Rear diff bushing mods
 

Just a quick question to satisfy my curiosity.
ES Poly bushings for the Miata fit the stock diff with no modifications i presume.
What is different about Martin's 7.5 carrier setup that allows it to use stock bushings, but requires you to modify the ES bushings?

I am progressing with my build and currently have the rear subframe out. Tried to get the stock bushings out, but decided I was going to destroy them in the process. Am going to order poly bushings for the carrier and the nose.
Since I couldn't get the old ones out and eyeball it, I can't picture what the difference is.
Thanks. Brad

I am going to be using ES bushings, but haven't gotten to the rear yet. I'd like to know as well.

Jason

For whatever its worth, Mazdaspeed Motorsports has a stock type bushing for this application that is a harder durometer rubber rather than poly. Might be a good alternative.

I would prefer to use a solid alum bushing, like this one.

Vintage Performance Motorcars

http://www.vpmcobras.com/images/alum-bushings.jpg

The harder the bushing, the more solidly the differential will be located, which potentially may help with reducing wheel hop. Also, the more noise and vibration will be transmitted into the cockpit.

The factory OEM bushings are designed to give, well, OEM level NHV levels. The MSM bushings are, I believe, around 30 - 40% harder but still of rubber material, so not too much noise and vibration penalty. Next step up is poly, then acetal plastic (Delrin), with solid metal generally reserved for the racetrack crowd.

Whatever material you choose for those large, rear hanger bushings, it would make sense to adjust to harder or softer on the differential nose bushings to keep things in balance.

What is different about Martin's 7.5 carrier setup that allows it to use stock bushings, but requires you to modify the ES bushings?

Thanks. Brad

I got matching poly bushings for the nose of my 7.5 as well as the martin hanger. Have not installed yet, so not sure on fitment.

Jason

The "tube" that the bushing goes in is around 1/2" longer. The ES bushings require that 1/2" or so to be machined off to make up the difference. If you don't, the mounting studs will be too short. Just get some & install them. They are worth the money.

Hello,

I am just installing the new ES Bushings into my diff. I see from the previous posts that these must be "massaged" a little. Just want to make sure that I am on the right page.

Do I shorten the metal tube so it is flush with the rubber bushing? See pic...

Thanks,
Denis

No. The other half of the bushing goes over it.

This may help: machining poly diff bushings - MX-5 Miata Forum

Thank you very much guys, that pretty much sums it up. The bottom bushing has to fit in Martins bracket flush with the upper bushing, makes sense. The ES bushings came with what appears to be grease, the instruction page does not specify how much to use or where. Anybody have any suggestions?

Thanks again,
Denis.

Use as much of the grease as you can. It goes on all the surface that contacts the bracket. You can't use too much. Smear a bit on the pin too.

Hi All,

I would use the Il Motorsport harder rubber bushings here for road use. I installed these in my setup and they work great. Solid mounts are good for a race car but not for the road. All new rear end car cradles are bush mounted for a reason, there needs to be some give for NVH and for absorbing shock loads. Poly bushes are OK, but can deteriorate faster (poor quality) or get squeaky over time (run dry). My choice for anything Poly is Superpro bushes. They have the best design and have lifetime warranty if installed correctly. They use a very high quality of poly which is rubber like and the tolerances they have on their products is excellent, so they will fit perfectly.

I used the complete IL Motorsport kit in all my control arms and diff mounts, they work very well and will last forever..AND not squeak :)

Cheers