R180 limits and failures

[theczechone]

So, I've been working on swapping my 240z with a rb25det. My target power is 350-400hp and torque around the same.

I don't quite have the funds to upgrade the diff yet so I've just rebuilt the 3.7:1 R180 (open) I currently have.

I've been loosing sleep over what will happen if it fails.

So I guess I have two questions.

What's the limit of the R180?

What's going to happen when it fails?

 

Appreciate the input.

[Neverdone]

Aren't the stub axles the most common point of failure?

[mtnickel]

I haven't been in the game long, but I'd think the U-joints in the side shafts are more likely to give out. I thought I'd be fine with them, but when I started putting down 280-300whp in my RB25 I blew one. Luckily it didn't completely shear, but instead clunk around like crazy. If there's one bit of advice, it would be to never launch the car hard, no burnouts, not hard 2nd/3rd gear shifts to try and chirp the tires, etc. Really limit the shock load you put into the system and it will go a long way.

If the diff itself fails (ring gear or pinion) you'll just be stranded and need a tow. If one of the half shafts fails it can spin around like crazy and muck about some of the sheet metal and perhaps your lower control arm, brake lines, etc. That's only if it completely shears on the wheel side. If it shears up top by the diff, probably be minimal damage.

But as I said, drive it smoothly and you'll probably be fine.

[seattlejester]

I think it goes ring gear, stub axle, half shafts if memory serves. 

 

If you break teeth on the ring and pinion then best case scenario it is going to miss those teeth and act like an impact where it will grab suddenly when it encounters better teeth, more likely will be the broken teeth will jam the gears causing it to seize. If you aren't moving when it happens, then no big deal, car just won't move. 

 

If you break a stub axle then the only thing holding your wheel on (if you still have stock drums) is gone. Your wheel will most likely leave the car. This is more of an issue with the 240z as it has the smaller 25 spline compared to the 27 spline of the 280z, not that the 27 spline is the definitive solution, but it does have more meat on it.

 

If you break a half shaft, best case is as mtnickel says it still stays attached, but has a ton of play as the caps basically blew out with all the bearings falling out in short order. Worst case scenario it actually separates completely and whips around hitting arms, lines, body panels.

 

If you slip the clutch quite a bit and use the clutch disk as a bleed off then you probably won't have too much trouble, like mtnickel said it is the shock loads that will destroy parts. I ran the stock half shafts and the 25 spline stub axles for a few hundred miles behind my 7mgte putting out maybe 300tq for a while. I had a stock clutch that I slipped a bit to prevent wear on the drive line components, even with a few hardish gear shifts in the wet, nothing let go on me, but I pulled that for a 280zx turbo/280z stub axle swap as soon as I could. 

 

I think Johnc said he had 275ft lbs put through an R180 for a while, his concern was the heat generated from abuse at that level. He didn't recommend me putting more then 300ft lbs through an STI R180. 

[jacky4566]

The weak point in an R180 and an R200 are the spider gears. Most R180s have two spider gears and these diffs have a torque limit of about 250 ft. lbs. Dragstrip launches tend to break these diffs. If you replace the centers with a Quaife, Torsen, or Nismo LSD then the diff is strengthened considerably.

 

Its Torque that breaks stuff not HP.

 

EDIT: Just as reference there are drift cars that push 600ft-lb through welded R180's dunno how long they last though. 

Edited December 5, 2016 by jacky4566

[theczechone]

I know to be cautious. My 3.1L stroker broke a half shaft u-joint. While I was trying to "launch" it at a drag strip. Luckily it was the one at the diff so there wasn't much damage. So based on what I'm reading, my diff will be fine as long as I baby it, and then when I hit the lotto I need to completely rebuild the IRS lol.

[seattlejester]

Right it was something there was two of, I looked at a chewed up ring gear on a friends diff a while back and I thought for some reason that was what failed. In retrospect that is really not the piece in question. I think the FAQ goes into a bit more detail.

 

You can use it, just don't shock load it would be my suggestion. There are guys running v8's and high hp inline 6's through stock R180's either by limitation of race class or financials. Just don't be surprised if it lets go on you.

 

Might be worth looking into an upgrade that replaces all the components in the rear, whether that is the TTT setup, wifrit's 8.8 swap, datsunparts 8.8 swap, CFJ rear end swap, or DSS swap. Each has their own bit of merit.

[HOT SAKE]

Hi everyone,

 

I have a 74 260z with a stock 180 behind a 350 chevy and T-5 manual, probably putting out 350hp at the crank.  I have been driving the car for 16000 miles since converting. I  drive it pretty hard with an occasional hard launch and slam between gear changes and so far so good.  My plan is to run it until something fails and then convert to a R200.