Well I've finally replaced my Blown to HELL 87 Bronco 3.55 8.8 L/S 31spline ABS rear with a 85 of the same minus the ABS (not sure what the spline# is, ASSume it was the same.... the gears looked great upon inspection)....replaced brake shoes (still got meat) w/original from old rearend and both wheel cylinders w/originals from old rearend also....put everything together (Castrol 80/90W w/o friction modifier) and on the test drive (w/same tires and rims as before).....I get a DEEEEP/BIG VIBRATION from about the center of the truck at 45MPH+. Its so bad that I can't really drive it.....I did step it up to 60-65 and the Vibration diminished a little but man......this is not cool. It almost feels like something's givin some resistence on acceleration.....and the tranny (auto/OD) feels like it won't get into the next gear although it sounds like it does shift correctly.....like tryin to drive fast in low gear??....anybody with an idea about this problem pleease let me know. I pray it ain't the Drive shaft or tranny, my last rearend blew a diff bearing with only 133,000 miles (I put only 7k on it)....but I don't know the previous owners towing or 4X4 habits.
You Folks on this Form are a treasure and have helped me out more than you know already....Thanks in advance.

 

Most common causes of vibration is bad u-joints/driveshaft, bad tire balance or bent wheel rim. If it were me, I would have the driveshaft thoroughly checked out, including the double-cardan joint and the balance on it, at a good driveline shop. Check to see if maybe it lost the weight mounted on it or if it seems to bind when rotated.

 

justshootme84....mmmm food for thought, I forgot to mention that the rims and tires were on my Bronco for a while but I had to remount them on my Father in law's Van (after my Rearend took a dump)......and the Van just had a slight accident which caused a little metal damage on one rim. The tire is still cool though and I didn't think this would be a problem...... how can you tell if a rim is really bent or warped?? Thanks for your really quick reply.

 

Putting it on a spin balancer is probably best. But you put the truck on jackstands and give it a spin too. It should be easy to tell if it's bent much at all.

 

Thanks fatfenders, I will try that tomorrow and maybe just maybe its that simple......knowing my luck lately though it probably will be someting tragic and expensive......ahh to be out of work and have your Bronco broke.....I still love my 87, and I wouldn't trade it or sell it or anything for a Dodge Ram or Chevy POS or anything else (except a 2 door Excursion maybe)...keep the faith!!

 

BroncoBuck

I remember some hungry days as well. It's sure no fun. Hope you find a good job soon. Here's a few more low buck tips to chase the vibe. Unbolt the driveshaft from the truck. You can get a much better feel for roughness or lack of lube in a U-joint that way. Good as taking it to the driveshaft shop? Certainly not, but it's free. I just disassembled the shaft on my 94 assuming the greaseless joints must surely be shot by now. Wrong, they looked fine and were still well lubed. Could have bought a tank of gas with that money I just wasted.

Also, get the truck cruising down the road where it rumbles bad, and put the trans in neutral and coast a bit. Does that change the vibe significantly? If not, you can probably eliminate horrible things like the engine and transmission as the source. Not a foolproof method but usually worked for me through the years. Again, it's free.

BTW, I agree with the guys who have already checked in. The driveshaft or rims/tires are the most likely culprit.