4L60E High Gear Clutch Pack Gone Again
 

For the 2nd time in 18 months my 3-4 clutch pack just went away again. I've never been completely happy with kickdown function at speed. I've suspected the converter unlock and O/D downshift (?)timing(?) might be out of whack> It's always tended to flair when down shifting and then would engage in drive /2nd with a bang!
I'm running a BlackBear tune with approx. 425 hp at the crank. Already sent them an email. Waiting their reply. Truck goes to my builder tomorrow.

Trans never gets any warmer than 170 degs. Fluid smells fine and looks great. Converter is a Circle D, 3200. 4.56's with 34" tires.

Any ideas?

Two factors; who built the Transmission and what components did they put in your transmission and 2nd did BlackBear do a in person tune or was it a data logging remotely.?

All components were Sonnax, except for Transgo Hd2. A local competent Chevy performance trans builder. Tune is a mail order tune.

Most tuners, mail order or in person, don't do enough on the trans side of things.

You just can't adjust shifts and a little pressure and expect it to hold together. Despite what some people will say, a "built" trans still needs tuning.

Understand and agree. I had my PCM back and forth to BB numerous times after my motor build for tweaks for shift quality, timing and to eliminate slow speed O/D in/out. I assumed that BB used a baseline that they kept in the can and did a make from. I would rather have a live in vehicle tune done.

Ok. After having left my trans builder's shop, I'm smiling ear to ear.

On tear down, his inspection found 3 of the 8 clutches in the 3-4 pack were toast. Odd. So based on lessons learned, new clutches clearance checked at .029. 1/2 of heavy return springs replaced with stock. (I have the billet snap ring elimination kit.) Centrifugal bleed hole restored to stock and checkball re-installed, (contrary to TransGo HD2 instructions.)

Trans feels better, crisper, quicker tire squealing shifts than it has ever had. Down shifts, O/D in/out crisp, concise and converter lock/ un-lock crisp and pronounced.

His recommendation is: Increase 1-2 shift 8-10 mile per hour. Same with 2-3. Part throttle or low throttle input races through 1-2-3 shifts. Thinking is that motor torque, vehicle weight, 34" tires and 3200 Circle D is putting loads of stress on 3-4 pack because of current trans tune low line pressure.

BB may have lowered part throttle/low rpm line pressure and sped the shifts up to soften the "BANG" that I first experienced with the tune loping across a parking lot or driving in stop and go traffic.

This is one of the bad HD2 side effects, especially if in combination with max apply billet servos...

I've approached BB, no reply yet. Trying to find someone local to fine tune the trans, (real-time behind the wheel), and I think I've got a winner.

That's good that they figured it out. I will tell you, aside from torque management tuning, and shift timing, speed in ms and mph, and making the converter lock pressures higher you shouldn't need to touch anything else in the tuning. A properly built 60e will have all of the hydraulic pressure mods done internally. I have seen pressure tunes kill the transmissions. I pushed 1k hp though one and no pressure mods. A smidge of TM and lesson the shift time on the solenoids. With power 4l60e hate repeated kick downs. Too much heat cycling in the 3-4 pack. They can hold some power if driven smart. :)