Rebuildable front differential mount
 

So I'm broke again and need a diff mount to get going so I'm making one from scratch. My goal is to spend less than $50 buck, and be able to change the bushing if it fails, or I want a stiffer bushing.


Here's what I got so far. Grade 8 hardware from bLowes, a bushing set (has a dowel not in picture) I had sitting around, two brackets I made from gussets, a pipe cut to fit the bushings, and the remains of my old diff mount. I spent $5.29 at bLowes and $5.50 at Alro steel for gussets and pipe. So I’ve got $39.21 left to make the other side.


https://www.rx7club.com/attachment.p...1&d=1258507155 https://www.rx7club.com/attachment.p...1&d=1258507343https://www.rx7club.com/attachment.p...1&d=1258507155 https://www.rx7club.com/attachment.p...1&d=1258507155

Here's what it looks like mocked up so far. (The bolt will go through the other way)

https://www.rx7club.com/attachment.p...1&d=1258507574 https://www.rx7club.com/attachment.p...1&d=1258507574

I still need to make an adapter to bolt to the sub frame; I'll get to that soon.
Let me know what you guys think.

im not really picturing it but overall i guess good work?
TwEaK

Imagine two bolts sticking out from the pipe, like the stock one.

https://www.rx7club.com/attachment.p...1&d=1258508612

I broke the bracket three times and fixed it differently three times hopefully it wont brake again ...... Damn clunking sound annoying and painfull to hear..
if it works out let me know

yes i remember that lol what are you gonna do just weld to bolts out the side?
TwEaK

I wanted to weld a 1/4 inch spacer to the pipe and try to cut the rubber off the stock one and reuse the metal part. The pic is rough but hopefully it makes sence.

https://www.rx7club.com/attachment.p...1&d=1258511674

Finished
 

I finished it today. It's in the car and ready for a test drive tomorrow. I'll write more after the test drive.

https://www.rx7club.com/attachment.p...1&d=1258847542https://www.rx7club.com/attachment.p...1&d=1258847542

Good idea :icon_tup:. Looking forward to some feedback on it.

Here's the problem, you just made a stronger part instead of fixing the problem. The real issue at hand here is why does the diff mount break? Well it must not be strong enough so lets engineer a stronger one! Nope, the problem is the mount is in sheer and it tears the bushing in half.

Install a pinion snubber with a new factory mount and you'll be good to go. A pinion snubber will take forces in compression rather than sheer and it works along with the stock mount. It's win win.

His goal was to make one for less than $50 bucks. New stock mounts sell for over twice that.

Maybe I missed something but I think this does fix the issue. The stock mount relies on the rubber as the structural and dampening. Rubber and all mounts break down in the elements, and when our mount breaks the whole thing is trash.

In this configuration the steel is the structure and the bushing is the dampener. The bushing is only in compression, so it should never rip. When is does wear out it I can replace it for super cheap.

I am using the factory pinion snubber, I just put it on after I install the mount. Are you talking about a different snubber?

I am not trying to say this is best way, just trying to understand your post,

So the final out of pocket tally is
$5.29 at bLowes for fasteners
$5.50 at Alro steel for gussets and pipe
$10.00 at Wideside Speed Shop for welding

$20.79 total versus $100+ for stock one, or $40 for a used one that might rip.

MOre pics
 

Heres the spacer I made, and the body side mount after grinding.

https://www.rx7club.com/attachment.p...1&d=1258898105

Heres it weloded together

https://www.rx7club.com/attachment.p...1&d=1258898105https://www.rx7club.com/attachment.p...1&d=1258898105

And heres the other side welded

https://www.rx7club.com/attachment.p...1&d=1258898131

Here's what it looks like installed from the back, Notice your can easily tighten the bushing after installation

https://www.rx7club.com/attachment.p...1&d=1258898366

Here's the front with the snubber on. The final assembly came in large by 1/4 inch but all the clearances checked out. If I did this again I would remove the sub frame so I could install and mock up easier.

https://www.rx7club.com/attachment.p...1&d=1258898366

I forgot to mention I cut the lower tab off the diff side mount after trying to install the first time (see second picture)

I had to loosen the rear diff mounts, remove the front sub frame bolts, and tip the sub frame down to install the mount. It would be much easier to do this while you have the sub frame off.

The real problem with the mount is Mazda designed it wrong. It's not an issue about service life or elements breaking down the rubber. People break brand new stock mounts all the time. The real problem lies in the design of the mount. The factory mount is in sheer in which the force of the diff snapping upward tries to rip the factory bushing in half. If Mazda had made a mount in compression instead of their design this would be a non issue. You just over engineered a new mount instead of fixing the issue at hand.

over engineering is not so bad.
I need to replace my front diff mounts also after seeing this thread. I bought a mazdatrix comp mount, still havent replaced it yet, waiting till next year, mean while a pinion snubber is in.

This is a stupid question but, have anybody welded a bracket on the diff and subframe and mounted a rod, or some kind of metal to them to make a somewhat solid mount??

test drive
 

I went for a 40 mile test drive today and everything worked fine. No thumps, no noise from rear end.

I found one issue when I inspected it after the drive. The 1/4 extra width of the bracket worked its way out. It's an easy fix with the grinder.
https://www.rx7club.com/attachment.p...1&d=1258921230


The mount moves up and down and to the passenger side fine, but it has a hard stop to the driver’s side.

I'll probable leave it be. I have 460 more miles of clutch break-in before I can give it a hard launch. If it starts to squeak I'll pop it out and fix it.

You'll break the tab off the subframe.

Happened to me with the stock mount...

I think it looks good though. :)

Yes, but do they do it with stock power and stock type tire and tire sizes? The issue may not be so much that they're designed "wrong" per-se, but that the loads that people are putting on them are just way higher than what the car was originally designed around so they break. It would seem to me to be more of an issue of exceeding the design strength more than it being a poor design.

Nice work!!!! But you should have been partying instead.

If you run a stiff or solid front diff mount you NEED solid rear diff mounts AND solid subframe mounts or you will rip the tab off the subframe.

I run a welded front diff mount, and MMR subframe and rear diff mounts. No problems at all after 1000 track miles and a few thousand street miles.

I think this was a job well thought out and executed. Just add a little clearance and you should probably strengthen and gusset the sub frame tab now. :thumbs up:

~Mike........

:lol::lol::lol:

Note: If you know S-FC then this comment is quite amusing.

Update
 

So I decided to correct the clearance issue so I pulled the diff mount off. I was surprised to find there was very little evidence of contact. Only one side had a clearance issue.

https://www.rx7club.com/attachment.p...1&d=1259349539

I ground the bracket down to add more clearance and to make install the top bolt easier.

https://www.rx7club.com/attachment.p...1&d=1259349539

The picture sucks but I had about 1/4 inch of clearance when it was reinstalled.

https://www.rx7club.com/attachment.p...1&d=1259349818