Drive Train

Rattling could be Loose A/T Rivets

Since our "engine marbles" discussion I've been researching my 87's (125k miles) automatic trans, especially the torque converter and the drive plate which connects the torque shaft to the torque converter.

I think Jim Bailey (of course!) and Colin Plastow are exactly right about these rivets loosening on the torque drive plate. With that clue I've listened more carefully to my "engine marbles" and the rattle does appear to start at the rear and echo forward through the torque tube.

The workshop manuals Vol II p.37-18 (dated 1982) has a good picture of the torque converter assembly. The drive plate is shown as being attached to the torque tube coupler (input flange) with 6 bolts (torqued to 39-46 ftlb). There is a note, "Two drive plates (each 1.5mm thick) have replaced the single drive plate (2.0mm thick). In conjunction with this change the input flange also had to be modified. Since spare parts of former version are no longer available, when repairing cars with only one drive plate they must be changed to the new version."

In Vol III p.37-126 (dated 1984) the picture of the torque converter assembly shows what appears to be a single plate attached to the torque tube coupler with 8 rivets. In fact there is no separate description of the coupler piece, and the entire plate and coupler are labeled "drive flange".

Later on p. 37-130 (dated 1987) there is a picture of the torque converter assembly for "'87 models onward". This appears to be a dual plate held with 8 rivets. I can't find anything that says the rivets were later replaced by bolts.

In my case last January I loosened the torque shaft pinch bolt at the flywheel and released the tension (which was definitely there). Over the subsequent few months this rattle slowly appeared and increased. I can understand that the rivets may possibly have been weakening and/or loosening over the years and now that the tension is released the rivets and two drive plates are left with some play. Sound right?

One thing that bothers me: several email posts in the archives and on the Rennlist 928 FAQ - http://tech.rennlist.com/ - show that owners have had this rattle and fixed it by replacing the torque tube. My torque tube does not have any bearing whine. I'm wondering if some tubes have been replaced unnecessarily? Could these tubes have been replaced such that a load was placed on the torque drive plate and silenced the rattle? Or am I missing a needed preload at the rear of the torque shaft on the drive plate??

The manuals do not show the internal view of the drive flange and I'm not quite sure what's there. If I drill these rivets out - is that something I can do with my Black & Decker or does it need a machine shop? What size bolts? Anyone sell a flange already modified, or can I use a later model year flange if it has bolts?

Many many thanks for any education and ideas you can share !

John Pirtle
87 a/t 125k - runs so much better with the window down! :)
http://members.rennlist.com/pirtle