Early KAM plated LSD setup

[oneandtwo]

Question mainly aimed at Hybrid_from_Hell!

I’m currently running a Truetrac in rear of an old 300tdi 90, with Ashcroft 4 pin up front. Vehicle is mainly used on road by my wife however is on occasion used on beach to launch and retrieve boats in soft sand, and has been stuck twice this year in sand. I have spare a KAM 4pin diff with LSD clutch packs that I am considering fitting to the front to replace the Ashcroft 4 pin in an attempt to gain an extra bit of traction on the sand.

Does anyone have experience of running the KAM LSD 4 pin in the front axle? My hope is that it would be un-noticeable during day to day on road use?

This particular KAM 4 pin unit is a very early model with three piece crosspin (similar to Ashcroft 4 pin centre) and has no spring plates to preload the clutch pack, and no method of any adjustment to the clamping force, it relies purely on the sun gears to load the clutch pack. On the later KAM LSD units, for front axle use, it is recommended that two clutch plates either side are placed side by side to reduce the total clamping area - I am presuming this would still be the case for the earlier units when used in the front?

Finally what is the correct torque figure for the twelve M8 12.9 carrier bolts?

Edited October 1, 2023 by oneandtwo

[uninformed]

For class 12.9, M8 you’ll be torquing to 40-44Nm. The variables are black vs zinc and coarse vs fine. 
 

That being higher end for fine thread, lower for coarse. And higher for black vs lower for Zinc. 
 

If they are an off the shelf size I’d buy some new good replacements. UnBrako, Brighton Best etc. 

BTW that looks like a nice red box 😍😎

[Snagger]

Nige will probably have the most useful answer, but based on my understanding of how these various diffs work and how they affect driving, I would suggest the LSD should go in the back axle and the ATB in the front, simply because the LSD starts from a locked state and breaks out with enough wheel torque load from turning on a grippy surface while the ATB starts off open and transfers the torque as needed.  That should both make the rear axle better “locked” for more traction and also reduce any undesirable steering effects.

[oneandtwo]

You may be confusing the Detroit Locker? The plated type LSD starts off open too (although there is some inherent drag from the clutch pack), and locks from centrifugal force from the planet gears - the faster the individual planet gear spins (ie one wheel lost traction and is spinning) causes that planet gear to be forced outwards, compressing the clutch pack causing it to lock up and send drive to the spinning wheel. 

As I’ve never driven the plated LSD I am assuming it would be unnoticeable when fitted to the front in it’s normally open state as the planet gears would only turn very slowly when cornering, presumably not enough to compress the plates, but would rather some first hand experience before is strip the front axle down to fit it and then find I have to take it out again when other half goes straight on into a tree!
 

[Snagger]

I had understood that LSDs operated much like the Detroit, just much more smoothly, so in that case, I have learned something very useful.  If that is the case, they may have a higher triggering threshold than ATBs, in which case they should be less likely to have steering input than the ATB (which is well documented but seems to be welcomed), in which case the LSD would be best in the front.  Very interesting, and I’d love to learn if that later speculation is right.

Still, an LSD needs occasional servicing with new clutch packs, and that will be easier in the rear axle as the half shafts are so much easier to remove.

[Peaklander]

I have the Ashcroft ATB in the front of my 110 and most of the time I have no idea it’s there.

[Snagger]

The comments from drivers with front ATBs seem all to be very similar, saying the car feels more planted and stable and the steering self centres better.  I think Maverik said something like that, though I may have  incorrectly.  I look forward to seeing the difference on mine - the 109 is getting front and rear ATBs after I get it back on the road whenever I get home, though the RR is being rebuilt with them now so I won’t have a recent drive with standard diffs to compare to.

[Hybrid_From_Hell]

 

Morning - sorry missed this !

Torque - 45-48 NM MAX

these bolts are 12.9 Grade, however, black self colour are better as plating has an effect on the metal by slightly making them more brittle, so I would always suggest self colour esp if you are torqing higher end.

Also use loctite 243..

 

Now...the unit itself ......

The problem is there are so many tweaks variants modification and versions that these can be a nightmare !

That looks like an earlier one - 16mm cross shaft is a key indicator - if its an 18mm cross shaft then later.

We also had One piece forged cross shafts - 18mm and super strong - I have these now remade, and then there were some horrors of a boss which you then screwed in 4 stubs - these often didn't work, weren't as strong, and can "Unwind" , if 16mm not much you can do - if 18mm you can put my one piece in if you so wanted. Screw tyres were both 16 and 18mm !

The way the plates are assmbled is how the "Basic" preload was reached, this was often a matter of swapping plates about using whatever bits were about and assembling then using a torque wrench see what load was reached ..

Fronts we looked at circa 25-35 Ft Lbs, and rears well, 45-55 and some for racers set up nearer 70 ! ...an Ashcroft ATB comes in circa +/- 40 ish as a comparison

The problem is the higher the clamping Ft Lbs you have the faster the plates will settle down / wear, and you need special LSD oil ....and regular changes.

The plates themselves have several versions and thickness (The MD constantly tweaked / changed / modified / drove everyone bonkers) so parts to replace can be a serious issue ! )

One the main flange plate that bolts to the Crown wheel, some (yours has virtually none - some he had made had maybe 20 holes to "Play" with  ...) had threaded holes that you can add in small grub screws which you can tweak inboard to press on the Bellevue washer increase clamping, a proper nightmare to do, each grub screw MUST be torqued up like a cylinder head and as you go around them what was torqued up changes so it check re check recheck again and so on - giant nightmare, best to avoid which we did 99% where we could

 

Spares can be a nightmare as plates come in differing designs and thicknesses, and it can take us hours to "Repair" these - thats if we have the parts .

Sometimes we actually convert these to a standard 4 pin and remove all the plates - again this is a pain to do, as dependent on the model / variant depends on the packer plates / thrust shims needed, BUT, even as a 16mm screw type 4 pin these are bloody strong, as an 18mm one piece shafted 4 pin - strongest prob even made.

 

Some were built properly - with plates of correct thicknesses assembled to the correct loading, often many were built with a HUGE "Bellvue" washer - a spring loaded washer to allow preload to be played about with easier....all in all these can / were / will be a pain to sort out ..

 

May advise is to clean it all up, re assemble and see what load you have - more than say 35 Ft Lbs and it will be too much for a front.

 

And then report back

 

Nige

Now...the unit itself ......

Edited October 29, 2023 by landroversforever
45048Nm sounded a bit high :P

[David Sparkes]

If you want to know more about 'Bellvue' washers, spell it 'Belleville'.

Regards.

[Hybrid_From_Hell]

David

 

With my  dyslexia its amazing its spelt that close............ sometimes I type stuff that looks fine to me- .....................then when I re read it even I don't understand what I've written

[oneandtwo]

Nige,

Thank you for info. The KAM diff centre assembly is one machined piece, it doesn’t split like the later ones so cannot be upgraded to a one piece crosspin - can only use the original cross pin - one long pin goes all the way through the diff, through a separate centre section, and retained by circlips each side. There are then two stubs that screw into centre section which make up the second pin. Quite similar in principle to the Ashcroft 4 pin system.

I ended up building it up with all new bolts and fitting it to a standard diff. Instead of running it in my wife’s front axle I was intending to give it to my brother to use in the rear of his road going 300tdi 90 to replace the standard 2 pin, reasoning that even if the LSD packs are not up to spec, as a four pin diff it is still going to be miles better than the 2 pin it is replacing.

As for my wife’s 90 I will purchase an Ashcroft ATB for the rear and convert the Truetrac to front operation.

[simonr]

On 10/24/2023 at 9:28 AM, Hybrid_From_Hell said:

Torque - 45048 NM MAX

Best put in a bulk order for Spinach / Wheetabix 🤪

[Nonimouse]

I'd be tempted to look at other options. If you spin out on sand, that's it, unless you have big BHP and high rpms

I would suggest airing down low - say 12psi, front and rear. And taking a long hard look at tyres. Avoid Mud terrains like the plague

There are countless different types of sand - all with differing traction characteristics. Two beaches in the same bay can be different

[Snagger]

Yes, different types of sand behave very differently.  It seems ludicrous on the face of it, but Dubai imports a lot of sand from the UK for construction.

[Nonimouse]

Size difference. 

Golf course bunkers are filled with AFS90 - 90% same size grains. Virtually never forms a crust, even in the rain

'Normal' beach sand is around 10 to 20% single size

Bull dust or Fech Fech is almost 100% super fine, super small particles. Doesn't bond, even when wet

Building sand needs to be 2-10% single size, without any salt in it - Sand near your gaff is a much higher level of single size particles

[Snagger]

Also how polished the grains are from blowing in the wind.  Desert surface sand is fine and polished, here the fine stuff is like fine dust, while deep sand is rougher and binds better.  Quite staggering how differently they behave.

[Nonimouse]

13 hours ago, Snagger said:

Also how polished the grains are from blowing in the wind.  Desert surface sand is fine and polished, here the fine stuff is like fine dust, while deep sand is rougher and binds better.  Quite staggering how differently they behave.

The fine stuff is called Feche Feche. It's weird.

Very little sand isn't polished, as even quarried sand is old sea bed.

We used to have a sand and gravel quarry here in the village - it was used to concrete the runways on the WW2 USAAF/RAF base down the road. The sand was gravel bearing and was good enough to simply mix with concrete (and oak wood chips) to make the hardest concrete I've yet come across. The size difference in the sand was <1mm to 40mm> at about 95%