6CYL Swap "The Real Truth"

[Dredder]

Well I have been researching the 6cyl differential swap for quite sometime now. There's a lot of misinformation about this topic. I have spoken to a few people that have done this swap personally and the answer was still the same. Well, I finally decided to prove myself and other that this swap is not as difficult as people try to make it out to be.

Here's the truth:
3.25 LSD from 5 series
Output flanges from 318ti is direct bolton to 6cyl differential. This way you no longer need to construct a hybrid axles as stated in the notebook section.


http://www.318ti.org/gallery/data/531/medium/IMG_0481.jpg
Output flanges 318ti left Vs. 6cyl right.
As you can see the 318ti extra seal. 6cyl is a little longer not by much maybe less than 1/4"

http://www.318ti.org/gallery/data/531/medium/IMG_0483.jpg
318ti output flanges fully assembled into 6cyl differential. Notice the 6CYl output flanges for comparison

http://www.318ti.org/gallery/data/531/medium/IMG_0484.jpg
318ti output flanges fully assembled sideview closeup

http://www.318ti.org/gallery/data/531/medium/IMG_0482.jpg
6cyl output flanges still intact. Notice the seal. Its as secure as the 318ti output flanges see above.

[Dredder]

Ill make a write up once i get my mcoupe cover.

[96cali]

nice! thanks dredder.

[aceyx]

318ti LEFT, 6cyl RIGHT?

[Dredder]

right...

[hellrot332ti]

I think i spoke with you on B.F c about this. I have the 3:73 LSD and i actually had to change my rear end in my apartment complex parking lot. Its real easy. Dont even have to remove a wheel or the axles. I too just popped the Ti axle input flanges into the 6 cylinder diff. Since the 6 cylinder diff is physically larger it taked some ingenuity (hammer) to get it in. Works great though and i love it.

[Dredder]

I too just popped the Ti axle input flanges into the 6 cylinder diff. Are you talking about image number#1 or image number#2 (4bolt patern - upper top left).

I recall talking to you on BFC and Kiley_sean in this forum. If I'm right, All i need to do is swap the output flanges from 318ti to 6cyl differential and Im good as gold.

[L84THSKY]

I've got my 3.45LSD with M-coupe cover waiting for install. I would appreciate the naked truth on what the install will be like. Too many people have said too many confusing comments.

Ill make a write up once i get my mcoupe cover.

[Dredder]

I've got my 3.45LSD with M-coupe cover waiting for install. I would appreciate the naked truth on what the install will be like. Too many people have said too many confusing comments.Will do. Im in the same boat as you are L8. From the people I've talk to all they did was swap flanges and its a direct bolt on. From my experience so far, it looks like they are right. Everything is going as planned. I will document everthing down to the last bolt.

[GDB]

so no cutting is required?

[Dredder]

so no cutting is required?
So far. But the size of 6cyl requires pounding the underbelly where the diff sits. The 6cyl is just a little larger. Shouldn't be too much

[hellrot332ti]

Yeah it looks like it isnt gonna fit when you bolt it up. Jack it up with a floor jack in place, put your bolts in the driveshaft and then start the 2 front bolts(towards front of car) Now lift it up and you will see that it hits the underbelly of the car before the diff cover mount bolt lines up. You must beat about a 3\4 inch deep dent in the floor of the trunk. Keep jacking it up unitl the diff cover bolt lines up an hit it thru with a hammer. Now put the 2 rear bolts in and bolt up the axles. Tighten everything up and youre ready to go. Took me about an hour in the parking lot of my apartment. The beating of the dent took the longest. Looking forward to a write up and pics from dredder.

[L84THSKY]

I agree about the inner portion of the flanges both seating the same depth. What I wanna see is how much width is lost flange face to flange face of the entire diff. Even in your pics, you can see how the 318ti flange sits deeper, from the outside view. That extra depth is going to leave a gap from flange to CV joint, when you attempt to bolt the halfshafts on.

Will do. Im in the same boat as you are L8. From the people I've talk to all they did was swap flanges and its a direct bolt on. From my experience so far, it looks like they are right. Everything is going as planned. I will document everthing down to the last bolt.

[hellrot332ti]

I agree about the inner portion of the flanges both seating the same depth. What I wanna see is how much width is lost flange face to flange face of the entire diff. Even in your pics, you can see how the 318ti flange sits deeper, from the outside view. That extra depth is going to leave a gap from flange to CV joint, when you attempt to bolt the halfshafts on.

You have to remember that the 6cyl diff is physichally larger than the stock unit. Its so much bigger that it doesnt look like it will fit and your stock rear cover is also alot smaller. This actually makes its a tighter fit between the CV and the flange. So tight that you have to start the edge of the CV against the flange and kinda roll it on.

[Dredder]

You have to remember that the 6cyl diff is physichally larger than the stock unit. Its so much bigger that it doesnt look like it will fit and your stock rear cover is also alot smaller. This actually makes its a tighter fit between the CV and the flange. So tight that you have to start the edge of the CV against the flange and kinda roll it on.
Thanks for the advice.....My diff cover probably wont get here until next week sometime, busy with the holiday season. Once its here maybe I'll find sometime to get it installed.


p.s. "F.Y.I. this differential upgrade was not required when I had my 6cyl engine installed. The stock differential is still going strong after 10k+ of driver the car hard. The only negative with stock diff is it revs high in the freeway."

[hellrot332ti]

I had an open stock diff and it last about 2 years before it broke. Mine broke on the drag strip so depending on your driving styles the 4 banger diff. could last forever.

[aceyx]

Where was the fault point?

[hellrot332ti]

Where was the fault point?

Well i broke about 4 teeth off of the input shaft that meshes with the ring and pinion, coming from the driveshaft. It just wasnt made to handle the torque i guess..

[tctwnd]

is swapping the flanges difficult?

[jdehaan]

so if the stock TI diff could potentially last for quite a while, what are the advantages of going to an Mroadster diff, besides the eventuality that it will fail if given enough time and hard driving. What are the performance advantages? Also, how much should a quality, used Mroadster diff cost?

[J!m]

It will break, and typically at the worst time, regardless of driving style.

Ben Liaw broke his at a stop light. He wasn't racing, just trying to move when the light turned green. No warning either- no noise, nothing.

If you plan to always be walking distance from home (you should be walking, not driving in this case...) you are fine. Also invest in AAA for the tow you will need.

When (not if) it fails, there may likely be zero warning of the failure, and no logical reason for the failure. Obviously, racing (particularly drag racing) will speed-up the diff failure, but simple street driving will take its toll.

[Hawkster]

So will a diff out of an E36 M3 coupe fit? I've got one in the bed of my truck... so if it will... I might not sell it...

[stormos]

won't fit.

[jdehaan]

What about an M Roadster, or an E30 M3. Which one is best?

[cali-ti]

What about an M Roadster, or an E30 M3. Which one is best?
i'm assuming you're talking about the diffs. believe the m-roadster/m-coupe are 3.23 and the e30 m3 is 4.10. there were m-coupe/roadster guys installing e30 3.73 LSDs into their cars even, but it really depends on what you're hoping to achieve, faster accel times or nice highway cruising rpms or what?

[racepad]

I recently purchased a complete rear end from a M Roadster and was led to believe that basically the whole thing was a bolt in into the ti. Ugh - no way. I was going to do the job myself but decided to farm it out to Turner Motorsport as I am in the midst of relocating. Here is what works and does not. The carrier will bolt up, the diff flange was 4 bolt and it mates with the drive shaft. Well that is about it. The brake lines come out at a different angle on the M3 brakes so custom lines had to be built and other lines from an E30 M3 used. The brackes on the carrier for the lines had to be removed and the old ones moved over to the new carrier. The Diff does not fit and some body work had to be completed. The old diff support removed and a new one fabricated and welded on to the body. The wheel base is now wider but that will create some wheel fitment issues for me (235x40x17 SSR Comps withYokohama AVS tires). May have to now have the rear fenders rolled. We stayed with the old sway bar as the roadster one required larger bushing mounts. This would have required cutting the stock ones off, fabricating new ones to fit the wider M roadster rear sway bar. When I get the car back in a few weeks I will share more.

[J!m]

I recently purchased a complete rear end from a M Roadster and was led to believe that basically the whole thing was a bolt in into the ti. Ugh - no way. I was going to do the job myself but decided to farm it out to Turner Motorsport as I am in the midst of relocating. Here is what works and does not. The carrier will bolt up, the diff flange was 4 bolt and it mates with the drive shaft. Well that is about it. The brake lines come out at a different angle on the M3 brakes so custom lines had to be built and other lines from an E30 M3 used. The brackes on the carrier for the lines had to be removed and the old ones moved over to the new carrier. The Diff does not fit and some body work had to be completed. The old diff support removed and a new one fabricated and welded on to the body. The wheel base is now wider but that will create some wheel fitment issues for me (235x40x17 SSR Comps withYokohama AVS tires). May have to now have the rear fenders rolled. We stayed with the old sway bar as the roadster one required larger bushing mounts. This would have required cutting the stock ones off, fabricating new ones to fit the wider M roadster rear sway bar. When I get the car back in a few weeks I will share more.

WOW. What did you do? you said you had the entire thing, but obviously you did not. I have to chime in as I have said (and done myself) this is easier than swapping the diff. You have dug yourself a deep hole there. I hope you have not cut anything, because the ENTIRE assembly DOES bolt right in (look under my car anytime). If you mix-n-match parts, you have problems, as I have said several times over now.


The diff fits the stock ti mounting locations; no cutting needed
The sway bar simply needs new bushings and bushing mounts; no cutting needed
I have fit 275-40/17's on M3 8.5 rear wheels with a 1/4 lip roll, 245-17s fit perfect, 265-17s (on my car now) fit with slight roll. Your SSR offset may be incorrect for the car.
Brake lines need to be modified; however the stock lines can be cut and re-flared to fit as I did, and the mounts do need to be moved; however the holes are pre-drilled for them on the M roadster sub-frame
Parking brake cable will not fit on the roadster locations, so large zip-ties are used to hold them to the tailing arms