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Scotts90

Ashcroft centre ATB

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When I rebuilt my 90 I refurbed the existing 1.41 LT230 with all the recommended parts (cross drilled input, HD cross pin and all the bearings) and it's been performing fine. However the old 200 is revving a bit when pushed along the bypass and rather than stripping my own to fit a gear set  I have a 28D 1.22 from a D1 awaiting a rebuild....

So whilst in the process of ordering stuff from Ashcrofts and drooling over some lockers I noticed they do an ATB for the centre diff. Anyone on here have one? I don't do any extreme off roading with field work being the worst it will see. 

Opinons/thoughts welcome 

Scott 

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Going by the write up on Ashcroft's site they are a must (if you can afford it) especially on snow or greasy mud field.

I am interested in the grown up replies that you get so will be watching with interest  - I'd love to get one into the TB as a higher priority b4 lockers imo.

As to the other 'issue' written into your post I'd be interested in what size tyres you are running.

I am saving to do the exact opposite with my TB. I have the Disco TB 1.22 in my 300tdi auto 90 and want to go 22D 4.10 because of a lack of lock up until 54mph (auto) and running out of puff on long inclines (like you) on 85 profiles - both of which are bit naff on a long journey.

Advised on here that your type TB would be better suited.....

I'm not advising - simply adding to the mix of considerations before expensive decisions are made!  :)

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I'm running 265/75r16 BFG KM2s, stock diffs in the axles and an LT77.

Putting the numbers into the ratio calculator on Ashcrofts site  my standard setup puts the revs at 2450/60mph and 2860/70mph. Altering to the 1.22 gives 2123/60mph and 2477/70mph. Not a vast reduction in revs but it should help a bit. There was no difference in fitting the r380 into the equation. 

My main reason for rebuilding the 28D is twofold: if it's not suited I can swap back and I'll also have a spare box if required.

I just thought adding the ATB would be an ideal, fit and forget upgrade.

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I'm watching this thread with interest, I quite fancy the ATB's all round, apart from anything else, I suspect the reduction in backlash compared to a standard diff would be a nice improvement.

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Ok

My 2p worth.

 

An LT230 centre diff, really should be either unlocked for the majority of driving etc, or locked if the terrain driving is liable to cause wheel spinnings. the centre diff is really designed to allow differential speed changes between the front and rear axles /diffs etc by being there - without it you will get transmission wind up - hence why you should never have centre diff locked on tasrmac.

Now, whilst driving on the road with an open centre diff, the diff in the lt230 allows and takes up the didffering sppeds going on front and rear there is an issue or 2.

 

1st issue is the centre diff has 2 x pins holding the planet gears and these are machined out at the centre points to half thicknesses so the 2 pins can lay on each other - as a resuklt this gives a weak area and the pins are prone to breaking here if over loaded.

this however can be overcome by popping a forged 1 piece cross shaft in there and makes it massively strong - I have so new old stock military ones around somewhere if anyone wants to upgrade ...anyway moving on 

 

2nd the centre diff is designed to even out and aviod speed differences, but to be honest small differences. if you go hooning it in the snaow :D then with wheels spinning the centre diff will be under immense stress and workloads, and the gears spinning faster than designed - note you should have the diff locked for this - mso learn not to do it.

 

However, if you had you open diff then the ATB would allow you to hoon about with the centre diff open - but I would ask why ?

The main usage for ATBs - LSDs (there are minor differtences see here : http://www.megasquirt-v8.co.uk/diff_a_z.php is racing not road going trials playdays or greenlanning ...ATBs are really the master on the off raod racing circuits. 

If you are racoing off road you canbenifit from having an open diff so its not locked up solid allowing differences of axle / wheel speeds to be sorted out, some swearthey have better control than if centre doff is locked, the ATB in the 230 is bloody strong, and if you have matching ATBs front and rear you sort of end up with a 4x4 which seems to glue itself to the track whatever you are doing, sliding about tends to be more controlled and traction seems toi be like each wheel has a brain, faster you go the more its noticable.

 

Not so for off road traisl playdays etc - there you wnat IMHO a locked centre diff and lockers front and rear than are on / off on command, not autolocker or LSDs ATBs, untimately for anything slow ie not flat out racing - the locker on command via a switch is king.

 

So, ATB in a center diff, - for road use and anything non racing I woulkd say save your money and get a forged cross shaft and lockers front and rear.

 

For racing - ATB cventre diff yes please and ATBs or LSDs front and rear - DEFO not lockers !

 

Its all about application :D

2p Over :D

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Thanks Nige, I'll save my pennies for when the axle diffs require some attention then. I know you are most knowledgable when it comes to all things "diff'd" :)

 

PM sent

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It's a more expensive option in the short term, but if you have the budget, I think overdrives are always better than changing transfer box or diff ratios (assuming tyre diameter is roughly standard) as the gear increase is selectable, normal ratios being available where conditions make other vehicle mods over-geared.  It'll have a taller final ratio but will allow easy acceleration, so is more fuel efficient than the other options and won't result in a vehicle that struggles on hills or when towing.  It might take much longer than the gear set swap to be amortised by fuel savings, but the increased driving flexibility is worth the cost.  Since you have a 90, you will probably get away with the transfer gear swap, as many report it's acceptable.  If you were driving a 110, that option just wouldn't work.

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Worth mentioning as I've not seen it above is that the ashcroft LT230 ATB still leaves the option to lock it completely as normal. So I can't see any downsides to the ATB centre. 

I went for it to remove one of the only LT230 weak points as my truck should be fairly pokey and able to spin tyres at will. I don't want that making the LT230 diff go pop when I'm not somewhere suitable for full difflock.

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Yes it's lockable but the centre diff should be locked imho if bling off road and wheel. Spinning is possible. 

 

Except racing speeds!!...the unlocked arb wins 

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If I had a Defender and deep pockets, I'd be fitting the three ATBs.  As it is, I have secured a RRC BW transfer box for my 109 - I don't like the way you need to stop to disengage 4wd on the Series transmission on wintry roads, and the viscous unit is ideal in UK winter.  The ATB would be a stronger equivalent with the added benefit of full locking in the LT230.  I can't see any advantage of the standard LT230 configuration (other than cost).

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Not sure I can add much that hasn't been said already. I would say, a 1.2:1 transfer box might help cruising speeds, but in a Tdi will blunt acceleration as a rule and make it feel a lot less peppy. If you don't have a tweaked Tdi you may also find you struggle to pull 5th gear in some situations, so might end up using 4th more so, making it worse for cruising speeds.

Remember a stock 32" on a Defender with the 1.4:1 gives almost the same mph/1000rpm in top as a Disco on 29" tyres with the 1.2:1

So putting the 1.2 in a Defender is like running a Disco on 32" tyres. Doable, but there will be trade offs.

As for the LSD, I can see a couple of benefits. If you use the vehicles for trials events, then it means you could likely drive a lot of off road terrain with just the LSD, but get a better turning circle than with a locked centre diff.

On a similar note, the LSD means you'll probably be able to drive further off road on more challenging terrain without the need to lock the centre diff. Although it's not exactly a hardship to engage difflock, so it's a very limited benefit. 

The other benefits are speed on mostly loose surfaces. If you think what rally cars do, or even compers and hill rally cars, where you will be potentially sliding the car about and getting different wheel speeds front and rear. A locked centre diff would be no good here as it'd generate huge understeer. And an open diff is prone to breaking easily (as posted above). But also you can end up with it spinning only one or two wheels at a time. Which can slow corner exit speeds and make it harder to drift and slide.

 

Things like the Subaru Impreza and Celica GT-Four use a centre and rear LSD in their 4wd systems for this exactly this reason.

 

In a Land Rover if you drive on snow, wet grass or gravel often. Then it could be a very good thing to have. And even for road use, if you have a highly tuned vehicle, say a stout V8 or maybe a torquey Td5 and tend to hoon and wheelspin quite a bit, then again it would be good. If you only trundle about on tarmac with a stock Tdi and don't do any other off roady speedy events, then there is likely very limited advantages to having a LSD in the LT230.

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So to summarise if I drove like an idiot in something considerably more pokey than my tdi it'd be worthwhile. I don't and it's not :P

I'll rebuild the 1.22 and see how it goes, if it's no use then I can see about adding the roamerdrive to the 1.41 whilst it's out....although hiding the £1500 price tag from SWMBO won't be quite so easy....

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I haven't seen their prices in a while - mine cost £800 in 2007.  £1500 accounts for a lot of miles at only slightly fewer mpg, and a lot of ear plugs...  I suspect the 1.22 230 will be ok in the 90, especially at that price comparison!

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To add some feedback from a users perspective....

Centre ATB in LT230 for some time now and really wouldn't know it's there....

I also have an Ashcroft ATB in the rear diff.

While touring in the Pyrenees earlier this year I got to a bit of an axle twister on a slow long climb and left the centre diff unlocked, where I thought I might need it locked... No real momentum... Just a bit of a test....

When the left front lost traction the truck stopped.... The two ATB's weren't enough to keep it moving.... Rolled back a few feet, locked the centre diff and on she went without issues.

On the road the vehicle shows no signs of the ATB's being there under normal conditions. I've pushed it around in the wet and dry conditions and the truck behaves itself. They are doing their work as I should be slipping around a lot more in some of these situations, but so far I'm happy that I can push the loud pedal when needed and all seems in control.
(Td5 is "tuned" with bigger intercooler, VGT and IRB mapping)

When I'm off-road it's normally lanes and at a fairly sedate pace, so I doubt they get a work out at all on those occasions.

Since they've been installed I've not really been in many wet, muddy scenarios apart from a few lanes in Thetford and I've only locked the centre diff on one occasion "just in case" and even then I doubt it was needed.

For me, just having good road manners in less than ideal conditions on KM2's they are proving worth it...

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