[WANTED] 8 1/4 rearend posi unit
- Thread starter Bill Ney
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What ratio as there are two possible options.
I believe the 3:55 and lower is one offset and the 3:21 and higher is another.
If I am off please correct.
I believe the 3:55 and lower is one offset and the 3:21 and higher is another.
If I am off please correct.
Bill Ney
Active Member
Either one would work, or just the sure grip unit
74 360 dart sport
Well-Known Member
74 360 dart sport
Well-Known Member
Montevideo Minnesota
NoCar340
The Original Partstitute
The numerically-low Sure Grip unit only fits 2.2x and 2.4x-series gears and is a bit of an oddball, being introduced with the A99x transmissions with the 2.74:1 first gear. Mega-steep axle ratios and a deep first gear were Chrysler's financially-strapped end-around to developing an overdrive automatic transmission.
All other ratios, 2.76 & numerically higher, used the same differential through 1996. For '97, the axle spline count changed from 27 to 29, so those later Dakota/Ram Sure Grips won't accept muscle-era axles.
Cool! Thanks for that info.
Syleng1
NoCar340
The Original Partstitute
The only thing specific about the Dakota diff is the axle-shaft spline count as posted above. A Sure Grip from a '73 Duster or '81 Diplomat will work in an '87-'96 Dakota, but not newer.
The only other difference to consider is that there are two different types of Sure-Grips: the Borg-Warner (now Auburn) cone-type unit, and the Dana/Spicer Trac-Lok (clutch type).
The Borg-Warner design is virtually invisible in use, meaning you never feel it engage or disengage. It's also fairly bulletproof if you maintain it, which just means lube changes at recommended intervals. The downside is that it's non-rebuildable (per its designers) although some have gotten away with milling the backsides of the cones to restore function. Doing so increases the clearances on the side/spider gear engagement, though, so it's still not ideal. That being said, I've had untouched B-W units with 150,000+ miles on them that still worked perfectly.
The Trac-Lok is easily rebuildable when it wears out, since the clutches are multi-plate units that are readily available and can be replaced. However, the Trac-Lok is not as seamless as the B-W unit in its operation. Engagement/disengagement is more noticeable, but it also locks harder. Trac-Loks in general--not just the 8¼" one--are also semi-notorious for clutch breakage, particularly in hard usage. Broken clutches won't stop you dead, but you won't love the noises from the rearend.
I believe all the factory Sure Grip units built for 29-spline axles were Trac-Loks, but I'm not sure of it. Trucks ain't my thing.
The only other difference to consider is that there are two different types of Sure-Grips: the Borg-Warner (now Auburn) cone-type unit, and the Dana/Spicer Trac-Lok (clutch type).
The Borg-Warner design is virtually invisible in use, meaning you never feel it engage or disengage. It's also fairly bulletproof if you maintain it, which just means lube changes at recommended intervals. The downside is that it's non-rebuildable (per its designers) although some have gotten away with milling the backsides of the cones to restore function. Doing so increases the clearances on the side/spider gear engagement, though, so it's still not ideal. That being said, I've had untouched B-W units with 150,000+ miles on them that still worked perfectly.
The Trac-Lok is easily rebuildable when it wears out, since the clutches are multi-plate units that are readily available and can be replaced. However, the Trac-Lok is not as seamless as the B-W unit in its operation. Engagement/disengagement is more noticeable, but it also locks harder. Trac-Loks in general--not just the 8¼" one--are also semi-notorious for clutch breakage, particularly in hard usage. Broken clutches won't stop you dead, but you won't love the noises from the rearend.
I believe all the factory Sure Grip units built for 29-spline axles were Trac-Loks, but I'm not sure of it. Trucks ain't my thing.
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