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98 blazer won't engage into 4wd

I have a 98 blazer s-10 series, replaced outer differtential seal. since then it will not shift into 4wd. Ran fine before the seal was replaced,Idon’t want to keep buying parts I don’t need. Blazer has 170,000 miles still runs great

Take it back to the shop that worked on it and see if they didn’t leave a wire or vacuum hose disconnected…

Did not have a shop work on the truck, they want’d try to charge me to rebuild the differential, never had a problem with it before, ran great in 4wd. I’m laid off funds are scarce, try to do is much as I can, keeping the cost down, some people say to replace the actuator switch on the differential, had a grinding noise in 2wd drive shift to 4wd no grinding sound but not locking in 4wd.

" replaced outer differtential seal. "

Do you mean “Pinion Bearing seal”, where the driveshaft connects? If so, how did you set the torque on that big nut that holds the U-joint flange in place on the pinion shaft? Did you use a new crush sleeve? Maybe yours does not have one, but “setting” the load on the pinion bearings is very important. Just cranking 'er down as hard as you can means the rest of your problems are minor…

The 4WD engagement systems and the “automatic locking hubs” were pretty Micky-Mouse and prone to failure. They “reconfigured” this stuff almost every year. You need a service manual with a troubleshooting guide to deal with this…

I think that also. The vacuum hose has either not been replaced or just has a hole in it. You have about 10 to 15 feet in this operation. I had to replace all my hoses around you mileage. And I was able to do it in my back yard in a day. Just take your time. Get the Goodyear part numbers and diagram from your local GM dealer then go to the local parts store to save money. Pull it out in one piece, replace old with new and reinstall.

My 99 blazer had a vacume problem because of a dry rotted part beneath the battery housing. I do not know what it is called but is about the size of a softball and used part cost me about $30.00 . Simple fix

My '99 S10 4wd had an electric shift for the 4wd. Maye it’s a fuse or a broken wire.

Try cleaning the contacts for the electrical on the differential.