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Conscript

OEM Differential Bushings / Whiteline KDT925

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(Cross-posting from Owners Club forum)

I wanted to try a relatively common modification for this car which is to install the Whiteline KDT925 differential bushing inserts (rear inserts only). I can occasionally feel a little bit of slop when modulating the throttle - nothing major, but apparently the bushing inserts help make the car feel a bit more "taught", and also apparently help alleviate the slight clunk you get when shifting into gear at a stop*. Usually, I wouldn't bother, but they are relatively cheap and it's the kind of install that one can do on the driveway. That, and I fancy a bit of tinkering :)

However, at the last service at Abbey back in January, Scott mentioned to me that the differential bushings were looking a little worn. Probably not unexpected at 75K miles, and not enough to cause concern, but he said keep an ear out for any clonking noises, etc, which might mean they need replacing. If I'm going to try the Whiteline inserts, I figured it would probably be best to replace the OEM bushing at the same time. But of course, I'm not having much luck looking for OEM parts, because most searches for GT86 bushings give results for aftermarket replacements.

Anyone know (A) somewhere I can look up the part numbers for the OEM bushings and (B) is it possible to replace the actual bushings yourself?
Installing the Whiteline bushing inserts looks easy enough. I just don't know about the bushings. If it's not possible then I'll just have to wait until I can get it to Abbey, but I'd like to have a try myself if it doesn't require any special tooling.


*For anyone who isn't aware of the issue I'm talking about, there's a good demonstration here. This video is made by Whiteline to demonstrate the effectiveness of their subframe bushings. But if you keep an eye on the differential bushings (on the left of the video, in the middle of the subframe), you can see how much they flex on acceleration/deceleration). The differential inserts can reduce this. I should also add, that I would only be looking to do the rear diff inserts - the kit includes front diff inserts, but they are much harder to install, and you can apparently get almost the same improvement without them, with slightly less NVH.

https://youtu.be/IDfJ_zYFPcs?t=24

Edited by Conscript
YouTube URL doesn't work; copy paste into browser if you need to see it.

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Anyone have any feedback on these? The slop/throttle lag is the only thing I don't like about the car, if it can be fixed easily and cheaply then happy days.

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1 hour ago, james_ly said:

Anyone have any feedback on these? The slop/throttle lag is the only thing I don't like about the car, if it can be fixed easily and cheaply then happy days.

I've not seen much from UK forums, apart from people mentioning they've installed them. There's more experiences on the US forums if you have a cast around, for instance: https://www.ft86club.com/forums/showthread.php?t=64364

I'm not too badly affected by it, but seeing that vid of the movement and seeing how cheap the inserts are, it's the kind of minor modification I'd like to make to see if it helps how the car feels.

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I've got them on mine and it has transformed the gear change to how it should be from factory. No slop, just smooth precise snappy gear changes. It's also made the car easier to drive in those first few minutes between first and second.

It does however increase significantly the amount of whine you hear in the cabin, but I quite like it. Pair this with the gearbox detente springs and you cannot go wrong.

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23 minutes ago, Dave86 said:

I've got them on mine and it has transformed the gear change to how it should be from factory. No slop, just smooth precise snappy gear changes. It's also made the car easier to drive in those first few minutes between first and second.

It does however increase significantly the amount of whine you hear in the cabin, but I quite like it. Pair this with the gearbox detente springs and you cannot go wrong.

This is where I get concerned. Most reviews have said there's only a small increase in noise, and generally at low speeds - but not even enough to be audible over a louder exhaust, or even the radio. My car isn't driven daily anymore, but I'd still like to keep increased in NVH to a minimum, but it can of course be a subjective measure.

Did you install the inserts to the front and the rear bushing inserts? I read that you can just install the rear inserts(which are easier to access), which takes out a lot of the slack without increasing noise too much. This is probably what I'd do. 

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"small" "tolerable" regarding NVH increase with less compliant parts is very subjective thing. Just like exhaust loudness. I'd be careful taking fully subjective feel of others.

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Yeah I only went for the rear insert. I have the Invidia N1 which is loud already, but I can hear the gearbox whine at lower revs. It's a nice sound though. Definitely shouldnt put you off because it makes a big difference to the car, especially with the MTEC detente springs.

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Managed to find an exploded diagram of the rear sub frame with the part numbers for the bushings...41651 and 41651A. Don't look to hard to replace so I'll see if I can get them from the local dealer before getting the Whiteline inserts.

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I replaced the diff bushes with the Superpro Poly ones (not the inserts but full replacement). I also have the subframe inserts.

Handling and shifting are better but the  increase in the NVH is there and over time it just got louder and louder. I don't it recommended for  a road car.

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So I’ve fitted these today. Big improvement! Very easy to fit, I’d say 30 minute job, and just a couple of sockets required. Makes the throttle more responsive which makes the gear change a lot nicer. And there’s less axle tramp on bumps. Basically, how the car should be from the factory. I only noticed a tiny bit of extra NVH, basically when lifting off with refs below 2k you get a whine that wasn’t there before. But, fine for a daily I reckon. 

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My experience was - to remove them :). They might be OK if fitted alone, but as i also had gearbox mount & bushing rigid aftermarket one, way less slop in diff bushings meant more backlash passed to gearbox/damped clutch, noises of which in turn got more audible. And if it's choice between gearbox vs diff bushings, i choose former (with different oil). Meanwhile i had ok experience with parts like whiteline rear subframe inserts, perrin steering rack lockdown, poly bushings for front LCA, NVH change from those seemed ok to me or sometimes unnoticeable. Diff bushings, pillowball camberplates - not so. Gearbox mount & bushing also added NVH but seemed worthy tradeoff to gearswitch change.

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I have the read subframe insert to remove some slop. I liked it as an upgrade it seemed to improve rear grip. 

I also installed the gearbox "positive shift"  which was nice. It removed the sloppiness from when the gearbox mounts got hot on trackdays but be warned in the first two gears a fair amount of gearbox whine gets into the cabin, so if you have a stock exhaust it could be very annoying. 

I haven't done the diff bushes. Partly because I believe the slop helps reduce strain on the gearbox and partly because diff whine can be an issue after going in cars with them fitted.  

For once I agree with @church 😂 better gear oil is also helpful in making it feel more slick. 

 

 

 

 

 

 

 

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