Quote:
Originally Posted by 68Stepbed
OK, I have a carbureted LS1 with a 92 4L60(non-electronic) transmission. The trans has been built with upgraded internals, 2800 stall, and I believe a Trans-Go(whatever the builder ordered) shift kit. It's been in the truck for over 4 years with no major issues. It always wanted to shift early, but was easily fixed by changing weights and springs in the governor. I've been overall patient with it, but now that I'm taking autocross a bit more serious, I'd like to step it up some.
First off, the "kickdown" or downshift under throttle. Many times while driving at certain speeds, the trans just won't kickdown low enough and work well with the engine's powerband. The throttle valve cable is adjusted correctly, even if a bit too tight. To get the trans to kickdown more, do I need to start looking at valvebody adjustments? I had a builder once mention a reverse boost valve. What exactly does it do? Would it help? Is there somewhere else I need to modify or adjust?
Secondly, Many times when driving back roads, I'll put the trans in 3rd instead of OD. Upon doing this, the trans will downshift from 3rd to 2nd on it's own during deceleration into a curve causing engine braking. It's really nice and puts the engine in a comfortable rpm range to quickly accelerate through and out of the curve. However, when I'm autocrossing, I usually have to run in 2nd gear because most courses I run lately have been longer with decent speeds. The problem in this, is the engine won't downshift into first on it's own when decelerating and braking into a corner and the engine has to lug it's way out of a low speed corner in 2nd. Is there any way to get it to downshift itself upon deceleration? Keep in mind, I don't want it to do a hard kickdown style downshift under heavy throttle as this would probably cause the rear tires to break traction or upset the truck's balance and cause other issues. I'd rather it downshift upon entering the curve, not coming out.
Does any of that make any sense? Something I may do in the future is install a floor mounted shifter and manually manipulate the gears, especially if I can't get these issues sorted out first.
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Rarely do we see such a well written question!
When you put a 700R4/4L60 in manual 3rd/D3, The Overrun Clutch comes "On" giving engine braking, The Overrun Feed can be blocked, But I don't recommend it as the Overruns help the Forward Sprag stay alive. IF it is falling out of 3rd into 2nd at speeds above 10 MPH upon deceleration...............Your Governor calibration is really wacky
The Intermediate/Reverse Boost valve boost pressure in Reverse, & Manual D1/D2, A Larger Ratio boost valve will just increase Line Pressure in those 3 Ranges, Does not effect shift timing at all.
We can dive into the hydraulics if you want. But, Your never going to get automatic downshifts at speed with minimum TV Pressure.