'90 Dakota rear end and question about rear main bearing seal

[Bobacuda]

While looking for a somewhat higher geared rear end with emergency brakes for my B4B (currently a 4.11), I found a '90 Dakota 8 1/4 rear end (3.55) with larger, finned brake drums at the local Pick a Part. On top of the center of the differential is some kind of factory electronic gizmo. When I first saw it, I thought it was the differential's breather, but then I noticed that it had and electric plug and wiring.

OK, I give up:

1. What the heck is that thing on top of the differential's center? Can I

ignore it or will it interfere with my use?

2. Is this unit a good match for my old truck?

One last question. My truck has a "T-306" 218 engine and fluid drive. Does this engine use a rope main seal or the 2 part neoprene?

Thanks for your input.

[Dozerman51]

Why not get a mid to late 50's mopar car third member and axle shafts. They should fit right in to your truck. The vehicles that had the V-8's usually had the lower numbered ratio's for more top end speed.

[FargoPanel]

I would think the wires on the diff would be for the rear anti-lock brakes. Not needed really.

[Dozerman51]

If you go the interchange route on third members, you will need to find an 8.25" third member not an 8.75" third member.

[52b3b Joe]

i second the ABS sensor, I just had problems with mine on my dakota's rear end

[wayfarer]

Ignore the sensor.

Now tell us how the spring perches and overall width line up with the existing.

[William Davey]

I have an 89 Dakota rear - dimensions are 62.25" between wheel mounting surfaces; 43.25" center-center on spring perches. The 1st generation Dakota's had 5 bolt hubs on 4.5" centers and a very wide range of available ratios.

My truck is a 2nd series 55 which I think is a little wider that the B1 and B2's. The 62" width matches the front with Charlie Akers' disc brake kit installed.

Why? I'll get 3.55 ratio and brakes that I can adjust. I've tried the method described on the DPETCA site, but always end up with one wheel that locks up early. I tried making my own "Ammco 1750" but that didn't work either.