8.8 axle question

[RET_COP]

I'm probably getting a little ahead of myself as I don't know if I have 28 or 31 spline axles or exactly what vehicle my rearend came from, but this fall I plan to install a Detroit TruTrac and in doing so will make sure I have 31 spline axles for the upgrade.
My question is : if I do have 28 spline axles, would I just need to get the bigger bearings and seals or are there 28 spline axles that also use the big bearings?

Do all 8.8 housings accept 31 spline axles?

Is there anything I should be aware of for this upgrade. I realize I will have to get the 31 spline carrier and If I don't change the ring and pinion ratio I can just swap the ring gear and check for proper backlash correct?

Thanks for any help

Lou

[Ant]

My understanding is the IRS axle side bearings and seals are the same for both 28 and 31spline, the axle bearing area diameter is larger than the spline OD.

All IRS housings will accept 31 spline axles if the carrier (True Trac/LSD) side gears are 31 spline. When buying the new True Trac carrier make sure the 31 spline side gears have the relief for the retaining clips.

When I purchased my Eaton Carbon Posi, the differential coy machined off the whole diameter on the inside of the side gear and clip wasn't encapsulated as it should be, they supplied new gears and I had the machining done. I purchased 28 spline axles from the Driveshaft Shop with 300m main axles and Chromoly Porsche style 108mm 28 spline CV's, I am not drag racing so they should hold up for road racing.

[RET_COP]

THANKS FOR YOUR REPLY Ant, This would be a straight rear. I'll make sure about the relief in the side gears but if I order the only 31 spline TrueTrac from summit for the 8.8 Ford rear your saying the side gears may not have the relief for the c clips?

[Ant]

Hi Lou,

I gather you have a conventional differential not an IRS?
The relief in the side gears on the IRS is for the clip on the short CV axle to hold it into the IRS Head, and the inner CV can be removed to service or replace by simply levering out of diff unit.

On a conventional straight diff you remove the rear cover and tap or push the axle in so you can remove the C Clip, before you can pull the axle from the housing, the clip is a chunky metal plate clip compared to the small wire clip on CV axles, so they are two different parts that do the same job. They make C Clip eliminators for the 8.8 that are bolted inside the brake drum and have a interference fit sleeve that holds axle in place.

Hope that helps, Summit will advise you and if you order an 8.8 TrueTrac for your non IRS application you shouldn't have any problems as that is what the part is designed for a straight differential.

[RET_COP]

Got it, Thanks

[Ron61]

Lou,

I changed my 8.8 28 spline axles for 31 spline ones and a built up Eaton Posi that never gave me any trouble and I raced it hard. That was in a straight axle car also. The Eaton would just squeak the inner tire on a slow turn but not lock and then snap loose like a detroit locker and that is why I went with it. Those set ups are pretty darn good and some of the drag racers around here use them. I also had the C clips changed so they couldn't come loose and let an axle come out. I am not exactly sure how the guy did it as he builds most of the rear ends for the racers up here.

Ron

[RET_COP]

HI Ron, If I need to upgrade to the 31 spline and have to change the carrier I wanted to try the worm gear TruTrac setup as I heard good things about it for autocross and it does well on the street and is still strong enough to make a 1/4 pass. I still have time to think this out. I've run posi (clutch plate) style all my life so this would be new to me. Not going to C clip eliminators as I'm doing this in my garage. I'm also keeping my 3.27 gears, so this should be a quick and easy swap. (Should anyway) It's always great to have your your input, you've had quite a history with Cobra's.

[Ron61]

Thanks Lou,

I also ran 3:27 gears and they worked out great on the tracks that I ran on. I wasn't trying to sell you on the Eaton, as I have heard good things about the TruTrac also and it sounds as good as the Eaton. I did run a detroit locker for a very short time but didn't like the continual unwinding when I was just driving around a corner or out crusing. With what you have planned you should have a really good set up. And as you are mostly going to be going in a straight line it seems, the C Clip eliminators aren't needed in my opinion. I just had it done because of the hard turns in road racing and to make extra sure one of them didn't fail and let an axle come out in the center of a turn. Good luck and I hope that everything goes well and you have no problems.

Ron