Is there a bolt in Diff Swap ?

[pred]

I would like to change gear ratios in my 97 318ti to something more highway friendly like a 297 or something there a bouts, But I would just like to swap the rear and not the axles too.
Is there a direct bolt in Rear diff that will work for me,?
I am new here and new to BMWs, So please be direct,
Like, I need a E-?? rear and it will swap right in,
Thanks all!
Peter

[Uber E30]

z3 is a direct swap, you can technically use an e30 diff too but it seems random who has fitment issues with half shafts and who doesn't.

[pred]

Fitment issues like what?
Shaft length or flange bolt pattern?
I would like to gather what I need and in the next 30 days have a more highway friendly rear,
Peter

[Uber E30]

So here is basic information about the diffs:

318Ti's use a small case diff

4cyl E30's use a small case diff but you wont find a highway friendly ratio there

6cyl e30's use a medium case diff which is a direct bolt on. You can find a 2.93 on ETA's

Most e28's use a medium case diff which is not a direct bolt on. You would need to take the cover and flanges off an e30 diff for it to work. You can find 3.25's on 528's

z3 4cyl use a small case, direct bolt on, not sure on ratios but i believe there isnt a highway friendly option there.

z3 6cyl are a medium case, direct bolt on. You can get a 3.15 ratio on any of the manuals

Here is where this fitment issues come into play. Because you are putting a medium case diff in, the width is slightly larger than the small case diff. Some people seem to have no issues using the Ti half shafts, while others either cant get them to fit or they explode rather quickly. If you want to be safe pick up a pair of e30 half shafts with the diff and you will be set.

[black98]

I found a guy locally to me with two med diffs. What is need to do the swap and pred maybe you can get one and i will get one

http://denver.craigslist.org/pts/3114147158.html

[cooljess76]

I found a guy locally to me with two med diffs. What is need to do the swap and pred maybe you can get one and i will get one

As Uber E30 mentioned, You'll need e30 halfshafts and flange bolts/plates. Plus you'll need to shim your ABS sensors(I used a washer on each one to raise them about 1/16th-1/8th of an inch.

[derek502]

I used a E30 diff with my stock ti axles flanges with no problems. Went from a 3.45 to a 2.97 ratio. Much better at highway speeds now. It is slower around in the stop and go but these cars are not know for speed anyway. BTW I now get 33-34 mpg!

[pred]

Looking at the Ti flanges VS the E30 flanges I see that the Ti splines won't fully engage, While It looks like they will work I would be afraid that I would wind up stripping out the Ti spline shaft.
I am looking for a reasonable priced pair of E30 axles.

[Noneone2]

Just some food for thought, I've been considering a ratio change from stock 3.45 lsd to 3.25 lsd and have gathered all the pieces except the time.
I see Derek stating 33-34 mpg after a change to a 2.97. I am achieving solid high 33-35 mpg with the 3.45 lsd. So I'm wondering if this swap is worth the time.
There are factors to consider and to compare; (my DD) '97 w/ sunroof/ active pkg., most of my driving is a highway (I-95) commute (160 rndtrip), nearly flat Florida, cruise control @ 32-3300 rpm (approx 66-68 mph), tire pressure @ 36psi, (those oh so lovely but light) 15" 10 spoke Style 27 rims, if I have to cut the muggy humid S. Florida air with a knife I'll run the a/c. The only mods are a COP with stock plugs and my version of the "fogged" airbox with std. Mahle filter (no K&N here). Redline fluids in the gearbox and diff. Amsoil 5-40 Euro in the engine. I don't have rook racks or carry excess stuff. Stock suspension with Bilstein Sports, 19mm rear sway. I run mid-grade 89 fuel, Hess or Chevron.
There it is. Apples to apples, oranges to oranges. Just for comparisons. I, like others, would like to knock a few revs off the tach easing the torture on the engine and drivetrain even if it is only 2-300 rpms (more with a 2.97) for the sake of longevity and (maybe) some improved fuel economy.
At this point if your thoughts of a pure fuel economy improvement is the goal where time invested and the expense are possible factors it may not wash out. If like me you enjoy spinning wrenches for therapy and don't mind trying a little experimentation for real world results I say go for it BUT let the rest of us know what they are under what conditions. I believe there are other Ti drivers that are interested as well. If I choose to go ahead with a swap I will post after I have some numbers.
Derek and others, this is not in anyway meant as a negative. I think the sharing of info and help among the members/ visitors on this forum is huge. I personally have been helped out of a jam or two and saved from getting into a few as well.

[mtlblue]

excellent description of your conditions! help a lot to know these details of what's going on with your car. so many times people post with so little info that it's hard to give advice to.

myself I find the 3.45 short on take off, and was looking for a 3.25 locally to add to my parts collection.

now my question , and I have used the search without the right answer,
I have a 97 sport

does the Z3M 3.23 diff fit easy in our cars?

I would think so , and it would be a medium diff so I would need the e30 stuff for it to work, is this correct?

[Uber E30]

does the Z3M 3.23 diff fit easy in our cars?

I would think so , and it would be a medium diff so I would need the e30 stuff for it to work, is this correct?

Answer is yes to both.

[Noneone2]

If I choose to go ahead with the swap I'll be using an E28 3.25 lsd (on the shelf) E30 output flanges and refreshed axles. The Z3M 3.23 will work but may be a little harder to find. As Jess always reminds, "Don't forget to shim the sensors!"

[cooljess76]

Also, if you source a Z3 diff, it's gonna have Z3 output flanges which might have a different bolt pattern than e30 output flanges. Depending on length, you may or may not be able to use Z3 halfshafts. Otherwise, you'll need to run 6cyl e30 flanges and e30 halfshafts. I don't have much knowledge about Z3 halfshafts, but I'd imagine that they probably have larger ABS tone rings like the e30 halfshafts, so as Russ mentioned, you'll likely need to shim your ABS sensors.

[M-technik-3]

There are medium case 3.46 lsd in E28's and there are Viscous and non Viscous 3.64 and 2.79 in E30's as well.

E30's had a wide range of ratio's available.

[Uber E30]

For the OP's intended purposes none of the viscous diffs would work (only 3.64, 3.73, 3.91 and 4.10 ratios). Although as you mentioned there are a lot more diff ratios than I mentioned above, I was only talking about ratios better for highway MPG than the stock 318ti diff.

[M-technik-3]

Just mentioning the variety, others might read the thread and be going toward a high say 4.26 or 4.45 lsd. I sold my 4.45 out of a parts car to an E30 318Is guy to suit his track needs.

[mtlblue]

only asking about Z3M because a diff just showed up locally for sale, but without the cover. is 250$ a resonable price for this? adding some good e30 parts and a cover will probably end up over 500$ I guess. as far a rebuilding halfshafts, how much could this cost?
http://qc.kijiji.ca/c-autos-et-vehicules-pieces-auto-pneus-autres-pieces-et-accessoires-BMW-Z3-M-ROADSTER-DIFFERENCIEL-W0QQAdIdZ397477017

[cooljess76]

250 seems fair. You don't have to use a finned Z3 M cover. You can use a medium case e30 cover or a Z3 non M cover if you don't want to spend as much. The finned Z3 M covers can be pretty pricey and they tend to break fairly easily, but the do look really cool. You could probably pick up a medium case e30 cover at a junkyard for 10 bucks. As for rebuilding halfshafts, only use OEM halfshafts. Aftermarket halfshafts and the so called "refurbished" halfshafts that places like AutoZone, Napa, Orileys etc sell are absolute garbage. Either take a set of OEM halfshafts and have them rebuilt by a shop, or do them yourself. It's pretty easy to do, just a little messy. All you'll need is 2 inner cv boot kits, 2 outer cv boot kits, a roll of paper towels, a pair of snap ring pliers and a set of crimp clamping pliers. If you do it yourself, it'll cost about 50 bucks. I purchased my kits from pelican parts and IIRC I spent about 25 bucks per axle.

[M-technik-3]

Finned cases jumped insane amount money. They double in price over the last 7 years. I bought 3 of them in 2005 at 139 apiece now they are about 250 plus hardware.

Agree with Jess on the halfshaft repairs.

[Uber E30]

I would also say beyond aesthetics the finned cover isnt going to be worth it unless you are on the track a lot. I had one on the m3 and using a laser thermometer it only seemed to drop the temp about 1 deg F for normal conditions.

[jimmypet]

Hey Guys
Bumping this thread. I just want to ask a clarifying question or two.

I have an E30 Med case 2.97 diff that I wish to put into my Ti.
I had the car on the lift today but it looks clearly like a no go.
The stock diff is approx 9 1/2" wide flange to flange and the Med case is approx 11 3/4"

It does not look like this is fitting (which on E30s, the swap between small and Med case is a bolt in,,, the width is made up in the flanges).

Is my next step to get a set of E30 half shafts and replace the stock half shafts with the E30 units?

I see when that is done you need to shim the ABS sensor. Will do that.
Anything else that needs to be hunted down to finish this swap?

I saw this post:
As Uber E30 mentioned, You'll need e30 halfshafts and flange bolts/plates. Plus you'll need to shim your ABS sensors(I used a washer on each one to raise them about 1/16th-1/8th of an inch.

When you say halfshafts, "flanges and Bolts" I am assuming you mean the output flanges on the diff itself and the correct size for an Med Case socket head bolts to fasten the half shaft to the diff?
I am also assuming these half shafts will mate with the Ti trailing arms and hubs?

If one of you who have done it could clarify those points, I will get a set of E30 half shafts, bolts etc and finish this up.

Thanks for any insight any of you can extend.

Looking at it I cannot imagine how anyone would be able to just bolt in a Med Case diff to a Ti, there is a huge disparity in the width and the half shafts do not seem to allow it.

I am in the exact same situation as Noneone2 above.
I have about a 2:15 commute all highway each way,,, and I would like "another gear" to get it down from 3800 RPM once I reach a flat cruise.
I can cruise around 80 MPH,,,so thats got the little thing wound pretty tight for 2 hours.
I am currently getting 32 MPG
Car is 1998, base model, 160K miles, Ported airbox behind the headlight with stock filter, stock exhaust, stock tune, 16" Sport package wheels, and now will have COP.

If someone can help me with the recipe to get this 2.97 installed, I'll report back with a Apples - Apples comparison once I get it bolted in.

Thanks
jimmy p

[derek502]

[QUOTE=Noneone2;334859]Just some food for thought, I've been considering a ratio change from stock 3.45 lsd to 3.25 lsd and have gathered all the pieces except the time.
I see Derek stating 33-34 mpg after a change to a 2.97. I am achieving solid high 33-35 mpg with the 3.45 lsd. So I'm wondering if this swap is worth the time.

Derek drives 80+ and still gets 33-34 MPG. I slowed it down for a week and was able to get 36.

[spidertri]

Jimmy,

If you get the E30 med case axles and flanges you won't have any problems bolting it up. The E30 axles mate to the ti hubs.

Driveshaft bolts up fine but the E30 diff flanges are a larger diameter than the ti flanges so you'll want any of the hardware that is E30 specific, those half moon washers that go on two flange bolts come to mind.

I found a nylon washer at Advance Auto that was the perfect size for the ABS shim. I posted the part number in one of the threads on here.

One thing that is new since I did my diff swap is the diff stud conversion kit that bimmerdiffs.com sells. I would have loved to had those when I did the swap.

[jimmypet]

Jimmy,

If you get the E30 med case axles and flanges you won't have any problems bolting it up. The E30 axles mate to the ti hubs.

Driveshaft bolts up fine but the E30 diff flanges are a larger diameter than the ti flanges so you'll want any of the hardware that is E30 specific, those half moon washers that go on two flange bolts come to mind.

I found a nylon washer at Advance Auto that was the perfect size for the ABS shim. I posted the part number in one of the threads on here.

One thing that is new since I did my diff swap is the diff stud conversion kit that bimmerdiffs.com sells. I would have loved to had those when I did the swap.

Awesome, thanks for the confirmation Dave.
Much appreciated.
I have started converting all my E30M3 race diffs to studs,,, I didnt know about the bimmerdiff.com kit, I just bought the studs myself though a Metric fastener vendor. What a PITA that was. Its an odd thread pitch (M12 x 1.5 I think).
Fastenal, McMaster Carr, Maryland Metric, no one had them in the correct pitch.
I finally found them from a Metric vendor in CA.

Its a much better way. I bought enough to do the Ti as well. No sense in leaving that one out haha.
Thanks again very much for the conformation.
I will get a set of E30 Halfshafts and finish this project up.
I am pretty sure I have at least one spare set in my parts room now for the race car.

Cheers
jimmy

[SSpeedracer]

Derek drives 80+ and still gets 33-34 MPG. I slowed it down for a week and was able to get 36.[/QUOTE]

Curious if you are using the stock axles with a medium diff? Also what size tires? thanks

[jimmypet]

All,
I wanted to post a followup to my diff swap.
I finally did it this weekend, 2.97 diff, E30 Axles and new rear wheel bearings "while I was in there".

Fairly straight forward as most on here have posted.
I had one axle nut strip / spin on removal which turned into a real cave man operation to get one axle out,,, involving things like chisels, 5LB hammers, and a plasma cutter,,, but it came out haha. No longer useable as a core,,, but its out.

Reassembly went smooth,,, other than plugging in the speedo.
I had to drop the spare to get the speedo plug in, that was a slight PITA after I was feeling pretty much done with the job. I shimmed my ABS sensors out as directed here.
I measured the depth of the hole and the ABS sensor.
It didnt seem like I needed to, but I followed the wisdom here on the forum.

I think I may have bent a backing plate taking "out" the wheel bearings and hubs because I'm hearing a faint metallic rubbing, I'll put it back up and figure that one out tomorrow.

DRIVING IMPRESSION:
I did 240 Miles today with it on a commute I usually do when I have to visit our Philadelphia office.
Its not as "punchy" as it was with the 3.46. I have to admit as a compromise to sportiness and economy, BMW did hit it pretty close to the mark with the 3.46.
Its amazing how sporty that little 1.9 feels and still gets in the 30's MPG at high speeds.

Now, with the 2.97, you must wind the gears out a little more, but you do gain a gear basically,,, or should I say effectively.
4th now does pretty much exactly what 5th used to.
5th is almost now like a highway only OD.
I was cruising at a dead on 80MPH at 3,100 RPM on the tach. Pretty leisurely.
The very nice part of the 2.97 is if you want to punch it up to 90 for a bit if you have clear vision for police, you can with the engine now only revving where it used to at 75 MPH with the 3.46.

I am satisfied with the swap, for how cheap the E30 parts were to swap in, I think this swap is a no brainer. Even if the gas mileage is a wash and is no better due to throttle opening / engine loading and aero drag, I feel like its a win because I am saving hours of engine cruising at 700-800 RPM less. I think that adds up over the years in engine longevity.
I could be wrong, but I feel better about it.

I monitored my fuel usage on this trip and tracking it, I am on track to be equal or better than the 32-33 I was getting with the 3.46
In my use of my Ti, which is primarily highway focused, I think this is a good swap.

On a side note, I also see the abundance of cheap E30 Diffs and wide amount of available ratios in E30 / E28 Diffs to make this swap really a good idea.
If you hate it, there are loads of other ratios about $200 or under away and now you are set up to swap any of them in. Plus, E30 axles are plentiful used or refurbed.

Hope this helps someone down the road. Let me know if you have any questions.
Cheers
jimmy p

[SSpeedracer]

I monitored my fuel usage on this trip and tracking it, I am on track to be equal or better than the 32-33 I was getting with the 3.46
In my use of my Ti, which is primarily highway focused, I think this is a good swap.


Great update, thanks.
What size tire? With the 2.97 are you cruising at the same speed as you were with the 3.46? Curious how your new mileage works out and whether its a direct comparison at same MPH.

[jimmypet]

Yes, same speed, between 75-80 once I clear Philly traffic and hit open road.
Wheels & tires are stock Sport 16"s with I believe the stock size 205 tire.
Honestly I never verified if they are the correct tire size however.
They were brand new when I purchased the car from its PO.

I will update thread after a few more trips and tanks of gas.
Cheers
jimmy

[stevenwrichards]

Sorry to resurrect this thread but wondering about need to shim ABS sensors with Z3 diff and E30 ABS halfshafts. If the halfshafts fit without contacting sensors, am I alright or do I still have to shim for proper gapping? What is the ideal / factory gap between tone ring and sensor?

[jimmypet]

I doubt there is a published gap (BMW probably doesn't want us swapping this stuff around),,, but I went to try and maintain the factory gap.

If you compare the ABS wheel diameter you will see how much closer the E30 wheel comes to the Ti sensor. I think I just shimmed it out the difference in the diameter.