Diff brace thoughts?

NissanParty

Will a rear diff brace remove most of the play between the rear diff and subframe bushing? It seems like it would, at least vertical play, is my thinking correct?

Averying

Diff brace will help remove play but you should replace the OEM diff bushings before installing a diff brace


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NissanParty

Yeah but installing a diff brace is a lot easier than replacing the bushing

With a diff brace, can the diff still move an appreciable amount within the subframe?

Edit: I am lazy, yes.

filip00

So the diff stock has 3 mounting points, and all have bushings. Let's assume they get a bit loose and they all have some play. You now introduce a diff brace which is most often - completely solid, it has no bushing whatsoever. What will happen is - you will eliminate a lot of play...but you will additionally introduce a whole lot of stress on the brace mounting point. If you have the version that's mounted using just two cover bolts - I can imagine that being a potential problem. If you have the version where you have an additional screw on the diff cover - that might be better, provided that the mentioned screw doesn't go to ****.

I think that altogether - it's a bad solution and you should change bushings.

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Averying

If you want a lazy-fix… look up the DIY for filling the diff bushing with epoxy. I think Motorvate DIY has a video on this. Supposedly this fix works pretty well but I can’t speak to how long it will last and/or how effective it is based on the condition of your existing diff bushing


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2009 Sport Touring | Platinum Graphite | GTM Stage 1 Supercharger | BC BR Coilovers | Hotchkis Swaybar | Z1 FUCAs | AME TM-02 Wheels | Z1 2-piece Front Rotors | Z1 Clutch & Flywheel | Invidia Gemini Catback | GTM Resonated Test Pipes

Kzonts

Oh boy… I have the diff brace with stock bushings. But I don’t track or abuse the car. Maybe just a little spirited cruising around.

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2019 Magnetic Black Roadster
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filip00

If your bushings are good, there's no need to worry, diff brace is OK as additional support.

disclaimer - not an engineer, but I have a pretty good understanding of physics and engineering (for a layman).

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Kzonts

Thx… The car has only 7,000 miles and I don’t see any bushing leaks

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phunk

All of this. ^^

A differential brace is a bit of a hack created as the lazy mans way to mitigate differential movement. Will it massively reduce movement in the rear differential? You bet. But like mentioned in the quote above, you are now focusing nearly all the stresses to a single mount at one corner of the differential. If you truly wanted a solid mounted differential, the proper way to do it would be to replace all 3 of the original mounts with solid bushings. This would keep the stresses spread out rather than focused at one bracket at one corner of the differential.

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NissanParty

Thanks both of you, I will take your advice!

I don't have a garage otherwise I would not hesitate to replace the bushing myself. But right now, the best I have is a parking lot with no access to 120v power. I was thinking of buying a cordless sawzall and cutting the old bushing out, that seems easier than using the bushing tool from Z1.

Also every shop I called does not have experience replacing this bushing, but said they can do it and it will cost a lot. I wish I could find a shop that was familiar with Zs and knew about the bushing issue and replaced them before.

As a guy who has done motor swaps and head swaps and lots of other stuff, how much of a pain in the "A" would it be for me to replace the bushing myself with hand tools? I don't want to get stuck somewhere in the process and not be able to finish the job.

NissanParty

I did that on my G37 and the epoxy crumbled after a while. I was thinking of trying again on the Z but I'd really rather get the Z1 poly bushings. I just don't want to do the huge pain in the butt bushing replacement myself if I can find a shop to do it correctly and for not too much money. A few places I asked said it is going to be over 500 bucks, which doesn't surprise me at all.

BoilardZ

I replaced my diff bushings last year with hand tools--no power tools. But I did use the bushing pressing tool from Z1. The whole job took a solid 4-5 hours. But it just requires a lot of patience as you very, very slowly turn the screw to get the bushing out. Good to have a long breaker bar.
There are some good videos on Youtube. The key is to remove ALL the parts that are in the way, including exhaust (just has to be unhooked at the muffler, and let the whole thing dangle down to the ground), and a few braces.

Kzonts

With that advice, I’m going to remove the brace for now. If I replace the bushings down the road, I’ll drop it back in…

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Kzonts

I did it without power tools as well on my previous Z. Using the tool was tough. I had to ensure the car was high enough off the ground for a LONG breaker bar. And it took all of my strength to get it out. This time if I need to do it, I will cut it out!

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phunk

Well.. let me also just state that I have not personally seen failure introduced by use of one of the differential braces. So, the practice sucks on paper, but in the real world I have not seen it cause any real consequences yet. So I dont want to sound an alarm that everyone immediately run to remove these.

If it were to eventually cause a problem... what would it be? Well, most likely mounting point failure. Whether it became cracks at the crossmember, threads torn from the differential or cracking of the differential housing or cover. Is it possible that there could be some internal wear caused by housing distortion when the differential is loaded with only 1 solid mounting point? Eh, maybe, but its a pretty beefy unit and you know its shape is round/arch which is inherently rigid, etc. I would probably be in more of a hurry to get rid of it in a 350z since they have the aluminum rear crossmember rather than the beefy steel unit the 370z has.

So if you are enjoying it or the benefits from it, I would say to keep it in and maybe just plan to one day put in a full set of solid urethane bushings. If someone doesnt already have the brace, that is where I would attempt to intercept the plan and encourage a full bushing swap instead.

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