looking into 90 xj, need advice and input

I found a 90 xj, 4.0 4x4 automatic. The mechanic told the owner it needs a new front seal. I have never replaced one before. Is it something i can do or should i bring it to a shop, and what would cause the seal to go, obviously i would replace that too

Front seals are what seal against the harmonic balancer (HB, or vibration damper). You have to remove your serpentine belt, remove the harmonic balancer, then pull the seal. Replacement is reverse of removal. Only special tool to have is a HB puller. It also helps to take the HB bolt to your local hardware store and get one that is about an inch longer. It makes it easier to get the HB back onto the crankshaft. Once its on far enough, use the original bolt and tighten to spec.

Its easy to do... You dont have to nessarily to replace the HB unless its starting to seperate from the outer portion...OR if its got a nice groove where it "rides" against the seal. Since you just acquired this Jeep, its probably a good idea to replace the HB as well (i would). There only about 50 bucks.

Hope that helps.

I've done a couple, and its not too difficult. You may want to unbolt and remove the fan to get some working room. The harmonic balancer puller from NAPA has too long of a bolt and it hits the radiator, so you might want a shorter bolt for that as well. X2 on the longer bolt to pull the balancer back on. You risk stripping the threads if you use the stock bolt to pull it back on.

The basic steps are remove the 4 nuts holding the fan on, loosen the harmonic balancer bolt (don't fully remove yet), then loosen the PS pump and remove the serp belt. Then use the puller against the HB bolt to pull it out. Dont put the puller against the threads if you can avoid it. I like to run a sheet metal screw into the seal and pry it out with a little crowbar or hammer. Gently tap the new seal in. Line up the balancer and slide it on, use the longer bolt and a large washer to pull it back up most of the way and then switch to the shorter stock bolt. In the famous Haynes manual works, simply reverse the previous steps to put everything else back on.

The seal hardens with age and eventually leaks. It may put a groove in the snout of the harmonic balancer which would require replacing the balancer or using a sleeve on it. I would also inspect the balancer to make sure it's in good shape and not seperating while your in there.