Final drive gearing

Zitat von Noggie

Why bother getting an old used diff that can break down any time.

I think cost is a big factor. Used diffs are affordable, custom-built ones probably not so much for most of us.

Zitat

For the 850.
http://www.quaife.co.uk/BMW-850i-ATB-differential

From the Quaife website:

£POA (Unit price exc. VAT)

"If you need to ask, you can't afford it"

A friend of mine got one from Quaife for his E30, with a custom 4.10 gear ratio.
and that was 1500£

What you do is open you'er diff and rip out all the gears and stuff that is in there, and then install the quaife unit.
You might want to have it installed by a pro, since you may have to shim it in place.

The reason why there is no price on the e31 diffs is probably because they don't sell to many of them.

I would guess it would cost about 1500-2000£
Sure you can have a used one for a few hundred, but atleast with this one you have a lifetime warranty.
and no trouble.

I have thought about an LSD for my car, but I really don't see the need for it.
I have my 325ci as a track day drive, and I only use my e31 for crusing anyway, so do I need an LSD??

Totally understand Martin.

I just wanted to give you an option.

Just make sure that the one you get is good.
I've seen to many that have got LSD's with noise in them, that completely failed within a month, that has no LSD function left in them to concider to buy one of those.
And some of these have been bought from well known breakers.

So you never know what you are going to get.
I'd rather spend 1500£ on a brand new one than 600£ (typical price over here) for a mystery box

Martin, I can can only speak from my own experience.... but on my e34 LSD there was a metal 'tag' with 3.91 stamped into it, attached to the case. Other than that the only external difference between stock and LSD was the large white 'S' stamped onto the base of the case.

I would assume, but obviously cant be sure, that this is similar for other diffs out there ???

regards

Tony

The pulse generator is the speed signal that the car uses in several places including the speedometer.

IIRC it is read from axle revolutions rather than drive shaft revolutions so changing the ratio has no effect on the signal. This signal is what is affected by tire diameter.

Martin, I've a 3.6 LSD and it came from an E34 535 Sport, there's plenty of these still being broken and prices are pretty reasonable.
From memory I'm pretty sure that the LSD units in these diffs are made by ZF, they're big and strong, even a `tuned` E34 wouldn't have produced enough power to worry this LSD and as you say, the average 7 series owner doesn't generaly skip maintenace and hammer this car around.

Very basic diff checks;
Following these checks should;
A/ verify if it's got an LSD in it or if it's just an open diff,
B/ allow you to find out what final drive ratio it has,
C/ hopefully stop you buying a very heavy paper weight/desk ornament,

First things first, turn the input (prop shaft) flange, if the output flanges rotate in opposite directions it's an open diff (not LSD) so just walk away.
As far as condition goes, as long as the LSD (and crown wheel and pinion set) has had a good belly full of oil to run in it'll all be good to go, the easiest check here is to take the rear cover off and take a look.
With the rear cover off, what you're focusing on are the crown wheel and pinion (though you can hardly see the pinion gear so go by condition of the crown wheel, they have to run as a matched pair so if one's shot so's the other) and the LSD unit, nothing else really has a value and can be replaced for a couple of quid, unlike the LSD or the crown wheel and pinion.
With the cover off and LSD and crown wheel now visible the first bad sign is metalic debris in the remaining oil or a thick sludge in the bottom of the diff casing, or rust, either probably means trouble, if in doubt, walk away.
If the gear tooth faces of the crown wheel still have a nice good shine (no grey dullness) and you can see no visible wear, sharp edges or anything that just looks plain wrong. If the oil isn't dark brown or black, and plenty comes out all over your feet when you take the cover off, you can be reasonably sure that the diff'll be fine to use.
Check that there's a small amount of play when you start to turn the input (prop shaft) flange before it in turn starts to turn the crown wheel/LSD assembly, what you're feeling is the back lash, if there's too much it's either knackered bearings or worse, the crown wheel and pinion set are worn out (this is why you're looking at the condition of the gear teeth of the crown wheel, to see if any exessive play you may find is just worn bearings or the crown wheel and pinion set that's shot).
When you turn the input flange it should turn nice and smooth, you should hardly feel the transition from the gear tooth pairs meshing to the next as it revolves, any `lumpyness` is a bad sign and your looking for the reason, it could just be bearings.
At this point it's probably worth mentioning that you won't be able to `see` a knackered bearing, not unless part of it's just landed in your lap!
It's not exactly practical at a breakers yard to go through the process of checking the condition and the setting of the LSD, and if you did want to you'll probably find that most breakers yard owners wouldn't be overly helpfull by now, (not after you had to borrow his tools to take the rear cover off, and then spilt oil all over his feet) and will be at the point of "look mate, do want it or don't you?"
Either way, they're very strong and we've never had to sevice one so if the previous signs have been all good the odds are on that it's a good one.
As far as working out the actual diff ratios goes, you'll need to do a count, take some tipex to the breakers with you and do the following.
Mark the input (prop shaft) flange and a put a coresponding mark in line with it on the diff housing main case, then mark an output flange (again with a coresponding mark on the case).
Now simply count the number of revolutions turning the input shaft flange to get one complete revolution of the output flange you've marked, that's the ratio, ie; if you've had to turn the input flange 3.6 revolutions to get one complete revolution of an output flange the ratio is 36:1.
You'll be suprised just how acurate this method can be and if you really want to get it spot on make up a couple of card discs to attach to the flanges or use wire pointers.
The most acurate way is to physicaly count the gear teeth on the pinion (input) shaft and the crown wheel and dived one by the other but that's far from easy when the diff is still assembled and the marking and rotating way will tell you what ratio it is if you know what ratios you're looking for, believe me, you'll not confuse a 3.6 with a 3.9, it's that obvious.

With regard to the Quaife ATB differentials, we sell plenty of these and they're a good product, they need no servicing and are totaly bomb proof, hence the life time waranty.
The POA on the Quaife web site has nothing to do with the price, where you see a POA on the Quaife web site is where they make that particular product for an idividual retailer on an exclusive basis.
The reason there's a POA is because Quaife themselves can not sell you that part but will simply direct you to the retailer that they supply that part to.
If you want to check this out give them a call and ask to buy a Cosworth/TVR T5 gear kit, Quaife will give the a phone number and your next call will most likely have me on the end of the phone
Just out of interest I'll give them a call on Monday and find out who has these ATB from them and then get a price and availabilty, just in case anyones interested. If the rest of the ATB price range is anything to go by I recon' you'll be looking at somewhere around seven hundred pounds (plus the VAT) for this one, but I'll check and find out.

With the OEM BMW LSD units there may be a problem, a couple of weeks back I gave BMW a call to price up a rebuild kit for an LSD from an E30 M3.
These kits nomally have a set of plates and bellville washers in them and as long as the housing and gears are in good servicable conditon are all you'll need to freshen up an LSD that's lost some of it's action.
BMW no longer sevice these LSD units and the kits are no longer available.
On the plus side, they offered us a complete new LSD unit at soemthing like three hundred pounds (plus the VAT) and for a new ZF LSD that's bargin money!

Again, I'll check with BMW on Monday and see how they stand on service kits for the LSDs from the E31 type diffs and get some prices.

The 535 Sport diff hasn't been fitted yet but I'm certain it's the right one, (I'll be very, very supprised if it isn't, but it wouldn't be the end of the world as it only owes me 50 quid so there's a potentialy tidy profit to be made there!).
As a rule of thumb if your unsure that the diff your looking at is right for your E31 just pick it up, all other BMW diffs are light by comparison, these are bloody heavy it the full size diff as fitted to big power E34, E31 and E32 cars.
I've a theory (that the more I learn the more it seems to hold water) in that BMW traditionaly use three diff sizes at any given time based on the power output (and weight probably has something to do with it) of the cars in the range.
You've one for the small cars (sometimes fitted to the mid size but with a small engine option), a medium size diff for mid size cars, (and small cars with big engines or big cars with very little engines) and then the big diff for the big cars (and mid size cars with a big engines), the M and Sport (with LSD) cars will always have there respective `big` option at any given time.
Where it gets confusing is where models crossover any given time line but if you look at, for arguments sake and because it's relevant to us, the E32,E34 and E36 you've probably got the three common examples.
Taking the E36, E34 and E32 models is a pretty good base line as they were delveloped within a simlar time frame and made up the three basic size cars that BMW usually have for sale at any given time (excluding the niche market sports cars). When you take into account that the E31 was developed along side the E36 it puts it into the `big diff` group, and it is.
If I'm wrong I put my hands up, but as I said, it's only a theory and it seems to work out about right.
If anyone knows better I'm sure we'd all be interested to know?

As promised I made a couple of calls today, the first was to BMW to see if the rebuild/service kit for the LSD for the E31 size diff was still available. It's not, the bad news is the only option now is a complete replacement LSD unit at... one thousand and seventy six pounds, plus VAT
I also had a chat with one of the guys at Quaife and it turns out that all Quaife ATBs for BMWs are now on an exclusive to Birds Garages, Quaife used to list it as a `BMW 850 fitment` ATB (QDF10N) at six hundred and ninety three quid (plus VAT) in the old catalogue but a call to Birds and we're told it's now at eight twenty nine (plus VAT), shurely shome mishtake .

I have an M5 3:45 in my six speed with a quaffe 100% lock up

the :345 was the right fit for me
Jim@e31parts.com

As far as I know the LSD is usually included as part of the `Sport` pack, though I could be wrong.......
The Quaife ATB is not a complete differential, it's just the bit inside that the crown wheel bolts to and the output flanges fit into (if that makes any sence).
If you supply Quaife with a complete rear diff' they'll either build the ATB into it for you or send you to a transmission specialists like ourselves (it'll be someone that Quaife have worked with for years and trust to do a decent job). Either way they'll be a labour charge and the cost of the bearings, seals and spacer, as well as the cost of the ATB.

Re: I have an M5 3:45 in my six speed with a quaffe 100% loc

Zitat von jdgavrity

the :345 was the right fit for me
Jim@e31parts.com

I believe these are Jims Gear ratios, 3:45 for his LSD.