Clunk Sound From Rear Of Car

[socal470]

Hi everyone,

I have a 99 LX470 with 120k miles. I took it to a Lexus mechanic for service. When I got it back, I would hear a binding/grinding sound coming from the rear differential when I turned. After trying to convince me it was normal, the mechanic finally looked at it and determined that they hadn't used LSD fluid in the differential (4 weeks and 1000 miles elapsed).

From the moment I got it back, I could hear and feel a "thunk" from the rear of the car when I let off the brake or accelerate. There is also always a lot of backlash in the driveline when i transition from coasting to acceleration. I hear a thunk and feel a shock throughout the car. Sometimes I also hear the same thunk while braking when the transmission shifts from 2nd to 1st. Everything looks and feels tight under the car. If I lock the center differential, the backlash goes away.

Mechanic claims the backlash is normal and the thunk is the driveshaft which is also normal. It wasn't doing it before he messed with it, though.

Any ideas? I'm thinking there's something wrong with the clutches. Any help appreciated.

[mscott]

I just purchased a '99 LX w/80K. FWIW there is no backlash in the drivetrain ever. No matter what type of transition everything is tight. I can only say from my limited experience that it would not appear to be "normal."

[denslexusgx470]

i don't know, but could this be the same clunk as the one in the GX (except we got our clunks from factory, not from mechanics that don't know what they r doin). :cries:

[lexus ls430]

i have the same problem in my 03 rx

[Romer]

i have the same problem in my 03 rx

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If the splines have been overgreased, that would cause the problem. Mark the location of the drive shaft in relation to the diffs. Take the driveshaft off. Mark the two pieces of the shaft so you can put it back together the exact same way. Separate the drive shaft and clean out all the grease. When completely clean, rub some grease on the splines. Grease the U joints while its off. Re-install the drive shaft and see if that fixes it.

It's about a 45 - 60 minute job the first time. Hardest part is getting the screws of. Have a breaker bar for your socket handle or use a long 1/2 inch socket wrench to give you leverage.

[Jim_Chow]

[snip]If I lock the center differential, the backlash goes away.

Mechanic claims the backlash is normal and the thunk is the driveshaft which is also normal.  It wasn't doing it before he messed with it, though.

Any ideas? I'm thinking there's something wrong with the clutches. Any help appreciated.

←

Just thought i'd mention that you shouldn't lock the center diff and drive on high traction surfaces. Reason is, the center diff lock forces the front driveshaft/axles to turn at the same rate as the rear. However, when you're turning, the front and rear driveshafts naturally turn at a different rate since they are travelling different distances (think of a big rig trying to make a tight turn... the front axles drive a much longer distance so the rear wheels can barely clear the curb). So your locked center diff wants to resist these forces, causing the drive train to "bind." If the forces are strong enough, you can damage the drivetrain (all that stress has to go somewhere). Off road or on slick surfaces, the wheels can slip and release the drivetrain stress.