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How to identify M635CSI diff casing please.

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Boggie
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How to identify M635CSI diff casing please.

Post by Boggie » Mon Aug 06, 2018 8:26 pm

Hi all,

I have been offered a diff casing which I am.told comes from a late 635CSI. According to RealOEM this should be the same case as mine and as the pictures show it is in excellent condition, I am.considering doing a case swap.

However, it is a fair distance from me and I have no evidence that it came from a 635CSI, any other model has a different case. Please can any of you who know their E24 diffs, give me some pointers on checking it is the right one for my M635CSI? E.G from looking on RealOEM, 8 bolts on the driveshaft bearing retainers seems to be a good start. What else should I look for please?

Thanks,
Ian
1985 M635CSI
Classic Car Collector & Restorer.

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Brucey
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Re: How to identify M635CSI diff casing please.

Post by Brucey » Mon Aug 06, 2018 9:15 pm

what is wrong with your extant case? If it is just grotty-looking, it is far easier to fix that than put the internals in a new case.

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Boggie
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Re: How to identify M635CSI diff casing please.

Post by Boggie » Tue Aug 07, 2018 8:31 am

Hi Brucey,

I am going to rebuild the diff with new LSD clutch, bearings, seals etc . My case is rather rough so I have stripped it, stabilised the rust with 2 coats of RC800 and I was planning to follow this with coats of Dinitrol primer and stone chip. However, whilst this should ensure the casing lasts another few decades, it is going to let down the rest of the underside which should look like new when I am done.

As am planning to fully recon the diff anyway I might as well rebuild it into this new VGC case as it does not mean a lot more work but I want to be sure it is the correct case before I buy it.

Any pointers in identifying the correct case would be very gratefully received.

Cheers,
Ian
1985 M635CSI
Classic Car Collector & Restorer.

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Brucey
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Re: How to identify M635CSI diff casing please.

Post by Brucey » Tue Aug 07, 2018 3:31 pm

"not much extra work". Hmm. You need to set up the preload on the front bearing using a crush washer and also to make sure the contacts in the gear teeth are correct. Both procedures are a bit tricky (and can scrap parts if they go wrong) and I would not choose to undertake them simply for the sake of the appearance of the diff casing. By contrast the parts of the diff that need to be maintained most often are easily accessed from the rear of the case and the rebuild work is a lot simpler.

But each to his own and all that.

If you are worried about not being able to identify the casing, just take lots of photos of yours and compare them.

BTW IME diff casings that look like boat anchors clean up pretty well. You need to remove the rust, not 'stabilise' it, BTW; the rust is invariably thick and scabby, and grit blasts off quite easily.

cheers
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Re: How to identify M635CSI diff casing please.

Post by Boggie » Tue Aug 07, 2018 4:53 pm

Thanks Brucey,

I media blasted the case (and rear subframe) before the rust stabiliser coat :)

The case, whilst still intact has lost most of the external webs to rust and the walls are very thin in places, the surface of the case itself is very pitted. Even with a coat of primer and stonechip it will stand out against the newly stripped and Dinitrolled floorpan, refinished and rebushed subframe, new suspension, brakes, lines etc.

As I am already pressing out the bearings and replacing internals it is only a couple of hours more work to rebuild the internals into the new case. Whilst I would normally agree with your POV on this, it seems a shame not to swap cases whilst I have the chance, especially considering the effort and time spent on the rest of the car.

So, as far as the case goes, if I ensure the case is the same size and design, the only real way to ID the case is the same as mine is the 8 bolt bearing retainers?

Cheers,
Ian
1985 M635CSI
Classic Car Collector & Restorer.

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Brucey
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Re: How to identify M635CSI diff casing please.

Post by Brucey » Tue Aug 07, 2018 7:59 pm

some obvious differences in a large case diff are

- the bearing retainers
- the bolt pattern in the rear cover
- the width across the drive flanges (or bearing retainers)
- the length from the input flange to the output flange

you may find this photo useful
Image

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Boggie
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Re: How to identify M635CSI diff casing please.

Post by Boggie » Tue Aug 07, 2018 8:29 pm

Brucey, you are a star.
That is exactly what I need and I am very grateful for the info. If ever we meet, I owe you a pint!
Ian
1985 M635CSI
Classic Car Collector & Restorer.

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Ralph in Socal
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Re: How to identify M635CSI diff casing please.

Post by Ralph in Socal » Wed Aug 08, 2018 8:08 am

This only applies to the first generation of rear cover BMW differentials as used in e23/e24/e28/e30.

The Medium Case units have the Fill and Drain Ports in the Rear Cover.

The Large Case unit has the Fill Port in the Cover and the Drain Port is located on the case under the left side drive flange.

Ralph
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
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Re: How to identify M635CSI diff casing please.

Post by Boggie » Sun Aug 12, 2018 5:27 pm

OK. So I have been measuring the diff on my M635CSI and comparing it to your information. It is a big case diff and I have checked it is LSD (wheels rotate in the same direction), just in case someone swapped it out in the past. I am off to look at the case tomorrow evening and will check various measurements but from what I can gather I ony really need to check the following:

It is the large case (measurements, drain hole in the side)
It has 8x bearing retainer bolts
The cover has the same bolt pattern

the one I am finding difficult to get my head around is input flange to output flange, mentioned by Brucey. Not sure what measurement I am taking here...

Thanks,
Ian
1985 M635CSI
Classic Car Collector & Restorer.

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Re: How to identify M635CSI diff casing please.

Post by Boggie » Tue Aug 14, 2018 12:38 pm

Thanks for all your help chaps,

After lots of careful measuring, my M635CSI and standard 635CSI are indeed the same large case. So I am now the proud owner of a 635CSI rear subframe, complete with diff, brakes, prop etc, all in great condition. I have also found a diff specialist nearby who will swap the internals from my LSD case into the good one for £395, including all new bearings, seals etc so rather than do it myself I will get them to do the swap.

Just got to disconnect prop and drive shafts then drop out my diff, which looks like just 4 large bolts (front and mid) on the diff housing and the rear mounting. Mid bolts look like a pain to get to but I might squeeze a 19mm ratchet ring spanner in there. Just hope I don't need to gat a breaker bar in as I will have to drop the subframe....

Wish me luck!
1985 M635CSI
Classic Car Collector & Restorer.

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Re: How to identify M635CSI diff casing please.

Post by Brucey » Wed Aug 15, 2018 4:42 pm

don't use a ratchet spanner to break the bolts on the top of the diff; use a conventional ring spanner with a cheater bar on it instead. You may even find that you need to sacrifice a cheap ring spanner by using it as a 'slogging spanner'.

By all means use the ratchet spanner to wind the bolts out after they have been loosened, but you will likely break a ratchet spanner if the bolts are properly tightened to start with.

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Re: How to identify M635CSI diff casing please.

Post by Boggie » Wed Aug 15, 2018 7:10 pm

Good call, will do.
Thanks
1985 M635CSI
Classic Car Collector & Restorer.

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Re: How to identify M635CSI diff casing please.

Post by Ralph in Socal » Thu Aug 16, 2018 6:11 am

Place a jack under the diff then remove the cover mount bolt. You can then lower the entire subframe assembly to gain better access to the bolts on top of the diff.

I use a 1/2 drive breaker bar and cheater pipe with a 19 mm 6-point socket to loosen the bolts. Ratchet the rest of the way.

Of course remove the axle flange and driveshaft bolts first and move those out of the way.

Ralph
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)

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Boggie
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Re: How to identify M635CSI diff casing please.

Post by Boggie » Thu Aug 16, 2018 10:13 pm

After all my concerns, it all turned out reasonably quick and easy work today. After a liberal coating of penetrating oil on the various bolts attaching my diff, I started by removing the 'new' diff from the fully-loaded rear subframe I bought. The main challenge was how to lock the diff so I could undo the bolts, without having a gearbox or handbrake attached. For the driveshaft bolts I was able to rig up an adapter to allow me to pressurise each brake calliper in turn using a foot pump but the prop shaft was a little more fiddly, trying to jam it with a spanner got me there in the end but it would have been easier if I had three hands...

The diff on the car was easier as I selected 1st gear to lock everything up so the only real challenge was access to the top bolts. Once I found a suitably cranked ring spanner, combined with the straight one from the BMW toolkit, I was able to encourage the 4 main bolts by belting the spanners, inch by inch, with a short lump hammer. One these, the prop shaft and the rear cover bolt were undone, I removed the off side drive shaft and undid the near side from the diff, letting it rest on the exhaust. Then it was simply a matter of slowly lowering the supporting hydraulic ramp and wiggling the diff a bit to free the prop studs and get the near side output flange over the exhaust.

So, after about two hours I had two diffs on the workshop floor. An old and very rough case with LSD internals and a very good condition case open diff. This has allowed me to clean and paint the subframe and floor above the diff too (bloody messy job). I dropped both diffs off to John at UK Axels, who are only about half an hour from me. He is going to swap the internals and rear cover from bad to good and fit new bearings, seals etc. I should be able to collect from him on Monday for refitting on Tuesday.

Ideally before Tuesday I want to replace the complete braking system; master cylinder, discs and pipes from BMW, hoses from Goodridge and refurb the calipers with the BMW refurb kit. So far I have stripped, cleaned and painted the front calipers, including reassembling one with new seals (the other's paint was still tacky) and the new front discs are fitted. If I can manage this there is a faint possibility I could go for an MOT next Thursday. Just to see what it fails on :)

Thanks all for your help and advice.
Wish me luck....
1985 M635CSI
Classic Car Collector & Restorer.

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Re: How to identify M635CSI diff casing please.

Post by plip1953 » Fri Aug 17, 2018 6:36 pm

Reading this reminds me that for many years I've had a brand new, never used, rear diff unit sitting at the back of my garage. The price was right at the time and it looks broadly the same shape/size as the one fitted to my '88 635 CSi, but it had attached to it a label indicating it was suitable for a 745i. From memory I've pretty sure that means it's a different final drive ratio, but I thought it was worth having in spite of that.

I guess these kinds of items are now N/A, but are they likely to be worth finding a home for for or simply kept "just in case"?
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Phil
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Boggie
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Re: How to identify M635CSI diff casing please.

Post by Boggie » Fri Aug 17, 2018 7:34 pm

They are indeed. The guy doing the swap for me used to have a brand new E23/E24 LSD in his workshop but ended up using it as a donor for parts. Imagine what that diff would be worth today! I was talking to a guy in Germany who had a low mileage M5 LSD but he wanted €LOTS for it.

The 745 / 750 (and probably other 7, 6 and 5 series) did use the same large case diff as the M635/M6/M5 but with differing ratios and most non-LSD. The 635 diff I found was from a very low mileage front end write-off. Can't wait to get it back and get mobile again (once I have brakes that is...)

Cheers,
Ian
1985 M635CSI
Classic Car Collector & Restorer.

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Re: How to identify M635CSI diff casing please.

Post by wattsmonkey » Sat Aug 18, 2018 6:23 pm

Hey Ian, good work on getting the diff out: heavy buggers, aren’t they?!

If you don’t mind my asking, how much does a diff specialist charge? I’ve got the internals from an M635 diff and a spare case, but like Brucey says the skill involved in setting up the tolerances is a bit beyond me.

Thanks,

Rob
"Most of it necessary; all of it enjoyable[!]" LJKS
'86 M635CSi #367 Bring the Noise.
'84 635CSi, dogleg fun

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Boggie
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Re: How to identify M635CSI diff casing please.

Post by Boggie » Sat Aug 18, 2018 11:10 pm

Hi Rob,

I got a few quotes and they range between 350 and 500 quid. The guy I chose, mainly because he is only 30 minutes away, quoted me £395 including new bearings and seals. I will let you know how I get on.

Cheers,
Ian
1985 M635CSI
Classic Car Collector & Restorer.

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Re: How to identify M635CSI diff casing please.

Post by wattsmonkey » Sun Aug 19, 2018 7:32 am

That’s great, thank you.
"Most of it necessary; all of it enjoyable[!]" LJKS
'86 M635CSi #367 Bring the Noise.
'84 635CSi, dogleg fun

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Boggie
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Re: How to identify M635CSI diff casing please.

Post by Boggie » Sun Aug 19, 2018 9:53 pm

You're Welcome!
1985 M635CSI
Classic Car Collector & Restorer.

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