109 Differentials, Oct 2020

Still being overseas and away from my vehicles, there hasn’t been much to report, especially since I can’t even travel back to give it a quick drive and check over.

Those who have read this blog in the past will be aware that I find the 109 undergeared with the Tdi, overdrive and otherwise standard gearing, and that my dalliance with 3.54 diffs from a 110 resulted in a horrible drive followed after six months by a broken gear box, its repair and their removal back in favour of standard SIII 4.71 diffs. Well, I want to do something about that.

I have bought some secondhand parts as little projects to do in Dubai and bring back home in the future. I mentioned a couple of years ago that I bought a Dana 60 (US equivalent to Salisbury) 4.1:1 ring and pinion gears for $100. I don’t know how much trouble they will be to install; they’re said to fit with just a little work and I hope that is just the Dana gears using 1/2″ bolts where the Salisbury (at least in later versions) uses 12mm. That might mean a little widening of the bolt holes in the diff flange for the ring gear. As for the pinion, I got a 10 spline version, which is very uncommon in the US but is what the Salisbury uses and why I bought this particular set. I have tried to find Salisbury pinion dimensions previously (as I don’t have access to a Salisbury pinion to measure) to see if the Salisbury pinion flange and bearings will fit the Dana pinion, but couldn’t find the information, so that’s a bridge I’ll have to jump off when I come to it. I did get the Dana pinion flange with the “kit”, so if need be, I can use that and suitable U-bolts to hold the UJ bearings, but I’d rather use the Salisbury and Rover configuration. What else may be needed, I don’t know, as none of the experts have replied to my enquiries. I suspect the pinion bearings may have some different dimensions, but bearing specialists can work out the matching combination of new inner and existing outer races to suit the old casing and new pinion. The plan will to be to fit these gears at the same time as an Automatic Torque Biasing diff. The choice is between Eaton’s Trutrac (US) and Quaife (UK). The Quaife is the higher quality unit and has six scroll gears each side compared to the Eaton’s three, but it’s about £200 dearer. If funds permit, I’ll be going with that. I also bought some very good condition used Salisbury shafts for the rear axle as I don’t fully trust the shafts currently fitted in a partially locking diff – the worn outer ends were welded and cross-pinned, which was fine for an open diff, but is a weakness with any form of locking diff. A genuine pair with no marks or wear on any of the splines was a gift at £25. That is a project that can only be done on the vehicle, so there is no rush, but I want to collect parts as and when good deals come up. I think I have done what I can there – I doubt any good used diffs will come up for good prices, so buying that new will wait until I permanently return home.

Obviously, the front diff has to have a matching ratio, so I managed to acquire a used long nosed Rover ring and pinion set. The pinion needs the finer splined flange from a “24 spline” diff, and I picked up a couple of those diffs today here in Dubai for about £40 (200AED). Again, the plan is to go with an ATB, and while Quaife also make them for the Rover axles, this being a Series vehicle, the front doesn’t need to be so bullet proof and so the choice is between the Ashcroft unit (which has the six scroll gears each side like Quaife) or the Eaton Trutrac, again with just three scroll gears each side like their Salisbury and Dana versions. The Ashcroft is a fair bit cheaper, but both have good reputations – I have only heard one person talking about their damaged Trutrac, but it had been badly abused by the person who sold it to him, and one person having a problem with the cone bushes on the scroll gears in an Ashcroft unit, which they supplied replacements for. I’m leaning towards the Ashcroft because of price, the doubled scroll gears and the fact that it is UK made, but I’m not quite certain; a couple of people have said the Eaton is tougher and performs just as well, and nobody has yet countered that. As with the rear diff, I don’t mind spending a bit more if it means I only have to spend once! In the same vein, I’ll be fitting Ashcroft 24-23 spline front shafts; there is no point deliberating over which is the most robust diff centre only to refit the same relatively weak 10-23 spline shafts; we have all seen how 10-spline shafts twist and shear where they enter the diff on a Series vehicle with a standard engine – it makes no sense to use those on a Tdi powered vehicle with uprated diffs that may be putting more torque through one side.

The plan is to build the front diff here in the first half of next year. I have been very fortunate during the current pandemic and resulting financial crisis in being on the Boeing 777 fleet in Emirates, which has shed very few people and looks to have a pretty secure future, while the A380 fleet and most other airlines have been shedding incredible numbers of pilots. So, buying the front ATB is contingent on me not joining the queues of redundant friends and colleagues, but I’m hoping that the future, one way or the other, will be clearer by my birthday in January and that I can then decide to buy or delay.

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