E70 Subframe was rusting quite badly

[Leslie]

Wirebrushed it down and added a layer of waxoyl to slow down the rot which was taking quite a hold (2009 car) and just turned 150k this morn , rest of floor under plastic covers looks good but the exposed rear subframe looked like it lived in the sea and the floor above the subrame had started to peel and rust too ! A dirty job but needed doing Oh and the front pinion seal of the rear diff is leaking too

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[X5Sport]

Could quite well be the road salt collecting underneath that caused this - it’ll have the same affect as the sea sadly A few years back I bought a Kärcher under chassis cleaner device and use it as soon as the ‘season’ ends to try to get as much out as I can. It has bothered me about just what could be lurking trapped behind all of the plastic screening underneath and suddenly pops up as a big problem. In older cars you knew where to look for rust traps but that’s harder these days, especially if you don’t gave access to a 4-post lift to work underneath from.

[Leslie]

It's almost certainly the road salt is causing this and I think this is the only rust problem area on the x5 ,although all the little fixing clamps on the heat shields are rapidly turning to dust as they are mild steel and the shield is ate though perfectly around 2 small bolts at the back panel which hold 30mm approx washers to hold up the shield. I have got 2 larger 50mm penny washers to reattach this if the nuts unscrew This should give it a few more years as id say in 2 years this would be serious if left , I noticed the ends of the flexi's, there seem to be 4 underneath are looking rusty too and will probably need changed in a year or so , a little bit crumpled away of the left flexi holder when touched so that bracket may need replacing too.

I was looking online for info about the pinion seal replacement but there is very little out there now tis is dead . this setup is used with e90 as well I think and bmw have used some silly over complex prop to diff coupling and done away with the diff flange , the 50mm nut (which must be replaced each time) has glue in the threads that sets like concrete in 5 mins and there is a 65 mm yes 65mm star nut to set the preload . Its all a bit much really and my usual mechanic has never done one before and assumed there was a flange like conventional diffs have.

[X5Sport]

These help……and don’t ask! You are going to need a serious torque wrench with at least 500Nm capability! The pinion bearing is seriously tight. The image sequence matches the ermmm ‘instructions’

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[X5Sport]

Page 2….and still don’t ask! These are the only two listed tools with data I can find. The others look like sockets etc.

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[Leslie]

Thank you very much x5sport that is a great help and whoever came up with this setup deserves a special place in hell.
I thought the main issue was getting the 50mm nut off the prop with the special glue holding it but it appears it gets worse, by the look of it that torque wrench has a splined socket that holds the diff pinion to unscrew the star nut which is coated in the special glue also hence the 500nm torque. The actual pinion torque to tighten it is tiny but you just tighten it to a point mark where it was before removing.
Nobody is going to have a pinion socket but if the handbrake is on it shouldn't be able to move anyway . What a nightmare mine only leaks a little on a slope downhill so may just top it up see how much it has lost first as this is a major job. I dread to think what BMW would charge!
I can buy the star spanner for 40 quid and a 50mm spanner cheap but the spline socket no idea

All this for a 20 quid seal

[Leslie]

Just thinking you could slide the prop back on and jam it while you undo the star nut with the proper spanner.

[X5Sport]

[cynic mode]”Change the seal sir? No no no, this is a BMW, you need a complete new differential.”[/cynic mode]

[Leslie]

Let's hope not lol, looking again torque wrench not needed it's just being used as a breaker bar.. Despite looking a good few times I still can't decide what the nut onto the prop actually does, it only sits into the diff star nut in a recess so essential the diff and prop are only joined by the spline :confused. Com lol
Think I will stick to topping up the diff oil as even the star nut needs bmws special nut glue you can't buy anywhere

[X5Sport]

My only thought was that it might be some form of pre-loading device given it must not go beyond a mark when being fully tightened. Other than that it’s just a dust seal/cover?

[Leslie]

Yes the big star shaped nut (number 1 in second pic) is a preload for the pinion bearing ,glued on so very tight but without the glue actual torque would be tiny .
,It seems confusing as the hex nut (number 2 in first pic ) on the driveshaft is tightened to I believe 55 ib/ft on reassembly ,it would be shown on the driveshaft installation how to and you would of had to remove the same hex nut of the driveshaft first before doing the above job as its already off the driveshaft in those pics but still on the star nut but its not actually screwed to it , its just sitting on top of it with the aid of the dust seal . confusing isn't it and I've trauled utube for vids already

[Leslie]

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Got this tricky diff pinion seal job done today , had left it down with my local mechanic but had left my work clothes in the car so came back down an hour later to find they couldn't get the 65mm nut off , I had left down a 12 point socket and 3/4 drive ratchet and a length of box section to go on the end ...this baby was tight ...
I had a go myself but it had cooled too much was stuck solid so I said heat it again with heat gun , when we had a good heat in it one mighty shove on the box section and it was away but it stayed tight and a few turns later it had to be heated again as it had set like concrete, when it was 1/2 way off it eventually became easy enough to not need the box .

I bought a 65 mm 3/4 drive 12 point socket( same as transit hub apparently for 16 quid ( forget 1/2 inch drive it won't be man enough and a 50 mm laser open ended spanner for the same price.The spanner can't bee too thick or it won't fit in the small gap between prop and diff . You can get by without the the £600 BMW special tools , not that you can find them anyway to hold the pinion as the handbrake will hold the diff from turning if its working correctly. Changing the actual seal is the easy part it just needs tapped on once the old one is levered out.
Not an easy job and not possible without a lift , the new 50mm nut has sealant on it already so loctite 262 red was used for the 65mm nut to reseal it

[Leslie]

Well had over a year and 10k with no issues and no oil leaks now a whine has suddenly started 2 days ago and I think a replacement diff will be needed Car now on 160k Bearing kits are 300 quid and people on ebay are looking 1500 quid for a refurbished diff exchange ! No point buying bearings as I don't know how to sort and torque the pinion bearing and suspect its tricky

[X5Sport]

Nothing that I can find in official documentary’s that gives any information at all about rebuilding the diff. I assume that means in their usual fashion that BMW will only offer a remanufactured unit with Dealers unable to repair - as is so often the case with transmission parts on these cars!

There should be an ident number on the diff somewhere so you know which variant you need. I’ll see if I can find the LCI/later engine codes too. These are the pre-LCI and seem to be the only ones.

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[Leslie]

Thanks there is a sticker on top of the diff after crawling underneath and about 50 pics with fone I was able to make it out , not much room above it. Your right bmw won't fix it would be new /refurb probably 5k . Got a lead on one trying to get it lifted , the sudden nature of the noise starting bearings might not fix it anyway as its high miles now ,no saying another will be better for long but at least I will be able to have a look at my leisure see if its fixable .