Guess what, other than a very few minor differences, the internal parts of a 700 and 4L60 are exactly the same. The later 4L60s did include some durability upgrades, but the basic design is the same. Same clutches, same band, etc. Obviously, the case, valve body and pump are different for the electric shift models, but the internals are basically the same.
The 4L65 and 4L70 are just upgraded 700/4L60. The additional strength is due to adding carriers with 5 gears instead of the stock 4.
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4 pinion on the top, 5 on the bottom.
The 3-4 clutch has always been a issue, especially in the early years. HydraMatic made some changes in the mid 80s to eliminate a lot of the failures. They originally had 5 clutches, then made design changes to add a 6th friction plate, the 4L70 added a 7th. In the aftermarket, the make a 9 clutch, which sounds great. Only problem, to fit 9 clutches where 7 fit means they have to get thinner. Thinner clutches don’t handle heat as well, they warp and glaze. Once that happens, it’s all downhill.
Raybestos solved the 3-4 clutch problem with their Z pac kit. It has 22 single sided clutches. That maintains the same friction and steel thickness. It’s really a slick setup.
Another weak point is the drive shell. The original part wasn’t heat treated. The internal splines either break or strip, leaving you with no reverse, no 2nd or 4th gear. Sonnax fixed that with their Smart Shell. I’m not even going to try to explain the difference, but it’s a much better design.
Bottom line, unless you have more than about 450-500hp, or really plan to beat on it, a 700 isn’t all bad. Unfortunately, like so many automotive things, they just can’t shake the reputation from the first couple trouble years.
The 700 will never be as durable as a 400. But the 400 eats more power, doesn’t have the first gear starting ratio, and no overdrive. The 400 has a 2.48 first gear, the 700 (and similar models) have a 3.06 first gear. I’m too lazy to do the math, but that’s like taking out a set of 4.10 gears and installing 3.42. Takes much more throttle to get the truck rolling. The overdrive makes those 4.10 gears cruise like you have the 3.42. Best of both worlds
If the 700 works ok, install a TransGo shift kit. Order a corvette servo, that will increase the clamping force of the 2-4 band. The shift kit will fix a lot of the durability issues designed into the trans. You need to keep in mind GM knew 99% of the new car buyers wouldn’t appreciate the soft girlie man shifts, so they designed the trans to kinda slide into gear. The instructions will specify what size to drill the spacer plate from basically stock to bang-screech, knock the dash of the truck.
You may also want to order a new spacer plate. There are several check balls (basically BBs) that seal against the plate. After a few thousand cycles, the check balls wear the plate, causing leaks. Transgo offers the plate and includes instructions on how to make it work in your particular trans model.
Lastly, if your going to work the truck, install a trans cooler. Make sure the TV cable is adjusted correctly.
