Solved 1996 Aerostar. Strange vibrations are coming from the rear.

[aerochris]

!996 Aerostar 130,000 miles second owner since 124,000. Upon hard acceleration (i.e. entering the freeway) the rear end shudders between 40-60 m.p.h. then subsides at 70 my normal cruising speed. Just dropped the pan and changed the tranny filter no change although it seems much happier. Do I need to do the same with the transaxle or does this indicate a suspension problem?

 

[BrooklynBay]

Welcome to this forum! Did you check the rear U joint? Does the driveshaft have any small dents on it? Sometimes a small dent could throw the balance off of it. Are the rear tires balanced? Rotate them to the front, and see if it makes any difference. Did you check the differential fluid level?

 

[aerochris]

Thanks for the insight Brooklyn Bay. I don't think it's the tires because the vibration goes away if you let off the throttle in the 40-60 m.p.h. range. Similarly, if you coast down from 70 to 60 the vibration returns. I am sorry that I didn't get a chance to check anything this weekend so that I could give you some more concrete deductive clues to work with. I would appreciate any hunches though. I am hoping for a best practice description of how to check and exchange the fluids in the differential.

 

[BrooklynBay]

There is a square plug on the top of the differential that is made to unscrew. This is the main plug to check the level. A way around it if you don't have the correct ratchet is to remove the speed sensor which has one small bolt. This is a short cut in a matter of speaking. You will need a small hand pump to pump fluid into the opening from a container.

 

[steelhead48]

Ford used 2 different size differentials in the Aero. 7.5" ring gear or 8.8 ring gear. should be tag under rear cover hole plate with ID size #. also listed on VIN door plate label as code

another cause of rear end shudder on acceleration is loose or worn out rear end pinion shaft bearings. is there any lube seepage around the rear differential front seal where the driveline goes in? if so, will have to be serviced
requries high level DIYer skills, best to have shop replace seal/bearings.
find and repair the shudder problem first, will probably save extra change of lube

Aero differential rear end, driveline to left
seal is part #13

Item Part Number Description
1 4851 Rear Axle Companion Flange
2 4662 Collapsible Spacer
3 4236 Differential Side Gear
4 — Upper Control Arm Boss (Part of 4010)
5 4209 Ring Gear
6 4215 Pinion Gear
7 4067 Differential Bearing Shim
8 4204 Differential Case
9 4221 Differential Bearing
10 4209 Drive Pinion
11 4630 Pinion Bearing
12 4621 Pinion Bearing
13 4676 Pinion Seal

To change lube, block front tires. set rear end on jack stands with rear suspension dropped down for access.
Draining the differential, remove bolts on lower 3/4 of cover, loosen the top bolts and let drain. wipe out bottom of differential housing, check for any metal cuttings in bottom and in lube.
to replace, clean both surfaces well of all old sealer and gasket.
use a sealer such as Permatex "Right Stuff"

Fill hole plug is 3/8" or 1/2" square drive, ratchet works best. use a GL5 rated differential lube 75w90. synthetic is best. Ford spec'd a high grade lube for these. don't have to change as often. use a funnel with a flex spout into hole and hold funnel up toward body pan, pouring lube bottle into funnel, will drain down in
Fill to 1/4" below fill hole.

 

[aerochris]

Thanks Steelhead and Brooklyn Bay. It only took me three years to post my solution, but it was the rear U-joint. I was shocked that it was still driving it was so worn out. $20 and an hour later( well maybe two) I was rolling smooth even took it all the way from Detroit to Sarasota FL without a single issue.

 

[BrooklynBay]

Thanks for the update! It sounded like it was the U joint. I'm surprised that it lasted as long as it did.