JimsGX

1991 LS400 - How common are problems with the rear differential on the first gen cars? Took my 91 with 84k miles to my local mechanic today. I've been chasing an elusive drive train vibration for the last 18 months. He put the car up on the lift and ran it up in drive. There was an obvious howling noise coming from the differential that you don't here when the vehicle has all four sneakers on the ground. He decided to drain the differential oil (which I had replaced 7k miles ago when the vibration first started) and found that the magnet on the drain plug was completely loaded with metal shavings. He's pulling out the differential and having it rebuilt by a local transmission shop that does a lot of differential work. He's of the opinion that this is definitely the cause of my vibration. It happens consistently between 25-30mph and has a howling noise from the rear on the highway between 60-65mph. Lexus had told me this howling noise was due to the installation of an aftermarket front exhaust Y pipe. I guess I'll find out after the differential is rebuilt if the noise is still there. He doesn't think its very likely a problem with the ring gears, more likely with one of the diff short shaft bearings or diff propeller shaft bearings inside the differential


Has anyone had their differential rebuilt before? I'm wondering what the cost was for it...

Thanks,
Jim

leboyd1

Obviously, metal shavings in the diff is not what you want to see. I don't think i've seen this at all. It seems someone has really torn it up.

Is your mechanic a Lexus mechanic? If this doesn't work, replace the rear transmission mount. What your describing is the vibration occurring at around 2k rpms. This is the most common problem with vibration on the LS. It's 8 bolts, 4 nuts, 30 minutes and $75 for the part.

Horsepwr

Yup ,mine had the same vibration ,replaced the tranny mount (easy and cheap) ,problem solved !!!

JimsGX

Indy mechanic at this point. I've paid Lexus twice to diagnose the problem and they said it was the driveshaft. So I had them replace the driveshaft which includes the carrier bearing to the tune of $1300... Did nothing to fix the issue. When I first noticed the problem at around 77k miles, I started chasing it. Full tranny flush and differential fluid at that time (by dealer), then replaced the tranny mount, then the steering damper. I've had UCA's & LCA's replaced in the front, 4 new tires, three balancings, three alignments, etc... Now that the rear end is apart, I'm also having rear UCA's put in as well...

The differential is out of the car now and the mechanic opened it up today. The ring and pinion gears appear to have some pitting on them. The shop he typically uses to rebuild differentials told him that these are very bulletproof differentials and thought it was unusual to see pitting on the ring and pinion. When I had the diff fluid changed at 77~78k miles at the dealer, I asked if there were any metal shavings on the drain plug and they told me there weren't. Since this was at the very beginning of when I started noticing the problem, I guess its possible that the shavings weren't there at the time.

Anyways, there's a used differential on the way and my mechanic guarantees me that this is the cause of the vibration. The three differential bushings are being replaced now as well. Hopefully this will finally fix the problem...

JimsGX

I'll be getting my 91 LS back tomorrow with a new differential installed, three new carrier diff bushings, and new rear OEM UCA's. I had them install new front UCA's as well while they had it. I had put daizen's in the existing front UCA's a while back and they were too hard and ruined the ride. We (mechanic and I) opened up and inspected the old diff. The small gear in the bottom center of the diff (sorry, I don't know the names of the individual gears in there) that directly turns the two larger side gears that directly run the two half shafts, had a lot of play in it and would raise up and get slightly cocked sideways when spinning just by hand. I can only imagine how it has been behaving under a true load. When the replacement showed up and we opened that up, there was no play in that small gear in the center and it spun true. I'm very hopeful that the new diff will solve the vibration problems I've been chasing for the last 18 months and throwing significant dollars at over that time period trying to fix (new propshaft, a variety of bushing replacements, new tires, tranny mount, steering damper, etc). I'll post the results after running it through its paces tomorrow night.

Jim

loperman

To Jim:
SO whats up?! Did you fix it? Is the vibrations gone? Please let us know! Because i might have the same problem on my 94 LS!

JimsGX

The differential was bad. Most noticeable problem was a howling noise from the rear between 60~65mph. Replaced the diff and the three differential bushings (two that go through the rear subframe and the one that bolts up to the floor of the car).

My mechanic and I put it way up on his lift and ran it up to to 30~40mph. We got under the car and you could hear a loud howling noise coming from the diff. Drained the diff and the magnetic drain plug was loaded with fine metal shavings.

Funny thing was that the howling when we were under the car was so obvious between 30~40mph, but when driving, you couldn't hear anything at that speed, only at 60~65.

Figuring out the problems with my car has been difficult because there were a bunch of things wrong with it at the same time when I bought it (only 76k miles on it). It's been like peeling back the layers of an onion in order to get each one fixed. Each time a problem was fixed, it would become a little easier to figure out the next one. As of right now, I only have one very slight/insignificant vibration left between 25~28mph and its coming from the front half of the car. I think its an aftermarket exhaust Y pipe that's causing it because I've been tweaking the hangers on the exhaust a bit, and have had some success in getting it to go away. Before fixing other problems, it was impossible to pinpoint where this was coming from...

Do.Man

dang man how much did that run you?
if you dont mind me asking.

trukn1

I had to have mine replaced last year on my 92. My diff was LOUD and nearly on the verge of lockup. I noticed that mine pretty much took a dump while I was in a store shopping. Car would not go over 20 mph and the noise coming from the diff was like a flat tire flapping around. I puled one from a junk yard and replaced. Has been fine ever since. I do, however, need to replace my diff bushings.

williamb82

does anyone have the part numbers for the rear diff bushings?

JimsGX

41651-50010 = Single front mount that bolts up to the bottom of the body.
41651-50080 = Right side thru subframe
41651-50090 = Left side thru subframe

The two subframe diff bushings insert and lock in differently. Note the position of the alignment marks / arrows on the old bushings before you take them out.

williamb82

thanks, that actually helps alot. after more reading, i think ill replace the carrier arm bushings first. all 4 of them. i have the pulsation when braking and this seems to be the cause for it.

JimsGX

If it were one or the other of these actually causing a vibration / pulsation when braking, I'd look at the Adus 505's and the associated strut bar first over the 583's and LCA #2 bushings.

williamb82

the 505's and 5056's is what i intend to replace first, though i will replace ALL the bushings in due coarse. once all the bushings are done, ill save for the megan ez street coilovers to finish out the package. and gonna try to grab a 2nd gen rear swaybar from the junkyard as its slightly larger.