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8.8" Ford Differential Woes

Marshall M.

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'89 Mustang AI car


340/360 HP/TQ for ABS

360/380 HP/TQ without ABS



So... At Hallett my stock Trac-lok diff from my high school '92 Mustang and the 3.55 gears that saw 90,000 street miles before 12 seasons of road racing finally bit the dust... The diff split in half and took out everything but the housing and bearing caps...


So, what do I do?? Stock diff again (3 spares at the shop)... Gears?? 2.87, 3.07, 3.27, 3.55. Had each of those at the shop...


Nope, none of those cheap options. I chose a Moser Engineering Wavetrac diff and 3.90 gears. Bought new 31-spline axles (Alloy USA), bearings, seals, solid pinion shim and some fancy Motul fluid that I was supposed to run.


So, on most diffs, the Axles slide in, C-clips are installed, pull the axles "out" and slide a cross pin/block to retain the axle/clip combo... Stock unit is that way and at least the Torsen units. Wavetrac... Nope. We rely on the custom clip to "snap" around the C-clip groove outside diameter...


I had a fundamental issue with this from my Engineering background. I even had one clip fall out when I was assembling the rear end. I called Wavetrac and they assured me it was "per design" and that I must not have seated the clips all the way. I drove them in as far as they could go and verified with the drawing that they were fully seated and buttoned the car up and towed to MSR-H.


Three turns into practice, going into Diamond's Edge, I hear a weird whine noise. I wrote it off to new rear pads (they do make a howl noise in the corners for the first few sessions typically). Finished practice and qualifying. I did seem a bit off pace and didn't really have an explanation as to why.


Before R1, I happened to look at the rear rotor when I was torquing lugs and noticed scratch marks on the rotor. My only thought was the rotor hitting the caliper mount bracket. This had never happened before and the only way that can happen is to lose a C-clip. Jacked the car up and sure enough, both C-Clips came out... Missed R1 while I tore the diff cover off (Thanks to Craig for his fancy fluid extraction pump... No muss, no fuss, no mess... C-Clips were chewed up in he bottoms of the diff. Weekend over.


I called Wavetrac Monday after the event and explained what had happened. They provided a return shipping label and I sent the diff back for analysis. I also provided diameter measurements of the c-clip grooves in seven different axles I had at the shop (3 stock 28-spline, 2 Superior Axle 28-spline, and the 2 new Alloy USA 31-spline axles). They all measures between 0.732-0.736". Heard back last Wednesday that the axles that I had were too small and the diff was designed for 0.750" c-clip grooves and that is why the clips fell out of my axles and that the Wavetrac was originally designed to use Moser Engineering 31-spline axles (guess they are 0.750").


My issue with this is there was ZERO mention of needing these specific axles. After going around and around, I had two options... 1. Custom make my own C-clips (Wavetrac did provide me with the engineering print), but i would lose my lifetime warranty, or 2. Buy new axles (even though I already did that...)


I mentioned that they might want to reach out to the aftermarket distributors so they can specify the specific Moser axle so others won't have this issue, as I couldn't see how it hasn't happened every single time for others. Wavetrac said I was only the second reported case of this. They didn't seem to willing to do that. Oh well. I even offered to machine a prototype set to use with other commercially available axles (0.731-0.736"). They even declined that "help"... They did "kindly" offer to discount a set of "correct" Moser axles for $175 (studs and ABS rings included) as well as cover the return shipping for the diff and drop ship for the axles.


I told them I still wasn't happy that I had to spend yet more money to make their issue correct. They said I could always run my own clips to keep my axles (lose the warranty though). In the end, I reluctantly hemorraghed more money to get the correct axles, and preserve the warranty.


Fortunately I called Summit Racing (who I bought all my parts from) and they gladly refunded my axles and provided free return shipping as the product description was also partially a fault of theirs (I guess)...


So, even though the experience with Wavetrac wasn't what I had hoped for (all things considered) from a customer service prospective (they really couldn't eat $175 for axles after i threw away an entire weekend of racing plus time and effort to tear down and rebuild the diff??). Summit on the other hand came to the rescue with what I can only describe as a smile and chuckle at my story of what 0.018" means to a C-clips' fragile life.


I did buy the Wavetrac for its on-track performance and not their customer service experience I guess.


Crossing my fingers that it holds at TWS. Needless to say, C-clip checks will be apart of my pre-race routine for the extended future.




PS... I did look into C-Clip eliminators and they required yet more expensive custom axles to work with ABS...

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