How hard is it to put in a new rear end( not rebuiuling just bolting in a new one), this is for an 87 k5

 

Well, if your Blazer is a 4x4, you'll need to ensure that the replacement rear end has the same gear ratio as the front axle (and the old rear). Both the front and rear axles need to have the same gear ratio.

Other than that, you only need to make sure that it has the required mounting provisions and that the driveshaft universal yoke matches up to your driveshaft and you should be set. You will probably want to check the angle of the rear when installing the new axle. Ofcourse, this is all only if the axle was taken out of a different vehicle to be used.

If you get an axle out from under another K5 or from a pickup of the same vintage, you should be set, but double check everything just to be certain.

 

whell i am replacing both the rear axle and the front, because the ratio i have is different, but both are complete even with brakes, so im assuming i just disconnect my brake lines, un bolt the rear and the suspension and thats all right?

 

Pretty much and unbolt, unhook type deal. Hydraulic brake lines, parking brake lines, driveshaft, u-bolts and unbolt at the shackles and you're out.

But like I said, if you are lifting it at all or using axles from a different application, you will want to check your driveline angles to make sure that you don't bind something up. Having a driveshaft come loose is NOT fun!

 

the truck is already lifted with a 4 inch block suspension lift, and it does have 35s , just curious what u exactly mean but checking the drivline angle

 

Your driveline angles include the angle of the rear pinion and the angle of the rear driveshaft. These combined give the angle that the universals are at. Too much angle will be bad and mis-matched angles in the upper/lower u-joints can cause vibration.

Here's just one site I found that describes what needs to be checked:
4crawler - Driveline 101

You can run a search on pinion angles in google and come up with MANY more websites explaining it.

 

i hope you dont have blocks on the front axle. thats just asking for trouble. also remeber to replace the ubolts for the springs. they can stretch, causing them not to tighten up correctly.