Rear diff and suspension mods for V8 swaps

[steel330i]

R3V Fam,

I’m interested to hear what everyone is running for their suspensions and rear diffs / axles/hubs on their swapped e30’s? I’m planning mine out now and currently have a running donor 98 SS with LS1/T56 and the Sikky kit for install. But my 91 318i is bone stock otherwise and original so needs everything to be replaced (e.g. bushings, FCAs, brakes, etc.).

I also picked up the Garagistic weld on reinforcement kit and a spare z3 full suspension from a junkyard but. It sure what I can use from it in this build.

Thank you for any replies and suggestions!

-Travis


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[varg]

How hard on it are you going to be? I'd reinforce it everywhere that is practical if you're going to be hard on it, instant Vee-Ate torque imposes a lot of shock load. It definitely needs a 188mm diff and quality axles, a second diff mount. I'm curious what the V8 guys will have to say about this because I was once told by an acquaintance that he has friend with a V8 E30 which went through several 188mm diffs. I strongly suspect this person may have been of questionable intelligence, powering through wheel hop and such.

[tyeler18]

I'm still on a stock rear end in my 318IS other than a 188mm 3.73LSD. My small case 4.10 lived no issue behind my LS1 also but that was probably because it had zero traction. I ripped the stock 150k diff bushing out 2 weeks in after the swap and I replaced the subframe bushings with condor bushings because they were toast at 150k also, Still on original control arm bushings, original axles and a single diff mount. Im on 245 R-compound tires and regularly road race and have done some drag events and plenty of street abuse. No reinforcements or anything done. *Car makes 390/390*

[e30davie]

A guy I know with a ~600hp 1jz in his e30 put in a large case differential from a 7 series i think. big dog of a diff. shoe horned it in on the standard sub frame (lots of cutting and welding of things) seems to be holding up pretty well.

[Northern]

Local guy with a 5.3, cam, and LSA supercharger ran a built 188 2.93 and didn't grenade it while beating it relentlessly.

Big difference in pinion size between higher and lower ratio 188s too.

[steel330i]

Thanks all! So I have a z3 diff (not sure in ratio but is LSD) and that is a 188mm? Will it bolt in? What are considered “good “ axels? Are there combos that I need to have picked out for this to work on my stock e30 subframe?

I have the Garagistic reinforcement kit but not access to a good welder…also I'm willing to wear the badge of “bought not built” but not for things are unnecessary… so I'm looking at good brakes and rotors, new fluid, and work the calipers…suspension refresh regardless, and finally good tires.

What am I missing to essentially just get it driving reliably? No intent today to auto x or drag just street and commute some this summer


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[jbontke]

Thanks all! So I have a z3 diff (not sure in ratio but is LSD) and that is a 188mm? Will it bolt in? What are considered “good “ axels? Are there combos that I need to have picked out for this to work on my stock e30 subframe?

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Z3 diff is a direct fit, don't use z3 axles, they are longer from what I understand. Use BMW axle parts. Oem axles are "good" axles, the ones with the bamboo knot in them. Quoted from the member Forced Firebird "Look for GKN or Lobro stamped onto the CV. Also, the OEM shaft will have the "bamboo knot" in the center. GKN replacement shafts are the same diameter through, but are as thick as the "knot" on the OE shafts"

[steel330i]

So I opted for the oem e30 axles… z4 hubs (rear) to support the 5 lug swap and bought a z3 S3.46 LSD differential. I’ll post pics of final assembly once it’s a in with the new bushings as well

[steel330i]

Having issues getting the OEM bushings out of the diff and rear subframe and RTABs… any tips aside from using a press?


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[bangn]

easy mate, get yourself a decent butane gun or blow torch. Heat the rubber up til they catch fire (rubber will melt) and you can smack them out with big socket and extension or a large punch of sorts. Pretty easy job and tbh I actually had a big of fun doing it.. because hey; setting shit on fire. They will come out easy when hot enough

for install of new bushes you can either lube them up dishwashing soap and smack them in with a large deadblow (what I did) or get a long bolt with big load washer either side thats wider than the hole and tighten the assembly to pull them back through the hole.

[steel330i]

Damn… didn't even consider heating them up… thanks for that

Cheers!


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[bangn]

yeh make sure they're properly on fire like a marshmallow

[Panici]

While it doesn't deliver the instant torque of a V8, my boosted M52 scoots pretty good.
I was getting brutal wheel hop when boost came on with the stock rear end setup. I was afraid something would break with the repeated shock loading as the tires gained and lost traction.

I spent last winter reinforcing and upgrading.
Didn't want stiffer bushings then necessary, but recognized that stock rubber wouldn't control the axle/suspension movement in some spots. Went with the softest Poly option I could find.

My theory is that eliminating the oscillation without hard mounting components will help to damp the forces and not just transfer them directly to the chassis or components resulting in breaks.

Still have a bit of hop, but it's controlled enough now that I'm comfortable powering-through. I have a lot of mechanical sympathy, so that's saying something.

• Weld-in reinforcements for Differential Mount Point, Rear Shocks, Trailing Arms
• Garagistic Secondary Diff Mount
• RaceGerman HD Differential Stud Kit
• Revshift 80A Polyurethane Differential, Subframe, Trailing Arm Bushings.
• Outer subframe trailing arm mounts reinforced/welded.
• 19mm ST Suspensions Rear Swaybar with boxed/reinforced chassis mounts.
• HDT Automotive Upgraded Driveshaft w/1310 Spicer U-Joints

Went beyond the off-the-shelf trailing arm reinforcement kit, and made some custom pieces to box in the rear shock mounts.
Hoping to transfer the force to the shock as directly as possible so it can do it's job.
Also, the trailing arm side should be beefy enough now for true rear coilovers if I go that route down the road.


There's a bunch more pics in my build thread (Post 443 onwards).

[steel330i]

While it doesn't deliver the instant torque of a V8, my boosted M52 scoots pretty good.
I was getting brutal wheel hop when boost came on with the stock rear end setup. I was afraid something would break with the repeated shock loading as the tires gained and lost traction.

I spent last winter reinforcing and upgrading.
Didn't want stiffer bushings then necessary, but recognized that stock rubber wouldn't control the axle/suspension movement in some spots. Went with the softest Poly option I could find.

My theory is that eliminating the oscillation without hard mounting components will help to damp the forces and not just transfer them directly to the chassis or components resulting in breaks.

Still have a bit of hop, but it's controlled enough now that I'm comfortable powering-through. I have a lot of mechanical sympathy, so that's saying something.

• Weld-in reinforcements for Differential Mount Point, Rear Shocks, Trailing Arms
• Garagistic Secondary Diff Mount
• RaceGerman HD Differential Stud Kit
• Revshift 80A Polyurethane Differential, Subframe, Trailing Arm Bushings.
• Outer subframe trailing arm mounts reinforced/welded.
• 19mm ST Suspensions Rear Swaybar with boxed/reinforced chassis mounts.
• HDT Automotive Upgraded Driveshaft w/1310 Spicer U-Joints

Went beyond the off-the-shelf trailing arm reinforcement kit, and made some custom pieces to box in the rear shock mounts.
Hoping to transfer the force to the shock as directly as possible so it can do it's job.
Also, the trailing arm side should be beefy enough now for true rear coilovers if I go that route down the road.


There's a bunch more pics in my build thread (Post 443 onwards).

Panici thanks for that insight and list… so far I'm installing the following:

Garagistic 80A(Red motor, subframe, RTABs, Centered Diff mounts)

OEM Front and Rear Sway bar bushings

Oem sway bars

Garagistic F/R Strut Bars

CAtuned 5 Lug Coilovers

CAtuned suspension hardware kit (10.8)

OEM axles

Z3 S3.46 LSD (Torsen)

5 lug swap with e36 brakes

Once I'm driving I'll reassess the reinforcements but I did buy the Garagistic kit for the rear end minus sway bar reinforcement

Thanks again!

Any noticeable improvement in the steering or front end action after you addressed the wheel hop?


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[Panici]

Thanks for that insight and list.

Any noticeable improvement in the steering or front end action after you addressed the wheel hop?

You're welcome!

Front end feels pretty dialed now, but I don't think any of that was due to the changes I made in the rear. I did upgrade to a 22mm ST Suspensions Front Swaybar (at the same time I upgraded the rear bar).
Actually, wish I would have gone a little thicker with the front bar as my springs are quite soft.
The rest of the front end I had already addressed previous to this.

I'm running a Z3 steering rack (2.7 turns lock-to-lock), 370mm diameter M-Tech I steering wheel, Lemförder E30 M3 Offset Control Arm Bushings, H&R Sport Springs (w/ 1/4 inactive coil cut from front), Bilstein Sport Dampers (w/ cut front internal bumpstops), AKG Front Swaybar Reinforcement Plates, E90 Drop Hats (10-15mm drop), 318i Thinner Front Spring Pads (6mm drop), Lemförder LCAs.