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Polyurethane Differential Bushing Insert Kit for NA and NB

Polyurethane Differential Bushing Insert Kit for NA and NB

Regular price $54.99 USD
Regular price Sale price $54.99 USD
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Emissions: Emissions do not apply.

There are no shipping restrictions on this item.

Warranty: lifetime

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The differential is mounted in the car with some surprisingly flexible rubber bushings. Replacing these with stiffer bushings will cut down on differential movement, but they're a headache to install. Looking for an easy answer? Enter these bushing inserts. These inserts, made by SuperPro, fill in the voids in the stock bushings to minimize the movement of the differential - this actually makes your shifting more precise due to the way the Miata's drivetrain is mounted. They're a pretty easy install, as you just have to lower the differential enough to get it off the studs in the subframe, slip the smaller part into place, then put the bottom piece in place. With full replacement bushings, you need to remove the differential altogether then remove the stock bushings (which typically requires fire. Seriously.). A definite plus for competition cars - you don't want to hit 5th instead of 3rd in the heat of competition!

Bushing inserts fit 1990-2005 only.

Customer Reviews

Based on 6 reviews
Victor S.
Worth the cost

I installed these over the weekend. Installation was 3/10. Had to drop rear tie and FM butterfly bracing and undo the muffler from the midpipe (I have the FM Catback) to give enough flex to the unbolted differential housing to be able to slip the poly doughnut rings (top part of the insert) into their intended locations. Of course, unbolting everything took longer than installing the parts.

Driving impressions are positive. No detectable NVH and more precise shifting. 1-2 and 2-3 are the most noticeable. Downshifting through all the gears feels tighter with much less bounce (when not done perfectly).

I'm a very satisfied customer.

Steve W.
Bang for the to Buck!

Installed these last November when I installed a rebuilt diff. Drove it for the first time last week.

My car has 50k on it and the original bushings are in pretty good shape. These still made a good impression during shifting. I am very satisfied with the performance.

Big Things; Little Packages

These were inserted in a 1999 10AE that is naturally aspirated and is never tracked but instead is driven at 7 to 8ths on the road when appropriate. My Rear Differential Bushings are OE, in good condition and I've never tried anything else but OE rubber RD bushings. All that said, these inserts changed the entire nature of the car with regards to the way it handles, how tight the overall feel of the car is and how it shifts. I've replaced the motor mounts, installed Paco Strong Arms and am running a FM level 2 suspension along with a short throw shift kit, along with the FM Happy Meal. All this is to say that this is a very worthwhile installation and I'd recommend it for three simple reasons: 1) the price point; 2) the results mentioned previously; 3) not needing an open flame during installation. As for the installation it took about an hour at my ASE shop of choice on a hoist, so it wasn't impossible but I wouldn't have wanted to do this in my driveway. In closing, the greatest trouble I've had with these part were finding them on the FM website; have to do a "bushing insert" search to find them; doing so through the drop-down menus would have been too challenging and taken too long. In short, buy these parts, do it now and reap the rewards of a better Miata (NA or NB).

Cheap Easy and Effective

For the price these are an amazing upgrade that you can install in about an hour including jacking up the car. After I had everything unbolted I did still have to use a pry bar to pull the diff mount down far enough to slip the top insert ring into place over the mounting stud, but that's no big deal if you're working one side at a time. I'm sure you could avoid this if you removed your exhaust or unbolted the diff from the PPF, I just didn't feel like searching for what was still holding the diff in position after unbolting the mounting tabs and using the pry bar to pull the diff mounts down worked just fine.

The car feels much "newer" after install without any increase in NVH. There's a more "solid" type of engagement feel when releasing the clutch. Shifting is also more precise, I haven't gotten jammed up on the 2nd-3rd shift since install, even shifting at redline. I imagine these paired with the stiffer-than-oem rubber motor mounts would be a killer combination.

Forgot to mention

Only part missing from the instructions was whether the flat side of the top insert faces up or down. Otherwise excellent.