I know this is an old thread, just wanted to thank you for having the info up. Just replaced mine, and this write up helped immensely. No more THUNK. Good day.

for a side note, i use Dorman #31052 found in the Help! section of most auto parts stores for the pinion snubber. the one in this thread will work but looks like it has too much clearance from the original photo to me to really do it's job well.

Good to note, but as I mentioned earlier in the thread, the picture was taken with the subframe drooping. The gap goes away with the addition of some washers and tightening everything back up.

Ok,does the snubber actually hit the diff itself,instead of the Diff Mount?

^ it should be on the diff.


okay i noticed that for my gxl, the NA diff has a lump like RotaryRocket's pics show, on a turboII(10th ae) it doesn't have that lump soo i had to use more shims/washers to have it preloaded, for the most part i dont feel any vibrations or any unusual noises.....im very satisfied with this mod.

Great info. I didn't realize you could have enough room without fully dropping the subframe. Guess I have no excuse to be putting this off any longer now lol.

Worn diff mounts = 50 mph rumble?
 

Hey, RR88 - I know it's an old thread but great write up. Thanks.

I tumbled to this 2009 thread while searching for info on the effects of worn out diff mounts. The problem in my '88 vert (178k miles) is similar to 1badgvr4 (12/2009 post). Rumbling and vibration that peaks in intensity at 45 to 50 mph. Maybe related - driver's side sits about 1/2 inch lower at wheel well than passenger side.

Changed to RB sway bar & springs with Tokico blues, installed Mazdatrix 'rear steer' eliminator and replaced nearly all of the suspension links. Wheel bearings seemed fine. All good mods...but did not eliminate the rumble. Could worn diff mounts be the problem?

How does this compare to solid diff mounts?

Riz.

Could be the diff mounts. A more certain way to tell is if you get clunks when shifting. If it does, then your front mount is most likely toast. Did you happen to get a good look at the rear mounts while you were doing all the suspension work?

I'd also look at the trans "y-blocks" and the crossmember bushing. The blocks will begin to sag, and the center bolt on the crossmember will push through the bushing.

From what I've read (I'm about to do this myself) this doesn't transfer as many vibes as solid mounts do. Otherwise I would have gone solid as well.

I did this mod along with doing all the rear subframe bushing with energy suspension bushings, and I don't feel anymore vibrations than before.

Also did a Mazda comp diff mount

50 mph rear end rumble
 

Thanks for the reply. I did the tranny blocks & crossmember bushing pretty recently at the time of a new clutch & driveshaft. Not much vibration through the shifter so I think I'm ok on the tranny and driveshaft.

I didn't inspect the front diff mount too closely. But no clunking going on...just rumble and frame vibration coming from the back end. When the car is on stands supporting the sub-frame (diff, axles, wheels hanging from the shocks), there is a noticeable gap at the top of the rear diff mount rubber - maybe 1/8th inch. I'll try to get my head in there to check with all the weight on them.

RobblyWally, I don't think the front diff mount could cause your issue. With mine sheared, there was no such vibration at any speed. Typically vibration like that is going to be caused by something that rotates (ie wheel bearings or driveshaft u-joints). But I'm not sure how the rear end would behave if the rear diff mounts were shot/loose. It isn't too hard to check them out.

http://www.mazdatrix.com/g2.htm

Thanks for this helpful write up, I just did this today. I was originally just going to replace the front mount but after seeing how cheap the stubbers were I ordered one and waited an extra week to tackle this.

Time wise, I spent an hour Friday evening getting the car securely off of the ground and removing the rear wheels. I went ahead and completely removed the rear link to swap in my adjustable one (the top bolt was a bitch, I ended up using +2' of extensions and a swivel 14mm). Saturday took around 6 hours since I took my time removing my RB Y-pipe. It's a true dual system so removing those 2 center bolts on the plate between the presilencer and Y pipe were a pain. The only problem bolt on the front diff mount itself was the front one on the diff nose. I used a 1' extension to get to the 2 bolts that mount it to the subframe, a 17mm ratcheting wrench for the 2 rear bolts on the back of the diff mount, and a regular basic 11/16" wrench for the front one (all I had that would fit in the tight space...). A 2' steel pipe cheater bar worked very, very well :biggrin:

For installing the snubber, I ended up using 4 washers on the bottom of the floor and 1 up top. I got them at home depot for $.25 each, they were 1-1/2" OD, 3/8" ID fender washers. It ended up with the snubber very slightly preloaded.

My one question- with the front mount that I used (it was a spare I had in the shed from an early 86 GXL), it had no front arm and weight. It doesn't look like any arm was ever there... Anyone know if that was another quirky early 86 deal? Just curious.

Thanks again for the write up.

Glad to hear it helped.

The mount w/out the weight could just be an '86 thing. There are a number of little things that changed between '86 and '87 models, so I'd guess it's one of them. Someone with another '86 may be able to confirm it.

What is the purpose of the weight anyway?

Bumping this excellent information up for a question.

I needed to crank down my adjustible centerlink to the maximum to get my negative camber within reasonable daily driving specs. I've replaced every rubber anything that mounts to the 3rd member and I still get the occasional "thunk" when shifting from a stop in my S4 TurboVert. So I'm looking to do this as a final tweak to make the thunking noise go away.

My question, has anyone who has also tilted their sub-frame to the max had any trouble fitting the snubber in?

When I had to replace the diff mount from too many drag launches, I didn't want to do it again to so instead of replacing JUST the diff mount (comp mount), I added a snubber with it. It's been 10+ yrears of occasional hard launches and never a thump.
Your occasional thump *could* be from a broken bracket the diff mount bolts to.

You'll have more than enough room if you loosen the 2 bolts for the rear sub frame and loosen the sublink. Put a floor jack there and lower it.

The indentation on the rear hump is right between the hand brake cables .
I had mine adjusted to sit on the diff .

I'd get the polyurethane one.

Thanks for the experience and advise. Trust me, there is no broken bracket or anything else. Everything and I mean everything including the 3rd member itself has been replace 3 times over trying to make the Thunk go away. It's just bushing flex complicated by area gap tolerance reduced to beyond the minimum otherwise.