87 - 89 Rearend Swap

[FMBL]

I found an 87 truck rearend with 4:10 posi that i want to try and replace my 3:08 with.

Would an 87 rearend be a direct swap to an 89? Both trucks are 1/2 ton 5 lug.

If so how do you correct the speedo on an 89 700r4. To my knowledge it is electronic without the old style speedo gears.

[ChevLoRay]

to the forum! We'll try to help you with your questions.

My basic instinct on the rear end swap is this: measure the width of the two between the backing plates. Then, measure the distance between the spring perches (on the top of the housing). If those distances are the same, no biggee in my opinion.

One point for contention might be the yoke on the differential where the driveshaft couples up. If there is a difference in the sizes of the U-Joints on the two rear ends, you'd have to have something modified, usually the rear yoke on the driveshaft, so it would mate up with the yoke on the rear end.


As for the speedometer error, I'm in the dark. My speedometer is optimistic. But, I've learned to compensate. I can actually drive an indicated 32MPH and still not exceed 30MPH. Good thing to know when John Law is makin' you paranoid....

[ToughBowtieTruck]

Yes 89 is electronic, however, I know there is some way to reconfigure it, as my OBD-I 95 speedometer reads about 5 mph fast now when I put stock tires back on it (so someone had it calibrated for big tires at some point) . . .

No, they are not a direct swap, as the 88-98 c/k bodies are different from the 87 R bodies and 73-86 C bodies (R was 2wd code as the 88-98 bodies were to take the new C code for 2wds--the 87-91 R and 81-86 C are the same body truck, 2wd 81-87 style body, but since crew cabs, suburbans, blazers were built into 1991 those also took the R (2wd) and V (4x4) coding).

The 88-98 C/K frames are wider than the 87 R/73-86 C trucks, so the spring perches would have to be moved. Some axles have both perches but not likely on an 87 truck.

Shock mounts may or not be different also.

If both axles are 10 bolts, the drive shaft should bolt up, though.

[ont_guy_38]

Boy I could use that rear end !!!!!!!!!!

[FMBL]

Thanks Josh. I think you answered my question.

[BIGphillip79]

if you got to move the spring perch thats pretty easy. Just a little cutting grinding and welding. New perches are cheap. If you can't do the labor yourself I bet you got a friend that can.

CHeck the cost for upgrading the guts of what you have as oppose to changing to this other rear end. See if its worth the work to make it fit.