I have a eaton posi trac 8.8 rear end with 3.55 gears. It drives good and is awesome but one question just for knowledge. How do you know your posi is working?? like both wheels going. How can you tell everything is a ok in the rear end??? Im new to this stuff.
there is the easy way and the harder way...go out and "light 'em up" and if you leave two black stripes of rubber on the pavement (empty parking lot on a Sunday comes to mind), you have a posi, single tire stripe, no posi or it's worn out. The other way is to jack up the car and turn one rear wheel by hand, if the other one turns the same way you have a posi, if it turns the other way, no posi
Quick test if the posi is working:You can also raise the rear axle off the ground and attempt to turn on rear wheel and see if the other rear wheel turns in the opposite direction (make sure the vehicle is in park so the driveshaft is locked). It should take considerable amount of torqure to turn the wheel if the posi is in good shape. This is because Eaton Posis have 400 lb preload spring packs. This is a quick test and will not necessarily indicate the condition of the differential but will give you an idea of the if it has a limited slip and if it is working.
As long as you do not have one wheel peel then it is not a problem. In order to check the differential it must be removed and then can be checked for bias torque and other internal measurements.
When a limited slip differential fails you will get one wheel peel. This is common with the Visteon limited slip (oem limited slip in Ford vehicles). Very common with Mustangs as well. When this happens many guys keep the throttlle matted. This will keep spinning the one wheel and they end up smoking the internals in their rear axle. This is because when one wheel is spinning on a limited slip differential and the other wheel is not the gears and clutch discs inside the differential are rotating. This produce tons of heat. This heat can be so high that the oil can break down and the bearings and gears can be damaged. It is very rare for this to happen with an Eaton Posi.
Ironically, I work for Eaton Corporation and I test build and test these differentials. These units are extremely strong. I have built 31 spline units for drag cars with horsepower with over 800 horsepower with no complaints. They are pretty much bullet proof The biggest complaints we get are for noise. This is mainly due to people using the wrong oil. The correct oil is a mineral based oil (75-90) with a gm friction modifer. If this is used then the differential will not have chatter. However, some synthetic oils will cause chatter. Although, the Eaton Posi does not like synthetics I have had good luck with the Amsoil synthetic gear lube and the Amsoil modifer. That is what lube I am currently using on my 91 Mustang LX notch with no chatter issues.
you should do a burnout turning both left and right. If you leave two black marks and/or go sideways, your posi is working great. Doing it in a straight line is not always a tell all story.