Differential and axle durability in high power cars
 

I am curious to hear what you high power guys have to say about diff and axle durability on track with high power cars.

Why did Mazda feel the need to upgrade the MSM axles and diff if the 1.8's are robust?

So far I have had no issues with my Rotrex powered car but then again it's not a torque monster.

MSM Axles/diff are more tolerant of high torque drag launches.

Over 300whp its a game of russian roulette. As long as you keep wheel hop to a minimum and have proper ride height/geometry its not too bad though. I'm talking about regular NB axles and diff. I'm guessing the MSM's take more abuse, but no personal experience with those.

CVs give up the ghost in 300wtq road race cars but uprated parts exist. The diffs are bombproof unless you are drag racing.

The fact that this thread pops up on the day I start hearing noises emanating from my diff is pretty interesting.
Low speed sharp right turns produce a binding type of noise.
I had the typical misalignment noise on sweeping turns with lift off, and "raising" the transmission in relation to the PPF solved that problem.
Now, I'm getting the same noise when turning sharply to the right.

I didnt realize the MSM diff was stronger too I thought it was the same 7" ring gear as the rest of the diffs just has a maybe different torsen maybe made by bosch or something. The MSM without a doubt has stronger axles.

You road race guys breaking them. Is it your actual CVs that eat themselves or the shaft right near the CV? Auto-x guys break the shaft right at the CV.

That's pretty impressive for stock parts. I wonder why Mazda felt the need to upgrade the components on the MSM?

Same 7" ring but the diff is a larger unit. It's reported to be the same as a S2000. Suppose to be a Bosch unit like the early torsens.

We stripped out something on the inner CV at the 25hr. I have to pull it apart to look. Either the cage shattered of the axle splines stripped out. The car had 200whp.

Road racers damage the CV, not the axle shaft.

It also may be shotpeened like the MSM 6 speed is?
I know their axle shafts are thicker and the spline is bigger.
As stated, s2000s use the MSM diff pretty much and there's a local person here making +600hp, but he's broken his diff 2-3 times. But then again, it's a luck game with drivetrain.

I’m finding after a year the inner CV's are starting have the balls divot into the housing crating slop and accelerated wear. Haven't had one catastrophically fail yet but it is obviously a significant wear item at elevated torque levels. Contact pressures are too high in the CV. I have been swapping them out more or less annually. The MSM are trypoid style and I believe don’t have the accelerated wear issue at the higher torque.

What are the symptoms of wear? Noise?

--Ian

I should pull apart the ones I just took out. The inner CV felt like it has way more torsional play than the used NB ABS axles that are going in.

What is funny about the MSM and the S2K sharing diffs is that the S2K guys manages to asplode their diff at stock power levels. I think they're actually blowing up the gears inside the torsen though.

Play in the CV, and on the extreme end of things, a box full of neutrals as all the power spins out of the diff on that side.

I never had a problem with the ring and pinion, but have gone through plenty of axles. They all break in different locations.

Axles stop breaking when I corrected the ride height. Also, I welded my diff, and it has held up so far with many 7000 rpm launches on slicks.

I wonder if the squat from launching is what did your axles in?

When new there is no slop at all when worn you can watch the outer shaft rotate several degrees without the stub into the diff turning at all. Take them apart and the balls have worn deep divots into the cup. At stock power that doesn't happen unless the boot is torn and your running sand for CV grease.

Just out of curiosity, several of you Miata folks do RX7 diff swaps, correct?

The FC RX7 guys are now routinely upgrading to Ford 8.8 IRS's bolted in the stock FC position, using Ford inner CV's and TII outers. I wonder if this would be adaptable to a Miata, or if the slight difference in housing size would make it unfeasible.

A few of us are using the stronger FC aluminum housing, but almost nobody has the FC third member. Switching to the Ford diff isn't necessary - DSS makes axles with Miata inner splines that have upgraded inner/outer CVs and a larger stub shaft that fits with the stronger V8R 0.500" hubs. No need to upgrade the diff to get that axle.

Gotcha, thanks for the info!