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Discussion Starter #1
my burb is doing some serious vibrating on the highway around 70 mph. the vibe is cyclical going from road noise to near bone shaking every 1.5-2 seconds at that speed. i haven't noticed it at lower speeds, other than what i attribute to regular road vibe from off road tires. i wonder if this may be related to the excessive play in the driveline, or if i have two problems to solve. the truck makes that good old heavy "clunk" when i shift from reverse to drive, or any other time the driveline changes in the direction it is loaded, like going from heavy throttle to no throttle in a low gear. seeing as how this old beast is to be my daily driver, and i hit the highway to commute to work, i need to get this problem corrected. the basic info is this:
1975 chevy k20 burb big 400 with 350th, np203, manuals on the 44 and a 14 bolt in the rear. should be 4.10 lsd's, but i haven't yet chiseled through the crap to find the casting numbers. shes got wagon wheels and 31x10 cheap mud tires. 68k original on the whole thing. sat at grand lake in ok for about 10 years and was only used about 4 times per year to move a 28' sail boat. ive had it a few weeks and have put new brakes on up front, thats all.
any suggestions are appreciated
thanks
robert
 

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I had a '79 chevy truck that had a similar problem. A tranny shop told me that i needed to replace the chain in the transfer case, but the chain alone costs like $120. He said thats what the clunk it, but i dont think i agree with him. when i pulled the TC apart, the chain didnt look like it had any slack, nice and tight. I think the clunk on mine was coming from the rear end (gears maybe).
I got the vibes too at freeway speeds, but my truck was such a piece that i just shrugged it off. sorry i cant help you much other than, "i know how you feel man".
 

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i was getting a clunking noise and a vibration on my 72 powerwagon the u joints on the drivlines where pretty trashed and after i replaced em everything was fine. I dunno it could be somethin as simple as that.
 

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Typically if the U-joints go bad it'll make the clicking/clunking at all speeds. I had a older chevy truck in work yesterday that NEEDED U-joints badly. When I was backing up and pulling into the shop it sounded like it was gonna fall the hell out.

We replaced them and it stopped... where does it sound like the noise is comign from? (below you, behind you, which side?)

-Chris
 

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Discussion Starter #5
the noise seems like it is coming from either the tc or in front of that. ive got all the new super joints i need to put in it, but, alas... time is never on my side. my dually had a similar noise coming from the rear after i lowered it and it turned out to be the whole rear axle torquing over in the ubolts. i can't see that happening on the burb given the completely stock status. if i can convince the wife to climb in to the beast this weekend i can lay down beside it and get a good look at whats going on under there. i figure if the front and rear shafts twist the same amount just changing from drive to reverse and vice versus, then its probably joints, as its not likely that both diffs would fail simultaneously (right?). if neither moves, than the tc input or trans output shaft is suspect, and if one moves alot more than the other i should really look into the tc itself. in any case she'll be getting new hd joints soon. i have to do the rear brakes soon as well, and i can have the wheels balanced again just to be sure.
thanks again for the help.
 

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The only thing that i could think og that could be causing vibration at speed would be bad u joints allowing the driveshaft to be out of center, an unbalanced driveshaft, of a worn and lopsided differential yoke.
 

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Discussion Starter #7
ok... i found a joint press to do the swap and ripped out the rear shaft. all went well and had it done in about an hour. left it out to take to the driveline shop and spin balance it. went to tackle the front and had to dig for an hour just to get to the nuts and bolts that hold the skidplate on. quite a bit of buildup under my tcase. lost track of time turning the wrench on the cv and finally got it pulled after dark. i hauled both shafts and a bag of ujoints down to the shop and told them to finish it up and spin them for me. 40 ounces off between the two of them. now there back and sitting in the burb waiting for me to get over this severe cold.
as soon as i get them back in, ill pass along the update. may be awhile.
 

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Discussion Starter #8
ok, color me pissed.
couldn't wait to put the shafts back in. climbed underneath and got to it. took my time to do it right, greased everything, torqued to spec and all. jumped in and warmed the motor up for a bit, bumped the idle down and then slid the tranny into drive and 'clunk'. same thing as before. chalked it up to a different problem and hit the road for the vibration test. just like it did before. hit 70 and it started to cycle. headed straight back to the house to call it a day. halfway home i wanted to check and see if having the tranfer case locked made any difference. don't know why, just wanted to cover all the bases. found the tcase to be stuck in hi. i have no clue if its locked or not. it wouldn't move. i even tried shifting into neutral with the truck in a slight roll. still nothing, and i was dang near standing on the thing.

this very much bad...
 

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I don't know if you've figured out your clunking problem however I do have one suggestion. Have you converted your NP203 from full time 4wd to 2wd? If not this might be a good time to replace the rear output shaft. It sounds like the crown gears might be worn which would cause the clunk. Replacing the rear output shaft will fix this by removing the crown gears completely. Mile marker makes a good kit (from what I hear)
http://www.milemarker.com/4-x-2-conversion.html
I'm thinking about converting my 73 blazer's np203 using this kit since it needs a chain replacement anyway. My dad had a 74 pickup with the same exact clunk and vibration you're describing and it wasn't U-joints, unfortunately the truck was a pile so no real money was spent on trying to solve the issue. Now for the vibration problem. I really don't think it's the chain because my chain keeps popping under heavy loads and looks like it's ready to fall off the sprockets but I can drive 70 with no problems. The only thing I can think of (and it's a stretch) is the angle difference on your driveshafts (angle where it comes out of the tcase and where it attaches to the diff) is more than 2 degrees (Why this is I don't know however I've checked out several websites which say it's a fact). I hope this helps and if not good luck.

Chris
 

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Discussion Starter #10
the truck is going into the shop for a locker and new ring and pinion. the clunk still hasn't been determined completely, but here is what i know:
if the tcase is locked and the front hubs are locked, no clunk.
if the tcase is locked and the front hubs are free, clunk
if the tcase is in hi, and the front hubs are locked, hard shift, but no clunk.
the rear shaft spins over 1/8 of a turn from drive to reverse or vice versus when the rear tires are stationary. everyone that has looked at it so far says the rear end is the culprit. i found its cheaper just to put in a new gear and locker than to have the old stuff inspected. the shop that is doing it is a true four wheel drive shop, not a honda shop that can do it if they have to. i'll let everyone know how it turns out.
 

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Discussion Starter #11
hold up, wait a minute...
okay, i went to the shop and told them to take a good look at everything before we start ordering parts that i may not need. the results were interesting. the front and rear diffs are in great shape all things considered. the noise is coming from the tcase and when they started probing around with the deathascope they found that the noise is strongest around rear output shaft. this seems to coincide with the fact that when you load the shaft it not only twists, but shifts ever so slightly to the side.
touchdown oilman!
lucky me: i still have a leftover 203 from a 74 3/4 ton. swap time!
i am still thinking about that locker, though...
 

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Discussion Starter #12
remember when i said color me pissed.
double that order, waitress!
had a driveline shop look over everything and they, too, thought it was the tc. the convincing factor was the dang thing not shifting out of 4hi into any other gear. i stood on the thing once and it didn't move. so... the tech pulls the linkage and manual shifts it into low range. now the truck won't move. bingo, rebuild the tcase and get me on the road. $725 later, the tc gets a new chain, sprockets, slider, a full rebuild treatment. takes an extra day to get it back together, big deal, i want it done right. i go down to pick it up mon night after paying for it over the phone because i couldn't get there when the shop was open, and the tcase shifts smooth as buttered silk. great. get the engine warmed up a little and put her in gear and
CLANK
same crap as before. put my wife behind the wheel and went through the whole drive reverse drive thing to be sure that it wasn't a fluke. no change. i jump back behind the wheel and take off with the appropriate amount of "this shop screwed me" tire smoke, and averaged about 110 on the highway back to the house. that along with shifting a big block at 6700 rpm prompted the water pump bypass hose to bust like a pinata. engines fine, my fault, i deal with that later. i called the shop tues and asked a few simple questions: where are my parts from the tc, why is the truck still making that noise, why didn't you tell me on the phone that it was still making that noise, and how can i be sure that you crackhead tech didn't put the tc into neutral and that was why the thing wouldn't move? no real answers, guy got defensive right away. understandable i guess. i'm not a nice guy on the phone. went tues night and picked up the parts that canme out of the tc and asked for a real explanation from the shop owner. nothing beneficial from that face time. they wouldn't even give me a discount of any sort to figure out what is wrong with the rear end, which they say is obviously the problem. duh, why didn't you fix it then?

sorry, just had to blow off more steam.
 

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That was nice of you to not rip that guys head off. I would have beaten my 725 dollars out of him, with a claw side of a hammer.
 

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Man, I feel for ya! Nothing worse than expecting to NOT hear a noise that's "been" fixed. Only to hear it still!
Could the "clunk" be emminating from the differential itself? Inside? (Just thinking outloud here) spider gears loose? sounds like everything else has been done. Don't know what to say!

I'm sure you'll let us know what it was when you find it.
Good luck
Troy
 

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Discussion Starter #15
i have a detroit coming for the rear and i'll tear into it and try and figure out where the slop is coming from internally.
 
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