4.2 D4D Rear differential noise & repair

January 21, 2019

I bought a 2005 D4D Rav4 in poor condition and have been gradually going through and sorting it out - turbo, clutch, timing belt and water pump, service, fluids, and so on.

I was hearing a knock from the back when dropping the clutch in 2nd gear, so I figured it was the rear differential mounts. I've just replaced them (the rear one was barely still attached to the metal ring that holds it) and the knock is definitely now gone. However I'm getting quite a pronounced hum, particularly between 40-70km/h. The pitch rises with speed, and it's only audible when using the throttle to cruise or accelerate. The rear differential has new oil in, and when I replaced it I didn't notice any sign of metal shards etc. The oil was done a while before the mounts.

Based on the sound, and the fact that the mounts were bad for probably quite a while, I'm guessing that it's an internal bearing on the diff. Possibly the pinion bearing if the diff has been off centre a lot.

Has anyone had issues with this previously?

If it's possible I would like to try to repair the diff rather than just replace with a 2nd hand one, which may well also have issues. Are there rebuilt kits available? Is it possible to repair these?

If I have to remove and disassemble the diff to identify and order bearings etc, this will take a while. Is it possible to remove the driveshafts, diff, and prop shaft and continue to use the vehicle as fwd while waiting for deliveries?

January 21, 2019

Before you do anything drastic, have a read here. Apparently, the transmission whine can be addressed by a lighter oil. I have the same symptoms, and I think it's worth a go.

January 21, 2019

Hi IanML, thanks for that information. When I replaced the oil I actually used a GL5 80W90, so it's already the slightly lighter oil mentioned in the linked post. Unfortunately it didn't do the trick for me. I hope that it does work for you though!

Luckily the diff looks fairly easy to remove. Easier than the front mount at least which was a bit of a pain to extract.

January 21, 2019

If I read the linked message correctly, the whine was allegedly from the transfer box, for which the recommended grade is 85W90, and the substitution of 80W90 the cure. Have you done that, by any chance?

January 21, 2019

I replaced the transfer box and the rear diff oil with 80W90 at the same time when doing the clutch, about 3 months ago.

There was a quiet whine before that I always thought was coming from the rear, and others said the front. However when I replaced the rear diff mounts (which were completely gone) yesterday the quiet whine was suddenly much louder - loud enough to hear over the radio. So it's definitely coming from the rear diff, and replacing the oil hasn't cured it.