Stronger diffs in E21 without E28 axle?

[PowerKraut]

Hey guys,

i recently rescued an E21 323i from the scrap yard.
I will swap a stronger engine in it and plan to swap my E34 LSD in it, for more reliability. I
know that some People use an E28 axle to make the larger diffs fit, but i really dont want to cut and weld the Chassis, as it is kinda rare nowadays in Germany to find a genuine E21 323i.

Is there a way to make the stock diff more reliable, like with stronger gears or something, or could i modify the stock E21 axle to make the E34 diffs fit?

Thanks and greetings from Germany
Max

[amarino]

Looks like the pictures are broken. https://www.bmw2002faq.com/articles....tial-build-r74

Sent from my Nexus 5X using Tapatalk

[PowerKraut]

Thanks. It's a shame that the pics are broken :'(

I'm not sure if the E36 318 diff would be up to the task tbh. The engine should be in the 300-400nm (220-300 ft lbs) tourqe range. :/ Thats why i would really appreciate to toss my E34 diff in.

[OLD MAN]

In our experience with are track 320/6 with a built 2.5 m20 in it now, the stock diff seems to hold up.

You need to keep in mind that to break a diff you have to have lots of power but more so LOTS of traction. So until you redesign the rear suspension and make it want to pull wheelies the only thing lots of power will do is spin the tires more.

We have broken a couple of half shafts while auto crossing the track car - and my past days of drag racing big heavy American muscle says drive shafts tend to be the weak link in most drive trains.

So I personally would freshen up the stock parts and call it good and save a lot of fab work.

[PowerKraut]

Hi there old man. read your entire build thread just this morning. awesome work. you know, the only thing that keeps me from turning up the boost in my upcoming E21 build is the weak drivetrain of the car... for the first few steps i want to limit the power to maybe 250-300hp.. but the setup is capable of way more, as i will swap almost the entire setup of my e34 turbo in the e21. i am lookin for a 5-6 pounds per horsepower car when i'm done. drag is one of the things that i want to compete in, but most of the time its going to be a sleeper sunday car.

i've seen even stock M30B35 setups kill diffs in the E21 :/ i do not think that my diff will last to long when i turn up the boost.

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Motorraum2.jpg

[Somjuan]

You put a boosted m50 in and you're afraid of a little subframe welding? If you're that concerned about keeping the rear subframe stock pull it out and replace it with a modified 320i one. There are way more options for an LSD with that subframe anyway.

What transmission are you using?

And worth noting, but is your brake system stock? Because that would be my priority after the subframe swap, bigger better brakes.

[PowerKraut]

You put a boosted m50 in and you're afraid of a little subframe welding? If you're that concerned about keeping the rear subframe stock pull it out and replace it with a modified 320i one. There are way more options for an LSD with that subframe anyway.

Hey there, i am not afraid at all. welding the axle is one of the mods i consider. I do not want to weld the chassis. The thing is: is there a proper way to make the big diffs fit, with just modding the axle of the E21, without cutting the chassis? Problem is, if german TÜV inspection finds out that anything on the rear axle or suspension is modded DIY-style there is no way to pass that inspection... they are the only thing i am afraid of, not the modding itself.

What transmission are you using?

Got several transmissions to go with. Stock E21 323i 5-Speed or a few E34 5-Speeds.

s your brake system stock?

Hell no. Thats what i got so far: 4-Piston 745i E23 calipers + E34 302mm vented rotors on the front. I got a few parts for the rear. maybe E34 300mm discs + E34 caliper.. God knows... The car needs a full rebuild anyways.

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m20b23_2.jpge21.jpg

[amarino]

The thing is: is there a proper way to make the big diffs fit, with just modding the axle of the E21, without cutting the chassis? Problem is, if german TÜV inspection finds out that anything on the rear axle or suspension is modded DIY-style there is no way to pass that inspection... they are the only thing i am afraid of, not the modding itself.

Ski made it look really easy. You can take the E28 subframe, cut the ends off your E21 subframe and weld them onto your E28 subframe.

First you need this beccause photobucket: https://chrome.google.com/webstore/d...flicjjgj?hl=en

And here: https://www.bimmerforums.com/forum/s...1#post23446761

[Somjuan]

Dunno why I said 320i and not e28, still waking up I suppose. Ski did have to move the rear strut tower bolt points a few millimeters if I remember right.

If safety inspection is a thing, I'd take a 1982 or earlier e28 rear subframe because it lacks the dogbones like the e21 subframe which might get noticed. The only 'chassis' modification you'll need is the differential mounting point bracket. If you think you can get away with it, absolutely keep the dogbones from a post '82 e28. I forget what his final solution for mounting a rear swaybar was though, there's a lot to interfere with one back there

That motor swap is actually my plan for my car, I scavenged up some e34 m5 brakes as well. Five lug conversion means big brakes and tastefully larger wheels, just watch the offset change. The rear'll widen to needing et46 or so. On top of that you could take e32(?) trailing arms with bearings instead of those awful rubber bushings. I'd love to pick your brain on how you shoehorned that m50 in with enough space for a turbo.

Sorry if I came off rude, just re-read my other post. Coffee was needed

[PowerKraut]

I'd love to pick your brain on how you shoehorned that m50 in with enough space for a turbo.

Really? I did not test fit the M50 yet (without Header), but i dont think it will be to hard on a LHD car. :P

Sorry if I came off rude, just re-read my other post. Coffee was needed

Did not seem rude to me.

[jaredmac11]

How was it getting those e34 calipers in? I'd like to consider a brake upgrade in the future at some point.

[Layne]

The old way to do it (Alpina did this, so it may be TUV approved somehow?) is to use a side loader diff from an E12, E9, E3, etc. You have to cut and weld the E21 subframe. A place in the UK called Fritz Bits used to sell the part you need to weld in, they may still have it. The side loader has the unique advantage of being exactly the same width as the E21 diff, and it bolts right up to the axles and driveshaft. No newer diff can do that. The problem is the side loader is hard to find in LSD, and only comes in a few ratios.

[PowerKraut]

How was it getting those e34 calipers in? I'd like to consider a brake upgrade in the future at some point.

I really dont know, those are just future plans i got. Not even tried to fit them in yet. I'll try to use as many parts of my E34 M50-turbo on the E21 cause i already got them and suspension and brakes on the E34 just got like 300 miles of very easy test driving on them. At the moment the E21 is just a rusty brick on a worn out suspension and no drivetrain in it.

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The side loader has the unique advantage of being exactly the same width as the E21 diff, and it bolts right up to the axles and driveshaft. No newer diff can do that. The problem is the side loader is hard to find in LSD, and only comes in a few ratios.

Whats side loader supposed to mean? Read that quite a few time when i googled for pieces of information. I dont really have to find a LSD. would be awesome, but yet not the highest priority.

[amarino]

I just realized I did not read the title that said "without E28 axle". My bad.

[Layne]

Whats side loader supposed to mean? Read that quite a few time when i googled for pieces of information. I dont really have to find a LSD. would be awesome, but yet not the highest priority.

The gears are installed from the side instead of the rear. Just a way of describing that particular diff. It's a 210mm ring gear, so equivalent to the 'large case' used on E32 and M5, M6, etc.

[cgifool]

Sideloader Porn

(BMW Group 5 320 differential)

group5diff.jpg

[OLD MAN]

Hi there old man. read your entire build thread just this morning. awesome work. you know, the only thing that keeps me from turning up the boost in my upcoming E21 build is the weak drivetrain of the car... for the first few steps i want to limit the power to maybe 250-300hp.. but the setup is capable of way more, as i will swap almost the entire setup of my e34 turbo in the e21. i am lookin for a 5-6 pounds per horsepower car when i'm done. drag is one of the things that i want to compete in, but most of the time its going to be a sleeper sunday car.

i've seen even stock M30B35 setups kill diffs in the E21 :/ i do not think that my diff will last to long when i turn up the boost.

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Motorraum2.jpg

Our current engine is putting out 183hp at the wheels so at the crank it should be over 210 or so. If you really want to be fast and get the car to hook up at the drags - a ford 9" swap should be on your wish list!

I played at / with drag racing some - this was a burnout contest.

Smoking for forums 2.jpg

[PowerKraut]

Our current engine is putting out 183hp at the wheels so at the crank it should be over 210 or so. If you really want to be fast and get the car to hook up at the drags - a ford 9" swap should be on your wish list!

I like the idea, but there is no way to pass the german inspections with a swapped axle, other than plug and Play. I consider modding & welding the e21 stock axle to accept 188 or 210 diffs and make it look stock. guess thats my only Chance to (illegally) pass inspection and get my ride roadworthy. I also like the idea of that Ford axle, but there is no way to get Ford parts easy and cheap in Germany.. and i guess a rigid axle total crap when it Comes to cornering. the car will be 99% road used and 1% Slalom / drag / drift. So all the racing is just for fun.

The side loader diffs look promising as well, but as i got to modify the axles as well to fit them, i could rather stick with a usual "modern" 188/210 diff, or did i mistake it?


thanks so far guys, nice ideas and knowledge over here <3

[autox320]

A 300hp turbo 6 with fat torque curve and drag launches will eventually kill a small case diff. True tires play a big role in that with how much grip to break something. Maybe choose crappy street tires and you won't break anything. Soon as slicks are involved it's rolling dice. I've seen V8 LS swaps get away with a small case for awhile, but eventually end with kaboom. You'll want a built med or large case if keeping BMW. Live axle would be best for drag, and yes a live axle can be made decent for corners ie 4 link or panhard bar setup. Sounds like your going to have to fab something nice that looks stock for a stealth inspection. If enough fab just use a E36 diff like the motor came from.

[PowerKraut]

Sounds like your going to have to fab something nice that looks stock for a stealth inspection. If enough fab just use a E36 diff like the motor came from.

That's the best Option so far, i guess.. I will have to take the axles out of my E34 and E21 and compare them and then make a decision. Does anyone know if the flanges on the diffs are the same at small, medium and large case diffs, or at least interchangeable? I would Keep the stock E21 cardan shaft, if possible.