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Don Del

Truetrac Selection

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After agonizing about it for a couple of years I have decided to fit Truetrac differentials fron and rear on my '99 Defender Station Wagon 110. The chassis number is XA159828 and the front axle serial number is M1400125A. The rear axle is a Salisbury unit and the half shafts have 24 splines all round. From my research I have identified part number DTL-912A407 for the front and TT912A593 for the rear. I am located in Bolivia and I spoke with one supplier in the States today and they didn't exactly inspire confidence in the selection of the right units which is understable considering the rarity of Defenders there. When you consider the base cost plus shipping plus customs duty and no possibility of exchange you can appreciate why it is important that I get the selection right. I am fairly confident that I have picked the right units but I would appreciate it if someone can put my mind at rest!

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I would suggest an Ashcroft ATB for the front.  https://www.ashcroft-transmissions.co.uk/limited-slip-differentials/ashcroft-atb.html

The Salisbury TT part number is 912A593

The Rover front TT is 912A407

The catalog is here: https://www.eaton.com/content/dam/eaton/products/differentials-traction-control/eaton-performance-differential-application-guide-en.pdf

 

 

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Thanks for the reply confirming selection and the links. I would be interested to hear why you would recommend the Ashcroft unit over the Truetrac for the front.

Cheers

Del

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12 hours ago, Don Del said:

I would be interested to hear why you would recommend the Ashcroft unit over the Truetrac for the front.

It is better designed and built.  They use twice as many worm gears.  They are designed to run in both directions (the TT only has thrust bearings for forward travel, not reverse).

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And yet Soren on here had one fail open in relatively short order...

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23 hours ago, Bowie69 said:

And yet Soren on here had one fail open in relatively short order...

That was my concern, along with the lower price and the "get what you pay for" adage.  I think they have a good rep, but which is best for durability I'm not sure.  As for the Ashcroft unit having thrust washers for use in each direction, I wonder if that's why it has 6 rather than 3 worm gears.  It certainly seems the better of the two for operation; a directional ATB isn't much use if you need to reverse, is it?  Makes me doubt my plans to fit the Trutrac to the Salisbury and think that splashing out nearly twice as much for the Quaife equivalent may be better value.

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what about fitting a later rear axle that used a short nose diff rather than a salisbury?  

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Why do that?  It's a weaker unit used for logistics streamlining, not product quality.  They're prone to pinion and pinion bearing issues, stronger than the long nosed Rover diff but nowhere near as tough as a Salisbury.  By the time you source the axle, the cost difference between using that with the Ashcroft diff and associate bits is not going to be worth the reduced strength of having the Salisbury with and ATB, especially if using ratios other than 3.54 that you already have.

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4 hours ago, Snagger said:

Why do that?  It's a weaker unit used for logistics streamlining, not product quality.  They're prone to pinion and pinion bearing issues, stronger than the long nosed Rover diff but nowhere near as tough as a Salisbury.  By the time you source the axle, the cost difference between using that with the Ashcroft diff and associate bits is not going to be worth the reduced strength of having the Salisbury with and ATB, especially if using ratios other than 3.54 that you already have.

i was led to believe its a standard rear axle casing with 4pin diff. 

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1 hour ago, Tim2809 said:

i was led to believe its a standard rear axle casing with 4pin diff. 

No, that'd be a P38 style or short nose diff.  The stud pattern on the axle is different, I believe, so a 4-pin (or 2-pin, for that matter) long nosed diff won't fit the axle without modifications.  Short nose diff is stronger than the long nose, but weaker than a Salisbury.  But if you already have the short nos rear axle, it's likely to be strong enough for you if you're looking at ATBs rather than full lockers.  As I understand it, the Ashcroft ATB will fit the short nose diff too, but I think you need additional parts.  Still cheaper than a Trutrac, and works in both directions.  Best to ask Dave on the phone before ordering.

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On 12/21/2018 at 5:03 PM, Red90 said:

It is better designed and built.  They use twice as many worm gears.  They are designed to run in both directions (the TT only has thrust bearings for forward travel, not reverse).

Are you sure that's what happens?  I know they only have the thrust washers on one side and have half the number of worm gears, and that when buying you have to specify front or rear, but I tough that was to do with the amount of preload not interfering with steering on road, rather than uni-direction operation.  This would be a major factor against Trutracs if correct.

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They function the same in both directions as far as bias goes.  In reverse, the center gears thrust to the outside, where they just rub on the casing.  It is fine for normal use.  You just don't want to drive in reverse in circles for hours on end.  In forward, the gears thrust to the inside where there is a thrust bearing.  The front and rear TTs are the same parts and have the same bias.  You just swap the gears from side to side, so that the thrust is to the center when driving forwards.

Edited by Red90
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Great.  I had misunderstood the earlier post and thought it meant a directional operation rather than wear issue.  I knew about the single washer and thus wear, but hadn't heard of the operation issue, and so I'm glad that was my misinterpretation!  It means I can stick with the rear Trutrac plan instead of spending double on a Quaife!

Any idea if it's: a) plausible, and; b) worth, having a Trutrac machined to take a thrust washer on the other side?

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it's an interesting one, when is wear acceptable?

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I've never seen one wear.  Of course, I've never seen someone put one in backwards either.

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Many thanks to everyone for their input. After a bit more checking I have decide to follow Red 90's suggestion and I placed an order today with Ashcroft for one of their ATB units for the front and a Truetrac for the rear. I have ordered up the additional parts that will be needed from MM4x4.With shipping and custom's clearance I don't expect to be in a position to start on the installation before the beginning of February. But all in all a good start to the New Year!

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Don, what front shafts do you have?  Nige recommends uprating to 24-23 Ashcroft shafts (and the CVs if using the 32 spline type).  I'll be interested to see your feed back on the ATBs.  Rather envious, too.

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On 12/23/2018 at 8:58 AM, Snagger said:

No, that'd be a P38 style or short nose diff.  The stud pattern on the axle is different, I believe, so a 4-pin (or 2-pin, for that matter) long nosed diff won't fit the axle without modifications.  Short nose diff is stronger than the long nose, but weaker than a Salisbury.  But if you already have the short nos rear axle, it's likely to be strong enough for you if you're looking at ATBs rather than full lockers.  As I understand it, the Ashcroft ATB will fit the short nose diff too, but I think you need additional parts.  Still cheaper than a Trutrac, and works in both directions.  Best to ask Dave on the phone before ordering.

All correct. Post 2002MY 110s have the P38 short-nosed 4 pin rear diff. I've currently got ATBs sitting in the garage waiting to go into my 110, and all I needed to order for the rear was the extra P38 spacer ring. Have to say the first impression of the ATB on unpacking one is that it's a solid lump!

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4 hours ago, BogMonster said:

All correct. Post 2002MY 110s have the P38 short-nosed 4 pin rear diff. I've currently got ATBs sitting in the garage waiting to go into my 110, and all I needed to order for the rear was the extra P38 spacer ring. Have to say the first impression of the ATB on unpacking one is that it's a solid lump!

I was going to PM you at some point to ask if you were on course to do this yet.  If I remember rightly, you were going to retain the standard shafts and CVs and see how they hold up as it's used for tracks, not competition.  I'm keeping my fingers crossed as I hope to do the same on my RRC and coiler axled 109, and don't want to spend on new shafts if not required, but Nige was pretty insistent and he does know his stuff.  I hate budgets!

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10 hours ago, Snagger said:

I was going to PM you at some point to ask if you were on course to do this yet.  If I remember rightly, you were going to retain the standard shafts and CVs and see how they hold up as it's used for tracks, not competition.  I'm keeping my fingers crossed as I hope to do the same on my RRC and coiler axled 109, and don't want to spend on new shafts if not required, but Nige was pretty insistent and he does know his stuff.  I hate budgets!

Yep, that is the plan.

The only thing that I have consistently broken in the standard drivetrain is the 2 pin LR diff centre, so I figure it is fine. I've never broken a CV or halfshaft in anything in about 25 years of driving off road. Red mist is saved for the garage!

But the decider for me was that I know of several vehicles here fitted with full ARB lockers, and I can't recall any instance of them popping a CV or driveshaft because of the extra strain. The ATB should put less strain on everything than locked ARBs, so I'm not that worried. Most of the time the circumstances where it comes into play will be where grip between the two wheels on an axle is not massively different but on open diffs enough to make a wheel spin out - the ATB will keep things going but probably with much less than the 3:1 torque bias. We'll see - I just don't want to waste money as if they are good, I've potentially got 3 vehicles to fit them to, and 3 full sets of Ashcroft gear is more than I'm really prepared to spend. If I blow stuff up on the first vehicle I'll reassess the situation then.

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On 1/7/2019 at 2:39 PM, Snagger said:

Don, what front shafts do you have?  Nige recommends uprating to 24-23 Ashcroft shafts (and the CVs if using the 32 spline type).  I'll be interested to see your feed back on the ATBs.  Rather envious, too.

The 24-23 Ashcroft shafts and CVs are on the wish list for next year! The ATB, Truetrac and various other necessary bits and pieces have got as far as Frankfurt courtesy of TNT. With a bit of luck I should be in possession of everything by the end of next week and on schedule to have everything installed by the end of the month. Feedback will definitely be forthcoming!

Cheers,

Del

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