shifting into 3rd clunk
TECH Junkie
Joined: Jun 2008
Posts: 3,197
Likes: 1,382
From: Nitro Alley
I am guessing the 4L75E uses some version of overrun mod to keep it on in all gears the plus side is greatly improves input sprag durability, The trade off 3-2 and some 2-3 clunk feel, Even without this mod GM actually did a pressure pull back in the tune at part throttle and coast down, which has probably been undone in favor of longer 3-4 clutch life.
Now assuming this is what it is , It's the nature of the beast, In really every durability / performance improvement the trade off is almost always some level of comfort or drivability loss wither it's a loppy idle from a big cam.
It always come down to which is most important, To the builder who warranty's it of course durability is going to take precedence.
Some things you can do . Lower your 3-2 coast downshift speed will make it less noticeable. or optionally check your tune see if shift time and adaptive pressure been altered.
Personally on my own car I just lowered the 3-2 mph coast and learned to live with the somewhat clunky 2-3 feel. Bear in mind on the 2-3 or 3-2 in the 60e you are not just apply or releasing a friction set but someplace in the middle while the band and 3-4 clutch or going on or off you have a neutral to some degree else you would have momentary 4th.
You would not have this with a 350 cause none of the friction applies work way you are simply adding or subtracting not both at the same moment.
Now assuming this is what it is , It's the nature of the beast, In really every durability / performance improvement the trade off is almost always some level of comfort or drivability loss wither it's a loppy idle from a big cam.
It always come down to which is most important, To the builder who warranty's it of course durability is going to take precedence.
Some things you can do . Lower your 3-2 coast downshift speed will make it less noticeable. or optionally check your tune see if shift time and adaptive pressure been altered.
Personally on my own car I just lowered the 3-2 mph coast and learned to live with the somewhat clunky 2-3 feel. Bear in mind on the 2-3 or 3-2 in the 60e you are not just apply or releasing a friction set but someplace in the middle while the band and 3-4 clutch or going on or off you have a neutral to some degree else you would have momentary 4th.
You would not have this with a 350 cause none of the friction applies work way you are simply adding or subtracting not both at the same moment.
Even the 4L75E is severely lacking in Hydraulic Modifications/ Improvements.
I would never recommend spending the $$$$ for this Transmission for that Main Reason.
Anyone can build with Bling Bling Aftermarket Parts...
Often being a waste, and not improving the Transmission anywhere near what it could be, by a Builder like Frank, Maroon Monster, or Myself (Dana is great too, just not as up to date on some of the Hydraulics, but I'll be spending time with him to change that soon).
The 4L75E uses the Sonnax HD 2-3 Valve for the Overrun Clutch to be on in all Gears while in the D3 Gear-Selector Position.
It also uses the Superior-Fairbanks Intermediate Servo (It has a Sonnax Overdrive Servo, but that is irrelevant).
Between the Sonnax Valve and the Superior-Fairbanks Intermediate Servo...
There is going to be some 2 - 3 UP, and 3 - 2 Down CLUNKING!!!
Nothing wrong, and nothing to do about it.
If it is really bothersome, I would swap the Superior-Fairbanks Intermediate Servo for one that uses a Cushion Spring!
Best bet is to just use the GM Corvette Servo, Have the 3rd Apply, 3rd Exhaust, and 3rd Accumulator Circuit Hydraulics set up by a specialist, block the 3-2 Control Valve, and keep the Superior-Fairbanks Return-Spring (or a THM400 Intermediate Servo Spring).
The Cushion Springs can even be changed for fine tuning (there are many Springs (Dual and Triple) available to try.
Also do not be fooled by the Marketing... a "Super" Servo is not really needed (I would consider the Sonnax Servo for my 1000+ HP Builds)...
Any of us Builders that specialize in these Transmissions, can...
MAKE THAT CORVETTE SERVO SHIFT HARDER THAN ANY OTHER SERVO AVAILABLE!!!
(Just takes the right Hydraulic Calibration).
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Joined: Mar 2023
Posts: 1,799
Likes: 1,142
From: BERWICK PA
None of the GM Transmissions have a Full Time Overrun Mod.
Even the 4L75E is severely lacking in Hydraulic Modifications/ Improvements.
I would never recommend spending the $$$$ for this Transmission for that Main Reason.
Anyone can build with Bling Bling Aftermarket Parts...
Often being a waste, and not improving the Transmission anywhere near what it could be, by a Builder like Frank, Maroon Monster, or Myself (Dana is great too, just not as up to date on some of the Hydraulics, but I'll be spending time with him to change that soon).
The 4L75E uses the Sonnax HD 2-3 Valve for the Overrun Clutch to be on in all Gears while in the D3 Gear-Selector Position.
It also uses the Superior-Fairbanks Intermediate Servo (It has a Sonnax Overdrive Servo, but that is irrelevant).
Between the Sonnax Valve and the Superior-Fairbanks Intermediate Servo...
There is going to be some 2 - 3 UP, and 3 - 2 Down CLUNKING!!!
Nothing wrong, and nothing to do about it.
If it is really bothersome, I would swap the Superior-Fairbanks Intermediate Servo for one that uses a Cushion Spring!
Best bet is to just use the GM Corvette Servo, Have the 3rd Apply, 3rd Exhaust, and 3rd Accumulator Circuit Hydraulics set up by a specialist, block the 3-2 Control Valve, and keep the Superior-Fairbanks Return-Spring (or a THM400 Intermediate Servo Spring).
The Cushion Springs can even be changed for fine tuning (there are many Springs (Dual and Triple) available to try.
Also do not be fooled by the Marketing... a "Super" Servo is not really needed (I would consider the Sonnax Servo for my 1000+ HP Builds)...
Any of us Builders that specialize in these Transmissions, can...
MAKE THAT CORVETTE SERVO SHIFT HARDER THAN ANY OTHER SERVO AVAILABLE!!!
(Just takes the right Hydraulic Calibration).
Even the 4L75E is severely lacking in Hydraulic Modifications/ Improvements.
I would never recommend spending the $$$$ for this Transmission for that Main Reason.
Anyone can build with Bling Bling Aftermarket Parts...
Often being a waste, and not improving the Transmission anywhere near what it could be, by a Builder like Frank, Maroon Monster, or Myself (Dana is great too, just not as up to date on some of the Hydraulics, but I'll be spending time with him to change that soon).
The 4L75E uses the Sonnax HD 2-3 Valve for the Overrun Clutch to be on in all Gears while in the D3 Gear-Selector Position.
It also uses the Superior-Fairbanks Intermediate Servo (It has a Sonnax Overdrive Servo, but that is irrelevant).
Between the Sonnax Valve and the Superior-Fairbanks Intermediate Servo...
There is going to be some 2 - 3 UP, and 3 - 2 Down CLUNKING!!!
Nothing wrong, and nothing to do about it.
If it is really bothersome, I would swap the Superior-Fairbanks Intermediate Servo for one that uses a Cushion Spring!
Best bet is to just use the GM Corvette Servo, Have the 3rd Apply, 3rd Exhaust, and 3rd Accumulator Circuit Hydraulics set up by a specialist, block the 3-2 Control Valve, and keep the Superior-Fairbanks Return-Spring (or a THM400 Intermediate Servo Spring).
The Cushion Springs can even be changed for fine tuning (there are many Springs (Dual and Triple) available to try.
Also do not be fooled by the Marketing... a "Super" Servo is not really needed (I would consider the Sonnax Servo for my 1000+ HP Builds)...
Any of us Builders that specialize in these Transmissions, can...
MAKE THAT CORVETTE SERVO SHIFT HARDER THAN ANY OTHER SERVO AVAILABLE!!!
(Just takes the right Hydraulic Calibration).
__________________
Frank formerly of Performabuilt, Now just me, What can I build for you today? Call or message me. Click sig pic for my facebook
Frank formerly of Performabuilt, Now just me, What can I build for you today? Call or message me. Click sig pic for my facebook