Getting yourself a Cheap strong 4 pin differential Unit

[Hybrid_From_Hell]

Hiya all,

There are a range of good lockers on the market, along with LSD units and other "Exotics"

ARB, Ashcrofts new loverly Unit, KAM Locker, Eaton, McNamaras, Quaiife and others, all are very nice

some better than others dependant on who you talk to and all rather exotic and Spendy.

An average £s for a unit, fully built up into a casing with an existing CWP set up, with all new bearings and seals etc

is going to be £700-£900 approx, and if a new CWP say £1000+ per differential <cough>

Not cheap, but good, front and rear Sir ? £1500 - £2000+ peg them ? maybe bill now £2500 a Pair

So, at the other end of the scale is the Playday off road enthusiast poss non competitive driver with 2 pin

diffs which go "pop" without much effort, and are often a source of extreme frustration.

Indeed, when I was working for KAM I took many calls from peeps looking for a "Cheap Upgrade" neither either having

the funds for "Lockers" or even wanting them, just wnating a serioulsy stronger diff unit, but without the trouser

tugging and wallet emptying involved

So, Here is a possiblity.

Steve Francis (ex KAM Operations Director) and Diff Builder extrodinaire.... and Moi a frustrated amateur engineer and

tad of a nutcase, have come up with a solution for the Keen DIYer.......... or a cheap purchase your call.

P38s have both 2 and 4 pin centres. Stuff the 2 pin, but the 4 pin is nice

The cases are completely different in both PCB and Lengths, and these units can be got

quite cheaply with a hunt about - yes there are dreamers who think they fetch £200 + but I have just bought 2 x for £40 each

so they are out there, ............prob is they don't fit a normal standard LR "Long Nose" Casing

Or do they ?

So, take a selection of bits, the HFH inventing shed, a lathe, a milling machine, 1 x mad idiot 1 x proffesional Diff builder and an 'idea'

and 2 days labour and there is now a 'new option' - a P38 4 Pin centred Long Nose Differential Unit

Lets start at the beginning,

4 pins diffs are still an "open" diff, ie not a LSD, not a Locker, ie a STANDARD diff, but bl**dy strong, much much

much stronger than the 2 pin standard diff. The standard 2 pin is a simple open casting, the 4 pin P38 a machined closed unit, so here

is what neds to be done.

What we did was take one of my shot blasted and cleaned Middle age Diff casings (there are varinats in diff casings but this is

a "Typical " One ) and a knacked old 3.54 Crown wheel and Pinion (CW & P) a P38 empty knackered centre unit (No internals) some old

bearings and a knackered input flange some bits and bobs........... and set to to see what we could do.

After a 1.5 days worth of machining and fettling it can be announced it will all fit, and uses the standard matched set of Long Nose CW&P

rather than a bodge of mixed parts, which would be poor practice, at best howl, and probably fail with probs with mesh, backlash, and preloads,

this is a more "Proper" Comercial enginnered solution, which can be done by an enthusiast with time and equipement, but do NOT underestimate

the work to do to bits to get it to be a 'proper job' as a one off, expect to spend a good weekend doing the changes.

So, ..........take one Shot Blasted and Chemically Cleaned diff casing :

Looking at the centres of both a standard 2 pin and a P38 there is a significant shape and size differences the flange the CW bolts

to is in a differing position, and is taller too

Strip the P38 unit apart, and take the side the the crown wheel bolts to and machine the living daylights out of it :

Remove the "Flutes" to be flush at the carrier end and machine across to the outer edge

Reduce the Actual OD of the unit as it fouls the casing due to positioning of Casing ribs

Machine a angle of the edge of the unit to allow additional clearance of the casing

Machine the bearing carrier significanly further to allow bearing to sit in correct position

Machine the Adjuster clamp to ensure clearances

Grind the insides of the diff casings to clear CW - top bottom and top Centre by several mm

grind and linish the inside of the bearing caps to remove flashing and give clearanes

remove CW Falnge Carrier bear and increase journal to allow bearing to sit in right pace

More pics :

Backplate to CW before and after maching - note the edge thickens the CW by aprox 7.2mm this adds a significant amount of strength

to what is a weak CW set up, this unit could equally be pegged for additional strength, we also belive we could use 4.1 4.75 3.8

thick CW&Ps and also add pegging too for even more strength,........... but back to the fabbing

This was one of the early "trial fits" the carrier is too wide on CW rear Side, and still fowls the casing even after some grinding :

On the picture above, this was initial grinding, to get clearnace the section raised to the side of the "Grove" has to be completely

ground away by 5mm - 7mm , this then allows the CW to rotate clearly.

The machined CW Plate shows here the increase in CWP Strengtth as it adds 7mm to the overall thickness, after machining to clear,

but the standard CW is far thicker than a P38, so this is a additional 7mm on a standard CW which is not that thick to start with,

the 3.54 Long Nose CW is quite weak as standard, this thick "Plate" is in itself a type of pegging system by having a 7mm thick plate

behind the standard CW, the normal CW Bolts can be used as the bolt holes are contersunk

We always upgreade the carrier caps from 8.8 to 12.9 cap heads for addition clamping and strength too 8.8 are often stretched and bent...

Once you have clearances within the differential the bearings in the right paces in the towers, and the adjusters machined down a tad to

fit and everthing lined up, it then drops together a la normal unit, and looks the part as shown below :

So, there you have it, a cheap and very strong 4 Pin LR Diif.

So, what are the costs ?

OK, you will need

A P38 Short Nose centre from a Short Nose diff (say £50-£75) ubless your lucky, bear in mind a P38 diff with say a chipped tooth

is worth F ALL

A Standard LR Diff, centre condition irrelevent - must be a Good CWP say £25 - £50 ? - or the one you have now £0

Some new bearings to do it properly Head Tail and 2 x Carrier (unless donor P38 are VVV Good ? ) and a Oil Seal say £60 total

And some serious machining time,

So, do it yourself, with all new bearing seal and a 2nd hand decent Long Nose diff and CWP say £135

Or

I think I'll maybe be selling these soon on my Webshop, see there later for info, but as a guide, give me a P38 Diff, and have it

back ready to fit for £125, or give me a P38 diff and your ong Nose one, and have it fully machined and rebuilt new bearings etc £250 ish

I'll be hunting for P38 Units myself, but may have some stock to supply "Outright" uits non exchange...

BUT

For around £130 its a 'DIYable' cheap and very effective upgrade - all you need to know as to how to do it is now shown above

Nige

[orangebean]

Nige

I'll take a punt (as I PM'd earlier) as it seems like a fair bet.

M

Just give me first/ second/ 3rd dibs

xx

[Hybrid_From_Hell]

Erm

you won't blow this one up

Its a 0 spline diff its just a scabby prototype with no central internals to prove it can be done

I will be making 3 x real ones now we know how, so bear with us, we are just both chuffed with the Prototype and

hence the thread

BUT = you get HFH=SF-P38-4pin-LN diffypoohs No 1 as offical tester ...........so be f patient

Nige

[M&S]

In reply to the build thread, I think you have done a good job and it's something that is well worth loking at but the problem with your pricing is that you require a P38 diff in exchange, which, as a Disco 2 owner, I wouldn't have...

Add that and I'm not far away from a LSD/Truetrac fitted to my current diff

[orangebean]

Erm

you won't blow this one up

Its a 0 spline diff its just a scabby prototype with no central internals to prove it can be done

I will be making 3 x real ones now we know how, so bear with us, we are just both chuffed with the Prototype and

hence the thread

BUT = you get HFH=SF-P38-4pin-LN diffypoohs No 1 as offical tester ...........so be f patient

Nige

Patience is my middle name

(actually it's not- it's David)

waiting patiently...

[bishbosh]

I think that is an impressive piece of work Nige. How many pints of blood did you loose in the process?

I suppose if you want open diffs (comp safari types?) then this might appeal but for the money for an off the shelf unit I would be biding my time to save pennies to buy a locker, new or second hand depending on flavour.

[mickeyw]

Nige,

I think this is a good solution for those of us that just want a stronger open diff, and have the machining facilities to hand. That's some nice inventing shed development you and Steve have achieved.

But for someone that just wants to pay another to supply a ready to fit kit, they could, as Bish has pointed out, add that £250 to the locker fund. However I feel sure you'll have a good number of interested parties emerge.

I would be in the make it myself category

[Ruuman]

Looks good, I think there's quite a large market. Many people are deliberately building their challenge vehicles with open axles to keep themselves in lower classes. Seems like a good solution at a fair price.

With my pikey hat on, most of the CW machining in the first stage could be done with an angle grinder as it doesn't appear you touched the mating faces. (low speed applications of course ) So apart from the adjuster machining, it looks like a cheap DIY solution too.

Good write up Nige!

[Hybrid_From_Hell]

^^^

Yup I think you are all correct - BUT - the £350 is worst case from Moi & Steve building and machining, buy yourself a P38 4 pin unit

and you can do this all yourself for the costs of the diff, your time and maybe some bearings, if the head & tail bearing are OK

in your Long nose unit, and maybe the seal to, then its 1 x RTC3095 (as you have to remove one to deepen the journal - so say £12,

and the rest is labour which if you DIY it would be P38 diff + "12

THAT way its no money to spend, and its a saleable unit later if you go ARB or Ashcroft etc ?

Trouble for many its lockers oh and HD Shafts oh and a Pump Ooooo Bl**dy hell !

Its been bouncing around in my Brain and Steves now for some time, the above is a "How to" do it, I may sell these later or might not

but as for angle grinding - erm I think "Rotational Balances" may not be as whoppie do as they need to be ?

Nige

[Off Road Toad]

Looks good, I think there's quite a large market. Many people are deliberately building their challenge vehicles with open axles to keep themselves in lower classes. Seems like a good solution at a fair price.

With my pikey hat on most of the CW machining in the first stage could be done with an angle grinder as it doesn't appear you touched the mating faces. (low speed applications of course ) So apart from the adjuster machining, it looks like a cheap DIY solution too.

Good write up Nige!

Unfortunately you do need to machine a mating face, where the bearing presses on to, This needs to be absolutely bang on so as not to create run out issues. You are correct about low speed application of a grinder job, you know how bad a prop vibrates when its out of balance! imagine 6kg of diff spinning at motorway speeds!

This is where a large part of the cost is - accuracy of machining, it really is critical.

Steve

[Ruuman]

Unfortunately you do need to machine a mating face, where the bearing presses on to, This needs to be absolutely bang on so as not to create run out issues. You are correct about low speed application of a grinder job, you know how bad a prop vibrates when its out of balance! imagine 6kg of diff spinning at motorway speeds!

This is where a large part of the cost is - accuracy of machining, it really is critical.

Steve

Man, I'm not really awake this morning, I somehow missed the bearing machining The grinder job is kind of out then, by the time you've got the bearing bit machined, you might as well do the whole thing!

I dread to think what driving a on a diff that out of balance would be like on the motorway.

[steve b]

Nice write up

I have an original V890 rear 4 planet in the back of mine , shortly to be followed by one in the front , out of interest how different is the P38 centre to the V890 rear?

cheers

Steveb

[Off Road Toad]

It is essentially the same unit, However it has a modified crown wheel flange in that it has a large chamfer on the outside edge as well as a smaller OD. Land Rover also use a combination of long nose pinion with a short nose diff thin crown wheel, they are able to do this as the gears are matched and lapped in together, As far as i know these gear sets aren't available at the moment from LR.

Steve

[moore101]

Very nicely done.

4 pin LR diffs have been in use by many CCV trialers for a few years now. But they do it the pikey way of running a long nose diff with original pinion and the entire P38 diff unit and crownwheel all in a ground out long nose case. For the small amount and low speed work that CCV trialers do this method works fine.

Having not seen a P38 diff in the flesh in its original case, how different is the case where it bolt in? Would it be possible to machine an original case or weld on a P38 ring? That way you could just bolt a standard P38 diff in and have the advantage of the shorter diff.

[forkrentfitter]

wasn,t going to mention this yet,but i am in the process of cutting the mounting ring out of the p38 axle and welding it back in to the discovery axle,cut them out with a plasma,got it tacked in all looks good,obviously will need a longer prop though.

[Off Road Toad]

wasn,t going to mention this yet,but i am in the process of cutting the mounting ring out of the p38 axle and welding it back in to the discovery axle,cut them out with a plasma,got it tacked in all looks good,obviously will need a longer prop though.

This is a good idea, Couple of things though, It requires the P38 doner axle to take a ring from (which would also yield you a diff aswell) or a new ring from somewhere? not sure if it's off the shelf? But secondly this needs to be welded in with super accurate precision or you'll be chewing side bearings and halfshafts up.

Steve

[RobotMan]

When the axles are made new we have a very large ram to re-true the casing and then they are machined and the Diff holes drilled.

The best solution would be to get a post 07 axle casing. They are the same as a 90 bar the Diff pcd (p38), the spring seats 10mm further outboard and of course the simple Diff pan behind the very worthwhile reinforcing ring.

If you are going to do your own then the most important bits Diff and shaft fit wise are ;

Diff face parallel to a line through the centres of each end flange.

The Diff face shoud be 42.1mm from that line.

The Diff hole rotation needs to be very tightly controlled too (can't remember without going back to the drawing).

The centre of the Diff flange needs to be on the projected line perpendicular to the face.

If you don't get that right it will eat shafts, drive flanges and probably the Diff centre too.

[Off Road Toad]

"The best solution would be to get a post 07 axle casing. They are the same as a 90 bar the Diff pcd (p38), the spring seats 10mm further outboard and of course the simple Diff pan behind the very worthwhile reinforcing ring".

2004> 110" rear axle

[RobotMan]

Whoops typo well spotted.

[forkrentfitter]

This is a good idea, Couple of things though, It requires the P38 doner axle to take a ring from (which would also yield you a diff aswell) or a new ring from somewhere? not sure if it's off the shelf? But secondly this needs to be welded in with super accurate precision or you'll be chewing side bearings and halfshafts up.

Steve

bought a 4.6 rear axle from breaker for £75,all taclked up and level square,seriosly thinking of using tig to limit any distortion.

[RobotMan]

That's why they are machined post welding.

Still with a hefty jig and careful welding it may well be useable. Its worth a punt if you get the bits reasonably priced and you are a decent welder.

PS. Forgot to say, top job on the hybrid Diff!

[inaine]

sounds like a load of hassle when you can buy them from ashcrofts for £250

or fit a trutrac and have the best of both worlds......

[Hybrid_From_Hell]

http://www.ashcroft-transmissions.co.uk/index.php?act=viewProd&productId=173

£570+ VAT = £684 plus / minus actaully, (when you add the bits and bobs and have it Built)

(and out of stock at the moment)

Vs £250 for Fully Built all new bearings and seal etc no VAT ready to drop in to axle - or £12 Maybe if you DIY it

Nige

[moore101]

Would I be correct in saying these units can only be used with 24spline halfshafts?

If so what's the easiest way of getting a strong front axle as I've read that the 24spline CV joints are weaker than the early 10spline ones (without spending lots of money on upgraded CVs and halfshafts)? Or would I only have to buy strengthened shafts to go between the diff and the CV? (do both the independant CV and the integral with stub shaft ones have the same spline count on the inner?)

And can someone give me a little bit of help regarding back axles as I've trawled through the net and confused myself. I want to fit one of these 4 pin units on my vehicle but currently have a 10spline back axle. Can I swap over the stub axles and hub assemblies from a 24 spline back axle onto my case or are the casings a different length or different bolt pattern? And if I can just swap 24 spline ends on, then would the front stub axle and hub assemblies happen to be the same? (struggling to find any complete 24 spline axles at the moment)

[miketomcat]

"Hijack on"

Moose I put 24 spline disco shafts and diff in a 10 spline disco axle case and hubs rear only never got round to doing the front and I have a pair of disco rear shafts if your interested.

"Hijack off"

Looks interesting nige.

Mike