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  1. #61
    Part of the furniture Deuce.'s Avatar
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    The only info I can add is:
    Pinion nut on/off with the rattle gun worked fine for me.
    Side bearing/retainer screw in thing goes on/off/adjusted with a simple tool made with the 304 alternator bottom bracket and spare Exhaust studs/nuts as the pins. Not as aweome as your made tool. Bit alot cheaper.
    As for oil, the Penrite LSD Holden specific stuff for $70-$80nzd 2.5ltr seems fine to me.

  2. #62
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    Shimming up the Posi

    Sounds vaguely rude dunnit? Not realy - the centre section of the Limited Slip Diff is often called the Posi, short for Posidrive I believe, and shims are required to take up any play in the centre gears to restore full LSD operation. There are a couple of ways to determine the required shim thicknesses, and its up to you which way to do it and how tight you want the LSD.

    Either way, you are going to need a selection of shims of varying thickness. The shims will be placed between the side gears and the diff cones, which have the following internal and external diameters:



    The surfaces don't (shouldn't!) actually rub/wear on each other - they are splined together by the drive shafts - so I'm not sure what causes the wear marks. From the pictures you can see you'll need shims with a minimum internal diameter of 34mm, and a maximum outside diameter of 62mm, although the cone surface is only 55mm wide.



    I settled on shims roughly 36/37mm i/d and 47/48mm o/d. You'll need several thicknesses - I went for 0.1mm, 0.2mm, 0.25mm, 0.3mm and 0.5mm (not shown) which are all avaliable from eBay for a few quid.

    Shim Selection Method 1
    The first way to select the shims, and the way described in the manual is as follows. Measure the depth of the cone inner surface from the edge of the housing. We've already done this :



    I repeated the measurements at four places around the circumference and got the following :

    Code:
    Cone 1	32.21	32.26	32.24	32.24
    Cone 2	32.35	32.27	32.25	32.24
    The manual says the following shim sizes should be used :

    Code:
    Measured (mm)	Shim
    31.84-32.00	No shim required
    32.04-32.14	0.13mm shim
    32.17-32.27	0.25mm shim
    So if doing it by the book, both sides of this diff should probably have 0.25mm shims installed.

    Shim Selection Method 2
    The second method is to see how much shim is required to remove all the play in the spider and side gears. This is a trial and error method, and will probably lead to a tighter diff. It's the method I chose.

    Start off by placing the cones into each side of the diff cases...



    and select a starting shim size...



    .. and place it on-top of the diff cone surface.



    Not easy to see against the background, but it is there. Then put the side gear on-top of the shim...



    ...followed by the side thrust plates.



    Now place the spider gears assembly into place in each housing in turn.



    Make sure it is properly seated, and the side gears are engaged with the 4 spider gears. Now try and rock the spider shafts by alternatley pressing on the A-A axis, and B-B axis.

    If there isn't any rock/movement then take it all apart again and insert the next shim size up. If there is some movement, then you have put too much shim in already, so take a bit out. Repeat the process until you get to a setting where you have meerest hint/suspicion of some play/rocking. The two sides may well be slightly different. In my case the settings were 0.65mm and 0.70mm.

    Now you have to decide how tight you want the diff. If you want it VERY tight (race/track use only), then you can probably use the shim sizes you've now got. This will cause a slight preload on the spider gears, and increase the wear rate. However, this is not recommended for normal road driving. For normal road use the suggestion is to remove somewhere between 0.15mm and 0.25mm of shim per side . This allows enough slip for tight cornering in car parks etc without the tyres squealing or the diff hopping and popping.

    I've opted to use 0.5mm shims (measured at 0.49mm) on both sides of this diff. We'll see how that goes. :shock:

  3. #63
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    Diff Oil

    The genuine Vauxhall/Lotus oil for our diff was part number VX-90393473, OP-19-42-386. If you ever bought this, it came in 1L bottles labeled "Mobil Mobilube SHC 80W140 (ID)" .



    It's been NLS from Vauxhall/Opel for years, and was discontinued by the manufacturer (Mobil obviously) in about 2007. If you google for it, you'll come across all sorts of conflicting information on suitable replacements. I've no way of knowing for sure who to believe, but this statement (https://www.ls1gto.com/forums/showthread.php?t=25959) seems fairly authoriative :

    Quote Originally Posted by Dana Rep
    We have ONLY approved the use of Mobil SHC-ID (hard to get in the States) and Castrol SAF-XJ which already contains 4.5% of Sturaco 7098 (there is also Castrol SAF-XA but only in Australia) . They need to add another 25 ml of Sturaco 7098 to the SAF-XJ or 100 ml to SHC-ID to raise the level to 6%. They could try to contact DA Stuart by looking them up on the web (or searching for Sturaco 7098). They should be able to tell them where to purchase Sturaco 7098. Alternatively Ford sells Sturaco 7099 which is close to 7098. See email from Mike Follis below. We did play with 7099, which I was told at the time was more seal friendly (ie not the same as 7098) but I thought it marginally less effective for chatter prevention. They should also steer clear of the LO version of Sturaco 7098.
    The implication of this is that Dana (who bought/own the BTR brand) believe that there should have been a 6% additive used with the Mobil SHC(ID) oil, and that that additive is called Sturaco 7098. This fact never seems to have perculated down the food chain from Dana to Lotus to Vauxhall though.

    If you do a bit more googling you'll find that several other users of the BTR diff (Morgan, TVR, Holden) and other cone type diffs (BMW, Jaguar) have had issues with noisy/chattery diffs, and the solution to this has always been to add more additive/friction modifier. Indeed BMW sell two versions of LSD oil - Bog standard Castrol SAF-XJ (p/n BMW-83-22-2-357-992) and a 'special' SAF-XJ with additional friction modifier (BMW-83-22-2-282-583) to be used in the M3/M5 diffs. This second oil is only available from BMW and is frighteningly expensive.

    The additive/Friction modifier appears to be something that makes the oil more 'slippy' which allows the LSD diff cones to break free in a more predictable and smoother way. Not enough FM causes the cones to break away suddenly and causes chatter. Too much FM and the cones break away too easily and in the extreme you could loose all LSD functionality. But baby bears porridge was just right.

    The DanaRep seems to be claiming that bog standard SAF-XJ contains 4.5% Sturaco Friction Modifier, and that you should add additional friction modifier to make it up to 6%. My suspicion is that this is what the expensive BMW M3/M5 oil is. The situation is further complicated because Castrol have re-branded the SAF-XJ, and replaced/renamed it as Castrol Syntrax Limited Slip 75W 140.

    https://www.opieoils.co.uk/p-736-cas...ly-saf-xj.aspx

    There is obviously no gaurantee that the new Syntrax stuff is the same formulation as the original SAF-XJ. So what to do?

    I'm going to take a punt and choose to believe what the Dana Rep said. We've been using neat Mobil SHC-ID for 25+ years with no friction modifier added to it, so using neat SAF-XJ/Syntrax which does have 4.5% of the recommended friction modifier as standard can't be a problem, can it? If it is a problem, then adding a bit (up to 25mL) of extra friction modifier (to make the total 6%) should get you to where Dana say you should be?

    The other option is to use a generic 80W140 GL5 fully synthetic gear oil (with no friction modifiers) and add 6% of Sturaco to it. You can get the Friction modifier from (ugg I can't say it) F**d suppliers. It's their part number C8AZ-19B546-A, and standard EST-M2C118-A.

    https://www.ebay.co.uk/itm/351166520048

    A 4 Fl.oz. bottle of this stuff is 118mL. The diff needs 1.65L for a total refill, so a 6% mix requires about 100mL of the additive - basically almost a full bottle. If you're adding it to the Castrol SAF-XJ/Syntrax which already contains 4.5%, then you only need about 25mL, or about one quarter of a bottle.

    So I'm going with this ...



    You'll need two bottles of the Castrol stuff. If you want to use it, the additive is about a tenner off eBay (UK).

  4. #64
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    Rebuilding/Reassembling the Posi

    Whist the case is at the powder coaters I'm a bit stuck, but I can rebuild the Pozi. It's basically the reverse process of the disassembly, but there is one gotcha. The splines on the side gears and the cones have to be aligned during assembly, otherwise when you come to refit the drive shafts at the end you won't be able to get them in. Therefore, you can't just throw everything back together willy-nilly.

    Start by thoroughly cleaning and degreasing everything. You don't want any dirt or grit in in your diff. You can use virtually any cleaner although I have been warned off anything that contains excessive silicone - I use aerosol brake cleaner and paper rags. An old toothbrush helps with cleaning up the gears. Once everything is scrupulously clean and dry.....



    <1> Pour out some of your chosen lubricant into a small bowl. I used a plastic bowl from the last Chicken Jalfrezi I had from the local curry house. Other curry options are available obviously, although I'd steer clear of Vindaloo, Tindaloo or any Naga until your experience level improves. If you are going to be using extra friction modifier, then mix it into the diff oil and then use this mixture. This will act as a bath into which you place the various components to give them a light coating of oil during assembly.

    <2> Take the longer of the two drive shafts [15], and stand it on a bench.

    <3> Give the splines of the drive shaft a good clean, and make sure you remove the old circlip from the splines.



    <4> Smear a light coating of oil on/over the inner surfaces of the deeper housing half[22], and place it over the drive shaft.

    <5> Coat the cone[33] in oil, and slide it onto the driveshaft splines and into the housing.

    <6> Coat the shim[31] for this side in oil, and place it over the driveshaft onto the cone[33].



    <7> Coat the side gear[27] in oil, and slide it onto the driveshaft splines and into the housing.

    <8> Coat the thrust plate[32] in oil and place it on top of the side gear.

    <9> Lubricate the 4 spider gears[26], washers[25] and the cross shaft[37] in oil, and sit it in place.



    <10> Coat the preload springs[34][35][36] in oil and sit them in position. I've had to re-use the collar because that's all I've got. However, all of the replies I've had say there should be a 3rd big spring here. I won't know for sure until I take my second diff apart.

    <11> Coat the other thrust washer[32] in oil and sit it into position.

    <12> Coat the second side gear[27] in oil, and sit that in position. It won't engage in the spider gears yet because of the springs.



    <13> Coat the shim[31] for this side in oil, and place it onto the side gear.

    <14> Coat the second cone[33] in oil, and place it on the shim/side gear. Try to line up the splines in the side gear and the cone.

    <15> Smear a light coating of oil on/over the inner surfaces of the wider housing half[22], and place it onto the cone. Don't put the bolts in yet!



    <16> Take the second shorter drive shaft (with the circlip removed) and drop it into position. You may need to jiggle, wiggle and twist it until it drops fully home. This is because the splines in the cone and the side gears need to be properly aligned.

    <17> Lightly lubricate the 8 case cap/cover bolts[40], and insert them into position. They should be long enough to get the first few threads engaged.

    <18> Give both drive shafts another jiggle, wiggle and twist to try and make sure the splines both sides are correctly centred, and then tighten up the bolts. Do it in an alternating pattern one turn at a time so that the casing pulls together evenly. It should be possible to completely close the gap in the case without too much effort. What you are doing is compressing the centre springs into their operating preloaded state. The stronger the springs, the harder this will be. Do the bolts up nice and snug, but no need to properly torque them yet.

    <19> Once the gap is fully closed, you can remove the two drive shafts. The friction/sticksion between the cone, shim and side gear should keep them lined up and in place.



    <20> Next a sanity check - Retest the cone clearances. I had no trouble inserting a 0.5mm feeler gauge in one side, and 0.6mm the other side. With a bit more effort I could probably have got another 0.05-0.10mm in too. However, if it's much less than 0.5mm, then probably best to strip it back down again and skim the cone as described earlier.



    <21> Thoroughly clean the back of the ring gear, and the 8 ring gear bolts. Install the ring gear on the diff centre, and insert all 8 bolts. Remember they're left hand thread. Do them up evenly so the ring gear pulls into place. Once you're certain the ring gear in on securely, transfer the whole lot to a bench vice.



    <22> Now it's time to torque everything up. The 8 diff case closing bolts should be done up to 35-45Nm.

    <23> The 8 ring gear bolts should be done up to 130-145Nm. Remember, they're left hand thread so you'll need a torque wrench that works in the 'wrong' direction for this. My cheap torque wrenches don't, so check first. If you just heave on a torque wrench waiting for it to 'click' at 145Nm, but it doesn't work in the reverse direction you may end up shearing the head off the bolt.

    <24> Finally another sanity check. Put the drive shafts back into the diff, and make sure the splines are still aligned. If they're not you'll have to loosen off the 8 diff closure bolts and do a bit more jiggle, wiggle and twisting. Get this right now - if the diff ends up back on the car with the splines non-aligned then you're in for a whole world of pain and it'll probably have to come off again.

  5. #65
    Sure why not? 76lxhatch's Avatar
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    Nice write up and photos again.

    I still reckon you're over-thinking the oil, but being too careful is sure not going to hurt anything.

    Quote Originally Posted by LC0112G View Post
    The surfaces don't (shouldn't!) actually rub/wear on each other - they are splined together by the drive shafts - so I'm not sure what causes the wear marks.
    They still squirm a little, and there can be a lot of pressure when the LSD action is working especially. Your surfaces don't look great but it will still work. I would recommend using shims that cover the majority of the area for longer life though. At least you required minimal thickness, I've built some with four times that!

  6. #66
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    I know this diff was rebuilt about 10 years ago and I'm wondering if it was rebuilt far too tight - I gave up on it because it used to whine so badly. If the ring and pinion are toast then getting heavy stuff over from Oz might not be straightforward.
    What worries me most is that before I removed the carrier I tried to measure the backlash - and there was none, absolutely nothing. And then I used some gear mesh paint to look at contact pattern, but all the paint was scraped off over the whole surface of the gear teeth.

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