99 Dakota 3.9 Posi Help

Ok, i've got a 99 dakota 3.9 4x4 with a Posi 8.25 rear end. Upon hearing some groaning and grinding in my corners I decided a fluid change was in order. I opened up the diff and saw metal shavings on the magnet in the bottom of the pumpkin. I inspected the spider gears and found some chipping, so i figured i;d change those out. My biggest issue and therefore th focus of my post is that when i have the rear end in the air, wheter in gear or neutral, i spin one wheel and the other spins the opposite way. now to my understanding this isnt supposed to happen with a posi. Now looking for a new posi unit i found that almost none of the replacement 29 splines had the tiny toothed ring around them that mounts flush to the ring gear. I dont know if the ABS comes into play with that or not, or if my rear end is even a 29 spline, to my understanding any dakota 8.5 after 97 was a 29. Any help is greatly appreciated.

first off, Chrysler 8.25 axles are NOT posi axles. A posi axle will spin both tires in the same direction when jacked up in air. As far as the number of splines, my 1995 Dakota V6 has 29 splines on it. As long as that ring gear has the ABS speed sensor tone wheel on the ring gear, you should be OK.
LG-CT810/V10h NetFront/v3.5 Profile/MIDP-2.0 Configuration/CLDC-1.1

My 2000 Dakota has an anti-slip axle. Isnt that the same as a posi axle?

if you are referring to limited slip, that's a whole different animal. Limited slip uses clutches inside of the carrier to limit wheel slippage & keep both wheels turning at the same time. Do you have a R/T Dakota? Those were the only dakota to have a limited slip axle straight out of the box.
LG-CT810/V10h NetFront/v3.5 Profile/MIDP-2.0 Configuration/CLDC-1.1

if you are referring to limited slip, that's a whole different animal. Limited slip uses clutches inside of the carrier to limit wheel slippage & keep both wheels turning at the same time.


Thanks. I always thought it was different names for the same thing. So, is a posi like a "solid" axle in that it is both wheels at all times?




Do you have a R/T Dakota? Those were the only dakota to have a limited slip axle straight out of the box.
LG-CT810/V10h NetFront/v3.5 Profile/MIDP-2.0 Configuration/CLDC-1.1

Nope, I have a 2000 Dakota Quad Cab SLT. It says on the sticker in the glovebox that it has an anti-slip axle.

Thanks. I always thought it was different names for the same thing. So, is a posi like a "solid" axle in that it is both wheels at all times?

Pretty much all pickup truck use solid axle, a straight hollow axle with seperate axle shafts that slide inside the axle housing. The only exception is the Honda Ridgeline that uses independent rear axle. Here's a brief rundown to Axles 101:
There are two basic types: semi-floating & full floating. Semi floating is commonly used on light-duty truck because it's cheaper. A semi-floating axle places the axle bearing in the middle of the axle, thus some of the vehicle weight lies on the axle. Good example of this is the Dana 30 & 35 axles found in Jeep Cherokees, Comanches, Grand Cherokees & Wranglers from 1984-2000+, if you put larger tires on the stock axles, they will break and leave you stranded. They usually break at the C-clip inside of the carrier.

Full floating axles place the axle bearing towards the end of the axle tube by the backing plate, thus putting all the vehicles weight on the axle housing, not the shaft, making it stronger & expensive and used more in heavy-duty trucks. Common heavy duty axles are Dana 60 & 70 axles, Ford 9" & Chrysler 9.25.

Open axles have the side gears inside of the carrier that turn in opposite directions, thus allowing one wheel to spin opposite the other. Good example: seeing a vehicle power-braking on one rear tire is an open axle. When making a turn with type of axle, the inside wheel spins faster than the outside thus causing spin outs if the driver is not careful.

Posi (or positive traction) have the side gears turning in the same direction thus both tires turn in the same direction, i.e. a car the power-brakes and both rear tires light up at the same time.

Limited slip as I mentioned before have clutches like that found in an automatic transmission or transfer case that lock up to prevent wheel spin provide superior traction over open axles & posi axles. Thus when servicing these axles there is a limited slip additive that must be put in to keep that clutch pack going for a long time.

Finally, there are full lockers, like Detroit Locker, that have a magnetic or electronic clutch that applies to prevent each independent axle from spinning faster than the other. These are commonly found in rock crawling vehicles, though they are used in on-road applications as well. All of these axles go from cheapest to expensive.




Nope, I have a 2000 Dakota Quad Cab SLT. It says on the sticker in the glovebox that it has an anti-slip axle.

Which engine do you have the crappy 4.7 or the bulletproof 5.9?

Which engine do you have the crappy 4.7 or the bulletproof 5.9?

Thanks for the excellent explanation!

I have the 3.9 V6. Would liked to have had the 5.9, but beggers can't be choosers. LOL