xyzgeoman Posted August 22, 2006 Share Posted August 22, 2006 Here's how it happened...The right rear tire got a bulge and the whole car would shimmy above 40mph. In my brilliant mind I thought that I'd just switch to the donut spare for the 60 miles home so I could at least go 50mph (donut's speed rating). After ~20 miles of ~50 mph I noticed a smoke trail behind me. I stopped and looked. The rear diff was SMOKIN'. It was then that I realized what I'd done. DANG! I changed back to the lumpy bumpy and limped home after a long wait to cool things down. At home I drained the rest of the oil and added new. No grinding noise now, but lower drain plug was covered with metal filings. What should I expect? How long until I'm needing a new diff? WHat do they run $? Quote Link to comment Share on other sites More sharing options...
nipper Posted August 22, 2006 Share Posted August 22, 2006 what model year and mileage is this? Did the donut have the same circumfrance of the other tires. I'ld be more worried about frying the AWD unit then the diff, unless the diff was a viscous rear and the tires didnt match. Diffs tend to roar when they die, and irs a slow painful process. You will want to have the diff lube changed if you honestly think thats what was smoking. WHat did it smell like, as gear oil ha s a rather unique smell. nipper Quote Link to comment Share on other sites More sharing options...
xyzgeoman Posted August 22, 2006 Author Share Posted August 22, 2006 90 Legacy Sedan. ~160K. Donut was way smaller than other tires. THe smoke was definitely gear oil from the rear diff. Stanky! I did change gear oil...So now I just wait until the rear diff grinds a slow death? Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 22, 2006 Share Posted August 22, 2006 rear diffs are a dime a dozen. $35-$100 depending if you can find it locally or need someone to ship you one. i'm with nipper, i'd be much more concerned about the center diff (manual) or transfer clutches (auto) in the trans. much more expensive and a much bigger job. rear diff is no big deal. perfect excuse to upgrade to an LSD unit while you got it off. Quote Link to comment Share on other sites More sharing options...
nipper Posted August 22, 2006 Share Posted August 22, 2006 If it is an automatic change the tranny fluid asap, if it is a manual cross your fingers and hope. Also see about getting a spare that matches all the other tires. I'ld be more worried about the AWD unit slowly chewing itself up. Rear diff it it starts to devlop a whine or a roar you know youve done damage, as a drastic tire size differnce could do a lot of damage in the driveline, period. nipper Quote Link to comment Share on other sites More sharing options...
cannonball Posted August 22, 2006 Share Posted August 22, 2006 I think I may have done the same thing to my rear diff as well. 2000 OBW with LSD. After I bought new tires I noticed that the rear end was noticeably louder which I attributed to tire noise. I went on vacation last week (5 hour drive at freeway speed) and noticed when I got there that the noise was a little louder. I had the car loaded down with stuff so the back end was weighted down. On the way back when I got of the exit ramp to get to my house I noticed that when I turned left at speed the rear left tire sounded like a whump,whump,whump noise. It didn't do this to the right or straight ahead. There was no smoke though. And no bucking at slow speed albiet I have a manual. I'm still driving the car right now back and forth to work until I can get it to the mechanic on friday. My other thought was a bad half shaft or wheel bearing. I guess I'll have to wait and see. Quote Link to comment Share on other sites More sharing options...
nipper Posted August 22, 2006 Share Posted August 22, 2006 I think I may have done the same thing to my rear diff as well. 2000 OBW with LSD. After I bought new tires I noticed that the rear end was noticeably louder which I attributed to tire noise. I went on vacation last week (5 hour drive at freeway speed) and noticed when I got there that the noise was a little louder. I had the car loaded down with stuff so the back end was weighted down. On the way back when I got of the exit ramp to get to my house I noticed that when I turned left at speed the rear left tire sounded like a whump,whump,whump noise. It didn't do this to the right or straight ahead. There was no smoke though. And no bucking at slow speed albiet I have a manual. I'm still driving the car right now back and forth to work until I can get it to the mechanic on friday. My other thought was a bad half shaft or wheel bearing. I guess I'll have to wait and see. check the tires, but unless you ran with a smaller tire on one side of the axle, you should be ok. LSD will fry and become a live axle (no diff operation) if you cook it. Your LSD is a vscous coupling, which like the AWD will die a fast death. nipper Quote Link to comment Share on other sites More sharing options...
cookie Posted August 22, 2006 Share Posted August 22, 2006 I'd wonder a bout a wheel bearing. A heavy load on a trip and whump whump whump and noise changes in corners? Take a look at the wheel bearings too. Regardless it need to be put up in the air and inspected. Quote Link to comment Share on other sites More sharing options...
xyzgeoman Posted August 22, 2006 Author Share Posted August 22, 2006 So, since Lil' Su is a manual I guess I just cross my fingers and wait for a new development. Is that what I'm hearing? Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 22, 2006 Share Posted August 22, 2006 This thread raises an interesting question. What do you when have a flat on a MT Subaru and an "emergency" spare? With the AT you can slip in the FWD fuse and drive away. Quote Link to comment Share on other sites More sharing options...
nipper Posted August 22, 2006 Share Posted August 22, 2006 This thread raises an interesting question. What do you when have a flat on a MT Subaru and an "emergency" spare? With the AT you can slip in the FWD fuse and drive away. If you have stayed with the factory size tires, you will be fine, just make sure its properly inlfated. If you have change tire size, you need to buy a full sized spare, it will fit in the sooby. nipper Quote Link to comment Share on other sites More sharing options...
cannonball Posted August 22, 2006 Share Posted August 22, 2006 What should I expect? How long until I'm needing a new diff? WHat do they run $? If the grinding noise was gone and when turning sharply doesn't cause any ill effects I would think that you got lucky and shouldn't have to worry about it. Quote Link to comment Share on other sites More sharing options...
nipper Posted August 22, 2006 Share Posted August 22, 2006 One other thing, the donut is only an emergency tire, they are not rated for speed or any great distahce, and are not all that great in the wet nipper Quote Link to comment Share on other sites More sharing options...
cannonball Posted August 22, 2006 Share Posted August 22, 2006 This thread raises an interesting question. What do you when have a flat on a MT Subaru and an "emergency" spare? With the AT you can slip in the FWD fuse and drive away. I drove on a half flat tire for about 25 miles like a DA one time. I was wondering why the steering was all cockeyed. That's before I learned of the importance of equal tire size. Quote Link to comment Share on other sites More sharing options...
ferret Posted August 22, 2006 Share Posted August 22, 2006 With a 5 sp manual, Subaru recommends the TEMP spare be put on the front. So if you have a flat in the rear, you have a tire to move as well as replace. That way if it is a smaller temp spare, it's on the 'open' differential and not on a possible LSD rear. WRX's and others with the LCCD front differential ( Torsen closed differential ) come with full size spares tires only. Quote Link to comment Share on other sites More sharing options...
xyzgeoman Posted August 22, 2006 Author Share Posted August 22, 2006 So why do they even put the donut in there? Just asking for trouble. Quote Link to comment Share on other sites More sharing options...
nipper Posted August 22, 2006 Share Posted August 22, 2006 So why do they even put the donut in there? Just asking for trouble. its meant for an emergency only. a flat on a major highway is an emergency, its even considered a 911 emergency in some states. Thats its only purpose. Well that and some crash protection. nipper Quote Link to comment Share on other sites More sharing options...
xyzgeoman Posted August 22, 2006 Author Share Posted August 22, 2006 So what symptoms should I be looking for to know that things (rear diff or center) are about to blow up? THings seem to be running fairly smoothly now, except for a faint humming noise coming from the rear diff. Quote Link to comment Share on other sites More sharing options...
nipper Posted August 22, 2006 Share Posted August 22, 2006 So what symptoms should I be looking for to know that things (rear diff or center) are about to blow up? THings seem to be running fairly smoothly now, except for a faint humming noise coming from the rear diff. Rear differnetial will devlop a loud roar that changes volume with speed. That hum is ominous. Center differnetial you will get torque bind. nipper Quote Link to comment Share on other sites More sharing options...
cannonball Posted August 22, 2006 Share Posted August 22, 2006 Rear differnetial will devlop a loud roar that changes volume with speed. That hum is ominous. Center differnetial you will get torque bind. nipper When you say ominous what do you mean? My roar is constant in pitch, yet fairly constant in volume as well oddly enough. I would say it's the same volume and pitch from 30-60 mph. This is what befuddles me. I would think there would be a direct correlation between tires rotating and pitch. Quote Link to comment Share on other sites More sharing options...
nipper Posted August 22, 2006 Share Posted August 22, 2006 When you say ominous what do you mean? My roar is constant in pitch, yet fairly constant in volume as well oddly enough. I would say it's the same volume and pitch from 30-60 mph. This is what befuddles me. I would think there would be a direct correlation between tires rotating and pitch. well lets get your tires fixed first. only thing back there that runs at one constant speed is the fuel pump. nipper Quote Link to comment Share on other sites More sharing options...
91LegLS Posted August 22, 2006 Share Posted August 22, 2006 rear diffs are a dime a dozen. $35-$100 depending if you can find it locally or need someone to ship you one. i'm with nipper, i'd be much more concerned about the center diff (manual) or transfer clutches (auto) in the trans. much more expensive and a much bigger job. rear diff is no big deal. perfect excuse to upgrade to an LSD unit while you got it off. Can an older Legacy be upgraded to an LSD? I have a '91 with 4EAT. Quote Link to comment Share on other sites More sharing options...
Manarius Posted August 22, 2006 Share Posted August 22, 2006 Can an older Legacy be upgraded to an LSD? I have a '91 with 4EAT. Sure. Either find a rear LSD that matches your final drive, or have an open one converted to VLSD for like $250. For you, you would need a 4.11 Final drive Rear diff with LSD - a rare find but found on newer Impreza RS's (99-01). Quote Link to comment Share on other sites More sharing options...
xyzgeoman Posted August 22, 2006 Author Share Posted August 22, 2006 So, I need to fear the hum and dread the torque bind? THe current hum does change with wheel speed, but it's not a roar. Also, I know torque bind from my other Subie...no torque bind at this juncture. So, I guess I'll be shopping around for a rear diff to put in so's I'm not stuck somewhere 80 miles out Also, I'll try to attach a photo of the rear diff drain plug (magnetic) when I pulled it last night. Quote Link to comment Share on other sites More sharing options...
nipper Posted August 22, 2006 Share Posted August 22, 2006 Sure. Either find a rear LSD that matches your final drive, or have an open one converted to VLSD for like $250. For you, you would need a 4.11 Final drive Rear diff with LSD - a rare find but found on newer Impreza RS's (99-01). they can be converted? who does that? nipper Quote Link to comment Share on other sites More sharing options...
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