Blew up my diff - options?

[SLEEPYDUB]

Whats up guys. Before you tell me to search, know that I have, Ive gotten some good information, but my specific situation is just a tad out of the ordinary.

I have got an E30 with a 2JZ & R154 tranny along with a 3.73 LSD out of a 325i making around 500+whp. Last night I blew up something in the rear-end. All fingers point to the diff, or ring gear. When I try to take off in 1st, the driveshaft spins, but the car doesn't move. You can hear some crazy shit going on inside the diff housing though haha.

This car is a drift car, with occasional roll race use (only when someones ego needs to be shattered). Doesnt see much drag racing use, I may hit up the strip just for shits and giggles, but probably not.

My 2nd gear goes to around 70mph, and my 3rd cuts out around 110mph. This is on a 205/55/16 (yea I know, free tires are very small). The diff broke on 245/50/16 Nitto 555R.

I have 2 questions.
1) If I go to a 4.10 from a 3.73, how drastic of a difference will I actually notice? Would that be too short to still hit 60mph in 2nd and 100mph in 3rd? Im assuming my gears seem so long due to the higher revving of the 2JZ accompanied by the gear length of the Transmission.

2) How bad am I going to blow up axles with a welded? I have 325i axle shafts.
My main concern is how much shorter the gears will be. The turbo is pretty laggy, and Im sure the lower gear is going to help with spool time so thats an added benefit, but I just dont want to hurt myself more than help.

Input would be great

[Wanganstyle]

R154 trans is the MK3 item; the TRD MK3 group A final drive was 3.90. I ran a 3.90 with 2JZGTE BPU setup with w58 (a touch shorter gearing than R154), it matched pretty nicely.


Are you running a APU single turbo setup? gt35R or T04Z size of turbo?

the R154 is happy with anything from 3.23-4.27; 4.27 would be on the tight track side - 3.23 would be on the wangan run side of things.

Welded diff is fun, the fuse will be the 86mm cv's of the e30 native axels.



Post some photos of the diff and its broken pieces when you get around to tearing it out!

[thebutterson]

If you're staying with a BMW diff, a 4.10 will be more likely to break. As the ratios get smaller the amount of torque they can hangle gets higher.

[atmobenzin]

If you're staying with a BMW diff, a 4.10 will be more likely to break. As the ratios get smaller the amount of torque they can hangle gets higher.

That is not true.

[Roysneon]

I don't follow that logic, either. You hear more about 4.10's and 4.27's blowing because they are most likely to be small case diffs.

[thebutterson]

Check this out, they have recommended torque ratings for each ratio for each size diff.

http://www.metricmechanic.com/pdfs/metric-mechanic-differential-booklet.pdf

The whole point of increasing the ratio is to put more torque out to the wheels. The higher the ratio, the faster you will be exceed the stress the material can withstand before failure. The PO already said he blew up his 3.73, if it was due to a pinion or ring gear failure I'm not sure how increasing the ratio is going to help.

[SLEEPYDUB]

Is it possible to put a 4.10 ring and pinion and welded diff in the medium case?

I have a small case 4.10 with a welded, and a 3.73 LSD. But I'd rather use the larger case. Will that work?

[bmwguy325is]

http://www.grimmjeeper.com/gears.html

To answer your MPH ratio questions.

[Wanganstyle]

Is it possible to put a 4.10 ring and pinion and welded diff in the medium case?

I have a small case 4.10 with a welded, and a 3.73 LSD. But I'd rather use the larger case. Will that work?

168mm ring gear + 2jz and any amount of boost = shattered ring and pinion. The 168mm unit will also not at all fit in the 188mm case. Sorry :(

I don't follow that logic, either. You hear more about 4.10's and 4.27's blowing because they are most likely to be small case diffs.

all ratios of 168mm small case diffs are prone to top cap implosion and ring and pinion failure from torque/shock stress.

There are plenty of 188mm medium case 4.10 and 4.27 and 4.45 ratios being ran in competition bmw's. They do not blow up because they are weak, they blow up from wheel to wheel impact; Just built a unit for a world challenge chassis that got hit mid corner and destroyed a rear corner of the car. When a wheel gets impacted the ring gear stops instantly. Shock stress from twin/triple plate clutch and heavy duty chassis/driveline is also not very diff friendly at all.


If you look to the root logic of gear multiplier you will see that the higher number ratios have more teeth in the same space confines; a 3.64 ratio 188mm will be stronger than a 4.27 ratio 188mm.

If you're staying with a BMW diff, a 4.10 will be more likely to break. As the ratios get smaller the amount of torque they can hangle gets higher.

Yeap. on the dot

[_r2h]

That MM pdf is a great read.