So, you've rebuilt a C4 and IL6

I keep hearing a C4 is the easiest transmission to rebuild.

If you have done both which one proved more challenging?

The engine rebuild was far more tedious with all of the clearance checks and cam indexing after getting everything back from the machine shop. The C-4 was more of a slap it together, do the air checks, and hope for the best. Other than chasing down a relined original front band after fighting with the flexible one it was a piece of cake. Like anything, do your research and be familiar with what you are getting into, the BadShoe videos are a must. You can look them up on YouTube.

Kevin

C4 easy to rebuild?? NO. They have more problems than all the other automatics COMBINED being built in the late sixties. It's the combination of aluminum valve body and lame screen for a filter and the #2 selective thrust washer. Disrespect this transmission and you'll spend a long vacation under your car. Slap an engine together and it will probably still run, but one little mistake in a trans, and it's no go. Here's some hints for beginners; if the reverse band is okay, then don't even take off the snap ring that's on the front of the output shaft, throw away the #2 thrust washer (only use the #1 SELECTIVE to take out most of the endplay; leave at least .020; you might need a size 3 or 4, sometimes hard to find, or make thin plastic shims for the original; you don't want the direct drum to wobble), and air check the drums on the pump; mounted in a vise. Make sure the direct drum isn't scored from the rings, and make sure the clutch clearance isn't too tight or loose; between .020 and .060; it will probably be in there somewhere easily, just double check. The hardest part is the direct return spring. Make something out of threaded rod, angle iron, and plastic sewer pipe. Flex bands are fine, it's what they sell, just make sure they don't sell you a C3/A4LD band; too big cuz the drums are bigger for the bigger clutches. If you can find a dacron filter then def use it. OR a Torkflite filter adapter. And grease the ring grooves to help center them so they don't snag. Take your time and ask questions. Nobody likes to r&r a trans twice.

the easiest automatic to rebuild is the powerglide. i have built a few of them for race cars. the C4 on the other hand has a lot of small parts that need to be put in the right place,with the right tolerances or as opel noted, you will be going through it again.

I guess I just got lucky. My only other experience with building an automatic transmission was a 4 speed fluid coupling Hydromatic from a 1962 Cadillac. It was an absolute beast. The C4 was much easier for me.