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I recently replaced the valve body on my 1998 GMC Sonoma, 2.2l engine, 4l60e transmission, 147,000 miles. I admit it was above my skill level, but it had to be done. I was getting p1860, p1870 trouble codes. The VB had all Sonnax upgrades, except the forward accumulator, which I did myself. The 1-2 accumulator had the plastic piston, two springs, and metal rod. It was replaced with the Sonnax upgrade, and a new large spring, (I couldn't find a small spring, and it was okay). The 3-4 must of had some previous work, as it had an aluminum piston, rod, and no spring. It also had the Sonnax upgrade, but I left out the spring. I then put in a new wiring harness. The codes are gone, but the harsh 1-2 shift is still there. If I let off the gas at 12 mph, it shifts smoothly.... If I lay on the gas, and let it shift with the gas on, the shift is harsh. What could be causing this? The truck is 15 to 20 degrees cooler since I completed this.
the sonnax accumulator is also taller so it will have a shorter stroke which will firm up the shift. this seems to be a common complaint with the pinless accumulators?
2nd Accumulator
housing-->piston-->spring-->separator plate
In this orientation, the stiffer the spring, the firmer the shift
Housing-->spring-->piston-->separator plate
in this orientation, the stiffer the spring, the softer the shift
The spring was from....whatever it takes Transmission..... Supposed to be the Sonnax recommended spring.....I suppose I did the correct thing leaving the spring out of the 3-4?
Could the spring be the problem? It was okay to leave it out of the 3-4 accumulator? The truck, once it gets through first gear, runs better than it ever has. Great acceleration. It's running at 140-145 degrees. It's unbelievable what the VB did for the truck. I'm planning to change the fluid and filter in the spring, which is why I'm asking, as I'll have access to the accumulators again.
Could the spring be the problem? It was okay to leave it out of the 3-4 accumulator? The truck, once it gets through first gear, runs better than it ever has. Great acceleration. It's running at 140-145 degrees. It's unbelievable what the VB did for the truck. I'm planning to change the fluid and filter in the spring, which is why I'm asking, as I'll have access to the accumulators again.
Could be the spring. Did you actually check the size of the feed holes?
Could the spring be the problem? It was okay to leave it out of the 3-4 accumulator? The truck, once it gets through first gear, runs better than it ever has. Great acceleration. It's running at 140-145 degrees. It's unbelievable what the VB did for the truck. I'm planning to change the fluid and filter in the spring, which is why I'm asking, as I'll have access to the accumulators again.
Reread bbonds post #2. there are 2 different ways the spring & piston can go into the accumulator housing. do you remember which way you installed it?
I held one plate on top of the other, and all holes seemed the same size. It was exactly the same as the stock plate. I installed the springs per Sonnax instructions. Placed the metal ***** in the accumulator housing, staked same, springs and then the piston.
you can try shrinking the 1-2 shift hole on the separator plate with an old metal checkball. or ditch the pinless accumulator and go back to stock. like i said earlier, this seems to be a common complaint when using the pinless pistons.
Using a thicker Accumulator Piston will shorten the stroke.
The main change in behavior should be a faster Shift (a good thing), and NOT necessarily a firmer Shift.
(It can soften or firm up the Shift).
The Spring and Piston arrangement... along with the Spring firmness is what mainly alters the Firmness.
Lets just say the Spring is on the Separator Plate and the Piston is in the Bore first...
Generally the Shorter it takes for the Piston to STOP, the Softer the Shift.
The opposite, generally the Firmer the Shift.
This section of the Post will be simplified as Fluid Pressure Regulation via the Frequency of the Valve-Train moving back and forth will not be discussed.
Look at the Image below (NOT of the 4L60E, but will work for what I am explaining):
The Accumulator Valve-Train regulates (using it's Spring) line pressure (called Drive Fluid in the Diagram) into the Accumulator Fluid below the Accumulator Piston.
The more often that the Accumulator Valve in the OPEN position, the closer in pressure that Accumulator Fluid will be to Line Pressure.
The Longer that the Accumulator Piston is not Bottomed-out (or stopped due to the Accumulator Piston Spring) the higher Accumulator Fluid Pressure will be (as long as the Accumulator valve has not closed)...
The firmer the Shift will be.
The Image below shown the Accumulator Valve closed and no longer allowing Line Pressure into the Accumulator Piston Bore:
Last edited by vorteciroc; Dec 21, 2022 at 08:29 PM.
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Harsh 1-2 shift 
