New Diff 3.91 OPEN - Now the fun begins!

[e34.535i.sport]

So I got the new 3.91 open diff (Aka tyre shredder! :p) from a 735i today.

Looks in pretty good condition - the oil came out pretty clean too which is a good sign. I'm hoping to get it in next weekend, so ordering new hardware/seals etc this week.

Question's:

1. What diff fluid should I use? After looking through the archives Redline seems to be the #1 choice, however it seems this is less readily available in the UK. I contemplated buying some Castrol (semi-synthetic) 75w90 today but thought I'd check first. If my best choice is go to the dealer I'll do that.

2. How much fluid will I need? (I searched extensively on this but absolutely no clue on any thread I found and the haynes is eluding me)

3. What should I renew... I'm thinking new bolts for the flanges... #6 in this diagram.
http://www.realoem.com/bmw/showparts.do?model=HD12&mospid=47382&btnr=33_0473&hg=33&fg=10

4. I plan to keep it for a little while to ensure the 3.91 works out, but is my 3.64LSD worth a shiny penny? If/when I sell it how much should I be looking for bearing in mind it's in absolutely perfect working order?!

Thanks... I'll keep updating this thread and get some pics of the swap when i do it!

[632 Regal]

75w-90 is fine for an open differential the LSD takes the thicker 140 weight dope. Try to use a full synthetic instead of the semi.

Are you going to replace the front input seal? If so good luck in getting the proper preload on the bearings.

I think mine took 2 1/2 litres to fill it

3:64 is a perfect gear for the 530 and I suspect a lightening upgrade for a 540. I paid around a hundred for mine a few years ago.

[Paul in NZ]

why not swap things over so you get a 3.91 lsd?With the extra go you will need it even more I suspect

[e34.535i.sport]

Thanks - I will make sure I get fully synthetic, I want to do this thing properly!

No I'm hoping I don't need to mess with the front end, if my flange is the same it can stay as it is. Fingers crossed! :)

[e34.535i.sport]

why not swap things over so you get a 3.91 lsd?With the extra go you will need it even more I suspect

Hmmm... The dude who I got the diff off suggested using the LS unit out of mine in this diff but suggested you need someone with experience to do it. I'm not sure if I'd trust any of our local 'specialists'! Also it would, I assume mean removing the front flange and having to preload the bearing. If my flange is different and I have to swap any way I might do some research and consider doing the lsd swap myself. :)

[632 Regal]

In theory it would be easier to drop lsd into the new case assuming the input flange is the same. As that would need to be done is setting the lash with proper side shims and preload. I wouldn't be afraid to do it as long as I didnt need the unit back in case the shims or shim kit needed to be ordered. Without any experience I wouldnt even fathom of such a project. :)




Thanks - I will make sure I get fully synthetic, I want to do this thing properly!

No I'm hoping I don't need to mess with the front end, if my flange is the same it can stay as it is. Fingers crossed! :)

[shogun]

75W-90 1,9 Liter

[e34.535i.sport]

Without any experience I wouldnt even fathom of such a project. :)

That's a roger :D

[e34.535i.sport]

75W-90 1,9 Liter

Brilliant thanks!

[e34.535i.sport]

Just been out to further clean the new diff up, and also got rid of the two pesky flange bolts that rounded... Angle grinder then molegrips made short work of them! :D

Also went underneatht the car and sprayed the bolts with WD40 ready for next weekend when I'll do the swap.

Seals will be ordered tomorrow, and I might ask the dealer if they do fully synthetic oil for it as I can't seem to get hold of it anywhere else... Bar ebay which will cost me FAR too much!

The countdown begins! :)

[whiskychaser]

Just been out to further clean the new diff up, and also got rid of the two pesky flange bolts that rounded... Angle grinder then molegrips made short work of them! :D

Also went underneatht the car and sprayed the bolts with WD40 ready for next weekend when I'll do the swap.

Seals will be ordered tomorrow, and I might ask the dealer if they do fully synthetic oil for it as I can't seem to get hold of it anywhere else... Bar ebay which will cost me FAR too much!

The countdown begins! :)

Thats 1:0 for mole grips:D Are you going to try to swap the LSD part too? I'm just thinking if you put more power to the rear wheels you might need it.

[e34.535i.sport]

Thats 1:0 for mole grips:D Are you going to try to swap the LSD part too? I'm just thinking if you put more power to the rear wheels you might need it.

I'd be tempted but Regal has suggested it's not for the 'novice'! LOL!

I might see how it goes and if i shred the new enduro's too quickly I'll consider it! :D

[e34.535i.sport]

I wouldnt even fathom of such a project. :)

I just got it :D

[632 Regal]

you can disassemble the old unit after it is out and get familiar with how it all works and things. How many inch lbs for the input to turn with and without the ring gear assembled. You may find that you don't need the LSD anyways.


I'd be tempted but Regal has suggested it's not for the 'novice'! LOL!

I might see how it goes and if i shred the new enduro's too quickly I'll consider it! :D

[e34.535i.sport]

you can disassemble the old unit after it is out and get familiar with how it all works and things. How many inch lbs for the input to turn with and without the ring gear assembled. You may find that you don't need the LSD anyways.

I like the idea, but I think I'll stick with plan A and sell mine on... Simply to offset some of the cost of the swap. It will end up in the region of the £250 which is not bad considering the diff purchase (£100), new seals and bolts (£40), a new set of tools which I need (£95) and the fluid (£26!) plus other costs. I reckon if I make £200 from my LSD I've not done too bad. :)

[Paul in NZ]

dont sell the lsd straight away...you might find you DO need it.

[e34.535i.sport]

dont sell the lsd straight away...you might find you DO need it.

Only time will tell!!! :)

Banging it in this weekend with my good friend the Whiskychaser... Can't wait! :D

[632 Regal]

Take pictures of all the BS you run into during the swap!

Make sure the add fluid plug unscrews before you drain the old stuff :p
Dont forget plenty of synthetic grease for the CV joints and input shaft.


Only time will tell!!! :)

Banging it in this weekend with my good friend the Whiskychaser... Can't wait! :D

[e34.535i.sport]

Take pictures of all the BS you run into during the swap!

Make sure the add fluid plug unscrews before you drain the old stuff :p
Dont forget plenty of synthetic grease for the CV joints and input shaft.

I will! Well, I'm hoping there wont be any problems but I don't want to jinx it!

I wasn't planning on removing the CV joints as such... Just take the hex bolts out and seperate the diff that way. Now this grease for the input shaft, does it have a name? Will the dealer supply it? I'm picking the seals etc up today. :D

[e34.535i.sport]

Take pictures of all the BS you run into during the swap!

TW*T! Already run into a couple of issues... First being the seals from my diff must be larger than the ones on this open diff. Ordered the ones off mine after looking at realoem when I shoulda ordered the ones from the 735i. Hindsight is a wonderfully annnoying thing. :(

Just been out and removed the old seals (killing them in the process!). Didn't have a seal pulling tool but I did have a gear puller... That did the trick. Don't even attempt it with a screwdriver, efforts are futile at best.

I'm hoping the dealer will swap the seals over for me as they cost me >£30! Grrrrr.

[leicesterboy15]

Why is a 735i diff different to a 535i diff? Will a 740i diff be different to a 540i diff? Is the 3.64 LSD diff a worthwhile upgrade to my 540i auto? I thought the LSD diff was the best? Questions questions......sounds like you're having fun anyway!

[e34.535i.sport]

Why is a 735i diff different to a 535i diff? Will a 740i diff be different to a 540i diff? Is the 3.64 LSD diff a worthwhile upgrade to my 540i auto? I thought the LSD diff was the best? Questions questions......sounds like you're having fun anyway!

Hey man long time no speaky! Err... I've no idea why it's different, but I done some research on realoem and there seems to be two versions of the seals I bought and murphys law ensured they give me the wrong one! AND they have to be ordered from Z Germany... :(

The only differences between diffs generally from my research seems to be case size (540i's/M5's have large case, 535i/530i/525i have medium case)... I think you can make smaller case diff works in bigger frame cars if you really want to. Input/output flanges can also differ, enough I think mine are the same so don't have to mess with them!

LSD is preferred for fast cornering and reduced wheelspin as far as I'm aware, whereas I'm more of a 'nifty off the line' kinda guy and I'm not adverse to the odd chirp of the enduros from time to time :D LOL!

Looking at this http://www.bmwe34.net/E34main/Upgrade/Recipe.htm , I think a 3.64 would be quite a big jump up and might make your gears quite short?! A 3.15, 3.23 or 3.46 might suit your car but I suppose it depends on your driving style?! I don't mind shortening up the gears a little in order to gain acceleration personally... This may also be of some use to you incase you haven't seen it before: http://www.vinesauto.com/diffratio.htm

Seems like the 3.15 out of a 750il *should* swap into yours easy enough... Tempted?!

[e34.535i.sport]

Good news! The diff's all cleaned up, new seals/snap rings are in and so is the fluid. :)

I'll post pic's soon as I get the laptop sorted to import pictures. Now to find the install disc... :p

[leicesterboy15]

LOL! You have a way with words!

Yes its been a while! I've been loitering but not really had any time to do any work on the car and looking on here gets me frustrated that I don't have time to do any jobs! The list is building up though so I need to put a plan into action (first I need a plan).

hmm...the diff from a 750? Sounds very tempting, thanks for the links - I'll do some reading up first.

Keep us posted on the diff upgrade!

[e34.535i.sport]

SCOUSE diff... :D

http://img27.picoodle.com/img/img27/2/5/15/entwicklung34/f_DIFF1m_695773d.jpg (http://www.picoodle.com/view.php?img=/2/5/15/entwicklung34/f_DIFF1m_695773d.jpg&srv=img27)

http://img27.picoodle.com/img/img27/2/5/15/entwicklung34/f_DIFF2m_dd6e59f.jpg (http://www.picoodle.com/view.php?img=/2/5/15/entwicklung34/f_DIFF2m_dd6e59f.jpg&srv=img27)

http://img35.picoodle.com/img/img35/2/5/15/entwicklung34/f_DIFF3m_89f6329.jpg (http://www.picoodle.com/view.php?img=/2/5/15/entwicklung34/f_DIFF3m_89f6329.jpg&srv=img35)

http://img31.picoodle.com/img/img31/2/5/15/entwicklung34/f_DIFF4m_d41a954.jpg (http://www.picoodle.com/view.php?img=/2/5/15/entwicklung34/f_DIFF4m_d41a954.jpg&srv=img31)

[whiskychaser]

When its installed you may want to show it off:

http://www.oznium.com/forum/topic3633

[e34.535i.sport]

When its installed you may want to show it off:

http://www.oznium.com/forum/topic3633

LOL! Should stick some of them neons on it and be a 'proper' scouser! :D

[e34.535i.sport]

It's in!! :D

First impressions... :D

Took it out for a short test drive (only a few mile) to check all is well and it certainly is! The new 3.91 is quiet and feels really smooth. The revs certainly rise quicker than before, which gives the feeling of effortless acceleration. I'm going to go on a more extensive test drive and report back fully but it certainly feels quicker off the line and at the lower end of each gear. Can't comment on the swap from LSD to open just yet, only time will tell.

I must say thanks a million to my good friend Colin (aka Whiskychaser!) for giving me a hand with the swap, he is a true gentleman! The job went *almost* perfectly too! ;)

I'm going to make a new 'informative' thread about the whole swap from start to finish for anyone who wants to research it in future, as I got a lot of my information from a variety of different sources. I will obviously be able to give details of my personal experience too, which may be useful to someone at some point.

Overall - great job, great result and had a great time doing it. Recommended! :D

[whiskychaser]

I'm going to make a new 'informative' thread about the whole swap
I'm sure you will include a section on loctite and nuts:D IIRC it was 1-all on the oops front:p

[632 Regal]

Glad it worked out pretty smooth. When I swapped to a taller gear in the 530 the mileage went up 2 in the city and stayed the same hwy even though the engine revs a bit higher.

[e34.535i.sport]

I'm sure you will include a section on loctite and nuts:D IIRC it was 1-all on the oops front:p

LOL - of course! And those little tab f*ckers! :D

[e34.535i.sport]

Glad it worked out pretty smooth. When I swapped to a taller gear in the 530 the mileage went up 2 in the city and stayed the same hwy even though the engine revs a bit higher.

Now that is good to hear. I felt this might be the case as the engine is not working as hard to get the thing going...

I'm going to try to analyse the MPG/acceleration/revs differences in detail over the next week or so, see how it pans out.