2G Identify the noise - rear end

[1LE]

So, for the past few months (and around 2000 miles of driving) I've had this obnoxious sound from the rear of my '95 GSX. Starts at about 20mph and is pretty loud. Sounds like it's coming from both rear wheels. Resonates quite a bit at expressway speeds (made worse by the fact that the car has virtually no interior other than dash and seats). It sounds a lot like snowtires, but also has a bit of a "wubwubwubwub" noise in it too. This car DOES have Nokian WR G2s on it, which are essentially "Summer capable" snowtires, but it was not making the noise with them before it. These tires have been on it for over a year and are not showing any tread wear of note yet.

The volume and speed of the sound is directly related to the speed of the car. No relationship to engine speed, gear selected, turning, accel or decel. No change when suspension load changes either (such as going over bumps). No change on dry/wet/snow/icy surfaces. No play in the rear wheel bearings (which were replaced about 2 years ago due to failure/howling noise). Rear brakes (including calipers) were replaced this Summer (probably a month before the noise in question started) to correct a sticking brake, a brake that was horribly rusted, and a different (scraping) sound in the rear end from a delaminated brake pad. Trans, t-case, and rear diff all checked for leaks and none found. T-case was rebuilt about 6 years ago as it had started leaking after trans rebuild. Trans is a roughly 6 year old TRE rally build. Rear diff is original, but kept current on fluid changes. Car now has 129,750 miles. No torn boots found.

Any ideas? I'm at a loss for anything further I can try that doesn't involve random replacement/rebuilding...

As a side note, just for completeness since I'm 99.999999% sure it's just a horrible coincidence, but the engine developed what sounds like a light rod knock at hot idle right at the same time.

 

[oneslowwdsm]

Tires can develop noise after a certain period. Maybe try rotating the tires and see what happens. Rear differential or driveshaft carrier bearings could also be going out. What brand wheel bearings did you go with?

 

[Drop Top Road Trip]

Swapping your tires front to rear would be a quick way to confirm / rule out the tires. Don't discount the wheel bearings just because they were recently replaced, I had to have my rear wheel bearing replaced (free - under shop warranty) 8 times each side before they got it right on my '04 Focus Wagon.

 

[Drop Top Road Trip]

...Also, a slipped belt on a tire can make these kinda noises and be hard to see.

 

[1LE]

Hadn't considered a belt issue in the tire. That does sound like it would fit my symptoms. I've got a set of old worn out Pilot Sports still in a pile in the garage. Easy to test the tires if the weather cooperates. If I can get a day when the roads aren't snowy/icy, I can swap those on for a quick test drive to check that theory.

For wheel bearings I'd just been checking play and listening for noise changes in corners (including brake sounds as I can hear a hiss whenever rear pads make contact). Nothing so far. Any additional checks I can run? The replacements are OEM.

For the diff, I was kind of expecting a change on accel/decel, but that probably would just be for an internal failure. I'd imagine there are bearings at the driveshaft interface? Are those the driveshaft carrier bearings mentioned, or are those part way up the driveshaft (not near the car or manuals at the moment)? Any easy ways to check these without disassembly? (I'm not blessed with much spare time at the moment, any disassembly operations I can avoid would be helpful)

 

[oneslowwdsm]

It's pretty simple to do.

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Check that out. However, play doesn't always necessarily mean the bearing is bad. Hard to judge what's excessive play. On my moms ML320, upon higher speeds, the rear end would make a horrid moan and one of the driveshaft bearings had some serious play in it. Replaced it and noise gone. I would start with tires first though. Simple rotate and you should know..

 

[1LE]

Update. Beautiful day today AND I actually had some free time. Swapped over to a different set of wheels and tires, no change. Checked every moving bit rearward of the t-case. Rear axles have the tiniest amount of play (just enough to click, right side only requires light force, left side requires moderate force). Found a brake clip had slipped and was periodically catching on some of the rust on rotor. Bent that out of the way. No change. Not sure what else to check now. I've got a spare set of rear axles here, but I hate just trying swapping parts without a proper diagnoses.

 

[Julio Mendoza]

You need a new engine and transmission complete 4g63 engine $2500 online, change components yourself.

 

[1LE]

It took another month of driving around, but the problem is visible now. "Front" carrier bearing is shot. It's got so much play now that my driveshaft has started hitting my exhaust. "Rear" carrier bearing seems OK, but will have that replaced too. Looks like it's going to be a big mess, will have my local shop do this one. When the guy there checked it out this morning, he said given the condition of my driveshaft that I should try and find a gently used replacement driveshaft too. So, off to order carrier bearings and hopefully scrape up a replacement driveshaft too!

 

[2gmitsueclipse]

Find a used driveshaft to rebuild to make an easy swap. JNZ has a kit to service the driveshaft: http://www.jnztuning.com/product_info.php?cPath=21_30_669&products_id=1174

For rebuild information should you try it yourself, invest in a FSM, and follow the tutorial found here:

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This is just the first of five videos in the series. The others should be easily located.

 

[1LE]

Well, it's been an adventure. The best used driveshaft I could get was still in really rough shape. So, I gave it to the local shop because they have better tools. They still struggled with the rebuild due to its condition, but were able to find another partial driveshaft and make one good one out of the pieces plus rebuild parts. Finally today we were able to swap it in. The squealing and horrendous vibration in the back are gone, but the loud howl above 20mph and the minor vibration in the middle of the car remain. So, still hunting for the rest of the problem... :-/

For completeness, once again, I've got another 1600 miles on the car and the "engine knock" is still exactly the same. Wondering if maybe it's a trans issue and not engine after all? If it truly was the engine, it should have blown up months ago...

 

[pksystems]

If you used pieces of 2 different driveshafts, then it isn't balanced. That's why you mark the driveshaft joints in those videos, before disassembling.

 

[oneslowwdsm]

You could have contacted our vendors here and got yourself a good used carrier bearing or driveshaft pieces. (miller import parts)

Off topic but is there really no aftermarket bearings for our driveshafts? What options aside from rebuilding do we have?

 

[1LE]

Yeah, I can imagine the balance might not be perfect. Don't the replacement parts and even the rust and mud covering the driveshafts/in the joints throw it off too though?

I don't see any point to used carrier bearings when new stock ones are reasonably priced. These driveshafts used are incredibly hard to find and the normal condition seems to be totally trashed. My used driveshaft did come from Miller and looked usable to me (with less rust than my old one), but the shop found and pointed out multiple major issues with it in a couple places that I was too inexperienced to notice until they pointed them out when they inspected it (yoke tube damage beyond any salvaging, damaged ears/u-joint fitment issue for example). They used what they could of it and swapped parts from an old partial they found (after much digging) as needed (at no extra cost to me). Either way I needed the stuff from Miller and the price seemed reasonable, especially with having to get it shipped all the way to me, so it's fine. Seemed packaged well enough, but it's possible some of it happened in shipping. That's the risk you take with used parts, especially bought sight unseen/by description only, that have to travel across the country. I'll use Miller again, I don't want anyone to get the wrong idea, I think they're a good operation.

All that said, if I could go back and do it again, I would just order a brand new OEM unit from Mitsu (yeah, they're still available per my local parts guy that got me the carrier bearings and was up on how the front ones were discontinued and replaced with rears...). Would have cost twice as much, but I'd have had piece of mind knowing that *everything* was new and fresh.