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Your cart is empty.Complaints: Burnt clutches & bands and poor shift quality. Cause: Wear at the piston pin bore due to repeated reciprocation. Correction: The Sonnax patented pinless design with dual seals stabilizes the piston in the bore and provides improved sealing characteristics. Use of the Sonnax part eliminates the need for the pins. In GM 4L60-E, 4L65-E and 4L70-E units it is common to have poor shift quality, burnt bands or clutches due to accumulator piston wear. Repeated reciprocation of the accumulator piston causes wear at the piston pin bore interface. After this wear reaches a critical point, fluid loss through the piston pin bore cannot be compensated due to lack of pump volume. In addition, the piston can get cocked and gall the accumulator bore due to the pin bore wear or the spring bottoming out. To prevent these conditions in the 1-2 or 3-4 accumulator bores, Sonnax offers pinless accumulator piston kit 77998-03K.
Kody
2025-08-20 15:59:47
No issues and nice upgrade from stock plastic piston with the rod. I noticed slightly better shifting
E. Poppitz
2025-08-14 11:03:15
So far this kit has made the 1-2 shift good and firm.After pushing the OEM pin out of the center of the housing, I taped the large ball into the hole. The ball was pretty loose in the hole and didn't take much to pop it out. I didn't want to take any chances so I took a large metal chisel and put it across the hole and gave it a few taps. This deformed the hole opening enough that the ball could not come out.After several days of driving, so far it's working fine.
Craig of MN
2025-08-04 18:13:11
2003 Suburban with 4L60E transmission. My 1-2 shift was harsh only when cold. Dropped the pan with no interference on exhaust crossover pipe and bent the shift bracket over a bit to remove. I just re-used the original springs. Installing was a breeze. Check out YouTube for a video with all the instructions. This improved my 1-2 shift by 75%. Might have had even more improvement if I had replaced the larger spring - who knows? Remove close to a gallon of ATF from the pan and replaced about the same. Chevy calls for Dexron III but the Dexron VI is backwardly compatible. (Don't forget to order more like I did). For the price and 2 hours worth of elbow grease it was worth it!
Daniel
2025-07-15 18:39:03
Bought this product after researching my hard shift into second gear. The shift is smooth again! But still get ocasional hard shift but not as bad. 02 suburban 1500. It is not hard to install after dropping the trans fluid pan.
James
2025-06-27 13:05:33
Easy install. Dont go crazy with the ball braring install. It only needs one or the other not bothStake it gently. All in all a good set up.
Music Lover
2025-06-09 16:39:35
Replaced the stock 1-2 and 3-4 accumulators with these. The difference in overall build quality of the part vastly improved my shifts. It uses two seals to keep the piston square in the bore, eliminating the guide pin, which seals any possible places for fluid to leak. A very minor modification is necessary when using in the 1-2 position, which requires tapping and staking a check ball into the housing. Easy as can be.
Dwarf15
2025-05-23 16:13:55
I was having issues with slip or delayed shifting from 1-2 on a Trailblazer. After some research and consulting with my transmission rebuilder he suggested trying a pinless accumulator. First, make sure to scotch pad the bore and oil the o-rings. I re-used the stock large outter spring and installed the Sonnax piston over the spring. You can also bump line pressure via the EPC torx. Fair warning: 1/4 turn is all i needed (i did this prior to installing the piston as step 1. did not eliminate delay but helped), you can go too far and cause damage. (DISCLAIMER: I am not a transmission builder so proceed at your own (transmissions) risk.) There is no longer a slip into second and the shifts are predictable based on throttle input. The more input, the firmer the shift.
Sunshine
2025-05-14 17:25:43
2007 Silverado shifted so hard I thought I was loosing my driveshaft. Replaced and now it is crisp and I'm happy.
narciso
2025-04-21 12:43:33
mejoro la transmisión recomiendo su uso es fácil de instalar lo pude yo mismo y no soy mecánico
Josh
2025-04-16 13:47:02
After doing some research on the harsh 1-2 shift in my 2011 Silverado with a 4L60E trans, I found that this was a common upgrade and fix for the issue. It's very easy to install with basic mechanical skills. If you can do a transmission service, you can do this upgrade. (see YouTube for instructional videos). After installation, and trans service, the truck shifts smoothly, as it should. My only complaint about this product would be that it is shipped in a bag, but it should be in a box for a little more protection, as the piston is aluminum and if it gets dropped, it could definitely damage it. Mine had a small dent on it that you could tell was likely caused by a drop, or it hit something, but luckily it was in a spot on the piston that had no affect on it's performance.
George
2025-03-15 13:11:14
Good quality product
Trevor Story
2025-02-02 15:29:05
Fixed my sloppy slide and bump 1-2 shift on my 2005 GMC Sierra Crew Cab with a 5.3l and a 4l60e. It started shifting weird out of the blue coming up on 250 000 miles or 400 000 kms. I changed the fluid, filter, shift solenoids and a new accumulator housing with this sonnax piston installed. Now it's a nice solid feeling quick 1-2 shift. Now I'm noticing a hesitation during the 2-3 shift under light to moderate acceleration so I'm thinking of replacing my stock servo with a corvette servo.
David antonio nerio
2024-12-06 17:17:23
Thank you im very satisfied im a mechanic and i recommend this item
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