Albi Blue 200 >> BMW E46 Track Car

Ordered myself a new diff. Didn't last long not touching it after Snetterton.

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Decided it was the end of the road for the quaife, it's been a great diff in the car which I've ran with a 3.38 and a 3.73 ratio. But I am finding the limit of it more and more with the car this past year.

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Removed the old diff with the 3.73 ratio and decided to sell it as a complete built unit, already sold and gone to a new home! It didn't make sense to strip down a perfectly working diff to make the new one.
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Bought another 3.38 ratio diff from an auto to use as a donor
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Started with disassembly of the donor, can confirm old diff oil still stinks. Ripped it open on an old towel and thrown them straight in the bin
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Obviously I couldn't leave the casing in the rusty old state so gave it a good jet wash, degrease and a wipe down with some thinners before giving it a coat of paint
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Put all the parts through the parts washer and laid everything out ready for building.
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Bearings and crown wheel fitted to the diff, getting some more use out of the press I bought many years ago on a bit on a bit of a whim, turns out I use it all the time.
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Started with setting up the bearings and the pinion drag and then set about putting the diff in the casing with the bearing on.
Got loads of photos but will keep the post short rather than a how to. In total about 6-7 hours worth of building, due to the size of the diff unit it doesn't fit inside the diff casing in one piece, so every time you want to take it out to adjust the shims you have to split the diff in two.

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Managed to get the bearing clearance to a spec I was happy with as well as getting the backlash to 0.1mm. Overall everything has gone together with the provided shims which come with the Kaaz diff but it's right on the tight end of the spec
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All reassembled with new seals. I have built this one with a 3.38 final drive and while the diff was apart to fit it inside the casing I have dropped the lock down to 65% as per the Kaaz Manual which they refer to as the "Medium Hard Setup"
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Back in the car it goes
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Bought a set of replacement discs for the rear while I was working on the rear end as well as a replacement ARB bracket, somehow managed to loose a bracket at Snetterton, I think I've forgot to torque the bolt up for the bracket when messing with fitting and removing the rear ARB and the bracket has left the chat
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Final job for the weekend was adjusting the splitter mounts, with the new bumper the splitter needed raising 15mm to bring it up snug under the bumper, adjusted the brackets and refitted.
Note- That isn't the placement for the reg plate... Just popped it on there for today as I didn't want to mark the new bumper

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Been a big job but it will hopefully be worth it, we'll see on the next track day!
 
So did the decision to move on from the Quaife come around the same time that you started running slicks?

Not from the slicks.
It’s something I’ve been putting a bandaid on for a year or two.
Unless the rear of the car is pretty flat coming out of corners with both wheels on the floor the quaife tends to slip the inside wheel still.

I’ve made improvements to keep the inside wheel on the ground.
Full rose jointed/uniball and solid mounted rear end
Running without ARB
Stiffer arb.
Experimented with spring rates
But still will never be as good as a plated diff but back in 2018 there wasn’t the choice of diffs and all the technical information which goes with it.
Interestingly this Kaaz diff isn’t actually listed as fitting my car and ratio anyway but did the research to check before buying.



The second corner at Snetterton is a perfect example of this.
I just put the inside right wheel onto the raised bit of the kerb and loose all drive coming out of the corner. I have to lift and wait for it to grip and then apply power again .

 
I went from the standard E46 M3 viscous diff to a plated drexler and the difference was night and day. I imagine this will be the same type of change. I don’t get any of that spinning up that you experience in your video when sending it over curbs etc
 
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I went from the standard E46 M3 viscous diff to a plated drexler and the difference was night and day. I imagine this will be the same type of change. I don’t get any of that spinning up that you experience in your video when sending it over curbs etc

Hopefully it’s worth it, lot of hours gone into putting this one together. I used to have a gripper in my clio box and it was fantastic. Driven a mini recently with a gripper and it just reminded me how good they are and the consistency every single time.

It’s gonna be an absolute savage with a proper diff

Hopefully! Just want to be able to get on the throttle through the corner without hanging to lift. RWD is amazing for corner exit but this should make a world of difference!

I’m also hoping by going back to a 3.38 final drive I can use the Rev range a little more. Peak torque hits about 4k and can Rev it to 7k at the moment and through that whole area it pulls really well. Hoping I can use less gears and stay on the throttle more. Lots of time I’m changing up to 5th for a few seconds to drop back down.

Will see if it’s any different. Will have to use second a little more I’d imagine for slower hairpins.
Going back to EFI tuning in August for a map check so will see if we can widen the power area a little more too.
 
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