 | Home > Maintenance & Modifications > Ashcroft Transmission's new HD P38 Diff replacement. |
 
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| Drover Member Since: 27 May 2011 Location: Central Coast NSW Posts: 53  
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Thought I would share a couple of pic's of my just landed. HD P38 replacement diff.
Finally a solution to all the problems and design faults that plague the standard P38. Big thanks to AshTrans for their effort and commitment to this project. Enjoy the pic's Cheers [URL=]  Click image to enlarge[/URL] [URL=] Click image to enlarge[/URL] [URL=] Click image to enlarge[/URL] Admin note: this post has had its images recovered from a money grabbing photo hosting site and reinstated  |
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6th Jun 2013 9:38pm |
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| landybehr Member Since: 17 Apr 2013 Location: -D- Posts: 173 |
Sorry for having to ask - which problems and faults were there ? (I´m asking because I do have such a diff in the back of the 110", and am quite fond of doing away with design weaknesses, but didn´t know there were so severe ones. First impression was, it´s a 110" back axle´s diff with the manuall Ashcr-AirLocker. Great reputation, no doubt. |
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7th Jun 2013 1:47pm |
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| Drover Member Since: 27 May 2011 Location: Central Coast NSW Posts: 53
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Really these are question best asked to Ashcroft's and yes it replaces the rear P38 centre.
But, in simple terms the pinion bearings are way to close together, this allows the pinion to "walk away" from the crown wheel under load, reducing contact between the teeth. Second due to the design of the stock diff centre, the height of the teeth on the crown wheel and pinion are to short. This exaggerates the first problem. Leadingto premature failure.....not if but when This new centre, fixes all of these issues and has a complete new centre casting. |
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7th Jun 2013 2:00pm |
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| landybehr Member Since: 17 Apr 2013 Location: -D- Posts: 173 |
Ah..ok.
I haven´t heard or taken notice of - but at a second look it appears to me as a hypoid design. Is a different prop-shaft needed ? |
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7th Jun 2013 9:57pm |
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| Drover Member Since: 27 May 2011 Location: Central Coast NSW Posts: 53
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The stock shaft needs shortened by 31mm.
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7th Jun 2013 10:14pm |
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| jst Member Since: 14 Jan 2008 Location: Taunton Posts: 8021  
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Low pinion then, nice.
particualry good of the Ashcroft design is the air pipework and fittings compared to ARBs. works really well. (and a better size pipe too!) Cheers James 110 2012 XS Utility 130 2011 M57 bespoke Camper 90 2010 Hardtop 90 M57 1988 Hardtop Last edited by jst on 21st May 2015 4:46pm. Edited 1 time in total |
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8th Jun 2013 11:21am |
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| ashtrans Site Sponsor Member Since: 08 Nov 2008 Location: Harpenden Posts: 257 
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Hi,
I hope to get this on our website this week but I will give a quick overview, its pretty well recognised that dropping the Salisbury and going to the P38 type diff was a fairly major step back on terms of strength, the main problem is not the shafts or the diff centre but the ring and pinion, in my view this is because the pinion bearings are too close together which increases the load on the bearings which causes either the bearings to fail or the ring and pinion to get noisy, early designs looked at making a new diff centre but this was a much bigger job and once I decided the centre was OK I decided to just design the new ring and pinion around the stock rover type diff, because of this we can supply this diff with any centre that fits the rover diff (not the P38 one) so you can fit, our air locker, our ATB, quaife, whatever, the only mod required is to drill out the 10 crown wheel holes as we thought it would be good to use larger bolts in the crown wheel seeing as we were making it from scratch and these bolts can be a problem, to get a significant strength increase in the ring and pinion meant 2 things : 1) space the pinion bearings further apart, like the rover diff with the longer 'nose', this moves the drive flange forward which means the rear prop needs to be shortened by 31mm, 2) make the new ring and pinion a hypoid design, ie by lowering the pinion you get far more contact area on the meshing teeth which reduces the load on them, this also makes the pinion much bigger in diameter : [URL=] Click image to enlarge[/URL] [URL=] Click image to enlarge[/URL] [URL=] Click image to enlarge[/URL] next we had to make a new diff housing, this bolts straight inplace of the stock diff, : [URL=] [/URL]
then put it together, note the super strong M14, 12.9 cap head bolts : [URL=] Click image to enlarge[/URL] [URL=] Click image to enlarge[/URL] this project has been driven by the Australian market for some reason, not sure why, but we have 4 running in vehicles now and another 4 being sent this week, I cant see one breaking easily ! Admin note: this post has had its images recovered from a money grabbing photo hosting site and reinstated Dave |
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8th Jun 2013 6:33pm |
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| diesel_jim Member Since: 13 Oct 2008 Location: hiding Posts: 6092 
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Ah I get it.... so it's a long nose diff to fit into the 110 "rover" type rear axle then?
They must be, but are all the axle studs in the correct place for this diff to fit in? |
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8th Jun 2013 7:36pm |
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| jst Member Since: 14 Jan 2008 Location: Taunton Posts: 8021
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it looks like it from the picture. so a pre P38 110's prop would fit anyway. this is the route i will be going with mine when it fails. Cheers James 110 2012 XS Utility 130 2011 M57 bespoke Camper 90 2010 Hardtop 90 M57 1988 Hardtop |
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8th Jun 2013 7:58pm |
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| ashtrans Site Sponsor Member Since: 08 Nov 2008 Location: Harpenden Posts: 257
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this can get confusing, lets confirm the terminology we are using : rover diff = longnose housing i.e. 110 front / 90 front or rear / disco 1 or 2 P38 diff = shortnose housing i.e. post salisbury (2002) 110 rear \ P38 HD P38 = special that we make to replace the P38 diff, we are not using the stock rover long nose diff, we are making a new housing and machining it with the P38 diff bolt pattern (which is different to the rover diff) Dave |
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8th Jun 2013 8:41pm |
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| diesel_jim Member Since: 13 Oct 2008 Location: hiding Posts: 6092
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Gotcha. Very nice
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8th Jun 2013 8:45pm |
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| landybehr Member Since: 17 Apr 2013 Location: -D- Posts: 173 |
I notice that all the hypoid diff centers have the pinion lowered. AFAIK they had been designed that way as a means of lowering the propshaft of passenger cars where under vehicle clearance was low and/or the floor could be lowered then.
On the 4x4 that design specification not really exists and, if already changing the pinion axis - why not moving it up and moving the propshaft away from rocks ? (just asking out of interest. And because I sometimes read about high-pinion diffs, i.e. on Toyotas. But could be that was in context of front diffs only. The Salisbury axle had the low-pinion obviously and it´s not that everybody moans about) |
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8th Jun 2013 9:28pm |
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| ashtrans Site Sponsor Member Since: 08 Nov 2008 Location: Harpenden Posts: 257
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Yes most passenger cars are low pinion for this reason but they can be high pinion, the force 9 axles we made were high pinion for rock clearance,
Our design is low pinion for 2 reasons, 1) high may give A frame clearance issues 2) high pinion can have lubrication issues not always but low pinion means the pinion bearings have plenty of oil, PS I think salisburys are bevel gears not hypoid, ie pinion is on crown wheel centreline, Dave |
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8th Jun 2013 9:59pm |
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| landybehr Member Since: 17 Apr 2013 Location: -D- Posts: 173 |
Dave,
if you think they´re bevel gears, then I readily can take it as a fact. You´re probably the very first person I might ask if I needed know sth. about LR´s drivetrain 
I´ve found a pic, but not sure if it helps to confirm. Click image to enlarge from: http://ollr.createaforum.com/technical-arc...tep-guide/ |
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8th Jun 2013 11:08pm |
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