Made my mind up: I'm gonna do a diff swap.. (a few Q's).

[e34.535i.sport]

I looked into doing a diff swap a while ago, and time has went by and I've procrastinated... I've read all the previous threads about diff swaps in the archive but this is kind of a personal thing I find, so thought I'd ask your advice/opinon.

Recently I asked about a diff for a friend in a scrap yard and the dude is willing to do them REALLY cheap if I take it off myself... Which in my eyes is preferrable anyway as I'll learn how to do it and make sure it's done carefully.

So the cost factor is out the way and nothing is holding me back. I should be able to afford it and some new seals when he gets the right one in... [Currently he has a diff from an e36 323i (1998) and an e36 320i (1998 I think)... I don't know if these are suitable or interchangable with mine, I doubt it.] Now, I've done some research and found this page really helpful: http://www.vinesauto.com/diffratio.htm so I know what I'm looking for.

First question is - What ratio would be best to move up to from a 3.46 if I want better acceleration and low end torque? The way I see it my choices are 3.64, 3.73 or 3.91. Any higher and I guess first gear is made redundant? :D I'm leaning towards the 3.73 but not sure, check this out:

3.64: It's a ~5.2% increase in revs meaning @ 80mph in fifth if I'm normally at 3000revs I'd be at ~3156revs...

3.73: It's a ~7.8% increase in revs meaning @ 80mph in fifth if I'm normally at 3000revs I'd be at ~3234revs...

3.91: It's a ~13% increase in revs meaning @ 80mph in fifth if I'm normally at 3000revs I'd be at ~3390revs...

Looking at that I surely wouldn't lose too much fuel consumption even using the 3.91 diff? Also, I normally shift by 5000revs in any gear meaning even in first if I wanted to get going in a hurry I would be doing the same speed if I just took it a little further to 5650revs...

Next question, which I hope someone can help me with: Which diffs have the same flanges as mine? I really don't want to be changing the driveshaft flange as it's supposed to be a lot of messing. I don't mind changing the output flanges as they're not supposed to be as bad but I'd prefer a straight swap to be honest... I'd really appreciate any info on this.

Ok, also, I have an LSD at present, should I replace it with another LSD? I don't want to lose out on anything by going to an open diff... Oh, and does it matter if the diff comes from a MANUAL or AUTO? I imagine not...


Lastly, what's the deal with this 'preloading - I've read a lot of information on swapping the diff (great resource here: http://www.bmwe34.net/Wiki/tiki-index.php?page=Differential+swap) but still in the dark with the preload. Anyone done it and can I do it?

[bubba966]

You're going to want another LSD.

You're going to want a diff out of an E34 (non M5/540 as those are much different) or one of the smaller ones out of an E32 (like the 735). Don't think the E36 diffs are interchangeable.

As far as which ratio to go with? Depends on how much you want your gas mileage to decrease. But the 3.73 should be your best bet for a good balance of improved acceleration/gas mileage loss.

Auto/manual doesn't matter in the build of the diff. Only difference between them will be the ratios.

Reminds me I need to figure out which ratio I've got in my car now to figure out if the 3.91 LSD I picked up is too low. Couldn't pass up a diff like that for $200 though...

[gale]

Definitely go with LSD. 3.64 would be my 1st choice. We put one in my son's 535i when we did the swap and in my opinion it's perfect. I have a 3.91 in my 7 and it's a bit too shallow. A 3.73 would be my 2nd choice but they are somewhat scarce.

Give no concern to swapping axle flanges, they pry out with a screwdriver and you'll want to put fresh seals in it anyway, so that's not an issure.

One issue with auto vs manual diff's will be the input flange if it's different than yours, but you can swap that too. Replace the seal if you have to swap input hubs, but don't mess with it if the donor hub is the same.

[e34.535i.sport]

Definitely go with LSD. 3.64 would be my 1st choice. We put one in my son's 535i when we did the swap and in my opinion it's perfect. I have a 3.91 in my 7 and it's a bit too shallow. A 3.73 would be my 2nd choice but they are somewhat scarce.

Give no concern to swapping axle flanges, they pry out with a screwdriver and you'll want to put fresh seals in it anyway, so that's not an issure.

One issue with auto vs manual diff's will be the input flange if it's different than yours, but you can swap that too. Replace the seal if you have to swap input hubs, but don't mess with it if the donor hub is the same.

Just the man - I was hoping you'd see my thread! I was reading yours from a while back recently and saw you had done the swap!!! Did your son find it much better off the line - a lot more torquey so to speak? I know what you mean about going too far and having the gears too short, but I just want the best compromise really.

I'm interested in this preload - If I get a manual diff should the driveshaft flange be the same then? Will I need to worry about preloading anything when putting the diff in and attaching it to the driveshaft? Thanks in advance!

[e34.535i.sport]

You're going to want another LSD.

You're going to want a diff out of an E34 (non M5/540 as those are much different) or one of the smaller ones out of an E32 (like the 735). Don't think the E36 diffs are interchangeable.

As far as which ratio to go with? Depends on how much you want your gas mileage to decrease. But the 3.73 should be your best bet for a good balance of improved acceleration/gas mileage loss.

Auto/manual doesn't matter in the build of the diff. Only difference between them will be the ratios.

Reminds me I need to figure out which ratio I've got in my car now to figure out if the 3.91 LSD I picked up is too low. Couldn't pass up a diff like that for $200 though...

Thanks, I was thinking I should stick with the LSD, I just hope I can find a good one.

[bubba966]

Definitely go with LSD. 3.64 would be my 1st choice. We put one in my son's 535i when we did the swap and in my opinion it's perfect. I have a 3.91 in my 7 and it's a bit too shallow. A 3.73 would be my 2nd choice but they are somewhat scarce.

What diffs were in those cars before? And what tranny is in the 535?

[gale]

What diffs were in those cars before? And what tranny is in the 535?

Someone correct me if I'm wrong, but I believe ALL e34 535i manuals have a 3.46, at least in the US. Getrag 260/6 was used in all of them,

[JoeS]

if you are going to see the highway or interstate at all the 3.64 would be the best, but want to exploit the torque go with the 3.73. Running 80 -85 down the interstate chews thru the fuel with a 3.73.

I AM VERY INTERESTED buying your 3.46 lsd when you pull the trigger.

Joe S

[attack eagle]

and all the auto 535 had the 3.64 in the US, correct?

i'm not familiar wit hthe 535 driveshafts but on the ones with carrier bearings, you can mix and match the rear shafts to make it fit whatever you want.

manual front + auto back would match up with the tranny and diff and not require the risky business of preloading without knowing exactly what you are doing. Probably cost the same or less to have it balanced vs. having an expert swap flanges 'the right way'.

[Paul in NZ]

if you have 535iS you prolly already have the 3.64....what revs are you running at 60
mph???I have a 3.64 and run about 2250 at 100 kph indicacted ..if i were you i would be going the other way...

[fin]

Pre-load.

Bearing in machinery are designed to run with a given amount of pressure on the sidewalls for them to run properly. It's commonest (and most critical) with cone bearings which can be thought of as three wedges (inner, outer race and the tapered bearings) working against each other. Too much preload (Torque) and the wedges bind. Not enough and the bearings are loose and can get slightly sideways changing the angle of their wedge shape. The bearing will start binding, wearing and heating the bearing at an increasing speed. In general when bearings are loose, the shaft can wobble around which transmits energy from the shaft by it's flopping motion to the bearings/races, which in turn heats things up and it's downhill from there.

Marking the nut and the input shaft when replacing a flange will put the preload on the bearing very close to what was when it 1. Left the factory, 2. was last rebuilt. You are trusting that they had it right. If the diff. is know to have a lot of miles on it, that is a very safe assumption.

If you really want to dial it in. Determine if the replacement flange is thicker or thinner and adjust the angle between the marks on the nut and the shaft to compensate for the difference. So if the replacement flange is 0.25mm smaller and thread pitch of the shaft is 1.0mm, then you would turn the nut a quarter turn past the matching mark point. (I don't know what the true pitch of the shaft is, don't bet your rear end on 1.0mm.)

Don't sweat it, the real difference in the flange thicknesses isn't such that the torque values would be outside the tolerance of the bearing's recommended amount. I don't think fine German engineers would neglect to think of that when writing the tolerances for the flange thicknesses.

At the factory, the nuts are put on with torque drivers that are regularly tested to ensure the proper torque being used. When you move into that world you will start hearing words like 'running torque', 'static torque' etc. That is why using the torque value to loosen the nut is not the value used to torque it on. Cleaning and greasing will greatly affect those numbers.

More than you probably wanted to know, but I just had to say it.

Cheers,

Ned

[Jeff N.]

What JoeS said. I have a 3.73 LSD. First gear becomes optional. Fuel usage at highway cruise is accelerated. A 3.64 is probably the best gearing if you want to shorten it up a bit.

Pros of the 3.73: No need to swap the input shaft. Since they are sourced from a 89 525 stick, (looow power), they tend not to be trashed. You will need to swap the output flanges put they just pop out and move over from your current diffy.

The real issue I think with the E34 is not the diff gearing, it's the long spacing in the gearbox between 2nd and 3rd that's the issue.

[e34.535i.sport]

Thanks for all the input so far guys... I've been away for a few days so haven't been able to respond.

I think the 3,64/3.73 may be the way to go by the looks of things, but I wanted the difference to be noticible- otherwise the effort of changing it won't be worth it if you know what I mean. However, I recently found that I can get some damn good mpg on the motorway which I wouldn't want to totally ruin!

I need to ask - can anyone outline to me plainly which diff's I can use that will NOT require preloading? Also, I read that there are a couple of different housings, which ones won't fit mine? I know the m5 diff is a no go...

I'm looking at a 525i/m (89/90) 3.73 (LSD hopefully) OR a 735i/m (89/90) 3.64 (LSD hopefully)...

It's a shame as a guy I've been to before has said he will do me a 535i auto 3.91 diff for cheap if I come and take it off myself. Tempting but possibly too short for me gear wise.

[bubba966]

I need to ask - can anyone outline to me plainly which diff's I can use that will NOT require preloading? Also, I read that there are a couple of different housings, which ones won't fit mine? I know the m5 diff is a no go...

I'm looking at a 525i/m (89/90) 3.73 (LSD hopefully) OR a 735i/m (89/90) 3.64 (LSD hopefully)...

It's a shame as a guy I've been to before has said he will do me a 535i auto 3.91 diff for cheap if I come and take it off myself. Tempting but possibly too short for me gear wise.

The M5 & 540 diffs aren't direct swaps. The 518/520 might not be as well, but I don't know for sure. M5 & 540 use 'large case' diffs, 525, 530, 535 use 'medium case' diffs. Not sure about the diffs in 5's, but in the 3's the 318 had a smaller diff than the 325. Which is why I think you should ask someone that knows Euro E34's better about the 518/520 diffs if you should come across those.

I'm not sure but I think the 735 diff is a medium case diff just like the ones in the E34's. I know the 740 & 750 used the same large case diffs the 540 & M5 had as those swap right in.

The 3.91 is going to be deep enough to effect your mileage noticeably. Not only that but if you don't have enough HP for deep gearing like that it'd actually accelerate from a stop slower than a gear ratio that's not as deep. And the gear ratio of the diff is only part of the equation as you need to look at the overall gear reduction which includes the gear reductions in the tranny.

For instance, my truck used to have a TH-350 tranny and a 4.10:1 diff. The TH-350 has a 2.52:1 first gear. That combined with the 4.10:1 rear end produced great acceleration. In fact it almost lifts the front tires off the ground.

But then I changed the tranny out to a 700R4 that has a 3.06:1 first gear. That combined with the 4:10 rear end gave me slower acceleration than I had previously with the TH-350 and didn't lift the front end nearly as much at launches.

Mentioned that to the guy that built my custom 700R4 during the follow up call and he didn't understand how that could be. I was putting more torque to the ground with the 700R4, but was getting weaker/slower launches. Which makes no sense.

But then I told him that the engine in my truck was built for torque, not HP and doesn't build HP very quickly. (torque is like the brute force, and HP is more about the speed of the power buildup. Which is why ricers with no torque don't get going well off a start, but go fine once moving along)

What was happening was that the 700R4 and 4.10 rear end was actually too deep of a gear reduction combination for the HP curve of my engine. As the engine didn't rev up quick enough, it wasn't putting out enough RPM's for the lower gearing to keep the old acceleration level.

Yes, it puts more power to the ground than it did (which is why I've snapped a pair of good quality 20,000 pound tow straps, and can lay 10" wide strips of rubber for blocks). But it'd doesn't accelerate from a dead stop as fast as it used to.

Anyways, I don't think a 3.91 is too deep to negatively effect acceleration. And I'm not even sure a 4.10 would be. But the ratios that are higher than 4.10 would probably be too deep for acceleration improvement.

I still think your best bet for optimum improvement and minimal loss of mileage is the 3.73 if you do actually have a 3.46 in the car now. Best make sure you've got a 3.46 and not a 3.23 or 3.15 or something even taller than that.

[e34.535i.sport]

The M5 & 540 diffs aren't direct swaps. The 518/520 might not be as well, but I don't know for sure. M5 & 540 use 'large case' diffs, 525, 530, 535 use 'medium case' diffs. Not sure about the diffs in 5's, but in the 3's the 318 had a smaller diff than the 325. Which is why I think you should ask someone that knows Euro E34's better about the 518/520 diffs if you should come across those.

I'm not sure but I think the 735 diff is a medium case diff just like the ones in the E34's. I know the 740 & 750 used the same large case diffs the 540 & M5 had as those swap right in.

The 3.91 is going to be deep enough to effect your mileage noticeably. Not only that but if you don't have enough HP for deep gearing like that it'd actually accelerate from a stop slower than a gear ratio that's not as deep. And the gear ratio of the diff is only part of the equation as you need to look at the overall gear reduction which includes the gear reductions in the tranny.

For instance, my truck used to have a TH-350 tranny and a 4.10:1 diff. The TH-350 has a 2.52:1 first gear. That combined with the 4.10:1 rear end produced great acceleration. In fact it almost lifts the front tires off the ground.

But then I changed the tranny out to a 700R4 that has a 3.06:1 first gear. That combined with the 4:10 rear end gave me slower acceleration than I had previously with the TH-350 and didn't lift the front end nearly as much at launches.

Mentioned that to the guy that built my custom 700R4 during the follow up call and he didn't understand how that could be. I was putting more torque to the ground with the 700R4, but was getting weaker/slower launches. Which makes no sense.

But then I told him that the engine in my truck was built for torque, not HP and doesn't build HP very quickly. (torque is like the brute force, and HP is more about the speed of the power buildup. Which is why ricers with no torque don't get going well off a start, but go fine once moving along)

What was happening was that the 700R4 and 4.10 rear end was actually too deep of a gear reduction combination for the HP curve of my engine. As the engine didn't rev up quick enough, it wasn't putting out enough RPM's for the lower gearing to keep the old acceleration level.

Yes, it puts more power to the ground than it did (which is why I've snapped a pair of good quality 20,000 pound tow straps, and can lay 10" wide strips of rubber for blocks). But it'd doesn't accelerate from a dead stop as fast as it used to.

Anyways, I don't think a 3.91 is too deep to negatively effect acceleration. And I'm not even sure a 4.10 would be. But the ratios that are higher than 4.10 would probably be too deep for acceleration improvement.

I still think your best bet for optimum improvement and minimal loss of mileage is the 3.73 if you do actually have a 3.46 in the car now. Best make sure you've got a 3.46 and not a 3.23 or 3.15 or something even taller than that.

Thanks that was really helpful... I've discounted the 3.91 as I think you're right. I would prefer to get my hands on a 3.64 if possible as it should improve acceleration without having negative effects being relatively similar to my own. However If I come across a 3.73 in good nick it may be worth a punt if I can get it cheap. Either way if I don't find it better I can always throw mine back in! If I do mine will be for sale...

I'm pretty certain I have the 3.46 but may jump under tonight to check for sure. I assume I should be able to easily see the number without dropping the diff or anything? At least I hope!

[bubba966]

Thanks that was really helpful... I've discounted the 3.91 as I think you're right. I would prefer to get my hands on a 3.64 if possible as it should improve acceleration without having negative effects being relatively similar to my own. However If I come across a 3.73 in good nick it may be worth a punt if I can get it cheap. Either way if I don't find it better I can always throw mine back in! If I do mine will be for sale...

I'm pretty certain I have the 3.46 but may jump under tonight to check for sure. I assume I should be able to easily see the number without dropping the diff or anything? At least I hope!

The M5 diff I picked up has a steel tag attached to the rear diff cover that's got the ratio stamped into it. It's also marked somewhere else that I'm not recalling at the moment. You should be able to find the ratio on the diff without pulling it out of the car.

A 3.64 will be an improvement over a 3.46. But I honestly think you'd enjoy driving a 3.73 over a 3.64 if you've got a 3.46. Shouldn't hurt to put either into the car. and should you get one of those and decide that you didn't care for it and want to try another one I'm sure you could sell the LSD you don't like for about the same price as you pay for it.

BMW LSD's are always in demand. Makes it easy to try different ratios if you're able to sell one for what you paid for it. Which is why I didn't mind picking up that 3.91 LSD without knowing if that was too deep or not for my car. It was $200, I should be able to sell it for more than that if I want to. And as I've bought new parts for it (bolts/seals/etc.), I will want more than $200 should I sell it.

[Paul in NZ]

The M5 diff I picked up has a steel tag attached to the rear diff cover that's got the ratio stamped into it. It's also marked somewhere else that I'm not recalling at the moment. You should be able to find the ratio on the diff without pulling it out of the car.

A 3.64 will be an improvement over a 3.46. But I honestly think you'd enjoy driving a 3.73 over a 3.64 if you've got a 3.46. Shouldn't hurt to put either into the car. and should you get one of those and decide that you didn't care for it and want to try another one I'm sure you could sell the LSD you don't like for about the same price as you pay for it.

BMW LSD's are always in demand. Makes it easy to try different ratios if you're able to sell one for what you paid for it. Which is why I didn't mind picking up that 3.91 LSD without knowing if that was too deep or not for my car. It was $200, I should be able to sell it for more than that if I want to. And as I've bought new parts for it (bolts/seals/etc.), I will want more than $200 should I sell it.

AFAIK if you have an lsd you can swap the clutch pack from one diff to another....or swap different ratios frm one case to another,as long as the diff is the same..ie two med case BMW diffs...one 3.46 lsd and one 3.73 open...you can make a 3.73 lsd with those two diffs...

[Paul in NZ]

Thanks that was really helpful... I've discounted the 3.91 as I think you're right. I would prefer to get my hands on a 3.64 if possible as it should improve acceleration without having negative effects being relatively similar to my own. However If I come across a 3.73 in good nick it may be worth a punt if I can get it cheap. Either way if I don't find it better I can always throw mine back in! If I do mine will be for sale...

I'm pretty certain I have the 3.46 but may jump under tonight to check for sure. I assume I should be able to easily see the number without dropping the diff or anything? At least I hope!

I asked you before....if you have a 535 sport,you should already have the 3.64...what revs are you running at 60 mph?

[GoldenOne]

eh if you somehow want a S3.91, i have one for sale!

[e34.535i.sport]

eh if you somehow want a S3.91, i have one for sale!

It seems I just might witht the recent revelations... how much are you looking for and what car is it off (535i?)?

It's probably going to work out a lot dearer with shipping etc - what do you think?

[e34.535i.sport]

REVELATION!!!!! It's a 's' 3.64!!!!

This has blew my mind... How can it be? I had to snap the plate off as it was so covered in crud... I left it in some coke for a while and got the wire brush on it: s3.64...

I suppose this has turned the situation sideways! I guess I'll be looking for a 3.73 now for a 2.4% increase in revs or a 3.91 for a 7.4% increase in revs.

Would a 2.4% increase in revs (if I get a 3.73) even be noticible?

I also confirmed that my car should have a 3.64 on REALOEM yesterday... Apparently the 3.46 ran up to 09/1989 and the 3.64 was used thereafter. The vineauto's page suggests otherwise and I used that as my baseline: A Sincerely good call by Paul in NZ - how did you know?????

I'll do a full rev review shortly... This has got interesting!

[e34.535i.sport]

OK it's looking like I have a 3.91 diff lined up from a 535i Auto for the weekend - he just needs to check for me if it's a LSD... Presuming it is I'll be taking it off the donor car on Saturday: Questions -

1. I know I'll need Ratchet, female torx sockets, breaker bar, normal sockets, Trolley jack... Can you think of anythin else?

2. Will I be good to go with this diff - i.e. no preloading of the front flange necessary?!

3. What should I do fluid wise - change the fluid in the 3.91 when I get it in, even if I don't know it's history? Or is it better to leave as it is?

4. Is there anyone who might be interested in my 3,64LSD if all goes well and the new diff is ok?

TIA

[bubba966]

Only need to preload the flange if you take it off. And it sounds like you won't be taking it off as you should be able to get the diff with the input and output flanges intact.

I'd change the fluid while you have it out. Don't wait until it's in the car and a pain to get at. There's no reason to leave the old fluid in it.

And I do think a 3.91 is the right step up from a 3.64. I felt the 3.73 would've been best if you had a 3.45.

[bubba966]

Just checked realoem on mine and it says I've got a 2.81 in it!

Really don't see how that could be right. If it is, then that 3.91 LSD I bought is waaay wrong. Should install a 3.15 in mine if it does actually have a 2.81 in it now..

[e34.535i.sport]

Just checked realoem on mine and it says I've got a 2.81 in it!

Really don't see how that could be right. If it is, then that 3.91 LSD I bought is waaay wrong. Should install a 3.15 in mine if it does actually have a 2.81 in it now..

It's worth having a look see - I was so surprised to find 3.64 rather than 3.46! Shame you don't live closer I'd have took that off your hands! :(

[e34.535i.sport]

Only need to preload the flange if you take it off. And it sounds like you won't be taking it off as you should be able to get the diff with the input and output flanges intact.

I'd change the fluid while you have it out. Don't wait until it's in the car and a pain to get at. There's no reason to leave the old fluid in it.

And I do think a 3.91 is the right step up from a 3.64. I felt the 3.73 would've been best if you had a 3.45.

Thanks man, that'll do me. :D

[e34.535i.sport]

Thanks man, that'll do me. :D

P.s: If I am replacing the seals on the output flanges is it just #6 I need on this diagram?

http://www.realoem.com/bmw/showparts.do?model=HD12&mospid=47382&btnr=33_0473&hg=33&fg=10

Thanks!!!

[bubba966]

P.s: If I am replacing the seals on the output flanges is it just #6 I need on this diagram?

http://www.realoem.com/bmw/showparts.do?model=HD12&mospid=47382&btnr=33_0473&hg=33&fg=10

Thanks!!!

I'd get #2 & #3 as well as #6. #'s 2 & 3 are cheap, and could be damaged or damaged upon removal. Pretty sure I picked those up when I picked up new output seals and a bunch of other stuff for this 3.91 (drain plugs, cover bolts, speed sensor o-ring, cover gasket, etc.)

You're probably going to want to change the cover gasket & speed sensor o-ring as well while you're at it. BMW no longer sells the cover gasket (got mine from Pelican parts). if you can't find one BMW now uses a flange sealant instead of the thing paper gasket they used to use.

[bubba966]

It's worth having a look see - I was so surprised to find 3.64 rather than 3.46! Shame you don't live closer I'd have took that off your hands! :(

I'd have been happy to sell it to you if I really do have a damn 2.81. But you wouldn't want it anyways as it's an M5/540 large case diff. Would require changing a whole lot of stuff on your car to get it to fit.

[e34.535i.sport]

I'd have been happy to sell it to you if I really do have a damn 2.81. But you wouldn't want it anyways as it's an M5/540 large case diff. Would require changing a whole lot of stuff on your car to get it to fit.

Of course, mine is a medium case so it's a no go. :( It seems like my options are very limited now (excuse the pun), as the 3.73 only seemed to be used on the 525i from 1989-1990, and the 3.91's were either on the m5 (no use to me) or on the auto's... Which I'm not sure will be suitable? My good friend Whiskychaser has an auto and on his there is a 'guibo' on the rear end of the propshaft but there isn't on mine (pretty sure)... Does this make any difference to the diff fitment, i.e would the front flange on the diff be ok mating straight to my propshaft without the rubber guibo there?

[632 Regal]

Have to change the input shaft which is where all the troubles start with bearing failures.


Of course, mine is a medium case so it's a no go. :( It seems like my options are very limited now (excuse the pun), as the 3.73 only seemed to be used on the 525i from 1989-1990, and the 3.91's were either on the m5 (no use to me) or on the auto's... Which I'm not sure will be suitable? My good friend Whiskychaser has an auto and on his there is a 'guibo' on the rear end of the propshaft but there isn't on mine (pretty sure)... Does this make any difference to the diff fitment, i.e would the front flange on the diff be ok mating straight to my propshaft without the rubber guibo there?

[Paul in NZ]

REVELATION!!!!! It's a 's' 3.64!!!!

This has blew my mind... How can it be? I had to snap the plate off as it was so covered in crud... I left it in some coke for a while and got the wire brush on it: s3.64...

I suppose this has turned the situation sideways! I guess I'll be looking for a 3.73 now for a 2.4% increase in revs or a 3.91 for a 7.4% increase in revs.

Would a 2.4% increase in revs (if I get a 3.73) even be noticible?

I also confirmed that my car should have a 3.64 on REALOEM yesterday... Apparently the 3.46 ran up to 09/1989 and the 3.64 was used thereafter. The vineauto's page suggests otherwise and I used that as my baseline: A Sincerely good call by Paul in NZ - how did you know?????

I'll do a full rev review shortly... This has got interesting!

beacause....:p No i had done a wee bit of research myself,and after hearing things about the sort of revs e24 (635)and e28 (535) do at about 60 mph i was considering the reverse of what you are doing....I then heard/found that the SPORTS 535 had slightly lower gearing than the normal 535 and this was confirmed when i did a dyno run...the guy checked the calibration of the revs the engine was doing vs his reading of the speed at the rear wheels.4th is 1 to 1 so he could see if i had a 3.64 or a 3.46.Euro cars are often slightly different to our stateside freinds(vines is a US site ?)

[Paul in NZ]

I'd have been happy to sell it to you if I really do have a damn 2.81. But you wouldn't want it anyways as it's an M5/540 large case diff. Would require changing a whole lot of stuff on your car to get it to fit.
yep the 540 have very tall gearing....its one reason why the 540 can get better mileage than the 535

[e34.535i.sport]

Hey - took her out and these are the revs at different speeds (in fifth gear):

40mph: ~1450
50mph: ~1900
60mph: ~2200
70mph: ~2600
80mph: ~3000
90mph: ~3450

Anyone else have any to compare? What's the score with this, is it supposd to be uniform - i.e. increase by the same amount between 40mph & 50 mph as 60mph & 70mph?

[anonymous1]

Hey - took her out and these are the revs at different speeds (in fifth gear):

40mph: ~1450
50mph: ~1900
60mph: ~2200
70mph: ~2600
80mph: ~3000
90mph: ~3450

Anyone else have any to compare? What's the score with this, is it supposd to be uniform - i.e. increase by the same amount between 40mph & 50 mph as 60mph & 70mph?

I reckon you should try the old 3.45 out like I have... I'm getting revs of about 3150 at 70mph. Think you might need to swap to my gearbox whilst there though. :D If yours fitted, I'd do you a straight swap... even throw in a free clunking noise at the diff end for you. ;)

[dkaarb]

It is no problem to swap the diff input flange. Just measure the turning torque of the input shaft on the diff you are going to use before you remove the flange, and then after you install new flange make sure the turning torque is roughly the same. Use a dial type torque wrench.

[Paul in NZ]

its constant..but your speedo will be out...at 100 k (62 mph) i reckon i am doing 2250.... but i know my speedo is out quite a bit.

[attack eagle]

like dodge bmw reads off the diff, so full diff swaps to get a ratio change don't affect the speedo

[fin]

I was at the local u-pull junk yard today. I went in the hopes that one of the two 525's had a LSD in the back.

I pulled one and found a S410 tab on the left side. It didn't give up easily, but nice to have found a LSD for the 530iT. I went to the other car to pull its diff to have one just to stuff into the car while I'm switching ring and pinions.

After getting the second pulled, it turned out that it too, had a S410 tab.

Nice to have a spare around.

So there seems to be a high correlation between the Winter Package option and LSD's in the back.

Now I need to get this done before snow flies. Trees are turning and the sumac is almost all red.

Cheers,

Fin

[ahlem]

I have a 3.91 diff 5 speed and turn 3100 rpm @70mph. I get 21.5 mpg typically. It gets up and goes pretty well and comes out of corners quite nicely. I got the 3.64 with the car and have pondered putting it back in to see if I picked up 8% on the gas mileage. The PO tracked the car and claimed it would beat stock e36 M3's.