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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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Indeed.

The good thing about this mod is it's easily reversible. I intend to give it a try but remove them if it makes the car too noisy. 

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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.

The  increase in the NVH is there. Same noise as the transmission mount poly bushing which I had on my other car, but the change in how the car feels is  100 times better.

For the first time in an 86 I had this feeling of the rear being really solid, like being in a 911  or Lotus.

Every throttle input is felt  simultaneously in the lower back, no squating, almost like my back is connected to the chassis.

It took the garage about 3 hours to do it, which is more than the inserts would have taken, but I'm happy with it more than with the inserts I tried before (just the rear ones).

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