This question was asked a few months ago. Did not find an answer so here is a list of parts required to convert a TC3 to TC4. The new chassis addresses 3 main problems. One the new motor mount should not warp the right rear corner of the chassis upward from motor heat. This messes up the tweak in hot climates where motor heat is more of a problem. The new chassis puts todays heavier batteries (high capacity NiMH) closer to the center of the car for better side to side balance. You get rid of the old steering which tends to build up dirt on center and causes loss of trim. The old rack can be cleaned regularly with the backside of an X-acto knife. Anyway I got a good deal at Stormer as the graphite chassis and chassis braces and shock towers came together in a kit at a reduced price.
ASC31003 TC4STEERING RACK 1 $4.50 $4.50
ASC31010 TC4 SUSPENSION ARM MOUNT SHIMS BALLS. 2.95
ASC31022 TC4STEERING BELLCRANK POSTS ~ 1 $4.50 $4.50
ASC31025 TC4 SUSPENSION ARM MOUNT SET 1 $4.50 $4.50
ASC31111 TC4 Factory Team Servo Mounts, carbon 1 $3.95 $3.9
ASC31042 TC4 MOLDED CARBON COMPONENT SET 1 $24.99 $24.99
ASC31019 TC4 DRIVE SHAFT ACCESSORIES 1 $3.50 $3.50
ASC31046 TC4 MOTOR MOUNT: blue aluminum 1 $14.95 $14.95
ASC31026 TC4 Front BUMPER 1 $4.50 $4.50
ASC2225 NITRO TC3 BUMPER TOP BRACE 1 $2.50 $2.50
ASC2229 NITRO TC3 Steering RACK HARDWARE SET 1 $5.95 $5.95
ASC31024 TC41NNER HINGE PIN SET 1 $2.95 $2.95
Subtotal, excluding shipping: $80
Add 4 Asc 3916 3/16 x 5/16 ball bearings (diff bearings work) for ball bearing steering. $10.00
I finished the conversion of my TC3 to TC4 with Associated parts. Here are some additional items you might need as well as some additional items that are different on the TC4
ASC 2230 TC4 front Body Posts, The old rear ones will work. The fronts too if you want to redrill them. They will be oversized in diameter though.
ASC7874 and 6926. These are 5/8 and 7/16 inch Socket head capscrews for the motor mount clamp. The old motor mount clamp from the factory team kit will fit, but the new one lets the motor breathe a little better.
ASC 2229 listed above for the new steering links was short two bushings to work on the TC4 so you will need at least two more bearings or bushings 3/16 x 5/16.
The New TC4 has thicker input shaft cups for the diff, but they are not larger outside diameter. The new driveshaft thus has a smaller ball on the end. The old shaft will not fit the new cups or vice versa. If your shaft is the least bit damaged get a new shaft and use the newer cups.
Photo of the finished conversion on my post 10843. Here is a link