'91 Aerostar 4.0 ext 4WD w/176,000mi has a resonate drumming sound at 45mph, proceeding to pronounced driveline vibrations as speed increases. I've crawled around underneath to where I've convinced myself the problem is excessive wear in the transfer case. The greatest amount of "driveline slop" seems to be from the transfer box. U-joints are original but have no looseness. Rear end has some give but the majority is upfront in the TC. Has anyone else rebuilt one of these? There seems to be tons of info for the 4x$ guys but very little info about these cases. Hard to even find a repair manual for the 4WD versions. Any advice or help would be greatly appreciated.

 

I've never rebuilt an Aerostar transfer case, but I took a look at the factory service manual and it appears that anyone with mechanical aptitude should be able to do it. However, there are some special tools that the manual says are needed to do the job so you could end up paying a bit for tools you'll only use once. You may be able to find a creative way around those tools (I have in the past on other jobs) but I can't speak from experience on this one particular job. If I had to do it, I wouldn't hesitate as long as I could stand the down time. Otherwise, I would pay someone else to do it and have it done in a day or two.

If you need any information from the manual, let me know and I can look it up for you.

 

Any chance that you could be looking at a drive shaft problem? This was mentioned to me one time when looking into problems with my AWD Aerostar. Not a mechanic type but may be something to also consider?

 

there's a recall on tail end of transfer case & shaft on 91-96 (in Canada anyway) Check the dealer.

 

Update for future thread reference; vibration turned out to be a combination of worn rear differential(cross shaft) and a loose pinon bearing nut. Rebuilt the rear end and all is well.

 

 

i have not rebuilt a transfer case, but my mechanic for my 89 2wd had told me my rear seals were leaking, so he went and removed the hubs, but he started from the middle.....NOT necessary?!?!?, he told me that the bearings , once removed, must be replaced.is this true...shouldn't he have known not to open the diff?
i am thinking of filing a claim of incompetence for the cost of the 'fixed seals' he said that fluid would leak into my rear brakes. This was required for him to safety it.

 

To remove the seals, you must remove the axle shafts. The inner ends of the axle shafts are held into the differential by large C-clips, so opening the differential was valid.

As far as the bearings, I'm assuming you are speaking of the outer axle shaft bearings. If so, these are separate from the axle seal, although they lie immediately behind the seal. The seals can be replaced separately from the bearings but both are usually replaced at the same time, as the bearings are minor cost items compared to labor.

It is true that once removed the bearing cannot (should not) be reinstalled. They are pressed in and require a serious puller to remove which usually damages the cage.

I think your mechanic is being truthful with you. The only issue is whether you authorized the bearings to be replaced. Even if you didn't, you're probably better off in the long run having them replaced as long as the price is fair.