LSD Units - Ask me anything.

[Demlotcrew]

Any questions about LSD configuration and possibilities?

Andrew

[Stonkin]

Ok, i have just purchased Theo's rebuilt 4.10 lsd, for use in the primarily track car, but will occasionally also be used on the roads.

I was planning to run either 15" wheels or possibly team dynamics 16's, only slightly unsure as it depends which size wms brake kit i go with.

I have also read that lightening the flywheel a couple of kg can be very useful for the m20b25 engine. Will this type of diff and a lightened flywheel be to much? Will the flywheel make the idle lumpy?

What sort of top speeds will i be limited to with this diff? and will it kake much of a difference to the 3.64 lsd i originally planned to use?

A few questions i know, just curious as to how these will work

Christian

[Demlotcrew]

Hi Christian,

From experience a lightened flywheel will not make for a rough idle, infact a lightened zero balanced flywheel in most cases will give you a much smoother idle.

In order to work out the top speed I would need the gear box you plan to use and also the size of tyres (this gives a rough idea of what you speeds you will be able to reach in each given gear).

Andrew

[DanThe]

How do you get 8 plates into a diff and what will the lock % be?

[popey7676]

Hi, I am at the moment doing a m50 2.5 conversion, I am running a m42 box with the engine, what do you think would be the best lsd for all round performance?
Regards

[Demlotcrew]

How do you get 8 plates into a diff and what will the lock % be?

To get 8 dog ear plates in you have a few options, all leading to Zero lock

[DanThe]

Comedy answer ftl

[randomspeedfreak]

apparently a z3m diff is a torsen diff.

have you any experience of this?

cheers,
matt

[Acox99]

What sort of % lock is best suited for the road in a mildly tuned m20b25 cab

[Mikey_Boy]

Here's another - how rare are 3.46 diffs?

[UweM3]

Here's another - how rare are 3.46 diffs?

very rare. I managed to buy ONE in the 12 years I owned my M3

[Rav335uk]

I have a 3.46 diff

[Duke137]

I have a 3.46 diff

I have one too though it is open not LSD

[Rav335uk]

I have an open one on the cab

[Das_BMW_E30]

I've been told 3.15 LSD's are not too common..?

A gear ratio calculator...

http://www.bokchoys.com/differential/e4 ... ulator.htm

[jonesy318]

i'm doing an m42 conversion, what are the diff options i could use on this, car originally had a knackered 4.10 open on it?? cheers Ian

[penton08]

Will a welded diff make my car handle better?

[Rav335uk]

Will a welded diff make my car handle better?

Yes, it will for you, it'll make you a better driver innit

[Andyboy]

I have an open one on the cab

So does Pete!

[Rav335uk]

I have an open one on the cab

So does Pete!

No he doesn't, he has it on the track car

[Motorhole]

apparently a z3m diff is a torsen diff.

have you any experience of this?

cheers,
matt

I have a Z3m diff and it's a clutch pack diff. iirc Z3 2.8 diffs are torsen diffs and SOME of the Z3m ones are. But most of the Z3m diffs this side of the pond are clutch packs.

On another note, I also have a spreadsheet where you can input tyre sizes, gear ratios and diff ratios and it will provide a graph of speed vs. rpm in every gear

[Das_BMW_E30]

http://www.bokchoys.com/differential/e4 ... ulator.htm

[ajay]

http://www.bokchoys.com/differential/e4 ... ulator.htm

MMM How acurate are these sort of calculators? Iv'e input my vehicle specific,s and its giving me a +200mph top speed at max rpm! I doubt that somehow. Anybody tested this type of calculator?

[Duke137]

Shocked this hasn't turned into a thread about someone called Hap and Pacerpete's served diff

[Rav335uk]

Shocked this hasn't turned into a thread about someone called Hap and Pacerpete's served diff

It has now
Pete's ar5ehole has now grown in size , as he has been served

[Das_BMW_E30]

http://www.bokchoys.com/differential/e4 ... ulator.htm

MMM How acurate are these sort of calculators? Iv'e input my vehicle specific,s and its giving me a +200mph top speed at max rpm! I doubt that somehow. Anybody tested this type of calculator?

I would imagine that's the theoretical speed of a given object, it would no doubt depend upon weight, and aerodynamics...

Who in their right mind would want to 200mph+ in a standard wheelbase E30...

[ajay]

EXACTLY . Idon't fancy trying to see if it will achive it either.

[Demlotcrew]

apparently a z3m diff is a torsen diff.

have you any experience of this?

cheers,
matt

I have yet to see a Z3M with a Torsen diff, they are all 25% lock, 2 clutch preloaded units.

The 188type LSD from the Z3M uses larger 19mm bolts which are M14 and not the typical M12, you can make spacer sleeves that allow you to use this LSD with a regular E30 Crownwheel.

The other interesting point to make is that the Z3M uses a GrpN style LSD case, this represents it self with four large oval openings that allow significantly more oil flow to cool the clutches. This LSD cage also has a very slightly different designed 'cap' which does not need to be machined down anywhere near as much as the regular E30 cap when converting to 4 clutch plates.

Below is a photo of a regular E30 LSD case on the left and a E36/Z3M/GrpN LSD case on the right.



This photo shows a very very rare E36 M3 Differential which has 1.5way action with 45% on acceleration and 25% deceleration.



This photo shows a stock E30 ramp cage that started its life out at 45º and has been ground down to 30º.



Below is a Torsen type LSD.



HTH

Andrew

[Demlotcrew]

Here's another - how rare are 3.46 diffs?

Not that rare Mike, they are to be had as Open, you then simply use the LSD case from your current LSD or source a worn LSD differential and swap round the CW and pinion.

Or

Better yet.

Source an E36 188type LSD case with the GrpN style openings and build a 4 Clutch, 30º ramp GrpN replica LSD!

Andrew

[Demlotcrew]

What sort of % lock is best suited for the road in a mildly tuned m20b25 cab

I would only stick with 25% lock LSD, no point in going any higher just for road use.

HTH

Andrew

[Jon_Bmw]

Good thread. I like the photos showing the differences too.

Is there any standard diffs that come with different accel / decel ramp angles?

Surely this would be worth doing / modifying to optimise corner exit and corner entry? I'm always quite suprised that the new in thing is to get mega 'lock' percentages with seemingly little regard to the understeer it might cause on corner entry.

[AdamGardner]

i have a e36/ z3m lsd that is brand new. i have been told that these can only be used with certain cwp set ups. i have a 4.445 cwp to build into a 4 plate lsd for my rally car. do you know if these parts can be compatable?? other wise ill use the 30 degree pressure rings from the inside into another lsd unit.thanks

[Demlotcrew]

Good thread. I like the photos showing the differences too.

Is there any standard diffs that come with different accel / decel ramp angles?

Surely this would be worth doing / modifying to optimise corner exit and corner entry? I'm always quite suprised that the new in thing is to get mega 'lock' percentages with seemingly little regard to the understeer it might cause on corner entry.

Jon, I dont find it so black and white, adding more lock on a car can induce more or less understeer, it all depends on the rest of the setup and driver. I find it as members cars and their driving evolves so does their requirements from the differential. It is very possible to drive a high lock 2 way LSD without it causing or adding to any understeer.

The ZF Clutch style LSD's fitted to E30's were designed and patented by the Dana Corporation and are also known as 'Salisbury' LSD's. This type of LSD is designed to progressively lock the two output shafts by using what are known as Spider gears (carefully designed wedge shaped gears that climb on each other #3 in the diagram below) these are inside two identical ramp cages #11 (Pressure rings) and this whole setup is totally under our control, you can therefore engage and disengage lock (to the set preload*) mid corner using the throttle, thus you can actually use the high deceleration lock to stabilise the car going in to a bend at high speed while braking, then change down, and then gently back on the power to neutralise the effect of the LSD by supplying torque to the spider gears before fully accelerating out of the bend.

Diagram of the internals of an LSD.



* Preload. Pre load is needed because if one wheel was to suddenly have zero 'drag' the LSD would act as an open differential. Imagine a race car hitting rumble strips/curb and getting some air.

[youtube][/youtube]

It really does depend on the car, the setup, the track, the weather conditions, the driver etc. Its hard to pigeon hole something that has so many variables.

The only factory fitted 1.5way LSD, I believe was a 'Track' LSD option on the E36 M3 3.0, it had an asymmetric ramp set and four clutches from factory. Unfortunately the clutches in it didnt last long, and this is why BMW didnt fit it in all cars as standard.

Andrew

[Demlotcrew]

i have a e36/ z3m lsd that is brand new. i have been told that these can only be used with certain cwp set ups. i have a 4.445 cwp to build into a 4 plate lsd for my rally car. do you know if these parts can be compatable?? other wise ill use the 30 degree pressure rings from the inside into another lsd unit.thanks

From what I understand, ZF made two offset LSD cages for BMW 188type differentials.

Final drives with 2.79-3.07 ratios use one type and those with 3.15-4.45 use the other (the only one fitted to E30's), I believe the offset to be about 7mm. You cannot machine a Low offset Case to take 4 clutches like you can with the high offset case, the most you will be able to get from it is 3 clutches preloaded or possibly 4 clutches with shims.

If you require to go any lower than 3.07 then the Z3M LSD wont be up to the task. The reason behind having such a range of final drives also comes down to the fact that the lower CW and Pinion sets can handle much much more torque. Which is why you will find all the Diesel BMW's use a very low final drive.

The easy way to tell if your E36/Z3M LSD Case is compatible is to buzz off one of the bolts and check its diameter, if its 12mm then you wont have any problems, if its 14mm then you will need to have spacer dowels made up and pressed in, then you can use your 4.45 CW and build it with 4 clutches. Just make sure to measure the stack correctly before having the cap machined as its different to the stock E30 one by 2mm (IIRC).

The Z3M Lsd is an awesome unit, you should try and see what bolts you have and take it from there.

HTH

Andrew

[Jon_Bmw]

What a great video, i think it is a front wheel shown but it paints the picture. I remember reading something that was aimed around single seaters (formula ford or something similar) and the general jist was to use the least locking percentage you could get away with to improve corner entry. The article made reference to the driver having to have a very good feel of the brakes as it is easier to lock an individual rear wheel. Everything is a compromise!

I don't agree with adding more lock will induce or reduce understeer. If everything else stays the same I think it will increase understeer. Perhaps you just worded it wrong? When you read the rest of that paragraph it is better summed up. I still think that the lower the diff locking the better it will turn in.

There is a compromise. On our fwd shit heap we run 45/45 which is quite a lot of lock, but the corner exit speed is much higher as we are not spinning an inside wheel. My point was that on a RWD car, where spinning the inside wheel on corner exit, isn't as much of a problem due to weight transfer could you get away with a less harsh diff. Heck if I wasn't a useless mug behind the wheel and used better throttle control I could probably use a less locking diff!!

I wonder if that track diff was to allow it (or modified derivitive) to be used on competition cars?