98 XC70 Intermittent Rattle Is Kicking My Assets!

[AJ1G]

Been doing a lot of highway hauling with lately with our 98XC, over 7K in the last few months, most of it with a heavy load of tools in the rear cargo area, and sometimes hauling a small 4X8 utility trailer with up to about 500 pounds of stuff in it. I keep the trailer tongue weight minimized, just nose heavy enough to keep the hitch from popping (happened once a few years back and it trashed my tailgate) XC has about 207K on it. Late last week, all hell seemed to break loose on one trip. Developed a really bad brake rub (turned out the right rear brake pads were down to the metal after about 20K, even though there has never been any evidence of a stuck caliper and it retracted as easy as pie when I put new pads in). The left rear pads showed very little wear - were almost at new pad thickness. Wierd. Quickly threw in a set of cheap Autozone rear pads to get through the weekend, bought new rotors and PBR semimetallic rear pads from FCP Groton to put on when I had more time. Brake rub eliminated with the new pads.

On the same trip where the right rear brake rub got really bad, suddenly, and I mean suddenly, developed a sharp speed dependent "bicycle card" metallic rattle. Seemed to be around once per wheel rev, turned into a mild rumble sometimes around 40-60 MPH coincident with the rattle character going away. Sometimes would have the buzzing rattle and no rumble at the same speed range. Sometimes I would have no rattle or rumble at all at any speed. First few miles after I replaced the brake pads, no rattle. Then it came back and got progressively worse,although it would sometimes disappear completely for a while altogether. The rattle rep rate was absolutely speed dependent, and was happening (tink.tink.tink) down to very slow speeds (just crawling). Sounded like it was coming from the left rear wheel. That, and the observation that my ebrake was suddenly not working at all led me to suspect that the ebrake shoes might have come adrift on that side. The fact that changes in driveshaft load (light and hard acceleration and deceleration) had absolutely no effect on the rattle character when it was present, also was leading me to think I had an ebrake problem.

I pulled the left rear brake rotor tonight. No obvious signs of anything amiss in the ebrakes, and no obvious signs of any impacting on the shoes or the inside of the e brake drum on the inboard side of the rotor. I took the ebrake components out of hub as a diagnostic to eliminate them as a source. Put on the new left rear new rotor and new PBR pads.

Road tested car - rattle was still present, just like it was immediately before I started working on the left rear brakes. So - not ebrake realted (at least not the left rear), probably not the right rear (don't hear anything on that side).

Back under the car..now suspecting drive shaft or viscous coupling...could feel some slight play across the various joints, but nothing gross, and no obvious noise coincident with exercising the freeplay by rocking the driveshaft and the rear wheels that sounded anything like the rattle. I then had an AHAH moment when I found the aluminized plastic heat shield above the driveshaft and cat converter adrift on its left side. The material had torn away from the two skirted retainer nuts on the left side of the drivehaft/exhaust tunnel and it was sagging onto the cat and the driveshaft. Shaking it caused it to impact against the cat and the driveshaft and made a metallic ringing sound that sounded exactly like the problem rattle. Thought I had a buzzkill. I was starting to think the noise was actually coming from somewhere a little forward of the rear halfshafts, and this location filled the bill. Re-secured the shield using a couple of beer bottle caps as field expedient fender washers, and took a long drive around town. Rattle was gone and stayed gone..life was good..was thinking about what a great posting I could write about how I nailed it......until...after about a five mile high speed run down I95, as I was slowing to a stop on the off ramp...tink...tink..tink..back to a light buzz as I sped up.......ITS BAAACK! ARRRGH! It's nowheres near as bad as it was before I fixed the heatshield, but the source apparently is still there. A quick look and reach under the car shows the heatshield is still secured the way I fixed it.

So its starting to smell like a bad CV/U joint on the driveshaft, or maybe a bad mid-span bearing/bushing. May end up pulling out the driveshaft and running FWD in the near term. What is hard for me to make sense out of though
is the total insensitivity of the rattle to changes in shaft torque loading. When its there at a given speed, it does not change at all when going into or out of neutral, accelerating, or slowing with and without braking. Only the repetition rate changes in proportion to road speed. Maybe that is pointing to the mid span shaft bearing? I remember sometimes getting a little rumble from the mid span bearing on our 83 240 Turbo, especially if the car was fully loaded. However, that rumble was very sensitive to torque loading. Any advice would be greatly appreciated. I need to get this squared away and get the car back on the road as soon as possible. In the AM, I am going to take all of the load out of the cargo bay to see if that has any positive effect (you can see that the car is squatting to the rear a little from the all load I've been carrying around lately).

[holler1]

Check the front CV joint on the front-to-rear driveshaft (propshaft) carefully for play, a bad boot and/or loss of grease. That is exactly what mine sounded like when it failed. If the driveshaft is the problem, Colorado Driveshaft sells rebuilt shafts. A good diagnostic is to remove the shaft and see if the noise goes away. You can drive it as FWD as long as you want.

[AJ1G]

Thanks for the info. The nominal 20 miles to work today sounded pretty good. The big bad rattling is gone, which must have been the heat shield impacting on the shaft and or the cat. There is still a low amplitude buzzing speed related rattle intermittently, and a light rumbling resonant response around 50 MPH that comes and goes. Most likely is the fron CV joint I think. Probably has been there all along, but was not easily audible over the heat shield rattle.

I think you were the one who did the tutorial on the driveshaft drop procedure. Any gothcas in the process? Is it particularly hard getting at the cap screws on the top of the coupling flanges to the point you need to rotate the shaft (and of course all four wheels) to get at them?

Thanks for the info on Colorado Driveshaft. Do they sell only the CV joints, why would I want to replace the entire shaft if the problem is only at the front CV?

I'm wondering if the root cause of the CV joint going out is that the dropped heat shield rubbed on the CVjoint boot and then the joint lost its grease...and the root cause of the heat shield dropping off was cat generated heat softening the plastic of the shield under the retainer nuts to the point that the shield literally fell down around the nuts- thats what looks like happened.

Go to Gemba to find the truth!

[AJ1G]

Problem got bad again - so I pulled drive shaft last night and early this morning. Problem determined to be worn out middle shaft steady bearing - was causing the middle u-joint to orbit around instead of staying centered and it whacked the shaft and exhaust tunnel. Lots of bright metal on the rear shaft's part of the u-joint yoke and a big shiny spot on the tunnel itself at about 10 o'clock looking aft from the impacting. The u-joint needle bearings themselves seemed OK, the aft CV joint seemed OK with boot intact, and the front CV joint felt OK but was on its way out with a trashed boot and grease thrown all over, most likely from being cooked by cat converter heat. The middle bearing damage explains the intermittent nature of the noise and I can see how it could be independent of torque load on the shaft and its bearings. I suspect the heavy loading and towing of late may have changed the shaft alignment enough to put extra stress on the bearing rubber insert and hastened its failure.

Two halves of a circular clamp that appeared to be riveted to each other at one point fell out of the middle bearing support area early on in the removal process. The rivets on the two pieces were rusted/broken, and its not clear what they were doing there or how they had been attached to anything else. From their size, they look like they may have been holding something around the shaft but they had no insert nor any visible means of attaching to anything other than themselves. What are these pieces? Please let me know.

The shaft removal info on this site was very helpful.

A few lessons learned -

Don't waste a lot of time trying to undo the hex bolts on the flanges that are up high and out of sight. I wasted a lot of time on this trying various socket extensions, hex keys and box wrenches. Turned a flex cable extension into a limp pretzel. Just take the car down off the ramps and jacks and reposition the car to move the problem cap screws into an easier access position.

I had to remove the four bolts of the middle bearing support bracket to allow the two shafts to sag enough at the middle to get the rear CV flange to clear the VC flange. As soon as the bracket went down the shaft then fell out on its own.

Although I haven't seen it mentioned in other shaft removal postings, it seems like it would be a good idea to put some short hex cap screws in to the remaining angle gear output and VC input flanges to protect the hole's threads form crud and rust while running around without a drive shaft. Going to put them in, but have spent way to much time under the car in the last two days to do it tonight!

Car so far feels no different driving w/o the drive shaft, but will be replacing it - going to check out a local shaft shop here in Montville CT, which was recommended to me and also into getting a refurbed one from Colorado Driveshaft.

Was very impressed how solid and rust free most everything was under the car after 13 years and 207K. Only had one problem bolt, one of the 4 middle bearing support bracket bolts that jammed up coming out.

[holler1]

AJ1G,
Sorry I didn't get back to you on the driveshaft hex screws, but you figured it out OK. Another way is to jack up the wheels and turn them to turn the shaft. My recollection is that it will turn with one rear and one front jacked up. The Colorado Driveshafts shafts include the center bearing and both CV joints. When my driveshaft failed the first time, I just replaced the front CV joint with a kit that cost around $200 at the time, but the repair only lasted a couple of years. The second time I bought the CD refurb shaft for $450 and it's still going well. Sounds like your front CV joint was bad (or going) as well as the center bearing.

I heard from some people when mine failed that it was important to mark the hex bolt locations before removing them, since some of the bolts are longer. However, I didn't do that and it didn't seem to make a difference. Putting screws back in the connectors while driving FWD is probably a good idea.

I don't remember the "mystery" clamp you mentioned. I looked at my pictures again just now and don't see anything might help identify it. I suppose it might be part of the center bearing if it came apart. Mine was intact when I got it out.

The lack of rust on these cars is surprising. Mine had rust on the old exhaust system and on the differential, but not much else. I've had two trucks about the same age and both had/have severe rust on almost everything.