FC3S Differential Pinion Brace (By Ray Platek)

[largeorangefont]

With the stock diff it is really easy to pull the arms off the car, just unbolt the halfshaft from the diff output shaft, leave the output shafts in the diff.

[atli126]

So got it all installed and back together!

Used the delrin subframe bushings and the lucky 10 front diff mount with red poly shock bushings instead of the hard mwmh bushings that came with it.
 
So far so good. Got it up to 50 mph on the way home and no crazy sounds. Will hopefully drive it to work and get up to highway speeds and hopefully it's still quiet. Remember I put a huge emphasis on "street car" 

Enjoy ☺️














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[largeorangefont]

Ahh so it comes with 2 sets of bushings? If it still moves too much put a UHMW bushing in the middle of the 2 poly ones.

[atli126]

Ahh so it comes with 2 sets of bushings? If it still moves too much put a UHMW bushing in the middle of the 2 poly ones.

nope. I removed the white mwmh bushings and bought a energy suspension red bushing tie rod link setup from autozone with 3/8's holes and used these. I only had to barly grind the little top nipple off of them. 

now the car rear feels solid with the upper bumpstop, lucky 10 front mount and the new level zero motorsports delrin rear subframe. No crazy NVH at 80 mph this am either

[largeorangefont]

I was gonna say, those look like end link bushings.

[atli126]

Oh yea we also cut out the broken tabs and welded in a thick piece of 3/8 steel and welded the tab on top too, to hold it all back into place. Im sure its a combo of all three but Im happy and hoping that this helps me have a legit good solid rear "street car" option.

The Differential Pinion Brace w dogbone mod was great but i think it just made the front mount and tabs the next target. Hopefully now itll hold up over time

[atli126]

Ok I'm back with some pretty hard-core clunking issues. That lucky 10 mount used wheel studs into aluminum and I think the nurls (small teeth) wallered out the alum.  I could never get the lug nuts tight enough to hold it down under the subframe tabs.

So tonight I pulled the mount back out. We are going to buy some steel and rebuild the C Part with steel that way I can get new studs and weld them to the new C part of the bracket...

I'm half tempted to go with the white delrin bushings this time. The new box on the subframe and tabs are find and holding but I also think I might have ground down the 2 bolt washer (oem) that holds down the mount under the tabs. I'll probably try to buy a new 2 hole washer or make one out steel that will fit better and not let them move up and down in the channels on the subframe.

I was Half tempted to go with the solid pbm mount... But I still don't think SOLID is the way to go.

I do mainly race and autox the car but I also cruise and travel to and from events.

I feel like I need to just save up and go with the ronin 8.8 to be honest...

[atli126]

Pic

[atli126]

Pic of c part of mount

[gc3]

you could weld a tab connecting the 2 studs into a stud plate so you can get the full torque you need on them.
If you never got them tight it isnt surprising to hear the aluminum opened up even more

[atli126]

The plan was to remake the c section (shown above) out of steel and tack weld the studs to the back of the plate that way they can't move. But we might look into that too.

I was trying to think about some way to do some sort of attachment that would allow the diff mount to be bolted down north to south thru the subframe. But that would require probably drilling holes in the subframe and some how attaching something to the studs (maybe an L bracket) and then bolting them down to the subframe so it can't raise up...

Thinking like a 2 hole washer but it is an L bracket  that I could use to bolt thru the subframe... Maybe that's crazy. I just woke up. [emoji23]



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[atli126]

Another question I still have the stock camber rod. If I upgrade that will that help with the subframe movement?

I only ever thought of that as a camber adjuster but I'd say my stock rubber are probably wore out.

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[DrKarrot]

I was trying to think about some way to do some sort of attachment that would allow the diff mount to be bolted down north to south thru the subframe. But that would require probably drilling holes in the subframe and some how attaching something to the studs (maybe an L bracket) and then bolting them down to the subframe so it can't raise up...

Had a similar idea way back when before I discovered this thread. You could run some beefy bolts all the way through the subframe, and bolt to an equally beefy L-piece on the stock diff mount location, but the subframe sheet metal isn't that thick, so you'd want to have some kind of saddle plates to spread the load out. In the end it really isn't any different than the front pinion brace this thread started with, though I guess there would be less of a leverage problem.

[atli126]

So my plan is to go buy the raw steel today to make the C part of the lucky10 mount in steel, weld the wheel studs to the steel, use the white delrin bushings and go that direction .

but...

It seems like I have 2 options, now that I have reinforced the tabs and rebuilt the box on the subframe, delrin subframe bushings, and pinion snubber..

I could just install the NEW mazdaspeed mount I still have and run this setup again. I also have poly bushings I can install into the dog bone.


What would you do?

 


 

 

this seems to be holding up fine. Have did a few autox's on it, a few road trips and now my t56 is in. So I can really bang on it now.

Thanks,
Bret

[largeorangefont]

The stock sublink rod does have rubber in it. A solid aftermarket one will yield less subframe movement.

IF you have a Mazdaspeed mount, run it and put the pinion brace back on to limit movement.