9 replies to this topic

[Seabronc]

By front end disengaged, I assume that you mean hubs unlocked and transfer case in 2WD.

Also, it sounds like you have replaced the frontend joints including the ones on the front drive shaft.

A vibration could be anything from slightly out of balance tires, a bad spot on a tire, bearings in the drive train, to the new driveshaft being slightly out.

For the drive shaft, You would need a runout gague or mount something that can hold a piece of chalk so that it is not quite toucning the shaft. Then lift your rear end up on jack stands and turn the wheels and see if the chalk puts a mark on any part of the shaft. That will tell you if there is a problem in that area of the drive train. I would do it at both ends of the shaft which should narrow down the possibilities.

The bottom line is that you could be spending a lot of money shotgunning the problem. So do some trouble shooting first.

Once you determine what it is, check with some reputable place like Jeff's Bronco Graveyard, LMC Truck for parts, or someone you know in your area that has a good reputation.

Good luck,

[Broncoholics]

I wouldn't think its the tires since it happens at 10mph. But how come the tire shop doesn't use stick on weights on the inside of the rim?
Is the vibration the same at speed or does it increase?

I had bad rear wheel bearings and rear pinion bearing in my 89 bronco. These both made a vibration but were easy enough to fix myself.
I don't think its the t-case at all, have you checked the fluid levels in everything?
Usually the pinion seal or t-case output shaft seal or yoke seal (depending on what you have)will leak if something is out of wack.
Do you have a lift and what size tires are these? I used to go thru u-joints every 3-6 months until I purchased some traction bars.

If the vibration goes away when hitting or letting off the gas its u-joints, light on the gas it vibrates. All the time its a bearing.

[Broncoholics]

Forgot to ask, did the splines on the drivelines get fixed or recoated? Check to see if there any movement by pushing on it where the shaft enters the driveline up and down or side to side? If there is movement in there it will vibrate.

[Seabronc]

The axle code is also listed on the truck safety compliance certificate on the driverside rear door post bottom line under "Axle". I believe that the 85 auto 8.8 only came with four possibilities;

18 = Regular 3750 pound capacity 3.08 ratio
19 = Regular 3750 pound capacity 3.55 ratio
H8 = Limited slip 3750 3.08
H9 = Limited slip 3750 3.55

If it is say 182, the 2 indicates limited slip front axle.

This assumes no one has changed the gears.

Good luck,

[Seabronc]

If there is no tag on the rear end, here is a way to find out.

Put the truck rear axle on jack stands.

Transmission in neutral.

Put a mark on the drive shaft at a point you can see it.

Turn both rear wheels at the same time and speed (need help for this, if you don't a non-locking differential will be doing its thing).

Count the number of revs on the driveshaft for one complete turn of the wheel.

If it turns just slightly over 3 turns, it is 3.08, If it turns slightly over 3 and 1/2 turns, it is a 3.55.

Good luck.