Valkyrie

I'm going to replace my subframe and diff mounts *eventually* (and probably at the same time since I'd be dropping the subframe to get to the diff mounts) and seeing as how the hard plastic ones are much cheaper than the Mazdacomp hard rubber ones, I'm curious as to how much more noise they generate, and whether they'd be suitable (or at least reasonable) for a daily-driven car (that has no sound-dampening removed, at least).

IIRC it would save like 100 bucks to get the hard plastic ones (both from Mazdatrix).


This is just for the rear diff mounts though, not the front diff mount.

fastrotaries

on the rear I don't think much more noise would come out. If you have a loud exhaust then it'll muffle most of it. Depending on your suspension you won't notice it much. The front Diff mount is another story.

scathcart

Those Delrin mounts are damn near solid. You'll see a large increase in NVH.

RotaryEvolution

iTrader: (30)

why are you replacing the 2 diff mounts that rarely fail?

scathcart

If you make a part to replace a stock one and market it as an upgrade, people will buy it.
I should market a replacement parking brake mechanism actuator. Pure carbon fiber, 12% more leverage over stock, double adjustability.

Racing car parts don't belong on street cars.

Valkyrie

Failure and being 20 years old are two different things (they're squishy).

And I didn't mean Delrin. I meant the ones that are in between polyurethane and delrin in hardness.

drago86

lol this is so true.

RotaryEvolution

iTrader: (30)

ok i will adjust my statement, they cannot fail because the support bushing is encased metal. they just support the weight of the differential is all, the front differential mount is the only one that takes any real abuse.

if you want to replace it with a stiffer mount that will transmit a ton of noise to the chassis and into the cabin then go for it.

dpf22

aeu contrair. Actually mine failed in my TII. I believe it was due to wheel hop from before I put in my energy suspension bushing kit, because it didn't happen till after the fact. nice little clunk every time I would accelerate and let off the gas. The front one broke as a victim of the rears going out. I put polyurethane mounts in the rear as I would prefer the diff not to move at all. However, I can take the noise better than others. Yes, coasting down a hill will make you want to shoot yourself sometimes. However, I think my diff needs a new crush sleeve and for the runout to be reset on the pinion shaft. There is a little more play when you rotate the driveshaft than I normally like, and you can actually adjust how bad the decel noise is by properly attaining a "footprint) on the pinion and ring gear teeth.
Just my two cents as I have already done this mod. I just got done doing the racing beat front diff mount and the rest of the subframe, toe eliminator and trailing arm bushings with delrin/urethane. actually it quieted down a little and got a smoother ride from them.

I am rambling

later
dpf22

Valkyrie

If it induces that much vibrations I'll just go with the hard rubber ones (which is why I started the thread, to ask if it did).

As it is, the rear mounts allow for probably a centimeter of up-down movement (when you pry on it with a crowbar, albeit not that hard), due to them being very soft and old.

My front mount is also soft but doesn't seem to be broken... so I can't figure out where the thumping/popping noise is coming from.


As for the subframe mounts, do having plastic ones make as much noise as having them on the diff? I ask this partially because I couldn't find the hard rubber ones on Mazdatrix's site, and partially because they're cheaper... it's not like I'm getting aluminum ones though.

dpf22

if you can move them that much, chances are that is where your "clunk" noise is coming from. And also, the front diff mount didn't look broken till I dropped the subframe a bit to do the rear mounts, thats when it started to fall apart. The way the front mount is positioned, when the subframe is in place, the front of the diff rests on the mount in one piece. However thats not to say it is/isn't broken.
As far as the subframe mounts. You will see a very minor increase in NVH (noise vibration and harshness). Nothing big in my opinion. For the most part, the bigest culprit in noise I have in my car is the rear differential mounts. I have solid motor mounts also, I got used to those quickly.
Its ultimately your choice, but if you are not wanting the noise, then go with rubber rear diff mounts and you can put polyurethane everywhere else and be very livable in my opinion.

hope that helps

dpf22

The Wankler

iTrader: (14)

Agreed. I replaced mine like a wookie, and now I get a light vibration around 3k. So, I am pulling another Diff and selling the one in my car..... Me no like the vibration. For a racer, it would be fine.

RotaryEvolution

iTrader: (30)

if it's making a popping noise then you probably have a CV joint going bad in one of the rear axles or possibly a bad u-joint in the driveshaft.

Valkyrie

The u-joints seem fine (no free play I can detect by hand). I don't know about the cv joints...

It might actually be backfiring from vacuum leaks, and a bad anti-afterburn valve, since it doesn't pop when you let off the gas, it pops (99% of the time) when I go to zero throttle and open it back up (ie, city driving), and occasionally thumps when I shift gears (or when I come to a stop from a low gear, with a KATHUMP sort of sound).

Sometimes the "popping" is as loud as gunshots, especially when you do it in a tunnel.

Strangely enough, it no longer has the shotgun-like backfire when shifting at redline (which typically went off AFTER changing gear).

RotaryEvolution

iTrader: (30)

sounds like a bad front diff mount to me.

classicauto

iTrader: (3)

+1

Your rear diff mounts failed? Were they shot before the front mount went, or after? Because really, as mentioned, the only support the weight of the diff and resist lateral twisting. The larger force that acts on the diff is the snout moving upwards from the torque of the driveshaft. Really the only way the rears could fail is if the front is gone (or going) and allowing far too much slop in the entirety of the diff's movement.....not simply because they "need" to be upgraded.