Looking over Moser's complete axle assembly offerings, it looks like their M88 (Ford 8.8 style) autocross/full floating axle assembly will cost about the same or a bit less than a Mopar 8.75 style assembly. Either can be had at custom widths, spring perches welded, etc. Both weigh about the same.

The advantages of a full floating axle are only now something that have become aware of and the M88 is starting to look a bit more appealing with the idea of enjoying the car on winding roads and the occasional autocross course.

Then again, the Mopar style 8.75" is well known for being strong, reliable and convenient for ratio swapping...

Any reason to pick one over the other?

Second, which limited slip type would be most beneficial for a corner-carver? It looks like there are a few choices on either axle.

Thanks for any thoughts.
-Mike

I like full floaters and 8,75's , you need a full floater 8.75.

Well...ok.
Do guys build these? I don't see an option for the complete bolt-in assembly; at leas not from Moser.

Its likely such a low demand item, not worth listing, but if they still offer fabricated Mopar housings, it should be a piece of cake to build, but "mopar/floater" is likely going to pay the dreaded mopar surcharge unfortunately.

Ok...so in that case, all else being equal, might as well go with an 8.75 built to be a floater...I will ask about that before I do anything rash.

If there's a significant price difference...any reason why the 8.8 would be a bad choice? It looks like they also offer a floater version of the Dana44...

No, until you drive cross country with nice 2.76 gear, arrive late to a track event, and wish you could swap in that 3.55, by just drain the fluid, slide the floater axles out a few inches, swap third members, and on the track.

Unless you're getting a screaming deal, I can't really see the 8.8 Ford being a big improvement. Full floating is nice if you really think regularly breaking axles are a probability. The 8.75 mopar is a semi floating design so if you DO break an axle, they are not going to come apart like a C clip axle would be. And, with aftermarket axles, 8.75 can be very, very tough.

Additionally, the 8.8 Ford lacks the easy and inexpensive gear changes of the Ford 9", so you don't gain anything there.

I think they beef up the 8.8 because of their popularity with/and/or rule requirements in Mustang racing classes.

Thanks, guys!

What my preliminary reading seemed to indicate was that non-floating axles that experience frequent/heavy side-loading would experience more friction, wear and risk of damage compared to a full-floating design...and while I don't envision my Dart ever running hot laps on a road course, it seemed like the kind of choice that would be easy to make now and more difficult later on.

So the semi-floating design is ok for Autox?

Is the stock type Suregrip ok or would a handling focused car be better served by an Eaton Trutrac?

What power levels would demand the 33 or 35 spline axles?

Thanks again for the info, guys!

It is probably true that non-floating axles experience more heavy side loading and wear. However, any number of us on here have mercilessly abused the 8.75 rear over the decades without detriment. Can they break, sure, but in many cases they are more than adequate for the application, especially when they are not being shock loaded like in a drag racing environment.

I have used them in oval track and drag racing since the '80s. I've never broken one, but I've also never dealt with more than 400-425 horse mills, and even with that I used a spool and 35 spline axles in my drag application. Since this was using slicks on a prepared track, I thought it a wise investment. On oval tracks, I used standard axles and sure grips. This has been both with treaded and slick tires. However, oval tracks never approach the level of grip you find on the starting line of a drag strip.

Will the 8.75 stand up to autocross, IMO, absolutely. Are there better components out there than stock, also affirmative. I've got no experience with the Eaton Truetrac but it looks like a good piece. To me, an axle swap at a later date is not a big deal that would require a lot of effort. If you want to upgrade now in anticipation of future power levels, you certainly could or you can wait until later. It all depends on your budget, effort you're willing to put in, power levels, and application.

I have a 8.8 in my 64 Fairlane that started out in an Explorer, narrowing 2" with 9" axles, carbon fiber cluch kit, Moser yoke and the cost of the used assembly I have $900 in it. The thing I like about it the cost and availability of parts.

I have a 8 3/4 in my Plymouth, the ability to change gears is nice but centers are getting harder to find and are fifty years old.

I'd go with a Dana, Ford 9" or 8.8.

I run a 3.91 Eaton TrueTrac in my Dr. Diff 8.75 and it works great! One of the few things left stock in my car is the axles but they have been holding up so far at the track with about 540 rwtq put on them. Going to change them out eventually with some Strange or Moser components. Sorry no auto-x though...

You can get brand new centers for the 8.75.

But honestly, how many of us swap out center sections and how of us that do, how may extra center sections do you have>

I'll bet few and one, maybe two extras.

Don't get me wrong, I like the 8 3/4, know I have red where the stock 9" is weaker than the 8 3/4 and a stock 9" is as strong as a 8.8...
But there's stock 8.8s in the 9s and 8s.

How many stock 9" or 8 3/4 ZERO......
GO FIGURE!

But the the upside of the OP's question, with a full floater, its almost easy to swap out, and you only need one extra 8.75 to make that happen, although more is nice.

Seriously? Running 9's?

Wrong forum.

I cant thank you guys enough for the insights here.

So it sounds like an 8.75" despite being a semi-floater is still plenty reliable for autocross and road course work so I guess the more important question would be whether to go for the Eaton Trutrac limited slip or save the money and stick with the regular clutch type...

I'm currently running a stock Magnum 300 crate motor with a mildly built A904...so pretty mild stuff at this point...but I do plan to run modern tires soon and I also catch myself daydreaming about swapping in a 6.4L modern Hemi and a T6060 at some point so I do want to leave some extra capacity for more power down the road.

IIRC, the Trutrac is a Torsen style unit, right? I gather that these last longer than clutch types but is there any other advantage?

FWIW the 8.75 (OE housing) has held up well for me with street + HSAX use, 590'ish HP and a manual transmission. I run the clutch type sure grip and Moser axles. Also 200 treadwear tires.

With tapered bearings, it takes side loads well.

If I did upgrade, I would be looking for a stronger axle that could handle sticky tires (eg 50 treadwear) along with the HSAX standing start and manual transmission. Likely a Dana 60 though an aftermarket 9" could do it also.

Comparing to an 8.8 I agree save your money. Use the 8.75, add sure grip of your choice and Timken bearings. Stronger axles would not hurt but not really essential IMO.

Also lose the drum brakes... from first hand experience, they do not like hard track use. The Dr Diff rear disc kit has worked well on my 8.75.