Regular rear diff in an IX

[atmobenzin]

you can. too bad there is no counterpart for the manual cars.

Huh? How is there not?

[flyboyx]

The diff is not the ring. If you are pulling the diff you would reuse the ring and pinion. I am not familiar with the bmw rear ends as I have yet to open mine up and take a look. But if the Posi is out of the same size case You should be able to swap the diff and reuse everything else.

the beauty of bmw is that you wouldn't have to open the diff to change the ratio. you can just switch out the entire final drive unit without having to open the diff or change the axles.

Huh? How is there not?

well, the good thing about the bmw e30 is that they have independent rear suspension. this means that you can just change the center section of the final drive and you have a new ratio(doesn't apply with ix's because you MUST match the front ratio)

auto ix's came with 4.10 axles. this is also a common ratio in 2wd cars. off the top of my head, auto coupes and sedans generally came with a clutch type 4.10 ratio. also, auto 6 cyl z3's also came with a 4.10 torsion. you can just switch out the entire center section(21 bolts) without having to mess around with the complication of resetting the ring and pinion.

manual cars came with 3.91. the problem here is that i can think of no other car that came with an e30 style final drive in that ratio. this means that unless you want to go through the complication of taking the diff apart and physically changing the gears, you are "stuck"(not necessarily a bad thing) with the viscous diff from a manual ix. there just aren't any other choices out there that i am aware of. certainly nothing readily available.

for those of you with the wheels spinning in your head, the answer is no, you cannot mix a 4.10 and a 3.91 in the same car. that will fry the viscous coupling in your transfer case in a heat beat.

[atmobenzin]

Too long, didn`t read.


j/k

So what you are saying is - there are no rwd e30`s with 3.91 diff ratio on your side of pound?

Ahhhh yes, the downside of not having 316i/318i/320i/323i models(for all your freaky ratio gearbox/diff needs). Edit: ...and diesels.

[The Dark Side of Will]

standard clutch pack diffs only have a 25% lock up. but where im confused is that it really shouldnt be rated in percentages, because power can change but clutch packs dont magically breed. i think its something around 65ft/lbs is the break away.

im not sure if it's called 100% lock up because the viscous has a break away torque spec at 160ft/lbs.

The torque between axles in the VC diff depends on the speed difference between the axles.

The torque between axles in the posi diff is the preload torque from the spring packs + the preload generated by the ramps squeezing the clutch packs.

So if the static friction of the ramp and clutch pack combo can handle up to 25% of the throughput torque of the diff before slipping, then it's a 25% locking diff...

I just figured that out recently... it's not very intuitive.

[The Dark Side of Will]

for those of you with the wheels spinning in your head, the answer is no, you cannot mix a 4.10 and a 3.91 in the same car. that will fry the viscous coupling in your transfer case in a heat beat.

But you *can* install *BOTH* 4.10 diffs from an automatic iX into a manual iX...

[Kershaw]

i think i get it. thanks. not very intuitive at all.

[mybimr]

[quote=flyboyx;3076577]
manual cars came with 3.91. the problem here is that i can think of no other car that came with an e30 style final drive in that ratio. this means that unless you want to go through the complication of taking the diff apart and physically changing the gears, you are "stuck"(not necessarily a bad thing) with the viscous diff from a manual ix. there just aren't any other choices out there that i am aware of. certainly nothing readily available.[quote]

Won't the clutch pack 3.91 lsd's from the e36 (I believe only the e36 m3 had the 3.91's) bolt up?

[nando]

E36 m3 had 3.23 & 3.38, not 3.91

[flyboyx]

the diff housing is also different. so, no...not a good choice.

[nando]

you'd have to swap it into an E30/E28 housing. the internals are pretty much the same.

I've got a 3.38 to swap into an E30 case when I get to it...