4 wheel drive or am I nuts!

[eagleman]

Need some help here guys. My 86 eagle is sitting on jack stands in the garage and has not been started in a while. So yesterday I started it to just warm it up. It started fine and ran fine so I put it in gear to warm up the trans and rear diff and thought why not engage the four wheel and warn up the front diff as well.All was going well and as I stood there watching the wheels go around I noticed the rear wheels were turning faster then the front wheels. I then start thinking this can't be right or is it? My question is, is it normal for the rear to turn faster then the front? In my thinking they should both turn at the same speed but thats not the case here. By the way its a automatic trans. I guess I am a might confused now. I then ran it in reverse then back to drive several times. Applied the brakes several times and all is nice and quite and seems to be working well except the rear wheels are faster then the front. Whats up with that.

[priya]

My guess is that the viscous coupling in the transfer case has failed and there is more rolling resistance on the front axel than the rear and this is allowing differential action in the transfer case to turn the rear wheels faster than the front.  The transfer case has a differential in it to allow the front and rear wheels to turn at different speed otherwise if they were locked together it could greatly accerate wear on those parts as inevitably the front tires are slightly smaller than the rear (or vice versa) or the front wheels take a wider line than the rear in turns and wind up travelling farther than the rear wheels and so on.

I know one year of eagle had an open differntial in the transfer case (no viscous coupling to slow down the difference in turning speed between front and rear wheels) so your car is likely operating similar to the way that year of eagle was designed to operate.  Some people think the viscous coupling isn't particularly helpful but I feel its well worth having if you're driving in situations with very low traction conditions.

I've had my eagle on the hoist after putting in the new viscous coupling and placed it in drive with all wheels off the ground and the front and rear wheels turned at the same speed.

[ammachine390]

1986 models did not have the viscous coupler in them, only a differential.

[carnuck]

Actually, it depends on whether it has a NP128 or NP129 case. The 128 has no VC and was used over the '86 model year but some got 129s and some 85s and 87s got 129s, depending on what was available at the time.

[eagleman]

I think what threw me off was last year I had my 84 sedan up on jack stands and changed the trans fluid and filter.When finished I started it and ran it through the gears and after that engaged the four wheel and let it run for a while. On it both the front and rear turned at the same speed. However the 86 did not and it threw me off. Was not quite sure what to think. I do remember reading somewhere that the 86 models used a open type transfer case with no viscous coupling so maybe thats the reason. Other then that all seemed well.Was kinda fun standing there watching all four wheels turn.But then again I believe thats why I bought eagles in the first place. Their just cool cars! Thanks for your responses.Feel much better now.