Do any of you guys have a thorough understanding of the operation for the overrun characteristics for a 4L60E in a C5 corvette? I'm trying to understand if what I'm feeling is baked into the DNA of the 4L60E or the C5 vette, or I have a failure or tune issue.

The scenario I have is this: If I'm coasting along at 70mph in 4th and manually pull the gear selector to 3rd, there is no engine braking and it feels just like neutral at zero throttle input. If I apply throttle it accelerates with no issues. Second gear is similar except after I have pulled the selector into 2nd, if I let it coast for about 2 seconds it will engage 2nd gear and have engine braking. If I manually pull it into 2nd and accelerate immediately, leave the selector in 2nd, lift off the throttle it will have engine braking until I select a higher gear. First gear has normal and expected engine braking anytime the selector is in 1st and I'm off the throttle.

The 4L60E in question has been modified/built with parts to handle more than 800hp and a 3200rpm converter, but it does not have the HD shift valve which sounds like a common mod many builders use. I did talk to the builder and they said I'm running too much line psi in the tune file and it's likely not allowing the fluid to bleed off at the appropriate time. I just ran a test with drastically reduced up shift/down shift pressures, and generally drastically reduced commanded pressure throughout. There was zero difference in the engine braking/over run character with lowering the pressure. I copied the original transmission tables from the OE stock file also as a test, also zero change in engine braking/over run character.

Thank you for your time.

 

You will have limited feel engine braking moving to D3 from D4 4TH gear depending on your gear ratio rear, It will be either just a bump or an actual drag down depending on speed . honestly kinda sounds like you have a broken overun hub, damaged leaky teflon ring top one leaking the overun oil off , HD valve without the gasket cut or chambers connected (But you say you do not have the HD valve) , Possibly some version of a OVERUN MOD done but with no feed passage connected , Or and 05 VETTE unit with the wrong VB plate unique to that unit, Though any plate can be easily modified.
They is no pressure situation or "bleed off" situation that would cause what you describe. You have engine braking in second because it works a different way not dependent on the OVERUN as much and fed differently.
And Manual first gear too is very different, I would say you have one of the issues I listed with the overun clutch or other leak in that circuit . You can have a substantial leak in that circuit and not affect any other function of the unit,
Now note many vets have pretty high ratios I think 3.05 or something like that do you may need to be going pretty fast when you pull down coasting to feel overun in D3 and if you have a high stall converter much higher speed to feel it.
Before I condemned the builder or trans I would cruise up to about 70-90 mph let of throttle and pull down to D3 if you feel a bump at all then it is indeed working correctly as a high stall and the typically High ratio the vet comes with could easily hide the engine braking or make it negligible unless at pretty high speeds.

 

Thank you for responding Frank. One of the transmissions is in a 1999 vette and the other is in a 2000 vette.
This week I will run it up to what would be 4500 to 5000 for 3rd then lift, pull the selector to 3rd and see if I feel a bump.

As of now, if I put the selector in 3rd, make a WOT pull up to 6,000 or so and lift, leaving the selector in 3rd, I don't feel any engine braking.

 

If you lose engine braking. When you are in 3rd gear (drive) and the engine goes back to idle. You have no engine braking. Plus if you give it throttle from the idle position. You can overload the sprag and shatter it. This is assuming the sprag is still working.

 

The I would have to concur with PBA.
POSSIBILITES
SONNAX VALVE WITH THE FEED NOT CUT,

SOME VERSION OF OVERUN MODS FOR D3 OR D4 NOT COMPLETED WITH FEED FROM FWD OR LINE.

AN OVERUN MOD SIMILAR TO MINE I HAVE PUBLISHED IN MY THREAD TIPS AND TRICKS WHERE ONE OF THE TWO HOLES AT THE BATHTUBE HAVE COME UNPLUGGED WITH NO BALL PRESENT AND IS DUMPING THE OVERUN OIL AND /OR THE GASKET NOT CUT AGAIN TO SUPPLY OIL .

BROKEN OVERUN HUB.

WRONG PUMP STATOR-INPUT SHAFT COMBO CUTTING THE RING FOR OVERUN DUMPING THE CIRCUIT.

DAMAGED TOP ORING DURING PUMP INSTALL

DAMAGED OVERUN PISTON

At that speed RPM even with the vet 3.15 gears you should feel engine braking. Now bear in mind with a large stall and that ratio it wont feel like alot. It should be notable in D3 with or without any sort of overrun mod.


Any of these things is possible.