Transfer case differences?

[xlt4wd90]

Howdy All,

New member here. Been reading some great posts for a while, but now I have a question I hope someone can help me with.

I have a 1990 Aerostar with the e4wd drive train, and it's had this clunking noise for a while, and it's gotten worse recently. It only happens when I start up from a stand still, and it happens whether I have the control module connected or not. I checked out the engine and transmission mounts for any loose parts, and everything looks tight. A few years ago, I found a cracked bracket that was supposed to hold up the front axle, so I welded it back together, and it's held up so far. But that did not have any effect on the noise.

One thing I did find was that with the front end jacked up, and the transmission in park, I can turn the front drive shaft by hand over about 45 degrees. That seems like too much play. When I'm doing this, I can hear light clunking in the transfer case. I learned that this case uses a Morse chain to drive the front wheels, like a lot of transfer cases.

I'm suspecting that the chain is worn out, and when I start off from a stand still, the noise I'm hearing is from the gears inside abruptly taking up the chain slack. So I think I should at least replace the chain. Does this sound reasonable? However, I wonder if I should also replace the chain sprockets, as they must have also worn with the chain?

An alternative is to just replace the whole transfer case. There seems to be a distinction between the early (1990, 1991) cases and the later (1992 and later) models. Does anyone know what the differences might be, and can I use the later model in my earlier van?

thanks for any information you can provide.

 

[BrooklynBay]

Welcome to this forum! We don't currently have a rebuild thread for this transfer case. It would be greatly appreciated if you could make one if you decide to rebuild it.

 

[xlt4wd90]

Thanks BrooklynB.

I have found the answer to my question from a tech at a place called Rockland Standard Gear, which sells transfer cases. Basically, all moving parts wear together, and it's generally not enough to replace just a single worn part, such as the Morse chain. The Aerostar TC has an additional disadvantage that Ford/Dana spec'd it for using ATF, which does not protect against wear as well as gear lube. And, while a number of places sell the master rebuild kits that include seals and bearings, nobody sells the gears or other parts that mesh against each other, which also should be replaced in a rebuild. So it's not easy for the DIY'ers to do a complete rebuild of this case. I heard from one hardy user who did, and saw no noticeable improvement in the amount of shaft play. So it may be better for me to just buy a complete TC rebuilt by one of these outfits.

Also, the big change after 1991 is that before 1992, the Aerostar had a gear driven vehicle speed sensor behind the front output shaft of the transfer case. In 1992, Ford switched to using the RABS speed sensor in the rear axle as the VSS, and eliminated that sensor in the TC, so it does not have that hole in the case behind the front output shaft. I'm going to guess that it also does not have the driving gear on that part of the shaft either, so you can't just take a newer case, punch a hole in that position, and install the geared VSS and expect it to work. There may have been a transitional period between late 1991 and early 1992 during which 1992 model vans got the earlier transfer cases.

 

[DoOver]

I love my E4X4!

Welcome the board and thanks for the input. I just got a 95 E4X4 and was really thinking about changing the transfer case and front diff. oil to 30 weight. Anyone have any ideas or concerns about this. Also, else where on this board, a member discribed the transfer case as splitting the power 70/30 all the time and shifting to 50/50 when needed for a breif time.
Brian

 

[xlt4wd90]

Thanks DoOver,

Yes, the unlocked mode of the Aerostar transfer case sends 30% of the torque to the front and 70% to the rear. This is from the gearing of its differential; it's almost like a gear type limited slip differential (like Torsen or Quaif), but with a much gentler slope on the helix of the teeth. When the computer senses a speed difference between the front and rear output shafts beyond a certain threshold (5 or 10%, I forgot), it will engage the clutches between them to lock them to 50/50 for a few seconds, but only at certain speeds, when you're not applying the brakes. It releases the clutches briefly to see if there is still that speed difference, and repeats if necessary.