I have a 66 Plymouth Valiant..3 speed..manual...having a hard time finding out exact type of transmission...and I need the right clutch to work with transmission...right now..I have a new clutch in it....but I have to adjust every couple of months...I can't find anyone to help me... thanks

Unless someone did a transplant for a later model it's most likely an A-745 non synchro 1st gear 3 speed.

The standard clutch for this is a 9 1/4" Borg and Beck clutch for the 1" x 23 spline input shaft.

The optional HD clutch kit is 10" Borg and Beck with 1" x 23 spline...but... these are tight in the 3 speed only bellhousings, and you will
need the special shouldered clutch cover bolts, as the standard hex bolts for the 9 1/4" clutch stick out too far and won't fit in the
relief in the clutch cover to sit right.... these bolts and clutches were standard on the slant six D-100 pickups in the late 70's and early 80's.

There are some 10" clutches that are of the diaphragm style , in which case you will have to remove the overcenter return spring for your clutch
pedal under the dash or the pedal will get stuck. FYI.

Great info...where can I get proper clutch...so I know it's right?..Thanks

You order at your local auto parts store and ask for the 9 1/4", they should have that info from the manufacturer...if they ship a 10" refuse it at pickup and ask for the correct one...(take a tape measure...)

You can also check Rock Auto, they sometimes list the clutch disk size...

Ok...I will research it..I am a novice..but learning everyday...I will keep you posted..I am grateful for your help...