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I think I need a new diff....

Posted: Mon 06 Aug, 2018 7:29 pm
by babington
The differential in my 1990 420 SE is starting to make quite a bit of a whining noise. It gradually builds in volume with speed, it seems to go quiet on a trailing throttle and grumbles when slowing/coming to a stop.

As far as I know it is not an LSD and has not been changed or repaired in 300,000 km.

What is the going price for a good used one? Alternatively, has anyone had one of these refurbished, can they be refurbished/repaired, is it economical to do so?

Does anyone in Western Australia have a good used diff they no longer need?

I am in Perth.

Thanks

Re: I think I need a new diff....

Posted: Mon 06 Aug, 2018 8:14 pm
by Dean 560 SEC
I may know someone with a spare in a 420 SEL that he's parting out in Perth - Ive just sent him a text.

Text me on 0451 059 901 and i'll send you his details when he gets back to me.

Dean

Re: I think I need a new diff....

Posted: Tue 07 Aug, 2018 7:41 am
by John Green
If the car is a "keeper", I would suggest getting the diff rebuilt, New bearings and seals will fix the noises, for the rest of your ownership. Should be around $1k plus the R&R. A used diff is exactly that, a part that is the same age as the one that has just failed.

Re: I think I need a new diff....

Posted: Wed 08 Aug, 2018 6:29 pm
by hents99
I’d suggest also repairing current diff.
New bearings (4 pcs) price could be 100-150 dollars... oem parts are usually 4x more expensive. Remove bearings and buy new ones with same bearing numbers from hardware shop.

Re: I think I need a new diff....

Posted: Wed 08 Aug, 2018 6:58 pm
by Lance
Check the oil first you might find that the noise is caused by low oil level. If it is not low then just change it, the noise might go away. If it is a bit worn and an oil change helps then you might get a few more years out of it.

Re: I think I need a new diff....

Posted: Wed 08 Aug, 2018 7:47 pm
by Dean 560 SEC
My mate got back to me - $300 for the diff, but you need to take the whole 420 SEL(included in price of diff).

Let me know if you want his number.

Re: I think I need a new diff....

Posted: Tue 04 Sep, 2018 7:24 pm
by babington
Thanks Lance,

drained all up a total of maybe (just) 20ml out of the diff, new oil in and no more noise.

Re: I think I need a new diff....

Posted: Tue 04 Sep, 2018 8:12 pm
by Lance
You're welcome, always good to try the simple things first.

Re: I think I need a new diff....

Posted: Wed 05 Dec, 2018 5:49 pm
by carina
I’ve had the same ‘whine’ in my 420se and had it rebuilt by Diftronics in Sydney at 370,000 km. It was so nice to get back to quiet. $1200.

Re: I think I need a new diff....

Posted: Sun 09 Dec, 2018 1:01 pm
by AMG
If you only got 20ml out, then you still have issues which need attending to - it also means that the damage to bearings is likely to be terminal, which means you'll have it out sooner than later.

clean the area of all dirt and dust, and look for any dark wet areas. Usually the side seals are weeping or have gone.
If there are any leaks at the rear hat, you're going to need to R&R anyway to fix, just the same as you'll have to pull that to replace the side seals.

Orings are the next to perish as well as pinion seal.
A poorly tightened pair od diff plugs can also contribute.

But the kicker for not having any oil (20 ml is not enough to even touch the crownwheel) is that almost certainly, the planetary gearset will have excessive wear damage, and it might be completely shagged.

Obviously rebuilding one is the right way to go - but a word of advice.

If you're going to rebuild the diff, rebuild the halfshafts with new boot kits and clean out the CV's and regrease at the very minimum. Preferably overhaul the complete pair of shafts.
Replace the rear hub bearings - they have just as many km as the diff - and while the halfshafts are out, it's a lot quicker.
replace the diff mount bushes - this will ensure that the diff is correctly aligned with the tailshaft and prevent any further vibration issues.
replace the tailshaft couplings, reat transmission mount and the centre bearing hanger, regrease the tailshft splines. Check the engine mounts are not collapsed.

A Diff-out service provides the opportunity to clean everything as well. It is by far and away the best approach to ensuring a long serviceable life.

If possible, get a spare diff and pair of halfshafts, have those properly reconditioned and then do a swap over, and rebuild the hubs / bearings. That makes the job quicker and less fussy (time on hoist costs $$$)

keep an eye on the oil.

Re: I think I need a new diff....

Posted: Thu 13 Dec, 2018 3:34 pm
by gazman
Well said AMG.
If you're in there do the lot :wav:

Re: I think I need a new diff....

Posted: Wed 23 Jan, 2019 6:32 pm
by babington
Thanks for the above advice, no doubt that you are right......but......I bought the old girl on a whim, sight unseen from the auctions as I had always liked the w126.

So far I have been more than happy to keep it running, attend to safety and minor issues and use it as a daily driver for my short commute.

The suggested works look as if they would be more than the value of the car. Yes, the back end would then last another 300km - which is a lot more than I would. Its quiet enough for me at present so that is probably it for the time being.

Re: I think I need a new diff....

Posted: Wed 23 Jan, 2019 7:14 pm
by CraigB
That sounds fair enough..... mind you, if i had the space I would grab the 420 that Dean said about for $300 - pick the eyes out of it and off to the crusher if you can't hold onto it (how much of the $300 will you get back from the crusher for the car?). For a few hours work its a cheap diff (assuming the guy has run it and knows it is quiet) - not that much work in changing a centre over. From experience if you have the $300 one on your shelf, the current one will last forever and must make a bit of noise - if you don't your diff will blow up soon! And making that recommendation on your last comment that this is a whim car you are enjoying and not looking at it from the angle of keeping it going and treasuring it forever.... at this stage anyway.