I recently rebuilt my 700r4 that came out of an s10 originally. All good parts installed the good red clutches and band, .500 boost valve, 9clutches in the 3-4 pack and a corvette servo. It’s mated to an unknown peanut port 454 that pulls surprisingly well. Doesn’t slip or have any problems in 1-2-3 shifts into 4th nice but doesn’t hold any real power without the engine revving way out. It cruises at 1750rpm at 60mph roughly and if I roll into the throttle it seems to rev up way more than it should so I dont stay in it for fear of frying the band. I air checked everything during assembly. I dont have lockup wired in yet, It has the stock 4.3 converter. Am I blowing through the converter? Is it slipping? I’ve done it enough to times in the last month I figure it would be toast by now. Any real insight would be much appreciated

 

Who keeps Hyping-Up and Selling-Up these "GOOD" Red Frictions/ Clutches/ Bands/ Etc for the THM700-R4 Transmission Family?
LOL! "good".


Unfortunately the THM700-R4 (and most 4-Speed Automatic Over-Drive Transmissions of the Era) were not designed to "Hold" 4TH-Gear.

We (Hydra-Matic & Buick/ Chevrolet) actually designed the Transmission to do the complete Opposite of holding 4TH-Gear...
By down-shifting to 3RD-Gear or 2ND-Gear as soon as a relative load has been placed upon the Engine while in 4TH-Gear.

Obviously Modifications came about to alter the behavior of the THM700-R4 while in 4TH-Gear.
Some Modifications were from Us (initially for Expressway Police Vehicles)...
And of course the Aftermarket has done so as well.

Many Automatic Transmission Builders offer high power handling THM700-R4 (as well as THM200-4R and others) Transmissions.
Some Builders (including Myself) even offer 1,000+ Horsepower THM700-R4 Solutions.

And all Builders with offerings at the higher-levels, will say essentially the same...
Have all of your fun in D3/ 3RD-Gear (or Lower Gears) (This keeps use of the Over-Run Clutch).
D4/ 4TH-Gear (and Lock-Up) is ONLY for light-throtlle cruising.
Always Down-Shift to at least D3/ 3RD-Gear for romping on it!


We can strengthen the Unit Hydraulically, and with some amazing Aftermarket Components...
Corvette (or Sonnax) Intermediate Servo with Sonnax 4TH Servo Piston, Alto Wide 2-4 Band (carbon graphite preferred), 0.0600" Target Clearance...
Borg Warner High Energy or Raybestos GPZ 3-4 Clutch with 8 to 10 Frictions (depending on choice of Input-Drum used), 0.0300" Target Clearance...
As well as many, many very fine details/ modifications...

BUT:

No matter all of that...
The Input-Sprag is just TOO SMALL!
...to handle any real power in 4TH-Gear (No support to the Input-Sprag from the Over-Run Clutch, unless in D3/ 3RD-Gear or lower).

 

Great information.