 | Home > Technical (L322) > Magna Steyr DD295 Transfer Box Teardown |
 
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| RRPhil Member Since: 22 Aug 2011 Location: Blackburn, Lancashire Posts: 1000  
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I�ve just bought a poorly DD295 transfer box off eBay for �50 as I thought it might be fun to strip one down to see what�s what. The seller�s description was that it �did drive but was noisy� and I can tell just from spinning the input shaft by hand that there�s something very wrong inside � it feels extremely rough.
This transfer box has been used ever since, and the same unit is also fitted to the Land Rover Discovery 3, Discovery 4 and the Range Rover Sport.
The original NV225 unit, used in conjunction with the 5-speed transmissions, employs a Torsen Type-B differential to apportion torques front-to-rear (the split being nominally 50:50). The Torsen design limits the torque biasing to 65%/35% in either direction and, as many of us found to our cost when our front propshaft spline failed and left us stranded, the Torsen unit does not allow the differential to be �locked�. The DD295 unit on the other hand uses a �normal� bevel gear differential, which again nominally splits torque 50:50 front-to-rear, and a multi-plate clutch pack is employed to vary the front-to-rear torque distribution with the clutch also having the capability to lock the centre differential.
As with the NV225, the DD295 has selectable low & high ranges, high range being direct (1:1) in each case but low range ratio is slightly different for the two boxes : 2.93:1 in the case of the DD295 compared with 2.69:1 for the earlier NV225 unit.
On with the teardown So the first job is to drain off the fluid. The casing has a combined filler/level plug and also a drain plug (head size 8mm hex.), each tightened to 22Nm
The fluid is Shell TF 0753 (as usual, Land Rover state that this fluid has been especially developed for the unit, contains unique additives, and therefore no other fluid must be used) and the capacity is just 1.5 litres from dry. The fluid that drained out looked nice and clean, so no particular clue there as to what the problem might be. The next component to be removed is the shift motor, which is held on with four, 55mm long, external Torx head screws (head size E10) which are torqued down to 25Nm
The drive gear in the motor is plastic :
It�s interesting to compare the cost of this shift motor (IGH500040) at around �200 with that of the NV225 shift motor (IGH500010) which is now priced at around �1600 ....and climbing Next off is the high/low range position sensor which is retained by two, 30mm long, external Torx head screws tightened to 10Nm. My smallest Torx socket is E8 and the head size is smaller than this so I used a plain 5mm socket to remove the screws, which seemed to work okay.
Unlike the low/high shift fork used to achieve range changes in the NV225 - which glides linearly along a �rail� - the DD295 shift fork pivots on an axis and this angular position sensor is attached to one end of this axle and therefore measures the shift fork angle directly.
From examination of the Patent for this transducer it is of the �non-contact� type - which is good to know considering all the problems people have experienced with the NV225 sliding-contact rotary potentiometer.
The Land Rover part number for this sensor is IAB500191 and it costs around �85 to replace The final component to remove before the casing is opened up is this solenoid :
The shift motor is �dual-function� in that it controls both the clutch actuation and the range changes and it�s this solenoid�s job to switch the mechanism (which is driven by the motor) over to perform whichever of these two functions is required at that time. The solenoid is attached to the casing by three, 12mm long, external Torx head screws, tightened to 6Nm. The socket size is the same as for the high/low range position sensor screws.
It can be seen in the photos above & below that the solenoid has a plastic T-piece attached to its centre plunger which engages in a fork at the end of the transfer box selector lever
It was a bit of a pain to detach from the casing because the solenoid is designed to be removed (& subsequently re-installed) in its �energised� position and this is achieved by using the diagnostic tool to power it up, which obviously means leaving the electrical connector attached until it�s lifted clear of the casing. Not having the right kit I just fiddled around until it eventually disengaged itself from the fork. The Land Rover part number for the solenoid is IGF500011 and its cost is similar to the high/low position sensor i.e. approx. �80 So, finally, we get around to splitting the casing halves so that we can have a look inside the transfer box. The two casings are held together with nineteen, 45mm long, external Torx head screws (socket size E10) which are tightened to 35Nm
and, following their removal, the casing can be split to reveal the innards....
That�s as far as I�ve got at the moment.....standby for the next exciting installment (bet you won�t be able to sleep now  ). I�ll follow up with what I find as soon as I�ve found it, hopefully within the next couple of days!
Phil Admin note: this post has had its images recovered from a money grabbing photo hosting site and reinstated 
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7th Jul 2012 9:40pm |
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| Joe90 Member Since: 29 Apr 2010 Location: Hampshire Posts: 6419 
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Great stuff Phil |
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7th Jul 2012 10:07pm |
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| 47p2 Member Since: 05 Oct 2010 Location: Gone Beyond, Subaru Posts: 8048 
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Still hitting the refresh button |
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7th Jul 2012 10:14pm |
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| kingpleb Member Since: 07 Jun 2011 Location: Maybe here. Maybe there, I get everywhere! Posts: 8455 
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Phil on behalf of the forum members here,
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7th Jul 2012 11:05pm |
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| 47p2 Member Since: 05 Oct 2010 Location: Gone Beyond, Subaru Posts: 8048
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7th Jul 2012 11:41pm |
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| RRPhil Member Since: 22 Aug 2011 Location: Blackburn, Lancashire Posts: 1000
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Unfortunately it�s not an option to swap the two transfer boxes as they were never designed to mate up to the same transmission. I would imagine that their installation sizes are different too. Also, their control systems will be quite different as the passive Torsen centre diff. in the NV225 was replaced with active clutch control in the DD295.
Just to keep 47p2 happy until the next instalment (hopefully tomorrow) here�s some pictures of a cutaway DD295 from Cutaway Creations (the photographs are theirs, not mine) : http://www.cutawaycreations.com/ ...now go to bed or the transfer box fairy won�t come... 
Phil Admin note: this post has had its images recovered from a money grabbing photo hosting site and reinstated
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8th Jul 2012 12:01am |
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| 47p2 Member Since: 05 Oct 2010 Location: Gone Beyond, Subaru Posts: 8048
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Thanks Phil, I'm off to bed right now |
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8th Jul 2012 12:44am |
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| RRPhil Member Since: 22 Aug 2011 Location: Blackburn, Lancashire Posts: 1000
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The two halves of the casing separate easily with almost all of the components staying with the rear casing
The exception being the front output flange which can be removed from its bearing by compressing the snap ring
There are two Bellville springs which react against a circlip on the input shaft which appear to set up a preload force against the inner race of the input bearing
and when I spin this bearing by hand it feels extremely rough & noisy. On closer examination I can see that the balls and races are very badly damaged
There�s a magnet in the bottom of the casing which is covered in metallic debris
which, when cleaned up, looks like this
Clearly therefore the failed bearing has been producing a lot of debris and it�s amazing that the fluid that was drained out was so clean. The input shaft can then be removed from the rear casing, and it brings the oil pump with it
Removal of a snap ring enables the oil pump to be separated from the shaft
This leaves the rear casing looking like this
Next off is the front driveshaft sprocket and the chain
It�s interesting to see that this Borg Warner Hy-Vo chain is exactly the same width as the chain fitted in the NV225, but is slightly shorter
The other sprocket can only be removed as part of a sub-assembly with the torque-biasing clutch. The two levers which move apart to engage the clutch can be seen
The bearings on the ends of the two levers sit on this cam which is rotated by the shift motor. As the actuator turns, the bearings ride up the ramps on either side, forcing the levers apart
A circlip holds together the assembly
and the photo below shows the ball and ramp mechanism which translates the levers� angular movement into an axial displacement to engage the clutch
The torque-biasing clutch has a total of ten friction plates
So here�s what now remains in the rear casing, ready for the next instalment...
Phil Admin note: this post has had its images recovered from a money grabbing photo hosting site and reinstated
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8th Jul 2012 11:50pm |
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| 47p2 Member Since: 05 Oct 2010 Location: Gone Beyond, Subaru Posts: 8048
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Really interesting Phil, I take it the bearing is the only problem you've found so far? |
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9th Jul 2012 12:56pm |
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| RRPhil Member Since: 22 Aug 2011 Location: Blackburn, Lancashire Posts: 1000
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Yes, just that input bearing � and I strongly suspect that�s all I�m going to find wrong with it. None of the box�s internal parts are available from Land Rover so I�ll get the bearing out, check its size and get a price from a local bearing factor (just out of interest).
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9th Jul 2012 7:39pm |
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| T24RES Member Since: 22 Nov 2010 Location: Henley-on-Thames Posts: 936
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Is it just a lack of fluid that has caused the bearing to fail? |
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9th Jul 2012 11:20pm |
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| 47p2 Member Since: 05 Oct 2010 Location: Gone Beyond, Subaru Posts: 8048
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Thanks Phil, top post |
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9th Jul 2012 11:32pm |
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| RRPhil Member Since: 22 Aug 2011 Location: Blackburn, Lancashire Posts: 1000
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The failed input bearing turns out to be a plain, single row, deep groove ball bearing of size 50 x 90 x 20.
Although I�d expected this 6210 C3 bearing to be manufactured by one of the �high end� suppliers such as SKF, INA/FAG, NTN, etc. it�s actually manufactured by a company I�ve never heard of � ZKL of Slovakia.
I�ve priced a genuine SKF replacement from a local bearing factor, available from stock, at just �10.95+VAT. Last week I saw two more of these transfer boxes on eBay, both for �50, both �still working but noisy�. If this is the start of an epidemic, someone should jump on this bandwagon quickly because re-manufacturing these �failed� DD295s is going to be a piece of cake and cost next to nothing. Phil Admin note: this post has had its images recovered from a money grabbing photo hosting site and reinstated
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18th Jul 2012 12:28am |
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| T24RES Member Since: 22 Nov 2010 Location: Henley-on-Thames Posts: 936
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Any idea of the bearing failure Phil?
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18th Jul 2012 2:24pm |
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