1998 7.4 rear seal

[stpat]

Got a 1998 2500 4X4 Suburban, been getting it back in good shape for a rather long trip, anyway, had the front end jacked up to make some repairs ( water pump, power steering pump radiator etc) now seeing engine oil leaking from what I think is the rear main seal, so, how big a job is this to correct, ie replace seal without engine removal, remove engine, rebuild the whole damn thing or just say the Hell with it and quit, sorry just upset. Thanks Patrick

 

[sneakingfart]

The first thing I would do is make sure it is the rear main seal, and not oil leaking from elsewhere and dripping down from what looks like the main seal. Clean up the engine bay, the underside, and go drive.

Assuming it is the rear main, how bad is the leak. Do you have a ton of crud from a slow leak over several years, or are you seeing a puddle of fresh oil on the ground? Are you having to add significant oil between changes? I have small traces of oil from what is likely the rear main, which doesn't even make it to the ground from what I can see, when parked. Probably the small drops blow off as I drive. But I did have a more significant leak from the oil filter housing, due to dry gaskets, and was tracking back to the area of the rear main.

Doing the rear main requires at the very least, removal of the transmission. Depending on your skill level and tools, you may or may not be able to do it yourself. I have experience working on smaller manual transmission (I'm not a mechanic at all), but i wouldn't take on this job. But I would not junk the truck just because of a problem that is bound to happen on any vehicle as old as this. Rebuilding the engine or trans is really dependent on if your engine or trans is tired and in need of a rebuild. If not, do the seal and call it a day.

 

[yevgenievich]

Rear intake to valley and valve cover leaks can look like rear main seal.

 

[Schurkey]

One would not need to "remove" the transmission. Buy long bolts of the proper thread size. (3/8-16) Remove a couple of lower bellhousing bolts, one on each side. Install the long bolts in their place. Then disconnect the torque converter from the flexplate, remove the other bellhousing bolts, maybe the trans dipstick tube, disconnect driveshaft, linkage, probably electrical connectors, the trans crossmember and trans mount while supporting the transmission at the pan area, probably by using a floor-jack on wheels.

Slide the trans back using the long bolts to support the front, and to keep it aligned, with most of the weight held by the floor jack as the trans moves rearward.

Of course, the rear of the engine also needs to be supported, or it's going to rock back at the rear--crushing the distributor cap and perhaps the entire distributor. Removing the cap 'n' rotor if not the entire distributor is recommended, 'cause you want to lower the back of the engine--and the transmission--at least some.

Remove flex-plate from crankshaft. You now have access to the one-piece rear main seal.

GM has "special tools" to remove the old seal, and install the new one. Most guys just cram a sheet-metal screw or three through the metal shell of the seal, and pry it out. Then carefully pop the new, lubricated seal into place with a small hammer. I'm not saying this is a great method--GM has the special tools for a reason--but it'll likely work assuming the crankshaft seal surface isn't damaged.

As said previously--make sure it's actually the rear main seal that's leaking, not oil cooler hoses/fittings, oil filter/filter mount, valve covers or intake manifold rear seal, oil pressure sending unit/oil pressure switch, and so forth. A rear main seal is certainly possible but not the first thing I'd be looking for.

You will be REALLY angry if you go to all the trouble of replacing a rear main seal, and then you find out the oil leakage was from something else, and the oil was either dripping down or blown rearward so that it LOOKED like the RM seal leaked.

 

[454cid]

I think I've read reports of oil pressure sensors leaking too, and on the 454, it's on the back of the engine. The hydroboost can cause a real mess too, if it starts to leak, but that's ATF.

Probably the messiest engine oil leak would be the angle adapter for the oil filter. It's a giant o-ring. When I replaced mine, I got the part at the dealer.