few days.. was like WTF.

then for poop and gigles decided to check lugs for some reason. Rear were all hand loose and one was only on by 3 threads.

yep.... way to put yourself your prego g/f and 2yr old at risk I kicked myself accordingly dont worry. Didn't re-tighted after few days of mounting new tires.
 
I meant put their front shaft in your rear.

wow. don't take that out of context.
 
cant, they are different lengths.
 
And I guess it could be a range of things all coming together at the shaft speed you get at 120 kmh. A sloppy shaft flopping around with a weak trans mount or a loose crossmember could all add up to it.
 
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