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Spartan Locker

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just purchased one for the rear of explorer . On ebay for $254.88 shipped . can't wait

Sorry , didn't take pictures . But will be installing one soon into my brother F150 . Could get pictures of that install. BTW it a 8.8 in the F150

. . The problem is the side couplers for the axles aren't machined to allow the axle circlips to clear the end of the side couplers to expand. The axles are hitting the cross pin. I'll have to machine the side couplers to allow the axle circlips to clear the end to expands. From what I can measure, I need about .110 machined depth around the hole for the axle.

I am running into this same problem on a 2007 Sport Trac, this thread is the only reference I could find that describes this issue with a Spartan Locker in a Ford 8.8 IRS.

Before mounting the differential to the truck frame, I tried to install the axles to check everything over. Here is what I found:
Spartan Locker Ford 8-8 IRS Pin Interference1.jpg
Spartan Locker Ford 8-8 IRS Pin Interference2.jpg

Ford 8-8 IRS Axle End to Clip Measure.jpg

My initial thought is to machine 0.100" off of the end of each axle to enable clearance to the carrier pin. This would give ~ 0.035" clearance between end of axle and pin on each side, and preserve side to side play of the axle shafts in the bearing, which feels right when the axles are clipped into the Spartan side couplers.

Per the Spartan instructions, OEM spacers were removed and not used.

Any suggestions?
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Paul, if you machine the axles and break 1 or need to replace it in the future, you'll have to machine the replacement axle. I decided to machine the side couplers to avoid having to modify an axle in the future. We had no trouble after installing after machining the side couplers. We had traded the explorer about 2 years ago for a Tacoma so I can't advise if there are no issues with it.

Thanks, I plan on machining the side couplers as you did. I will create a separate thread on the 2007-2010 Sport Trac forum with additional findings.

I had correspondence today with Gus at Randy’s Worldwide, he confirmed what you and I discovered regarding interference of the pin/axles. There is no way the axles will clip in an 8.8 IRS without machining the side couplers as you did to enable the circlip to seat.

Based on Gus’s analysis of an 8.8 IRS dimensions, machining 0.100” pocket as you did puts the axle in the correct position when seated. Without this relief pocket for the circlip in the side coupler, retention is only via friction and not recommended.

He acknowledged their catalog should not list SL F8.8-31 [17005] for a 2007-2010 Sport Trac or 2002+ Mountaineer. Note their current catalog lists this for Explorer 2001 and earlier only. See SL F8.8-31: Spartan Locker for Ford 8.8", 31 spline, includes heavy-duty cross pin shaft
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I can advise that this modification to a Spartan Locker SLF8831 works in a Ford 8.8 IRS open differential. Axles clipped in both sides with good retention and could be removed in the conventional manner.

Pictures are of the axles clipped into position, side to side play of drive shafts in the bearings feels correct.

Attached are instructions that a good machinist can follow to make these changes so that this locker works in an 8.8 IRS. Gus at Randy's Worldwide advised that future production units will have this change.

Side Coupler Mod Ford 8-8 IRS Finished Left Axle Seated.jpg
Side Coupler Mod Ford 8-8 IRS Finished Right Axle Seated.jpg


  • Spartan Side Coupler Mod Ford 8-8 IRS.pdf
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