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aerobod
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Titan LSD Rebuild

With my 2012 S3 R400D at 8 years old and 34,000km of which about 5,000km has been track days and the preload on the LSD below 20lbft, it is time for a rebuild as my main winter project this year.

Although there are various methods of removing the diff, the method I use is to remove one wheel and the hub, brake disc, ear and driveshaft on that side. The A-frame and rear anti-roll bar also need to be removed to drop the diff. I have the car stored in the winter on a steel frame that is 1.5m above the ground but is up against the wall on the left side, so this method works well when the car is high enough.

After the right rear wheel was removed, the A-frame was removed, making note of the number of shim washers on each side:


 

The end links on the anti-roll bar were disconnected by removing the locking clip on the spherical joint attached at the hub carrier end, the four bolts attaching the anti-roll to the chassis tubes were then unbolted and the bar was extracted out the right side:

The brake caliper was then unbolted at the sliders and tie-wrapped to the coil spring (I have the flexible rear brake lines, if not the brake pipe needs to be carefully bent to lift the caliper off the brake disc):



After removing the two rearward hub carrier nuts that also secure the ear to the deDion tube, together with the two rear bolts that attach the ear to the deDion tube and unscrewing the speed sensor and moving it out of the way, the driveshaft, brake disc, deDion ear and hub can now be extracted, the two left hand ear attachment bolts are shown screwed loosely in place after removal, so I don't misplace them, something I tend to do with most bolts as I work:

The driveshaft bolts are now removed, I place a conventional Allen key in the bolt above the one I'm loosening to stop the shaft rotating as I use the hex socket key with my ratchet and an extension:



The lower diff carrier bolts are now loosened, making note of any shim washers between the chassis and carrier, but kept hand threaded in place until the diff is lowered:


 

Now the top carrier bolt is removed, making note of the shims on each side between the carrier and chassis. My bolt came out fairly easily with a few light taps from a mallet and a rod inserted to drive the bolt out. The diff can now be lowered with your equipment of choice. I used my wheeled tool box with a hydraulic floor jack, using it's natural arc to move the diff sideways as it was lowered, enabling the left driveshaft to be extracted from the diff, but left in place:



With the diff on the bench, the top carrier bolt, 6 hex bolts and top Allen bolt are removed and a thin blade inserted at the top to break the sealant bond to remove the cover:


 

The side seals can now be removed, preferably with a seal hook tool to avoid any contact with the bearing. A large pair of circlip pliers is now needed to remove the locking circlip. Be careful to mark these clips, they have a specific thickness on each side to give the correct crown wheel and pinion mesh. My driver's side (left side being in Canada) circlip is marked as 3.44mm thick, my passenger/right side is 3.62mm thick. After removing the circlip the outer bearing races can be extracted using finger pressure and sideways movement of the crown wheel and LSD, no tapping  or levering required on my diff:


 

After both external races have been removed the crown wheel and LSD can be carefully rotated and extracted:


 

The 6 Allen bolts holding the LSD cap in place can now be removed. Make note of the alignment dot on the cap (it is obscured by the ratchet in this picture, but you can see the matching dot on the LSD casing just below the ratchet head). The cap is a fairly tight fit, so three of the Allen bolts can be used in the threaded holes to lift it against the casing by tightening them gradually in sequence.



Now the guts of the LSD can be extracted, laid out in order, cleaned and inspected. The parts order in mine are as follows, bearing in mind the number and thickness of shims can vary, listed from left-hand side (closest to casing cap):

- Thrust shim for diff gear, diff gear Belleville washer, diff gear thrust washer (with the 2 tabs, depressed face towards gear).

- Clutch pack Belleville washer, clutch pack shim, 1st clutch pack steel disc (6 tabs), 1st clutch pack friction disc (carbon or sintered), 2nd clutch pack steel disc, 2nd clutch pack friction disc, 1st LSD cup/cage (marked as L.H.).

- Left hand diff gear, 4 spider gears with 2 cross shafts, right hand diff gear.

- 2nd LSD cup/cage (marked as R.H), 3rd clutch pack friction disc, 3rd clutch pack steel disc, 4th clutch pack friction disc, 4th clutch pack steel disc, clutch pack shim, clutch pack Belleville washer.

- Diff gear thrust washer (depressed face towards gear), diff gear Belleville washer, thrust shim for diff gear.

The ramp angles for my diff are either 30/90 or 45/60, depending on which depression the spider gear shafts are placed in, I will probably stay with 30/90 for most aggressive locking on acceleration and zero on deceleration:



My inspection found the following:

- All ball bearings, races gear teeth  and sliding surfaces are clean, bright and show no noticeable wear.

- There was some "paste" from friction plate wear on the bottom of the diff case and in the nooks and crannies of the cups/cage, but not evident elsewhere.

- One friction plate on each side was almost totally worn out, but the other friction plate on each side had only a small amount of wear.

- Both of the clutch plate Belleville washer were in good condition.

- Both diff gear Belleville washers (the small ones) had wear on the surface and one was cracked through, but still in one piece. I will do some measurements when I refurbish the diff and determine if the thrust shims need to be reduced or eliminated.

Left side friction plates:


 

Right side friction plates:


 

Cracked thrust Belleville washer:

As my diff has been quiet and really predictable on the track with smooth locking and the condition of the diff besides the plates and thrust Bellevilles, I've just put in an order with Caterham for the £426 sintered plate rebuild kit (no VAT for my Canadian order). The Titan rebuild kit is about 2/3 the price, but doesn't include any shims, whereas the Caterham kit provides a whole set that will allow fine tuning of the clutch pack preload,

Dave Hardcastle
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Although I've had a Tracsport LSD fitted this year, that is a cracking addition to the club pages. Very clear photos with plenty of explanation. Good job aerobod, hope it goes well.

David_Long
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Good post, I suspect the shims are not critical to performance - in other words the pre-load is very quickly exceeded by the ramp forces when in use. But moving to sintered plates from carbon may make a difference and ordering them is probably not a bad idea. 

John Vine
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Well done, James -- very informative, with excellent photos.  (Makes me glad I have the Quaife ATB!)

How about turning it into an official "Maintenance Guide"?  Shaun will advise how to do that, I'm sure.

JV

aerobod
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Hi John,

I can do that when I complete the reassembly part. There are a couple of important tips such as ensuring the spacers on the driveshafts are in place to keep the CV spring load on the bearing and that the seals are only inserted to be flush with the casing to avoid leaks.

James

7 wonders of th...
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I'd also check the pack movement before altering the shims, although shimming will alter the preload it also alters the travel and can put the Bellevilles in the wrong position - ie overloaded and working through more than their intended range of travel, which will lead to premature fracture.

Belleville have a massive range of springs in their range and are very helpful if your looking to change the spring whilst maintaining the pack height.

They took the dimensions from the old springs and ran a calc for me and emailed it over.

I removed the OE ones from my ZF which gave 70lb/ft preload and replaced with lighter ones, stacked 3 per side, whilst maintaining the pack height... and now have 14lb/ft of preload.

Geoff Brown
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Aerobod - I have 'permissions' to create a guide. Would you be OK with me attempting to transfer it to GUIDES 'Maintenance'?  Before I do you could add how to assemble & set up the LS unit/diff along with relevant torque loadings?

Once approved you can review & ask for amendments etc if required.

 

I suppose that leaving the support frame in situ was not possible the way the diff was dropped?

The diff internals are in pretty good nick considering the mileage & age. One in a million probably as every one else who suffered from the 'curse of the Titan' did not come off so well or cheaply.

As you state correctly when removing the A Frame, collect & make a note of the shimming washers from each forward end for re assembly. I did just that but could I reintroduce them all back in - NO!  It was as if the gap had shrunk by a couple of very thin washers. The A Frame alignment is correct after re measurement & alignement. There is no side play.  Strange.

 

 

James B
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Great post James - very informative.  Many thanks Thumb Up

James

aerobod
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Hi Geoff, that would be great if you could transfer it to "Guides, Maintenance" once I have finished.

It will probably be a month or so until I do the reassembly, I just ordered the parts this weekend. I'm also planning to drill and tap a drain plug hole in the bottom of the casing, but will need to make a jig to hold the casing on my rather undersized bench-top combo lathe/milling head, to mill a flat spot before drilling and taping the hole. I've also ordered an M12x1.75 magnetic drain plug.

A couple of my thin shims are damaged from being caught by the thread of the long bolt, so I will measure the clearance of the support frame to the chassis when reinstalling and machine custom shims for each side. I have found there is too much flex of the support frame to the diff when bolting up, so prefer to get it fully installed and "flexed" as a unit to ensure the frame to chassis dimensions are stable, before shimming and centralising in the chassis.

One of the challenges is going to be holding the LSD and crown wheel when checking the torque, but I think I have a method of suspending it under the car without the casing so that I can insert the driveshafts to check the breakaway torque without putting the whole diff back together, while I play around with the clutch pack shims. Using a longitudinal length of wood with a couple of vertical blocks to support and  "trap" the LSD to keep it in position with the driveshafts straight, is what I think will work.

I think I was lucky with the diff wear, probably the case that the early carbon plates were more durable, seems to be sometime after the 2012 car that I have that they changed the composition to the most troublesome carbon plates before changing again to the sintered plates. Although two of the plates are worn out, the clutch pack Belleville washers don't look as though they would be over flexed with the other two plates close to original thickness, hence no fracturing in my case.

James

ScottR400D
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James, have you considered putting the drain hole in the back plate? There's space below the filler plug and it might be easier to hold, machine and tap the back plate than the main casing. It's also only a £150 part you're machining, just in case!

BTW, what is that 'notch' in the top of your back plate? I haven't seen that before. 

aerobod
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Hi Peter, I was initially going to drill and tap the backplate, but any low position to get the most oil to drain is in a thin area of the backplate, as it is significantly relieved on the inside. I would only be left with about 5mm of wall thickness after machining a flat on the outside to seal against, which isn't enough without welding in a boss, which could be iffy without knowing the exact alloy that the backplate is made from to use the right welding wire. The machined area below the fill plug is too narrow to get an M12 or even M10 bolt with crush washer to seal against and the last bit of the casing slopes in a lot as it meets the flange, so even with a boss welded in I could probably only drain 80% of the oil as the drain hole would need to be about 15mm above the bottom of the casing. You can see the back of the backplate in the photos in my original post, the bottom of the backplate is on the right in the photo.

In the end the casing is 20mm thick in the area I will put a flat and drill and tap a hole, between the bottom two back plate attachment holes. The casing is easily obtainable from any scrap yard from BMWs that have used the 168 diff over the past 20 or more years, in the slight possibility of some form of disaster while machining.

The notch in the top of the backplate on my car is to allow clearance around the fuel line, this is due to the fact that my car had the old style carrier and a different backplate originally that had clearance above it for the fuel pipe, but there was a recall on that backplate to replace with the new style due to interference with the deDion tube under high suspension loads. I decided to notch the backplate where there is plenty of spare material, instead of having to redo the fuel feed, which currently passes through a grommet in the steel angle bracket under the middle of the boot floor.

James