I recently acquired a 78 d100. It has a 318 w/ 3spd on the tree. It needs a clutch, but two different sizes show for this app on Rockauto. Is there a way to tell what size clutch is in the truck without taking it apart? I really would like to get the entire job done in a day if possible and not have it sitting waiting on parts. Thanks.

do you know what model trans it is?

I don't, all I know is that it is a manual 3 spd trans.

I suspect the differences is in the clutch diameter. Are your choices 9" and 10 1/2"? You should be able to pull the inspection cover on the bottom of the bell and get a rough measurement of the outside edge of the disc that should get you close enough to be able to determine which clutch is in there. Gene

Thank you I will give it a try. Clutch is either 10.5 or 11 on this one.

Call a dealer, give them the serial number, see if they can tell you what it is.

I'd bet on the 10 1/2", but measure it anyway. Remember the size is determined by the outside edge of the disc, not where the cover bolts to the flywheel.

I think the dealers around here threw out everything concerning anything older then 1994 out when the 1994 trucks came out. When you bring up anything concerning something older then 94, they get that deer in the headlights look and start talking funny. Gene

My 72 3 on the tree was the 11". Went to a833od and its 10.5.

Just my 2cents.

It's an A230 but it could still be 10.5" or 11.0" clutch.