help: something loose in drivetrain?

I have been noticing a disturbing trend in my driveline lately. It's gotten to a point of good consistency, now, so I'd like help in trying to diagnose the problem. If any of you can give me some pointers on what parts to check (and possibly how to check them), in order of likeliness, I would appreciate it greatly!

My Jeep: 1997 TJ I6 4.0L, 4" lift, 33" tires, D30 front, D44 rear (w/limited slip), AA SYE kit (installed myself), brand new CV front and rear driveshafts (front installed < 6 months ago, rear installed w/SYE kit in October-ish). Still original AX15 and NP231.

The Problem: Whenever I first start from a stop, and often when apply the gas after a shift (especially in 1st through 3rd gears), I am getting a small but noticeable "thunk". I can't so much hear it, but I can feel it both through my seat and through my pedal (I can feel it when riding as a passenger in my jeep as well). This thunk also occurs when I let off the gas pedal quickly while in gear, especially noticeable in lower (more torquey) gears. It has become a futile battle of me trying to match my engine RPMs EXACTLY when shifting, and pulling the clutch out VERY slowly, in order to try to get the thunk to not occur; I am successful probably 40% of the time when I try this. So, it seems something is loose in my drivetrain or in something that has tension under forward and rearward drive direction, and thunks when extra power is applied, or if a deceleration force due to engine braking occurs. BTW, all of this is happening in 2-high mode.

What should I check? So far, I've put the t-case in neutral and tried moving both the front and rear driveshafts. The rear had negligible play (pretty close to none); the front had quite a bit more play (but I have ruled that out as the cause since it is not even engaged at the transfer case end when I get this problem). Could this be control arm related? I have brand new teraflex adjustable rear control arms on it (installed at the time of my SYE kit), which I've kept greased properly... I haven't tried prying on them yet to see if they are the issue.

Thanks in advance for any advice or suggestions!

/Bob

Reply to
Bob
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Most likely your engine or tranny mounts. There's 2 under your hood and 1 mounting your tranny to the skid plate under your jeep. For the engine ones, visually inspect them and for the tranny, see if you can move it up off the skid with a pry bar. If it moves your mount is probably bad. If you do have 1 bad one, replace all three. I'd bet your shifter gives a good shake when you start from a stop also. Nick

Reply to
Nick N

If you get some jumping around when you use R, then I would be looking at motor mounts.

Reply to
CRWLR

Thanks for the suggestions. I will do that this weekend (tomorrow) and see what I can find out. What should I look for when "visually" inspecting the motor mounts, aside from obvious cracking? Does anyone (Bill? ;-) ) have any links to pictures of good and bad motor mounts so I have a good reference point?

Thanks. I appreciate the help. I'm also extremely pleased that no one is suggesting my tranny is going out or anything! =) I didn't think it was that, but it is still a worry in the back of my mind...

/Bob

Reply to
Bob

They could be cracked, torn, missing...also check the metal brakets that hold them. I've had one of those split. The same on those, you could get some play out of them if you use a prybar. If you don't see anything, simply check to make sure they are bolted down tight. Nick

Reply to
Nick N

Thanks for your suggestions, Nick and Crwlr!

I ended up deciding my motor mounts still looked ok, and my t-case mount was still good and tight as well. Then, I decided to roll back to the rear axle and check the control arms and any other suspension components...voila! My trackbar bolt was hanging halfway out; its nut had gotten loose and fallen off somewhere along the way, so my trackbar had been banging around in its axle mount, and the bolt had also been banging against the gas tank as it tried to back out (enough to put a pretty good dent/scar in the gas tank skid plating).

So, I went out and got a new bolt (to replace that nast torx bolt) and nut, put it in, torqued it down, and it's fixed. No more thunking; it drives 10 times better now, with none of that annoying thunking when I step on the gas.

/Bob

Reply to
Bob

I've had that happen with both my front and rear trackbar. In fact I've lost many a bolt here and there! You can take your rear trackbar off and sell it for a 6 pack, with the front I suggest putting some strong lock tight on the bolts, or atleast on the rear trackbar bolts also if you don't decide to toss it. Sheeess... I've even been driving down the road, hit a bump and heard ringing like a bell going off into the distance, I look and a bolt of mine is cruising down the street beside me.. nick

Reply to
Nick N

Oh yes. While I was down there, I went ahead and replaced the TORX bolt with a regular hex-head bolt, and got one that was a slight bit longer, adding a lockwasher to the mix. On top of that, I used liberal amounts of red threadlocker to keep that nut in place. If it falls off again, I'll be rather surprised (and annoyed ;-) )

Reply to
Bob

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