Downshifting vs. rpm at cruise (200-4r)

[Caveman Tony]

So here's the issue:

At cruise, the trans is in OD, motor is happy...

If going up a long grade, or attempting to do a cruise-pass (i.e, slow accel in passing lane, not a "hammer it" type pass) the trans downshifts OUT of OD, just to get that little bit of extra. Secondaries open, and now I'm screaming along in the passing lane, but only doing 3-5mph faster.
I make the pass, let off the gas, the trans upshifts into OD, and the truck slows back down a little. Aaaaand repeat. Multiple times.

If I'm simply trying to cruise at at faster speed, same deal. Won't stay in OD. Downshifts.

**Why won't it stay in OD?**

I'd like it to stay in OD, and allow the motor to push the truck the extra 5-10mph to make the pass or go up the grade. Or just cruise faster than 70.

Is this a function of the motor needing more rpm to make enough torque for the pass?

OR

Is this a function of throttle position, i.e., the little extra throttle input pushes the kickdown cable past its threshold for downshifting?

OR

Is this a function of the motor not making enough torque (at that certain rpm ~ 2600ish) to keep it in OD?

Is that just another way of stating the first question?

Truck has GM Goodwrench 8.5:1 (probably more like 8:1) 350 with Edelbrock carb, 4.10 rear gears, and a 30" rear tire. (Yokohama Geolanders) Stock cam. Stock heads. Brain-numbing loud exhaust.

Any ideas?

[TheSilverBuick]

I think it's a function of the TV cable adjustment. Feel the tension it has at WOT and take just a tad out (slacken it). If you can tell only a click or two of the adjuster.

[Caveman Tony]

Or do I just need 3.89s or 3.73 gears?

[Caveman Tony]

Thanks Rand.

Any danger to having it too slack? Just in case I dork up the adjustment...

[TheSilverBuick]

There is no vacuum modulator for the transmission to really "sense" load, it's all in the throttle opening. Too much slack could cause problems/excessive wear at WOT or heavy loads, but otherwise it's mostly just lazy shifting and will upshift sooner, and downshift later.

[Caveman Tony]

the builder put a 'shift kit' in it... it hits a little hard on upshifts now and then. How would that affect it at cruise? I wouldn't think it would... but I dunno squat about auto trannys. (Transmissions! Get your minds outta the gutter...)

[squirrel]

The TV cable adjustment and set up (bracket, angle, distance the cable travels) is critical on those things. Be careful. What it does is adjusts the pressure depending on how much load it thinks is on the transmission, so if you set it so it thinks there isn't much load when there really is, it will not engage the clutches with the necessary force, they will slip, and it will burn up. That's the scary warning

It could be that the cable is slightly out of adjustment or not quite set up right, which could make it think it needs to downshift at lower throttle than it should.

Having steep gears like you do, is better for this issue than having milder gears. Milder gears will make it want to downshift even more.

Is it the stock rear end? most of them were 3.90

[Bamfster]

More slack on the TV cable lowers shift points and makes the automatic downshifts later .....

Less slack raises shift points and quickens the downshift .....

Governor weights and springs play into all of this as well ....

A good base line to start with on the cable is 1/4" of slack on the cable w/throttle at WOT .... and like randal said, a few click on the adjuster after that and test drive, repeat till it works the way you want it.

[200kss]

Engine needs more power. Like driving a stock Monte SS with the 305. 2004R with 3.73 gears, 2500 rpm at 75mph. Pull out to pass, it downshifts but you rally don't go any faster.

[Caveman Tony]

interesting tidbit, probly unrelated: it behaved pretty much the same even with stock manifolds vs. headers. Not a huge power difference, but not insignificant.

At part-throttle upshifts, it sometimes shifts HARD. Yet, on full-throttle upshifts, the shifts seem firm, but way less of a 'hit'.

Is that a function of a TV cable that's a little too tight?



**edit: almost forgot, it's a 9" with 4.10's. With the old TH350, same rear 30" tire, it SUCKED out loud on the highway. Secondaries open all day long just to keep up with traffic. Good if you like noise and have quality earplugs.

[squirrel]

It sounds like a TV cable that does not have the correct lever arm or something. It might be too tight at lower throttle openings, but not tight enough at full throttle.

How much does the end of the cable move from idle to full throttle? in inches?

[Bamfster]

I'm with Jim, sounds like throttle lever geometry is wrong .... do you have one of these to correct the geometry?

http://www.summitracing.com/parts/HLY-20-121/

[Caveman Tony]

Engine needs more power. Like driving a stock Monte SS with the 305. 2004R with 3.73 gears, 2500 rpm at 75mph. Pull out to pass, it downshifts but you rally don't go any faster.

Not quite the issue. When I *want* it to downshift while passing, it does, and it'll get up and go.

It's when I'm trying to be stealthy, easing down on the throttle to go *just-a-little-bit-faster* and keep it in OD... is when it downshifts every time... and I end up doing the "blast around 'em" routine anyway.

[squirrel]

How much control do you have on the throttle? In my old chevy trucks that I swapped in big blocks, using the original V8 pedal and linkage, they are very sensitive--not much movement on the pedal gives a lot of movement at the carb. I wonder if this is the issue? The fix would be to move the throttle linkage connection (from the pedal) to a higher location on the carb throttle arm.

[yellomalibu]

I'm with Jim, sounds like throttle lever geometry is wrong .... do you have one of these to correct the geometry?

http://www.summitracing.com/parts/HLY-20-121/

Late to the thread, but this is what I was thinking all along.

Tony, where and how is the TV cable hooked up at the carb? With the wrong geometry, it won't shift properly in all rpm ranges - only in some rpm ranges.

If you don't have one of those brackets, I would start there and adjust the TV cable as recommended, then see how she drives.