enrgy

I am installing non-mazda rear differential to my fc and will be using original fc half shafts through adapters. Everything in the rear will stay as it is except the diff. Should I make bracket to mount diff to rear subframe similarly to how it comes originally or it is not necessary? Any pros or cons from not having diff mounted to subframe? I will have solid subframe risers, adjustable camber bar etc. from PBM if that makes any difference, car will be used for drifting.

misterstyx69

iTrader: (142)

I'm kind of Interested in what you will be using as an alternative.
Got any info on the "new diff"?

88_N/A_GXL

iTrader: (3)

In for info on this. Would love a nice alternative to the Mazda and 8" diffs. Or even just a different mounting style.

enrgy

I will be using bmw e36/e34 diff, but at the same time I am swapping in 4cyl. turbo engine and using bmw zf gearbox so everything will be custom made to fit.
On the front of fc diff there is a mount to the rear subframe (as pictured below), what I would like to know if there are any cons if I don't have diff mount on the subframe? I have read that diff is acting like additional support of the subframe, but have no idea how important it might be. Bmw diff is shorter and probably won't reach the subframe and propshaft might still go through the diff mounting point and connect with diff only behind the subframe.

misterstyx69

iTrader: (142)

Well if the diff is not mounted at the front it will flex the drivetrain.
When the FC diff Mount is "shot" there it creates a BANG and that alone tells you that it needs to be mounted there in order fr the driveshaft to safely get the power to the diff.
Without having the diff securely mounted to the frame or the car you will not be safely providing power to the rear of the car.The whole rear end will flex and you may end up with a diff and driveshaft in the floor of the car.
That Pic is of Bumpstart's mod to the Front Diff mount..is it not?

clokker

iTrader: (2)

No...just no.

How could anyone look at the relationship of the diff and subframe and conclude that the diff is a structural component of the subframe is beyond me.
A simple thought exercise proves the point:
Is the structural integrity of the subframe compromised when the diff is removed?
No, you've removed nothing from the subframe that affects the suspension in the slightest.
Is the mounting integrity of the diff compromised when the subframe is removed?
Yes, it flops around helplessly.
Thus, we see that the subframe supports the diff, not the other way around.

Engine/trans swaps typically try to retain the stock diff due to the difficulties engineering mounts for an alien unit. There are a lot of forces at work back there and engineering solutions are not easy. If you can retain the stock setup by fabbing a custom driveshaft (which you may need anyway, even with the BMW differential), you're way ahead of the game.

If your presumed power output is going to overwhelm the stock FC unit, which is common for V-8 swap cars, there are already aftermarket options that can be used and even if you still choose to mount the BMW part, looking at how they do it would be instructive.
Ronin Speedworks is an excellent example.

What is the thinking behind this swap?

enrgy

I didn't mean that diff is part of the subframe, I guess I should have used a bit different wording. I would have a mount for the front part of the diff but not necessary on the subframe, but now I think that I should try to mount it to subframe anyway. Thanks for the input and pictures on the website do help a lot.

As for the reasoning of swap, I live in small country in Europe and we don't have any shops that are working with rotaries and also I got the shell with no engine so I am just making my life easier with piston engine while still having the chassis that I really like. There are only few fc's in our country. We don't have the abundance of old Ford transmissions/rear ends in Europe so you will see a lot of bmw transmission swaps over here since there's plenty of them for cheap and they hold power very well. I am not using fc diff since its gearing is way too short for bmw gearbox, you would want to have something like 3.3 or similar ratio for differential with these boxes which is not available for fc. Plus bmw diffs are dirt cheap, easily hold high power and have tons of gearing options to choose from.

clokker

iTrader: (2)

Tying the diff nose to the subframe (somehow) is probably close to inevitable due to the lack of other suitable structure in the area.

I'm a fan of engine swaps and have no qualms about "ripping the soul from the FC", so good luck.

It's interesting that to you a BMW drivetrain is the "easy" solution.
They are way too exotic and expensive over here compared to the ubiquitous V-8 options or even the (slightly) less popular Japanese choices.

Another question...
You mentioned you'll be using the stock axles "with adaptors"...what are your stock axles?
NA axles are a known weak spot, I'm not sure what the point would be in keeping them.
Turbo axles...maybe, but I'd still look into what it'd take to use the BMW axles instead.
In for a penny, in for a pound, as it were.

enrgy

In Europe bmw transmission IS easy solution, 325/525tds gearboxes can be bought for 100-150usd and can stand up to 800nm (almost 600lbft). People are putting these gearboxes on everything in here, plenty of 2JZ swapped cars successfully running these gearboxes with pretty impressive numbers.
My chassis is n/a but I have bought turbo halfshafts. By adapter I mean similarly like wheel spacers to accomodate different bolt pattern wheels. Here's a photo of adapters on a Lithuanian S14 running 2jz and bmw transmission and diff, black part is the adapter. He didn't had any issues with adapters while putting out 700hp and I'll have only half of that power.

sp0ngebob

iTrader: (1)

custom axles are easier than you think toi get made. with an IRS suspension basically you go to an axle shop and say "i want this inner and that outer and this overall length" they may ask a few more questions to help get the dimensions and materials right but thats basically it.


as for the diff mount, i would mount the nose of the diff to the sub-frame if i could. while it may or may not be structural (im inclined to think it does have some loading given the design compared to other diff housing designs ive seen) i would definitely do it to support the weight and keep it from pitching up and down. more or less just to locate the diff properly on two axes while under the car.

some fabbed up bracket on the subframe is probably good enough.