Rotational clunking

[kit]

I've got a fullsize 89 blazer with an automatic 700r and auto lock hubs, that has, on occasion, a rotational clunking. At first I thought I had driven over a brick, then it did it again and again.

I got it at a police auction, it seemed to have been parked for quite a while, bottomed out, in the middle, over a large mound.

The previouse owner had run the motor dry of oil and seized it. A few days of penetrating oil and manual turning with a bar, and amazingly it runs fine.

At low speeds,both in drive and reverse, there is sometimes a clunking that seems related to speed. As I increase speed so does the clunking, until, at about 15 or 20 mph, it stops.

It's 33" tires with no lift and I know that the clunking isn't the fender interference. That's just on turns and is quite distinctive.

My joints all seem fine, there doesn't seem to be any play in front of or behind the transfer case. Just the tiniest play back and forth on the rear drive shaft. The front axle joints show no signs of wear and I don't see evidence of any loose suspension bolts or a loose transfer case mount.

Having opened the 10 bolt rear differential I know that it's an open differential with all of it's teeth intact. The fluid was relatively clear with no broken bits, just the fine stuff stuck to the magnet and at the bottom.

The bugger is that it's not constant or predictable, and it hasn't done it in a month. After having been much more frequent, like 1 out of 2 times driven, and then less frequently. So it's difficult to pin down.

Any thoughts?

 

[muscle]

When doing a tranny swap i had put in the front shaft and finger tightened the bolts. next day i finished her up and took it for a test drive. got about 1/4 mile and heard a clunking noise. was the cv clunking on the crossmember. it was just loose enough.

 

[Emmettology 101]

I'd check and make sure all your lugs are tight. Also check and see if all your crossmember bolts and tranny bolts are tight. Go over most everything making sure all the bolts/nuts are tight.....

Also slide a long screwdriver inbetween your d-shaft u-joints and see if they have any play. And check the front and rear rearend yokes too. May have a pinion bearing loose.

One other thing to check is the front driveshaft slip yoke. I've had those go bad/get loose and cause some funky noises...

 

[goldwing2000]

Glad to see you finally registered!

I'm kit's mechanic and we've already checked most everything I could think of. The only thing that might still be suspect is motor/trans mounts but it just doesn't sound like that kind of a noise.

I haven't personally gotten under there to check out the driveshafts but I think that may have to be the next step. I've already checked ball joints, tie rods, wheel bearings, replaced the upper steering link and gave the underside a quick once-over (hey, it was dark and raining). Since it does it in 2wd with the hubs unlocked, I have my doubts that it's the front driveshaft but I think we're just going to have to take a Saturday afternoon and check out everything. Since the noise has been absent for a month, that makes it that much more difficult.

And this is all in between tearing down my '80 K10 for scrap and swapping in a D44 and 14BFF into my '89 Blaze.

If the weather ever cooperates, that is...

 

[Leper]

Could it be the autohubs?

 

[goldwing2000]

Could it be the autohubs?

They have already been disassembled, inspected, greased and reassembled.

(not by me, though)

 

[cegusman]

Pull the auto hubs and drive around and see if the sound goes away. If so they are the problem.

 

[goldwing2000]

Like Kit said, the problem is that it hasn't made the noise in a month or so, so we don't know if it's fixed or just on vacation.



If it starts up again, then we'll start pulling non-essential parts and see what's what.

 

[kit]

Hey, thanks for the discussion.
It's nice to have my mechanic at my back.
I'm hesitant to do more than necessay but at the same time would'nt mind swapping the auto hubs for manuals, the 700r for a 400 turbo, and the 10 bolt for a 14 bolt rear end.
Luckily my mechanic reighns me in.

 

[francis]

I would suspect the u-joints in the rear driveshaft. I had a 82 chevy lwb 2wd truck that did the same thing! I am a mechanic (of three years now) but at the time I had only been working on vehicles for like a year and a half. I would be driving along and as I sped up the noise would get louder and more rapid but if I punched it it would go away. well I checked the u-joints and they were tight. so I went to my boss and told him that at times it sounded like someone was going at my driveshaft with an air hammer he got in my truck and put it in nuetral then told me to get under my truck and check the u-joints and sure enough one of them was about to fall out!!!!! so needless to say I replaced them. so what I learned is that with the truck in park the driveshaft was in a bind because the truck was trying to roll and it was in park so there was pressure on the drive shaft keeping me from moving the joint! hope this helps. I think this has been the longest post I have ever posted!!! WOW

 

[kit]

Well, I've just checked the U joints, in neutral, to find that they do have a bit of play.

I also topped off the transfer case to find it to be 1 1/2 quarts low.

While down there checking the joints I spun the front drive shaft back and forth enough to have the auto hubs lock. That seemed normal, until on the last turn from stop it was still engaged.

Turning the rear drive shaft to check the joints and backlash, I could hear what sounded like slack in the transfer case chain being taken up, as it came to it's abrupt stop.

After all this I drove it down the block to the turn around and the clunking came back as long as I held the left turn. It stopped as I straightened and came back with the right turn into the drive way. Stopping again as I backed out and stayed gone as I made a couple of turns when parking, on the street.

This takes me back to the last time it clunked, a month or so back. That time when it clunked, I thought it may be the hubs, and on a tip from this forum, I immediately stopped, put it into reverse, backed up a bit, and returned to drive. That was the last time it had happened.

Being the first time, it has clunked, in over a month of driving. I suspect that it was the shaking or rattling that I was doing, while checking the various joints.

As it feels to be in the front end, should I suspect the auto lock hubs, even though the inspection didn't show any wear?

This weekend I'll be replacing all of the U joints, just to eliminate that variable.

Any thoughts?
Thanks
Kit