Horrible Mystery Subaru Sound

[Hamilton Felix]

I have a 1987 Subaru GL 4x4 wagon with 5-speed.

It has recently been through various troubles. I forded water and bumped over rocks and debris during the October floods.

My Mechanic friend fixed a few things, including the "Y" style catalytic converter that had been thumped and plugged itself with dislodged carbon buildup until the engine would do no more than a fast idle.

The car sat a bit, then I picked it up. I have a horrible dragging/grating sound, like a brake dragging metal on metal or a bearing going bad. It's road speed related, not engine speed or gear connected. Couldn't find any hot hubs after driving for a while. Puzzled and fiddled for a while.

Finally put the car in the shop, up on four jackstands. Then I tried "driving" it with the wheels off the ground. The sound is there, and it doesn't need to be in four wheel drive. Put it in 4th, and a good fast idle shows about 20 mph on the speedo. Suddenly step on the clutch and turn off the engine, and the sound continues until the wheels stop turning. Have an assistant hold one front wheel while doing the same thing, so the other wheel is really turning at 40 mph: No change. Same if the assistant holds the other wheel.

The Subi has a transaxle, with a transfer case of sorts tagged onto the back, all in one gearbox (it has a low range with about 1.6 to 1 reduction). I think this test narrows it down to transmission output or past that, but before spider and side gears in the differential.

We drained the gear oil. If memory serves, I have Redline gear oil in it. Magnetic drain plug had only a little soft gray sludge. When pouring the clean-looking gear oil back in, I saw a few "sparklies" in the bottom of the drain pan, but not many.

The only thing I realize I might have tried but didn't: The Subi has a neutral position in the transfer case. It's not marked on the lever, but between 4 Hi and 4 Lo there's a neutral. I might try the above experiment with the transfer case lever in neutral. That might narrow it down a bit more.

My Mechanic friend suggested "LubGard" as being one of only two oil additives he believes in. He thinks it may help. I am willing to gamble a few bucks, but I think there's something serious going on. I suppose I can drive it until it self destructs, but that could be inconvenient.

Any ideas?

 

[Opus Dei]

Try looking around the front wheel assembly/brakes for something like a piece of gravel. It makes the same sound, and only while moving. I've had them get trapped in the caliper or between the caliper and metal shield on the spindle assembly. You may have got some debris from dragging mud or flowing water.

 

[Hamilton Felix]

We looked for anything obvious that was dragging. At one point, I actually did have the left brake dragging because the parking brake had been used and the cable isn't all that free. But remember, the sound is the same if the left wheel is stopped and right wheel turning, or right wheel stopped and left wheel turning, or both wheels turning.

I considered that maybe this was a "normal" noise that should have been isolated from the car but a rubber mount had failed and put a gearbox in direct contact with the unibody No such thing; Subaru has good isolation mounting of engine and transaxle.

 

[intothatgoodnight]

Hmmmm -- my 98 Subie was making all sorts of gear/drivetrain noises AFTER I had a safety inspection -- noise seemed to be associated with drivetrain, and sounded as if rear diff was headed south.

Took car over to Subaru, and had them put on lift and pull rear diff plug -- everything seemed normal, and fluid level was correct.

Had two senior Subaru mechanics and myself poking around under the car -- test drive around the block and back up on the lift -- could not locate the source of the noise.

Finally, one of the mechanics noticed that the rear body to subframe steel mount was slightly bent upwards, allowing the rear (axle) subframe to touch the the steel body directly, which allowed the transfer of normal axle and rear drivetrain noise into the body shell, which was acting like a sounding board in a piano, amplifying the noises of the diff/axle to a very audible level.

Here is how this occurred -- when the safety inspector needed to check the rear brake pads, he used a hydraulic floor jack to lift the rear tires off of the ground, so that the rear tire could be removed and a visual of the rear brake pads could be made.

Unbeknownst to him, he had misplaced the jack lifting pad, forcing it to press against the steel edge of the rear subframe mounting point, directly adjacent to the rubber body-to-subframe bushing, as it lifted the full weight of the rear half of the car. Since the "unbent" space between the subframe and the body appeared less than a few millimeters normally, it took very little bending to cause the contact.

A quick yank with a crowbar solved the problem.

Check the body-to-subframe bushings for proper integrity, and that the two are distinctly separate and not touching.


intothegoodnight

 

['plain o joe']

a Lesbaru?

sounds like a main bearing....jmho

or a cracked Fly wheel

 

[Hamilton Felix]

I've been wondering about unintended axle-to-body-or-subframe contact. This is in front, since it sounds the same with the car on jack stands and in two wheel drive. It's definitely road speed related, but had to be ahead of the spider and side gears in the differential -- because having an assistant hold one wheel still makes no difference. And it's behind the transmission, because changing gears has no effect.

 

[intothatgoodnight]

Check the front and center subframe mounts -- make sure that there is NO metal-to-metal contact, either caused by bent mounts OR because of mount rubber doughnut deterioration.

Also check the engine and center drivetrain rubber mounts -- same thing -- the rubber doughnuts DO dry-rot over time, allowing the possibility of metal-to-metal contact, and the direct transference of normal engine/drivetrain noise into the body shell.


intothegoodnight

 

[Hamilton Felix]

Thanks, I'll take another look when I can get it up on stands again. I thought we'd ruled out "unintended contact," but you've mentioned places we weren't looking. It would be great if this is all just "normal" noise that is accidentally being telegraphed into the car.

And if it is what I've suspected, I can confirm by just driving until it self-destructs, right?