400fanboy

'm noticing a dull"thud" that's been getting louder and louder when switching between reverse and drive. While investigating, I noticed quite a lot of geometry change in the rear driveline. Is this amount of flex normal?

Transmission mount was (supposedly) replaced ~20,000 miles & 4 years ago.


Bonus points you can hear just how creaky some of the bushes in the rear multi-link are. I wish it wasn't so expensive to replace all of them

Gerf

It looks and sounds like your idle speed is high, the rear driveshaft coupling really hits hard. I would just lube the crap out of those bushings and see if it helps.

400fanboy

Yeah the car was still in open loop cold start for the first clip, so the revs were ~1200.

A few of the clips in the vid are with the engine a lot warmer. For example the side shot at 0:07 the engine was pretty close to operating temp.

400fanboy

Thud between reverse and drive is getting louder. Vibration from the rear (on smooth pavement) is getting worse. As seen in the video, it feels like someone is back there with a 50lb rubber hammer hitting the rear axle. Sometimes it feels like there is a wheel balance\road force vibration. The rear of the car never feels "settled'. This is after I fixed the preload issue with the shocks, which was something ELSE ontop of this, that was causing undue 2nd order vibrations on impacts and a too-stiff damping rate.

Got it up on a lift and I'd love to get your guy's thoughts.


Rear toe arm and front diff cushions are allowing the entire knuckle is rotating. I'm sure some level of play is allowable, the car is up in the air after all. But those bushes seem to be moving quite a lot, as is the differential. Behavior which is mirrored with the car on the ground.

There are aftermarket Ebay (yuck) bushes you could re-do the rear knuckle with. OEM diff cushions are available.
https://www.ebay.com/itm/222750936937

On the plus side, my driveshaft flex discs on both ends look super healthy. The only cracking is on rubber covers for holes that go through the disc. The structure of the disc itself on both ends don't have any cracking or spider-webing. Driveshaft center support bearing (not pictured in video, I shined a light up there later) looks healthy, no red dust or undue movement as far as I can tell (nor symptoms of it failing). The car is holding up incredibly well for being 25 years old. It's just this one ****in thing.

Losiracer2

looks like your trailing arms are bad as well as the bushing on the knuckle that keeps it in place. These help the diff from rotating so much when in good shape, so I would have those replaced and then inspect the movement after to see if its still clunking. I would take everything apart and inspect the bushings on those 6 arms more closely. My rear UCAs were bad on my car with play in the balljoint and the 2 arm bushings, which helped stabilize the rear a lot on the highway. Lexus still sells them for about $177 a pop for UCF20 95-00 models, at least they did in May 2020 when I did it.

fondu

Ah yes, the joys of trying to keep the old LS going smooth down the road.

In all honesty its very impressive how the original suspension has held up in these heavy cars. However at this age there is no doubt you will have to replace many of these parts if you want to get her back to the original suspension tolerances when going down the road. As it stands, the rear alignment is always slightly moving out of spec going over bumps etc. with faulty suspension parts. The front diff bushings being toast are causing excess movement in the intended driveline operating angle which can cause vibrations.

The rear is labor intensive and expensive to repair. I say do it piecemeal, starting with the front diff and trailing arm bushings.

400fanboy

The last time I looked at this, I could have sworn each knuckle was $750+. Or maybe that was the cost of both...

I just looked again, Lexuspartsnow has it for $325 + ~$20 in shipping. Amayama has it for 175 + $60 shipping.

I imagine, to redo the rear axle, you would need: knuckle with bushes pressed into it, wheel bearing to go inside of it, all of the rear control arms. Is there a seal kit for the axles? Anything else you would address?

I just came up with this to re-bush the rear axle. I have no idea what I'm doing. Just doing this up so I have the ballpark parts cost of what it would cost.



And a separate question - can the front diff bushings be replaced independently? Without diss-assembling the rear end? Because I think the first thing I would want to try, if applicable, is to replace those and only those. And have a chance at a partial fix and get some more life out of the rear end.

fondu

The knuckles probably don't have the bearing/hub etc. but I really don't know. Might be worth it to call the dealer and ask.

You have to remove the diff to replace the bushings. You don't have to remove anything, just disconnect the axles and the driveshaft from the diff. You may need to loosen the large locking nut on the slip joint of the driveshaft to allow it to be "pushed forward". This will give you clearance to drop the diff and press out/in the front bushings. Your rear diff bushings in the subframe look ok but if they are torn you may want to knock those out as well.